34

The Evolution of the Ophthalmic Surgical MicroscopeILLUSTRATIONS

Fig. 1: Bishop Harman binocular loupe

Fig. 2: Bi-convex lenses on extended arm

Fig.3: Berger loupe

The microscope has for long been anindispensable tool in ophthalmic surgery.The first reported use of a binocular surgicalmicroscope in ophthalmology was nearly 100years after Richard Liebreich described hismethod of using magnification in ophthalmicexaminations in 1855.

If this was a long interval, perhapseven more strange was the lapse of 25 yearsbetween the first use of a floor-stand-moun-ted binocular microscope used in otology anda table-mounted microscope used for ocularprocedures in 1946. To add to the mystery,during this same period, the binocular slit-lamp microscope had become an essential in-strument for examining the cornea andanterior chamber. It would have seemed verylogical to have mounted the slit-lamp micros-cope in a similar way to the proven system ofsuspension used by the otologists but this didnot happen.

This article will trace the evolution ofmagnification systems used by ophthalmicsurgeons until the late 1960s, and will at-tempt to throw some light on why it took solong for the stand-mounted binocular micros-cope to be used in ocular surgery.

HEAD WORN MAGNIFICATION

Before the advent of the binocularsurgical microscope in the 1950s, ophthalmicsurgeons had been using a variety of specta-

cle or headband, mounted magnifying sys-tems, as had reported Edward Landolt in areview of surgical loupes in 1920.1 These me-thods can be grouped into three categories:single-lens magnifiers, prismatic magnifiersand telescopic systems.

SINGLE-LENS MAGNIFIERS

Single-lens magnifying loupes in theirsimplest form were spectacles with convexlenses suspended at the end of the nose, suchas the Bishop Harman binocular loupe (Fig.1),or convex lenses with added base-in prism at-tached to a spectacle frame on extended arms(Fig.2). One of the most popular forms ofmagnification over many years was the Ber-ger loupe (Fig.3) which used sphero prisms inan enclosed hood attached to the head witha strap. There were a number of variations ofthis design of loupe. For instance, illumina-tion was added in one option, and in anotherthe instrument was constructed in a skeletonform (Fig.4, see p.36). In 1908 Edward TreacherCollins used the same sphero prisms (Fig.5,seep.36 ) and attached them to a spectacle frameto which the operator’s prescription could beadded. This type of loupe in which the singleconvex lens was used in combination with thesurgeon’s own prescription was quite com-mon. A popular loupe was the Beebe (Fig.6, )seep.36, first produced in 1914. This used lensesof +7.50 dioptres with 5° base in prism adju-stable to a range of interpupillary distancesand providing a magnification of 2.3x. Thesurgeon could use his own prescription or triallenses in conjunction with the magnifying len-ses (Fig.7, see p.38). The Bausch and LombDualoupe (Fig.8 see p.38) was a form of Beebeloupe but the lenses were hinged so thatthey could be swung out of the way when notrequired.

35

AbstractThe use of magnification in eye surgery goes back to the 19th century and consisted of a

spectacle frame with single plus lenses worn towards the end of the nose.The ophthalmic operating microscope was first introduced in the 1950s but was slow to take off.This paper will explain the reluctance to adopt this new tool and the early developments that have ledto today’s sophisticated microscope

The Evolution of the Ophthalmic Surgical MicroscopeShort title: Ophthalmic Surgical Microscope

Richard Keeler

Richard Keeler1 Brookfield ParkLondon NW5 1ESUKrkeeler@blueyonder.co.uk

Hist Ophthal Intern 2015,1: 35-66

36

Fig 4: Berger loupe - skeleton form

Fig. 5: Treacher Collins loupe

6. Beebe loupe

Stewart Duke-Elder had designed forhim two loupes (Fig.9 see p.38), both of whichused the surgeon’s prescription in the hostframe with the convex lenses suspended onarms to give a magnification of approximately1.5x. Angling of the frame front could be in-creased or decreased by engaging a metal pegin a small vertical extension arm. The clip onversion could be attached to most frame sty-les but could not be swung out of position,unlike his other design (Fig.10 see p.38).

PRISMATIC MAGNIFIERS

Binocular magnifiers using prismoculars and lenses were first introduced in1912 by the Carl Zeiss Company (Fig.11 seep.39). Their binocular loupe gave a magnifica-tion range of 0.75-3.0x depending on the eyelenses. Initially this loupe was worn on thenose with a strap around the head, but thediscomfort due to its weight, especially whenillumination was added, attracted alternativemethods of wear, such as an over headband,or the facial cage with headstrap as illustra-ted in Fig.12, (see p.39).

TELESCOPIC SYSTEMS

With the limitation of power andworking distance in single lens systems, thedesire to have more magnification at a longerworking distance in a spectacle, or head,mounted form meant that an alternative sys-tem was needed. The Galilean telescope pro-vided this. The simplest form was an ‘open’Galilean loupe (Fig.13) with small high minuslenses at the back separated from high pluslenses held in front and mounted on a frame,with the surgeon’s prescription incorporated.This Galilean combination was hinged so thatit could be flipped up out of the visual pathwhen not required.

One of the first closed Galilean sys-tems was designed by Edward Jackson of Phi-ladelphia in 1897.2 He mounted convergingtelescopes on a bar attached to an overheadband (Fig.14 see p.39). The telescopes focussedat 15cm and gave 3x magnification. But itwas the introduction by Carl Zeiss, Jena, oftheir 2x miniature telescopes, designed by DrM von Rohr3 with the advice of Dr W Stockin 1912, that transformed the surgeon’s abi-

lity to work comfortably with higher magni-fication. Allvar Gullstrand was the first to trythese spectacle mounted achromatic telesco-pes, and they rapidly became the standardsurgical loupe for ophthalmic surgery. Ini-tially the focal length was 20 cms, but laterZeiss and other manufacturers provided achoice of focal length and magnification.Zeiss had various ways in which the telesco-pes could be mounted, including adjustable(Fig15 see p.39) and individually fitted framesfor normally sighted people (Fig.16 see p.39), aswell as a method whereby the telescopescould be attached to the surgeon’s own cor-recting glasses mounted in a metal frame(Fig.17 see p.41).

The Keeler Galilean telescopic sys-tem was introduced in 1952 at the sugges-tion of Charles S Hallpike, an otologist inLondon. The telescopes of 2x magnificationat 25cms were mounted in angled rings ona fixed bar, individually measured accordingto the surgeon’s interpupillary distance. Themounted telescopes on their bar were screwedon to prongs protruding from the spectacleframe (Fig.18 see p.41). With this system Keeleroffered a wide choice of magnification from1.75x to 9x, and working distance from 34cmsdown to 16.5cms (Fig.19 see p.41). Later, thefixed interpupillary bar was replaced by a con-tinuously curved bar enabling the surgeon toadjust the telescopes to his own interpupillarymeasurement, and, importantly, to correct anydifference of the two eyes from the medianpoint (Fig.20 see p.41 ).

HIGHER MAGNIFICATION SYSTEMS

1855 – 1921

The discovery of the ophthalmoscopeby Hermann von Helmholtz in 1850 hadopened up a new world to the ophthalmolo-gist in his examination of the internalstructures of the eye, especially the retina.However, at that time examination of the cor-nea and anterior chamber under magnifica-tion was restricted to a simple high powerbiconvex lens or the use of a combination of-convex lenses mounted behind the mirrorof the ophthalmoscope. Light was reflectedby a mirror or directly towards the patient’seye from available daylight, a candle or an oillamp.

37

38

Fig. 7: Beebe loupe with corrective lenses

Fig.8: Bausch and Lomb Dualoupe

Fig.9: Duke-Elder loupe

Fig.10: Duke-Elder operating attachment

39

Fig.11: Zeiss Prism binocular loupe

Fig.12: Zeiss Prism binocular loupe on face frame

Fig.13: Open Galilean loupe

Fig.14: Jackson binocular loupeFig.15: Zeiss 2x Galilean adjustable loupe

Fig.16: Zeiss 2x Galilean loupe

In 1855 Richard Liebreich (Fig.21) wasthe first to examine the eye with a (monocu-lar) microscope 4 with which his table-moun-ted ophthalmoscope, that he had justdesigned, provided the essential structure

(Fig.22 see p.42). Instead of the tube carrying atits end the perforated concave mirror for di-recting the light into the patient’s eye in theindirect ophthalmoscopy mode, he replaced itwith the body of a Schieck table microscope.This gave a very high magnification of up to90x. Illumination of the cornea was fromlight focussed through a biconvex lens held tothe side of the instrument (Fig.23 see p.42 ).

In 1863, Louis de Wecker (Fig.24) con-structed his three-legged ophthalmo-microscopeusing a Hartnack monocular microscope sys-tem.5 De Wecker’s microscope was hand-heldbut used the three legs to stabilise the instru-ment on the patient’s head. It had a magnifi-cation range of 40-60x at a close workingdistance and was impractical for anything

other than examination of the cornea and an-terior structure of the eye (Fig.25 see p.42).

Theodor Saemisch of Bonn can layclaim to be the first to use binocular magnifi-cation in ophthalmology in 1876.6 He em-ployed a large 9 to 10 cm diameter singleconvex lens of six or eight dioptres, each eyelooking through the outer diameter of thelens. Binocularity was aided by the base-inprism effect of the thick lens, but true stereo-psis was not achieved.

For the first truly binocular systemused in ophthalmology we must look to a de-vice constructed in 1886 by H Westien for the

zoologist F E Schultze and soon taken up andadapted by the Rostock ophthalmologist KarlWilhem von Zehender 7 (Fig.26). Westien, alsofrom Rostock, was the court mechanic. Hecombined two monocular Bruecke microscopebodies so that they converged, giving the ope-rator a stereoscopic view of the patient’s eyeup to 10x magnification (Fig.27 see p.44).

The Bruecke loupe was a Galilean te-lescope arranged for a short working distanceand was sometimes known as the Chevalier,after the man who had devised the instru-ment before Bruecke had knowledge of it.8

Illumination was achieved by focussing thelight through a lens held on a jointed rod, asfirst devised by von Zehender (Fig.28 see p.44).

40

Fig.21: Richard Liebreich 1830-1917

Fig.26: Karl von Zehender 1819-1916

Fig.24: Louis de Wecker 1832-1906

41

Fig.18: Keeler Fixed Galilean loupe Figi.19: Keeler Galilean loupe range

Fig.20: Keeler adjustable Galilean loupe

Fig.17: Zeiss 2x Galilean loupe

42

Fig.22: Liebreich’s Large Ophthalmoscope

Fig.23: Liebreich's monocular microscope

Fig.25: de Wecker's monocular microscope

In 1887, Ludwig Laqueur of Stras-burg employed the Westien microscope forexamining the eye, using a system of large-diameter condensing lenses in combinationwith a remotely positioned light source (Fig.29see p.44).

In order to adapt the same opticalprinciple for surgery, Westien mounted smal-ler telescope tubes, giving 5x to 6x magnifica-tion, to a head-mounted system (Fig.30 see p.44).

Theodor Axenfeld reported on thisinstrument in 1899.9 The combined weightof the telescopes and lamp of the Zehender bi-nocular loupe was excessive at over 250g andfor this reason it was not popular. Therewas no weight problem when it was mountedon a column with chin rest, but of course thiscould not be used in surgery. The same fate,due to its weight, befell the R & J Beck surgi-cal loupe of 1908 (Fig.31 see p.46) which had amagnification of 3x at a working distance of7.5 cm and was described by its originator, LBuchanan of Glasgow, as a portable micros-cope.10 The interpupillary distance could bechanged by moving the left telescope in itsangled holder. The binocular loupe was heldon the head with a strap attached to paddedforehead rests, with a further padded rest,placed at the brow of the nose.

Carl Zeiss at this time produced a bi-nocular telescopic magnifier which was a com-bination of simple magnifiers and a prismtelescope giving a range of magnification of 2-3x. This unit with electrical illumination waseither attached to a headband, (Fig.32 see p.46)or mounted on a floor stand (Fig.33 see p.46 ).

In the same year, (1897) the first sig-nificant binocular microscope for examiningthe eye was designed by Siegfried Czapski

(Fig.34) and F Schanz and manufactured byCarl Zeiss of Jena 11 (Fig.35 see p.46). Czapski,who had succeeded Ernst Abbe at Carl Zeiss,designed the microscope with a system oferecting eyepieces with porro prisms, toget-her with pairs of interchangeable objectivesand eyepieces, to give a wide choice of magni-fication. Czapski improved on the binocularcorneal microscope that H Aubert had pre-sented to the Ophthalmological Congress inHeidelberg earlier in 1891. A rather inade-quate low-voltage diffusely radiating lampwas added to the Czapski microscope. Laterthe lamp was attached to a Lucanus curved

rail (Fig.36 see p.47) which was in the form of aquadrant that always left space on one side of the microscope available for observa-tions on the eye. It also admitted light beingdirected upwards when the quadrant was pla-ced in a vertical or oblique position. In 1911W H Leudde modified the microscope by ad-ding a 6-volt tungsten lamp with double con-densing system, and placing it on a ball andsocket joint attached to an extendable arm.If one was to trace the origin of the modernbinocular ophthalmic operating microscope,it would seem natural to start with theCzapski microscope. However, in 1911, a bril-

43

Fig.37: Allvar Gullstrand 1862-1930

Fig.34: Siegfried Czapski1861-1907

44

Fig.27: Westien's binocular

microscope 1886

Fig.28: Westien's binocular microscope with illuminating lens

Fig.29: Laqueur's binocular mi-croscope arrangement

Fig.30: Westien/Zehender

binocular surgical loupe 1899

liant innovator of optical systems and NobelPrize Laureate, the Swede Allvar Gullstrand(Fig.37), introduced the first instrument of itskind, the “Slit Lamp” (Fig.38 see p.47) or as itwas later termed in 1925 by Jacques Mawasof Paris, the ‘Biomicroscope’.12

So in 1911 ophthalmic surgeons hadin their hands the essential ingredients for abinocular operating microscope for ocularsurgery, but with one major drawback: thefree working distance was too short for sur-gery. As will be seen, there were other rea-sons why ophthalmic surgeons werereluctant to use such an instrument in theoperating theatre, but these do not fully ex-plain why it took another 40 years for thefirst production model to be manufactured.

Otologists however had seen the bene-fits that magnification could bring to their pro-cedures when Carl-Olof Nylén from Sweden(Fig.39) described (1954)13 how he first startedusing experimentally, in 1921, a monocularBrinell-Leitz microscope giving 10-15x magni-fication (Fig.40 see p.47) for labyrinthine fistulaoperations on temporal bone preparationsfrom human beings and living animals.Later, Nylén took advantage of an opportu-nity to use an otomicroscope especially con-structed by engineer N Persson and himself(Fig.41 see p.47). However, it was Nylén’s chief,Professor Gunnar Holmgren who, in 1922,started the development of modern microsur-gery by developing and popularising the useof a Zeiss binocular microscope (8-25x mag-nification) which had been adapted for fenes-

tration operations (Fig.42 see p.48). This micros-cope, until 1938, had a very small field of viewof 6-12mm and a working distance of 7.5cm.

Between Nylén’s use of a monocularmicroscope in 1921 and the first reporteduse of a binocular microscope in ocularsurgery in 1946 numerous microscopes weremanufactured. In fact there were more thaneight different manufacturers involved inclu-ding Ernst Leitz, Carl Zeiss, Bausch andLomb and R & J Beck.

Seven years later, when Zeiss startedworking with ophthalmologists in 1953, noless than nineteen surgical micros-cope designs had appeared, the first two ofthese being monocular. As has already beenstated, it was Holmgren who had popularisedthe use of high-power magnification with thebinocular microscope in surgery. Theotologist’s requirements in a microscope weresomewhat different to those of the ophthal-mologist. Maybe it was the small field of viewand short working distance that had deterredthe ophthalmic surgeon in the first instance,or the potential slowing down in well-estab-lished procedures, but the fact remains thatbinocular microscopes, a number on floorstands, were being used by surgeons, mainlyotologists, for thirty two years without theophthalmologist becoming involved.

The Dawn of the Modern Ophthalmic Microscope

The title of “father of ophthalmic mi-crosurgery” goes to Richard A Perritt of Chi-cago. He reported his use of a microscope forvarious surgical procedures as early as 1946and was the first ophthalmologist, on record,to use a microscope in ocular surgery on asystematic basis. Perritt used a modifiedBausch and Lomb (1942) bench-mounted dis-secting microscope (Fig.43 see p.48) with spot il-lumination, which he placed on a trolley atthe side of the operating table. For operati-ons he swung the magnification head 180oover the patient’s head, the weight of the mi-croscope base keeping the arrangement sta-ble. The microscope had a short workingdistance of 12.5cm. There was a choice ofmagnification by changing eyepieces to give3.5x, 7.0x and 10.5x. According to Perritt,this microscope was shown in public at the1950 corneal surgery course of the American

45

Fig.39: Carl-Olof Nylén

46

Fig.31:Buchanan binocular surgical loupe by

R and J Beck 1908

Fig.32: Carl Zeiss headwornbinocular prism loupe

Fig.35: Czapski's corneal microscope

Fig.33: Carl Zeiss standmounted binocular prismloupe

47

Fig.36: Czapski's corneal microscope with Lucanus rail

Fig.38: Gullstrand's slit lamp by Carl Zeiss

Fig.40: Brinell-Leitz monocular

microscope

Fig.41: Nylén-Persson monocular microscope

48

Fig.42: Holmgren using Zeiss binocular microscope

Fig.43: Richard Perritt's

binocular microscope by Bausch and Lomb

Fig.44: Shambaugh's binocular microscope by Bausch and Lomb

Fig.46: Zeiss OPMI microscope 1953

Fig.48: Zeiss OPMI rotating on axis microscope

Academy of Ophthalmology. The Bausch andLomb instrument bearing the name ‘PerrittCorneal microscope’ appeared in the 1951 ca-talogue of V Mueller & Co, Chicago. In the1956 V Mueller catalogue there is an illustra-tion of G E Shambaugh’s fenestration micros-cope on a floor stand (Fig.44 see p.48). It is thesame Bausch and Lomb (Perritt) microscope,but with a longer working distance of 20cm. At the 18th International Congress of Oph-thalmology in Brussels in 1958, Perritt gavea paper on micro-ophthalmic surgery, inwhich he briefly described his earlier experi-ences with the microscope used since 1846.14

THE CARL ZEISS COMPANY

In 1954 Dr Hans Littmann PH.NAT.D., M.D.(Hon) of Carl Zeiss (Fig.45),Oberkochen, published a paper15 announ-cing the launch five years before of an ope-rating microscope used in colposcopy, and

shortly afterwards in otology, for surgeryof the inner ear. Littmann had developed abench-mounted binocular dissecting micros-cope for Zeiss and in 1948, a slit-lamp cornealmicroscope with rapid, click-stop change inmagnification without the need to refocus.The slit- lamp microscope also had coaxial il-lumination. Littmann quickly realised thatthis instrument only needed a suitable stand-mount for it to be used in ocular surgery. This‘otological’ microscope was used by the earlypioneers of ocular surgery, such as Harms,

Mackensen, the Barraquer family, Dannheim,Becker, Roper-Hall, Troutman and others.

One year after the introduction of theZeiss Opton microscope in 1952 (Fig.46 see p.48),Professor Heinrich Harms of the Eye Clinicof Tübingen University (Fig.47), reported tothe German Ophthalmological Society in195316, the use of this instrument for the sur-gical repair of traumatic lesions of the eyeand for keratoplasty. In reviewing his earlyexperiences at the 1st International Sympo-sium on Microsurgery of the Eye held at Tü-bingen in 1966, Harms recounted how he hadsought a means of developing a suitable sup-port to suspend the slit- lamp corneal micros-cope which he and his teacher ProfessorLöhlein had been using for severe traumaticocular lesions during world war II. Unknownto Harms, Ignacio and José Barraquer werealso using the same microscope and reportingtheir initial experiences. The microscope wasused by José Barraquer in Buenos Aires inApril 1953 during the 10th Argentine Oph-thalmological Congress.

The Zeiss Operating Microscope17,adapted for ocular surgery by Harms, had aninterchangeable tube for straight or obliqueviewing, the eyepieces being slightly conver-gent to assist binocular fusion. Magnificationchange was manual, and there was a choiceof five powers using a Galilei changer withoutloss of focus. Focussing was also manual. Il-lumination of the eye field was by a coaxiallamp of 6 volt 30 watt. The microscope was-

49

Fig.45: Hans Littmann 1908-1991

Fig.47: Heinrich Harms

mounted on an articulated arm attached to asolid moveable stand. Shortly after this, anew arm designed especially for the ophthal-mic surgeon was introduced. This allowed themicroscope to be rotated around its own axis,thereby avoiding tedious realignment and re-focussing (Fig.48 see p.48). A combination ofeyepieces and two objectives of 125 mm and200 mm focal length gave a wide choice ofclick-stop magnification from 6x to 40x.

This microscope was also designedfor a range of surgical procedures, includingotoscopy, dermatology and colposcopy, wherea longer working distance was available.The most usual set-up for ophthalmic proce-dures was the inclined binoculars with 12.5xeyepieces and objective lens of f = 200 mm.This combination gave a choice of magnifica-tion (diameter of visual field in mm) of 4x(50mm), 6x (32mm), 10x (20mm), 16x(12mm) and 25x (8mm). The coaxial illumi-nation covered approximately 32 mm of thesurgical field. For changing the magnifica-tion, a sterilised metal or rubber cap was fit-ted and sterile sheets covered the ocular

tubes for easy adjustment without gettingcontaminated. It was from this basic surgicalmicroscope, itself having evolved from thecorneal microscope with slit lamp, that manyadditions and adaptations were made by Zeissand others during the next ten years.

Throughout the early years of the de-velopment of the ophthalmic surgical micros-cope, Gunther Mackensen (Fig.49) assistedHarms at the Eye Clinic in Tübingen, and theteam of Harms and Mackensen became syno-

nymous with the development of microscopesand microsurgery. They co-authored “OcularSurgery under the Microscope” in 1966.17

The coaxial illumination provided bythe first Zeiss microscope was not ideal for anumber of ocular procedures, not only be-cause of its glare but for its tendency to flat-ten the image of the eye, losing shadow detailand thereby reducing depth perception. Inaddition, any instrument introduced into thefield cast its own shadow. Lateral illumina-

tion was soon added by mounting a lamp onan arm attached to a ring circling the ob-jective holder.

In January 1956 Henri M Dekking ofGröningen (Fig.50) in Holland reported18 on asimplification of the Zeiss surgical micros-cope. Dekking contended that a single mag-nification of 10x was all that was requiredand he stripped out the elaborate magnifica-tion changer. In place of the coaxial lampwith its 33 mm of illuminated field, he hadhis own built-in light source using a conden-sing lens system, which gave a wider area ofillumination of 45 mm (Fig.51 next page).

Dekking also identified another dis-advantage in the original Zeiss surgical mi-croscope. This was the inability of thesurgeon to focus or make small adjustmentsin the horizontal and vertical directionswhilst looking through the microscope andkeeping his hands free at all times. Dekking’ssolution was to build a new support standwhere the X-Y horizontal movements couldbe made by the surgeon rotating wheels withhis feet, giving lateral and transverse move-ments. Focussing was achieved by move-ment of the surgeon’s knee against a long

50

Fig.49: Gunther Mackensen

Fig.50: Henri Dekking 1902-1966

51

Fig.51: Dekking's light system on

Zeiss microscope OPMI

Fig.52: Barraquer's bolster headrest and trolley

Fig.53: Zeiss microscope with slit lamp attachment

52

Fig.54: Zeiss microscope with Harms arm for slit-lamp

Fig.55: Zeiss diploscope optical path

Fig.56: Ronald Pitts Crick

Fig.57:

Pitts Crick microscope on

Keeler stand

Fig.58: Dermot Pierse

lever half-way up the support column.52. Barraquer's bolster headrest and trolleyIn an attempt to stabilise the patient’s head,Dekking devised a padded head-clamp consis-ting of a three-sided wooden box which fittedinto the existing fixation clamp at the headof the operating table. This device succeededin giving firm fixation to the patient’s headthroughout the operation. In a similar vein,Montague Ruben (London) in 1959 designed 19

an operation table head pillow which, in a si-milar product, was to become an essential in-gredient of Dermot Pierse’s microscopesystem a few years later.

At the Barraquer Clinic a bolsterheadrest was employed which stabilised thepatient’s head. The height of the head couldbe adjusted by rolling or relaxing the con-necting strap wrapped around the bolsters20

(Fig.52 see p.51). An additional advantage ofDekking’s head-clamp was that it could beused as an arm/hand rest for greater steadi-ness of the surgeon’s movements. A furthercontribution to the evolution of the surgi-cal microscope by Dekking was not a practi-cal one, but an addition to the language inthis branch of ophthalmic surgery. In thepaper he wrote in 195618 the term ‘microsur-gery’ was used for the first time.

Another early user of the originalZeiss surgical microscope was Bernard Be-cker of St Louis. In 1956 he reported21 ha-ving used the instrument for two years insurgery principally for goniotomies, discissi-ons, corneal transplants, repair of lacerati-ons and the removal of foreign bodies.Interestingly, he does however state that “theuse of the instrument in routine cataract ex-traction has proved disappointing thus farbecause of the limited visual field andawkwardness of grosser movements”.

By the end of 1956, José Barraquerhad adapted a slit lamp to the Zeiss micros-cope22 and added mechanical fine focussingoperated by footswitch (Fig.53 see p.51). Thisworked well when the microscope was in thevertical position. With the addition of aminus 10D lens, Barraquer’s surgical slit-lamp microscope had a longer working dis-tance of 15cm than the combination of slit-lamp and surgical microscope that Littmanhad designed for biomicroscopy of supine pa-tients. Barraquer advocated the use of slit -

illumination to observe the optical section.When the slit was completely open, lateral il-lumination, with its many advantages inclu-ding improvement in depth perception, wasprovided. The slit lamp was attached to themicroscope with a special arm allowing theinstrument to be used in any position. At thesuggestion of Harms, Zeiss constructed a cur-ved arm so that the slit-lamp light came notfrom the usual position at the side of thesurgeon but was turned through 90°opposite the surgeon (Fig.54 see p.52).

In 1961 Littmann developed a systemof two microscopes to allow an assistant toview the same surgical field as the surgeon.The microscope was known as the Diploscopeand was designed for teaching and demons-tration (Fig.55 see p.52). This new arrange-ment consisted of two surgical microscopesattached opposite to one another, and bymeans of a series of prisms which enabledboth operators to share the same illuminatedfield of view but from opposite sides. The as-sistant or observer could choose a lower mag-nification than the surgeon and also focus themicroscope independently. The usual wor-king distance from the base of the objectivewas 23cms, but this could also be 15cms.With the combination of the longer objectiveand the 20x eyepieces a choice of magnifica-tion of 6x, 10x, 16x, 25x or 40x was available.Using the shorter objective each magnifica-tion was increased by 20%.

Harms was the first to use this in-strument in ocular surgery, and it fulfilled anincreasing demand by students to be trainedin microsurgery. The students usually chosea smaller magnification than the surgeon.Harms emphasised the importance of settingup the Diploscope accurately so that therewas a superimposition of each visual field ofboth microscopes at various magnifications.Harms found several deficiencies in this in-strument: its bulkiness, focal working dis-tance and the fact that the surgeon andassistant had to operate opposite each other.In 1966 Harms developed with Zeiss a doublemicroscope, the OPMI 5, an altogether moreeffective instrument.

THE KEELER COMPANY

The Keeler Company’s initial invol-vement in the development of the ophthalmic

53

54

Fig.59: Keeler-Pierse binocular microscope

Fig.60: Keeler-Pierse microscope on head-rest

base

Fig.62: Keeler-Troutman stereozoom microscope byBausch and Lomb

Fig.63: Keeler-Troutman zoom micros-

cope on base

Fig.64: Keeler-Troutman zoom microscope with slit lamp

surgical microscope was with Ronald PittsCrick of London (Fig.56 see p.52). In 1956, PittsCrick, as a result of experience gained ori-ginally in ocular trauma, realised that it wasfoolish to examine patients with the slit-lampmicroscope before surgery and again examinethe results post-operatively, but not duringthe operation, when it could influence theconduct of the procedure. Experience withthe operating microscope also showed that theonly limitation in carrying out fine manipula-tions was magnification; and the poor qua-lity of the micro instruments, also that averageproprioception was well able to cope with any-thing that could be accurately visualised.

After the initial use of a hand-held bi-nocular microscope in a sterile towel, onemounted on a special stand was manufactu-red by Keeler and shown at the Oxford Oph-thalmological Congress in 1958.

There followed several months of theproduction of prototypes of a floor-mountedoperating microscope employing, at first,pneumatic and then more accurate electricfocussing mechanisms with foot control.With increasing experience the microscopewas used for the whole or part of almost alleye operations. The ‘steaming up’ of ocularswas avoided by an electrical warming de-vice.23 The use of a Beck microscope pod wasfollowed by mounting the original Zeiss sur-gical microscope head on the same standwhich also included integral illumination(Fig.57 see p.52). One feature that failed to be in-corporated was Pitts Crick’s suggestion of aninterpupillary distance gauge which wouldhave allowed the oculars to be preset preci-sely to the surgeon’s individual measurementprior to the operation.23 The microscope wascharacterised by its horse-shoe support armwhich gave great stability to the whole appa-ratus and the head of the patient immobilisedby a Ruben pillow.

The Pitts Crick microscope wasshown at the 18th International Ophthalmo-logical Congress in Brussels in 1958, by Kee-ler, it never went into production. The phase2 prototype microscope was used extensivelyat the Royal Eye Hospital, London from1958 and registrars were trained in its use.Becoming surplus to requirements in 1982, itwas presented to Dr Abhay Vasavada FRCSFRCOphth Senior Registrar at Kings College

Hospital, on his return to India as a consul-tant. It is still in daily use in his departmentat the Cataract and IOL Research Centre inAhmedabad. In the early part of 1960, Der-mot Pierse of London (Fig.58 see p.52), an inve-terate and brilliant inventor of a wide rangeof surgical instruments and equipment, sethis mind to the development of a microsurgi-cal system, working with the Keeler Com-pany. He recognised early on, like Dekkingand Pitts Crick, that one of the barriers to thesuccessful use of a surgical microscope wasthe movement of the patient’s head in rela-tion to the microscope. He overcame this withthe novel idea of combining the microscopeand operating table head-rest in afixed relationship. A shaped pillow made ofhard rubber, similar to the Ruben pillow al-ready referred to, was placed in a rectangularmetal base from which an arm holding themicroscope was fixed. This arrangement en-sured that the relationship between the pa-tient’s eye and the microscope was alwaysconstant and stable. The first Keeler-Pierseprototype model used an R & J Beck micros-cope of the Greenhough design with inter-changeable eyepieces which gave a choice ofmagnification of 6x, 10x or 13x (Fig.59 see p.54).Illumination was from one oblique lamp. At-tached to the head-rest metal base were twoadjustable arm- rests and a tray for instru-ments. The head rest base with attached mi-croscope was placed at the end and on top ofthe operating table. In a later model themicroscope unit rested on a Krahn hydraulictable, the complete unit was pushed up to theend of the operating table, and the head flapof the table was lowered. With both models themicroscope could be in position prior to the pa-tient being supported then lifted on to the pil-low. This microscope was shown for the firsttime at the American Academy of Ophthalmo-logy and Otolaryngology Exhibition in 1961.

When the Pierse Eye Operating TableHead went into production it included two 18-watt operating lamps giving strong, oblique,homogeneous and shadow-free illuminationon the eye. The lights could be left in positionwhen the microscope head was swung out ofthe field of observation (Fig.60 see p.54).

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56

Fig.65: Dekking operating with Olympus zoom microscope. Jan Worst assisting

Fig.66: Original letter from Dekking

THE FIRST MOTORISED ZOOM

MICROSCOPE FOR SURGERY

The next significant development inthe Keeler-Pierse unit was the substitutionof the single magnification R & J Beck mi-croscope for a Bausch and Lomb zoom mi-croscope.

The origin of the aberration-freezoom lens24 occurred shortly after the SecondWorld War when the British BroadcastingCorporation (BBC) asked the optical firm WWatson and Sons to produce a zoom lens foruse in televising sporting events. Dr HaroldH Hopkins, senior lecturer in technical opticsat Imperial College, London who was a con-sultant to W Watson, in due course success-fully tested his invention at Lord’s Cricket

Ground in 1948. In a further three years thelens was perfected. It was at this time thatHopkins was also acting as an optical designconsultant to the Keeler Company.

Little was he to know that his inven-tion of the zoom lens would enable Keeler tolaunch the first surgical microscope with mo-torised zoom optics sixteen years later. As amatter of record Watson and Son was one ofthe companies to produce a surgical micros-cope as early as 1948.

The Bausch and Lomb StereoZoommicroscope, with manual magnificationchange, had been available for some time asa laboratory microscope. Richard C Trout-man of New York (Fig.61) had tried unsuccess-

fully to adapt it to a Zeiss stand column 25 butwhen he saw the Keeler Pierse unit at theAmerican Academy of Ophthalmology in LasVegas he suggested to Charles Keeler that aBausch and Lomb StereoZoom microscope,with an uninterrupted magnification rangeof 3.5x to 15x, would be highly desirable forthis unit.26

Keeler took up the idea. With the ad-dition of a minus lens attached to the end ofthe standard zoom power-pod to increase theworking distance to 16 cm and motorisationof the magnification change knob, operatedby a heel and toe footswitch, the first motori-sed zoom microscope for use in any branch ofsurgery was launched in 1963. For the firsttime in ocular procedures, the surgeon couldselect the most suitable magnification wit-hout taking his eyes or hands away from theoperating site. The ‘sealed optics’ zoom mi-croscope was now mounted on the KeelerPierse head-rest base instead of the singlemagnification Beck microscope, and in addi-tion more powerful, obliquely mounted lampswere provided (Fig.62 see p.54). The unit hadnow become significantly heavier with thetransformer mounted on a column five feetabove the ground to conform to operatingtheatre electrical safety regulations.

At Troutman’s suggestion the mi-croscope was given its own dedicated hydrau-lic base. The ‘jaw’ between the head rest andthe hydraulic base could now envelop the firstpart of the operating table or stretcher whenpushed up to it (Fig.63 see p.54).

By 1965 the Keeler Micro Ophthal-mic Surgical Unit had incorporated furtherimportant additions.27

The call for fine focussing was metwith the attachment of a motor-driven eccen-tric cam attached to the objective lens of thezoom unit. This was operated by a simplefootswitch on a continuous one-direction-change basis so that the surgeon lifted hisfoot when he had achieved focus. In addi-tion to the more powerful oblique 30- wattlamps, slit illumination had been added.There was also a simple, fixed 6x magnifica-tion microscope attached on a ring of the mi-croscope pod which could be rotated to themost advantageous position for the assistantor observer(Fig.64 see p.54).

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Fig.61: Richard C Troutman

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Fig.67: Diagram of Dekking light attachment fittedto Keeler zoom power-pod

Fig.68. Dekking light attachment

Fig.70: Ignacio Barraquer 1884-1965

Fig.71: José Barraquer

1916-1998

Fig.72: Joaquin Barraquer*1927

At about this time Dekking hadmoved on from the original Zeiss microscopeto a Wild microscope with click-change mag-nification, and then to zoom magni-fication,using an Olympus zoom microscope. Like theBausch and Lomb microscope, the Olympuswas designed for labo-ratory bench work. Ithad a magnification range of 5.5x to 22x, butits free working distance was short at 12cms.Dekking had discovered a use for the mirrorwhich was positioned so as to reflect the illu-mination. He fixed a telescopic system, withbeam splitter, to the mirror aperture so thattwo observers could watch the operation at9x magnification and up to two feet away(Fig.65 see p.56).

After using the Olympus zoom mi-croscope, Dekking acquired the power-pod ofthe Keeler, Bausch and Lomb StereoZoommicroscope which he considered the bestzoom type microscope because of its free wor-king distance and fine optics. However, hemissed the occasional use of coaxial illumina-tion provided by the Zeiss microscope, as isoutlined in a personal communication in Feb-ruary 1965. (Fig. 66 see p.56 )

“As you will be aware, the only advantage ofthe old Zeiss operating microscope over alllater types is that it has a built-in light sourcewhich gives an almost co-axial illumination.This means that there is a bright red fundusreflex, which is extremely helpful in all opera-tions on the lens: the smallest impedimentsare clearly perceived as black spots or veilsagainst the red background, which cannot beseen at all with light coming from the side. I therefore built a small projection unit witha prism that extends just to the border of themicroscope’s objective lenses and which fitsexactly on the B & L microscope. Thoughonly a 15 watt built is used, the light at thefull voltage of 6v is so strong that most pa-tients cannot endure it, so we mostly run it on4 to 5 volts. The diameter of the light field isexactly the same as the viewing field of the mi-croscope at its smallest magnification. I think that most surgeons which use yourequipment would enjoy this addition verymuch once they are acquainted with it.” (Figs.67 and 68 see p.58).

Dekking had now motorised the X-Ymovement of the microscope column and in-troduced a second motor which slowly turned

the vertical column from which the micros-cope was supported on a long horizontal bar(Fig.70 see p.58). This small movement descri-bing part of an arc gave a fine backwards andforwards movement to the microscope head.

The indefatigable Henri Dekking,who had probably experimented with moremicroscope systems than anybody in theearly pioneering years of ophthalmic micro-surgery, died in November 1966.

BACK TO ZEISS

The story of the ophthalmic surgicalmicroscope is not just about magnification,working distance and forms of illumination,but of the various ways in which the micros-cope could be mounted. An alternative to thefloor stands of Zeiss and the head-rest systemof Keeler was the ceiling mount devised bythe Barraquer family, firstly in Barcelona byIgnacio and Joaquin, and then in Bogota byJosé28 (Figs.70, 71 and 72 see p.58).

The suspension of the microscopefrom the ceiling was achieved before 1962 byJoaquinBarraquer, employing a special co-lumn devised by his father, Ignacio, for use incinematography and the holding of otherequipment and instruments (Fig.73 see p.60).The control of lights and focussing of themicroscope was done by foot operation of anelectric motor mounted in the base of a spe-cial chair, complete with arm rests. In 1962,Barraquer added an X- Y mechanism to theoperating table itself.

Another system for mounting the mi-croscope was devised by Troutman. He pla-ced a modified Barraquer chair on to thebase of a shock-proof, motor driven hydraulicunit from Ritter which was on heavy-dutycastors and could be blocked for stabilisationwhen in position. The Zeiss surgical mi-croscope, complete on articulated arm but re-moved from its base, was attached to the backof the chair. The whole unit could then bemoved up to the operating table.26

The recording of operations either bystill photography, movie or video was an im-portant development in ophthalmic surgerypioneered by Zeiss. Their surgical microsco-pes, including the Diploscope, had a varietyof attachments and adaptors to cover all me-thods of recording.

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Fig.73: Barraquer ceiling mounted microscope

Fig.74: Zeiss OPMI II zoom microscope

Fig.75: Zeiss OPMI II zoom microscope with lights

Fig.76:

Storz-Troutman-Zeiss

zoom microscope

Zeiss’s first venture into zoom opticsin a surgical microscope was in 1965. Themicroscope was known as the OPMI II29

(Fig.74 see p.60). Mounted on a sturdy standwith completely internal wiring, the zoom mi-croscope was built on a modular basis. Apartfrom its simplest mode of zoom microscope,with two focusable lamps, (Fig.75 see p.60) abeam splitter allowed, as an alternative, theuse of an assistant’s microscope, observertube and photographic attachment all on thesame instrument. The specially designedzoom system for microsurgery provided acontinuous change of magnification at theratio of 1:5. By using different objectives andeyepieces, already available on other Zeiss mi-croscopes, the surgeon could choose a zoomrange of, for example, 2.5 to 12.5x or upto 10.7 to 53.5x. The most usual choice wasthe range from 5 to 26x. Both focussing andzoom change operations were carried out byremote foot controlled motors.

Before Zeiss’s zoom microscopeOPMI II was commercially available, a hybridzoom microscope had appeared in 1964,constructed by the Storz Instrument Com-pany of St Louis with the assistance of Trout-man (Fig.76 see p.60). The microscope used thenew Zeiss zoom optics which had been deve-loped for the line of laboratory bench micros-copes and later their range of slit lamps. Itfeatured a motorised focussing device andmagnification changer, both foot- operated,leaving the surgeon’s hands free for opera-ting. This was the first zoom microscope tohave both these features. The eyepieces wereangled and convergent. Illumination wasfrom two oblique lamps which could be placedin any position.30

After the introduction of the Diplos-cope, the first Zeiss microscope specificallydesigned by Dr Littmann for ocular surgerywas launched in 1966.31 This microscope be-came known as the Zeiss OPMI 3 (Fig.77 seep.62). It was the Barraquer brothers whoestablished the requirements for this designfollowing a question that José was asked atthe Cornea World Congress in Washington in1964 as to what he thought would be the idealsurgical microscope. In his reply he categori-cally stated that the microscope should allowthe surgeon to operate from a comfortable sit-ting position and that the distance from theoperator’s eyes to those of the patient should

be as short as possible and no more than30cm. The microscope should have a move-able lamp with homogeneous illuminationand also a slit- lamp that could be rotatedin the desired meridian. This lamp shouldhave a diaphragm that could be opened to pro-vide secondary homogeneous illumination.

The Zeiss OPMI 3 microscope waslaunched two years later in 1966, by whichtime a third arm for a lamp with homogene-ous illumination had been added. The OPMI3 was, in effect, a fixed magnification micros-cope during the operation. In the Barraquerclinics the microscope was suspended fromthe operating theatre ceiling and fine fo-cussing was by motorised footswitch.

A busy year for Zeiss ended with thelaunch of a new double microscope to replacethe Diploscope, which was considered to betoo bulky and unwieldy. The Harms doublemicroscope known as the Zeiss OPMI 5 wasaltogether different (Fig.79 see p.62). Two com-pact binocular microscopes could be rotatedindividually around a central column so thatthey could be positioned at any angle to eachother. Each microscope had a Galilei manual‘click’ magnification change system and thedual microscopes had illumination from twooblique lamps. The oculars for the surgeonhad a broken angle, whereas the assistant hada choice of straight, or broken, angle oculars.

THE OTHER ZEISS

THE JENA

OPERATING SLIT LAMP MICROSCOPE

While Zeiss, in Oberkochen, West Germany,were developing operating microscopes inthe 1950s and 1960s, under their chief scien-tific designer, Dr Hans Littmann, the originalJena branch of Zeiss had been producingtheir own general operating microscopes.In 1963 an operating slit-lampmicroscope for ophthalmic surgery was ma-nufactured under the supervision of Pro-fessor Karl Velhagen of the University EyeClinic in Berlin (Fig.80 see p.62).

It was designed to bring the advan-tages of slit illumination and the stereoscopicmicroscope to eye surgery on recumbent pa-tients. The microscope and stand was of asturdy construction (Fig.81 see p.62). The move-

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Fig.77: Barraquer-Zeiss OPMI 3 microscope

Fig.79: Harms double microscope.

Zeiss OPMI 5

Fig.81: Velhagen's microscope by Carl Zeiss Fig.80: Karl Velhagen 1897-1990

able pedestal contained a foot- operated hy-draulic pump for height adjustment. At thehead of the pedestal an extendable arm waspivoted giving an arc of 60° through which itcould be swung. At the end of this arm therewere two shafts, the inner shaft holding ahead rest, while the lower one carried the mi-croscope and slit- lamp. The slit-lamp couldbe swung through + 45° in the horizontalaxis and + 330° in the vertical. The micros-cope and head rest were independent of theslit- lamp and could be swung + 90° roundthe vertical axis. The microscope had electri-cally controlled fine focussing. The micros-cope had a click-stop magnification choice of4x, 6.3x, 10x, 16x and 25x. The slit lamp wasof a standard manufacture and because ofthis the free working distance was very close.

MÖLLER-WEDEL

In 1966, at the 20th InternationalCongress of Ophthalmology in Munich, acompany new to ophthalmic surgical micros-copes, J D Möller-Wedel of Germany introdu-ced a complete microsurgical unit which wasboth highly complex and expensive (Fig.82).This was the brainchild of Professor HansSautter and Jorg Draeger of Hamburg 32, 33.Although the Barraquers, with their highlyindividualistic installation, had pioneered cei-ling suspension of the microscope, illumina-tion and recording facilities, the Möllerunit was not only mounted from the ceiling,but was the first fully comprehensive micro-surgical unit. In addition to the motorisedzoom microscope giving a continuous magni-fication range of 3x to 15x at a free workingdistance of 16cms, there were two lamps,film, TV and microphone. The suspensionalso incorporated equipment such as cautery,diathermy, ophthalmoscope, anaesthetic out-lets and erysophake. All of the equipmentwas connected to a single flexible cable. Con-trol of the various instruments was by a se-ries of footswitches mounted at the base of aspecial chair. The chair incorporated armrests and could be adjusted in height andangle to suit the individual surgeon’s requi-rements. The Sautter/Draeger system alsohad an operating table with an electricallyoperated X-Y mechanism operated by foots-witch for centring the patient’s eye in theoperating field. Coaxial illumination and anassistant’s microscope were later additions tothe microscope.

DANNHEIM MICROSCOPE SYSTEM

The idea of orientating the patient onthe operating table under the static micros-cope was reported by Dr Helmut Dannheim(Fig.83) some years before, in 1961.34 Dann-heim pointed out that perhaps the lack of en-thusiasm for the operating microscope on thepart of ophthalmologists was the frequentneed to recentre the microscope and refocusthe eye after every small movement by thepatient.

To overcome these difficulties, and tobe able to continue to operate with bothhands free, Dannheim used his feet to controlmovement while operating in the sitting po-sition. His operating table (Fig.84), con-structed with the assistance of Zeiss andKlopfer of Stuttgart, consisted of a flat boardcovered with a layer of thick foam rubberwhich lay on ball bearings on top of the maintable structure. Using a foot pedal with atransmission ratio of 1:15, he was able to

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Fig.83: Helmut Dannheim (1907-1993)

64

Fig.82:

Möller-Wedel

microscope system by

Sautter/Draeger

Fig.84:

Dannheim's floating operating table

Fig.86: Dannheim's ceiling/floor microscope column

Fig.87:

Marian Barraquer being presented to Princess Margaret

with Joaquin Barraquer (left) and Louis Paufique looking on 1967

move the padded board in all directions re-gardless of the patient’s weight. Very preciseorientation of the eye and its surrounding tis-sue could be achieved quickly by foot control.On the foot pedal there were two switchesconnected to an electric motor to focus themicroscope. One switch pulled the micros-cope down at the rate of 2.5mm per secondand the other raised it at the same speedagainst a counterweight. The apparatus hada safety mechanism whereby the microscopewould rise automatically if there was an elect-rical fault: in that event focussing would be-come manual. Dannheim found the large,heavy base of the Zeiss microscope distur-bing. Instead of the moveable, base-mountedcolumn, he attached the microscope with itsarticulated arm on a pole which stretchedfrom floor to ceiling and was rigidly fixed inone position. The transformer and motorwere clamped on to the lower part of the co-lumn.

Following Harms’s example, he hadconstructed a roll-around chair, with adjusta-ble armrests, connected to the footrest (Fig.86see p.64). He was able to move in an arc of 180oaround the patient without losing the advan-tage of adjusting the microscope with his foo-trest mechanism.

CONCLUSION

Even by the late 1960s, many oph-thalmic surgeons were yet to be convincedabout microsurgery. At the Corneo-PlasticConference (Fig.87 see p.64) held in London in1967, Ramon Castroviejo was asked why hedidn’t use a microscope. His answer echoedwhat many ophthalmic surgeons were stillfeeling: “Use of the microscope is a matter ofpersonal adaptation. It requires patience astime is lost manipulating the instrument.Many people prefer to use loupe glasses whichare made as strong as 5x now with a strongilluminating source of light. I use a micros-cope in all cases of corneal grafting, not du-ring the whole operation, mainly for insertingstitches. I find that if the microscope is smallenough, I can work as fast using it as withoutone, and with much more ease.”

In July 1963, Dr Gerard DeVoe wrotean editorial in the Archives of Ophthalmo-logy35 with the title “A forward look at oph-

thalmic surgery”. He concluded that ophthal-mic surgery had attained a high level of effi-ciency. He went on to state: “It is probablethat with present instrumentation little furt-her improvement in technique is likely tooccur. I would like to propose that the real fu-ture of ophthalmic surgery, from a technicalstandpoint at least, lies in the development ofmicrosurgery”.

In 1966, the first meeting of the Mi-crosurgery Study Group convened a sympo-sium in Tübingen in Germany on the subject‘Microsurgery of the Eye’.36

There were 38 participants from 14countries, including four representativesfrom industry. Many issues were discussed atthat meeting, covering the future of allaspects of microsurgery including microsco-pes, surgical instruments and sutures.These early pioneers of microsurgery had nodoubt about the importance of producing theright design in surgical microscopes and in-struments for the future of ocular surgery.Their commitment duly bore fruit, and fewophthalmic surgeons today work without themicroscope for most procedures, enjoyingsurgical instruments and sutures which wereonly a dream in the 1950s.

REFERENCES

1. Landolt I E: Review of surgical lou-pes. Handbuch der Augenheilunde. Berlin,Springer 1920, 354-360. 2. Jackson E: Magnifying lenses for usewhen operating. Arch: Ophthal 1897; 26: 274-277.3. Rohr M v, Stock W: Ueber eine achro-matische Brillenlupe Schwacher Vergrösse-rung. Klin. Mbl. Augenheil:1913; 51, 206-210. 4. Liebreich R: Seitliche Beleuchtungund mikroskopische Untersuchung am leben-den Auge. Arch. f. Ophthalmologie 1854;1.1,a 1, 351-356. 5. Wecker L de: Études Ophtalmologi-ques 1863; Vol I, 272. 6. Laqueur L: System of Diseases of theEye Vol II, ed. Norris W F, Oliver C A. J B Lip-pincott Co 1897; 58. 7. Zehender K W v: Beschreibung derbinocularen Cornea-Loupe. Klin. Mbl. Augen-heil. 1887; 25: 496-499. 8. Laqueur L: System of Diseases of the

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Eye Vol II, ed. Norris W F, Oliver C A. J B Lip-pincott Co 1897; 57. 9. Axenfeld T: Eine neue Westien'schebinoculare Handloupe (Brillenloupe). Klin.Mbl. Augenheil. 1900; 38: 20-25. 10. Buchanan L: A new portable cornealmicroscope. The Ophthalmoscope. 1908; 957.11. Czapski S: Binokulares Corneal Mi-kroskop. v Graefe Arch f. Ophthal. 1899;Band XLVIII S: 229-235. 12. Mawas J: La Biomicroscopie de l'oeil.Bull. et mém. Soc. Franc. d'opht 1925; 38,527. 13. Nylén C O: The microscope in auralsurgery, its first use and later development.Acta Oto-laryng (Stockh) Suppl 116 1954;226-240. 14. Perritt R A: Micro Ophthalmic Sur-gery. Belgica Acta Vol II 1958: 1680-1683.Perritt R A :The Operating Microscope inpractice. Adv. Ophthamol 1968 ; 20, 21 15. Littmann H: Das Operationsmikros-cope. Zeiss- Information 1953 ; Heft 10 Litt-mann H: Ein neues Operations - Mikroskop.Klin. Mbl. Augenheil. 1954; 124: 473- 476. 16. Harms H: Augenoperationen unterdem binocularen Mikroskop. Ber. Dtsch.Ophth. Gesellsch Heidelberg 1953; 58: 119-122. 17. Harms H. Mackensen G: Augenope-rationen unter dem Mikroskop. Tübingen.Verlag. Stuttgart 1966. Ocular Surgery underthe microscope. Year Book Medical Publis-hers Chicago, 1967. 18. Dekking H M: Use of the binocularmicroscope in eye operations. Arch. Ophthal1956; 55, 114-117. 19. Ruben C M: Operation-table head pil-low. Brit. J. Ophthal 1959; 43: 117. 20. Barraquer J : La extraoción intracap-sular del cristalino. Barcelona, Soc. Oft . Hi-spano- Mericana 196.. 58-59 Barraquer J:Comments on Microsurgery. Adv. Ophthal.Karger 1968; 20, 7-I5. 21. Becker B: The Zeiss Operating Mi-croscope. Amer. J. Ophthal 1956; 42, 302-3, 22. Barraquer J 1: The Microscope inOcular Surgery. Amer. J. Ophthal. 1956; 42,916-918. 23. Pitts Crick R. Discussion. Trans. Op.Soc. UK 1967; 87, 237. 24. Hopkins H H: Biog Mems. Fell. R.Soc. Lond.1998: 44, 233-252. 25. Troutman R C: The Operating Mi-croscope in Ophthalmic Surgery. Tr.Am.Ophth. Soc. 1965; 63, 335-348 26. Troutman R C: High Magnification

in Surgery of Cataract. Symposium on Cata-racts. Trans. New Orl Acad. Ophth. C VMosby: 1965; 115-136 27. Keeler C R: The Keeler Micro Oph-thalmic Surgical Unit. Adv. Ophth. Kargcr1968; 20, 51-61. 28. Barraquer J I: The History of the Mi-croscope in Ocular Surgery. J Microsurgery.Jan/Feb 1980: 288-299. 29. Littmann H : The Microscopes ofZeiss. Adv. Ophthalm: Karger 1968: 20, 65. 30. Troutman R C. The Operating Mi-croscope in Corneal Surgery. The CorneaWorld Congress. Butterworths. Washington1965; 428. 31. Barraquer J I, Barraquer J, LittmannH: A New Operating Microscope for OcularSurgery. Amer. J. Ophthal 1967: 63, 90-97. Barraquer J I, Barraquer J, Littmann H :Ein besonders geeignnetes operationsmikro-skop fur die Augenchirurgie. 32. Sautter H, Draeger J: Technical Im-provements in Ophthalmic Microsurgery.Adv. Ophthalm: Karger 1968; 20, 66-79. 33. Draeger J: Discussion. Trans Ophth.Soc UK: 1967; 87, 230-234. 34. Dannheim H: Ein Beitrag zur Mikro-chirurge. Klin Mbl Augenheil 1961;138, 874-876. 35. DeVoe A G: A forward look at Oph-thalmic Surgery. Arch. Ophthal 1963; 70, 2-4. 36. Mackensen G, Roper-Hall M, Trout-man R C (Eds): Microsurgery of the Eye. Adv.Ophthalm Karger 1968; 20.

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