direct opthalmoscopy

Direct Ophthalmoscopy

Sanket Parajuli

Introduction• Jan Purkinje (Latin -1823) - Complete technique of

ophthalmoscopy • Next 25 years: Kussmaul, Cumming, Brucke, and Babbage

worked on the ophthalmoscope

• 1851 Helmholtz - First useable direct ophthalmoscope

I had to explain to my students that the theory of emission of the reflected light from the eye was discovered by Brucke. He was a hair’s breadth from the invention of the ophthalmoscope. He failed to ask himself what optical image was formed by the rays reflected from the luminous eye.

To obtain an optical image of the retina, he had only to devise an instrument in which his eye could be placed in line with rays of light entering and leaving the observed eye.

Helmholtz invented the first useable direct ophthalmoscope, which he described in a letter to his father

Ophthalmoscope

• Consists of a single aperture through which light is projected into subject’s eye and examiner views the eye

• Magnifies image (×15) and a field of view ~ 6.5–10 degrees

• Magnification = power / 4 60/4= X 15

• Hand held instrument (electrical or battery – powered)• Parts :– Handle – Head with a light source – Peep hole with a set of built in dial-up lenses – Reflecting device to aim light on to the patient’s eye

Ophthalmoscope head , neck, body

peephole

On/off rheostate

Contains battery here

Instrumentation

Direct Ophthalmoscope • Illumination system & observation system

Illumination system• Light source• condensing lenses• reflecting prism• an aperture

Observation system –• Peephole• bank of spherical lenses

Concave mirror with a hole in centre

Selects light size, filter & grid

Connects to rheostate and handle containing batteries

Bulb in here

Lens strength selector wheel

Principle

hhhMIRROR

Emergent rays from the fundus of the observed eye (O1) showing formation of retinal image on retina of observer's eye (02)

In emmetropia (E) - emergent parallel rays are brought to a focus on the retina of 02 if the accommodation of this eye is absolutely at rest.

In hypermetropia (H)- the emerging divergent rays are brought to a focus on the retina of 02, either by means of accommodation or by placing a convex lens in front of 02.

O1 O2

In myopia, M, the emergent convergent rays can only be brought to a focus on the retina of 02 by placing a concave lens in front of 02.

O1 O2

• In 1970s, a camera company designed a flashbulb that fitted tightly onto a small, flat camera - red pupils

• Optically: occurs when axes of light source and observation system of camera are almost coincident

• Redness of pupil = unfocused image of blood-filled choroid

• This system of concentric illumination and observation is the very essence of the optics of the ophthalmoscope

• To bring red fundus reflex into sharp focus, modern ophthalmoscope has a disc of lenses, developed by Rekoss

• Most important advance = halogen tungsten bulb in quartz jacket

• A quartz jacket can withstand higher temperatures vs glass jacket

• Use of halogen vapor (bromine or iodine) within quartz envelope extends life of filament and maintains an almost constant light output

• Field of view ~ 10°• To enlarge field of view examiner’s eye must be closer to patient’s eye

with patient’s pupils dilated

• Enlargement capacity of any magnification lens = 1/4th of lens power

• Retinal image in emmetropic eye (60 D)- magnified by 60/4, or ×15• In aphakic eyes (20 D natural lens removed ) =magnification for the observer is reduced to about 40/4 or ×10.• Hyperopic eye of +10D ---power of eye= 50D Thus magnification = 50/4= X 12.5 • Myopic eye of -10D---power of eye= 70D Thus magnification = 70/4= X 17.5

Characteristics of the image• Virtual• Erect and • Magnified image.• Magnification ME = 15XFor emmetrope, ME =15XFor myope ,moreFor hyperope, less.

M= 250mm/16.67mm=X15

05/02/2023

Methods of Ophthalmoscopy• Distance direct ophthalmoscopy– Illuminating eye from 25-40 inches

• Direct ophthalmoscopy– Approach closer to patient.

Procedure1. Ideally should be examined in a dark room.2. Ask the patient to fix stare at an object.3. Turn on scope and set dial at 0.4. Hold ophthalmoscope in right hand and look through

examiners’r right eye at patient’s right eye5. Begin at arms length6. Examine for red reflex at arm’s length (20-40cm) - distant direct

I. Normal - red glow from choroidII. Look for opacities or loss of reflex

7. Move close until optic disc is visible – direct ophthalmoscopy8. Turn dial until disc is in focus - +/-

Red free filter

Slit

Grid and fixation targetBlue filter

Red free filter

half spot

Small spot

Large spot

Clinical Uses Fundus examination Media opacities can be detected Estimation of patients refractive error Small aperture and half moon: when pupil is miotic and in case of media opacities

Slit beamTo view the contours in iris and retina

Red Free filter—nerve fiber layer defect & to estimate CDR Blue filter- staining Light to check pupillary reflex To estimate AC depth—shadow technique

Clinical Importance

• Anterior segment: # Grossly examine the cornea, lids, sclera, lashes and iris. # Use 10D-13D lenses in ophthalmoscope# 2-3 inches away

• Vitreous: Vitreous floaters are best seen with a + 6 or 7 D lens in place.

Evaluating fundus

• Find optic disc following blood vessels• Examine the peripapillary area

• Use red free filter examine arcuate nerve fibre layer defect• Follow blood vessel outside to examine

– Superonasal– Inferonasal– Superotemporal – Areas around the posterior pole

• Note: vascular color, caliber, bifurcation, crossing, surrounding background

• Examine macula– Use slit beam to detect distortion of retinal surface

• Use focusing dial to approximate height of elevated lesions (choroidal tumour, disc edema)

Systematic examination withthe direct ophthalmoscope

Optic Disc

• Move as close to the patient as possible.• Find the optic disc

• • Shape-round to oval; diameter (1.5-1.7)• Margin-sharp or dull• Colour: red-yellow • Vessels emerged from disc

Features to note when examining the opticdisc.

• C/D ratio (cup/disc)

ISNT rule

Retina

• Periphery- lighter than central area• AV ratio (normal 2:3)• Fundus colour :– Darker with pigmented skin or retinitis pigmentosa– Pale with arterial occlusion

• Macula- appears darker than central area -3mm temporal to disc. - Central foveal reflex- Healthy/ dull

Examples of optic disc abnormalities

Normal disc: note the distribution of the neuroretinal rimaround the disc.

A swollen disc: the margin is not clearly demarcated; the patient had papilloedema.

The cup is enlarged, neuroretinal rim thinned and the ISNT pattern lost

New vessels are growing at the disc

The disc has an irregular lumpyappearance and optic disc drusen

Myelinated nerve fibres at the disc margin

Exudates in a circular (circinate) pattern with a retinalhaemorrhage in the centre.

Drusen at the macula; margins are less distinct than those of theexudates.

Preretinal haemorrhage.

Limitations of direct ophthalmoscope:

• No stereoscopic view• Inadequate illumination if opacities are present• High myopia– too large image• Astigmatism—distorted image• Small field of view

References 1. Ophthalmology – Yanoff and Duker 3rd edition2. American Academy of Ophthalmology, practical

ophthalmology 3. Ophthalmology Investigation and Examination Techniques-

Bruce James, Larry Benjamin4. Parsons’ Diseases of the Eye, 22nd Ed5. Internet sources

Thank you