REFRACTIVE SURGERYREFRACTIVE SURGERY

Refractive surgical techniques have evolved rapidly Refractive surgical techniques have evolved rapidly over the past three decadesover the past three decades. .

Emerging as safer and more reliable means of Emerging as safer and more reliable means of treating myopia , hyperopia and astigmatism ,thus treating myopia , hyperopia and astigmatism ,thus reducing the need for corrective lensesreducing the need for corrective lenses

Although a wide range of refractive procedures Although a wide range of refractive procedures exists , we will discuss the following refractive exists , we will discuss the following refractive

proceduresprocedures : :

. .

A) Radial keratotomyA) Radial keratotomy. .

B) Excimer laser photorefractive keratectomy ( PRK )B) Excimer laser photorefractive keratectomy ( PRK )

C) Laser assisted in situ keratomiliuses (LASIK)C) Laser assisted in situ keratomiliuses (LASIK)

D) Laser assisted subepithelial keratomiliuses ( LASEK )D) Laser assisted subepithelial keratomiliuses ( LASEK )

E) Laser thermokeratoplasty (LTK )E) Laser thermokeratoplasty (LTK )

D) Intracorneal ring segments (ICRS)D) Intracorneal ring segments (ICRS)

G) Phakic intraocular lenses (IOLs )G) Phakic intraocular lenses (IOLs )

History of keratorefractive surgeryHistory of keratorefractive surgery

Radial keratotomy to correct myopia was Radial keratotomy to correct myopia was introduced in Japan in the 1940s using anterior introduced in Japan in the 1940s using anterior and posterior corneal incisions . This approach and posterior corneal incisions . This approach fell into disfavor 10 to 20 years later when fell into disfavor 10 to 20 years later when resulting endothelial cell injury led to irreversible resulting endothelial cell injury led to irreversible

corneal oedemacorneal oedema. . Russian investigators improved the procedure Russian investigators improved the procedure

in the 1970s by using only anterior incisionsin the 1970s by using only anterior incisions..

Since it's introduction to the United States in Since it's introduction to the United States in 1978, RK underwent continual refinement,but 1978, RK underwent continual refinement,but long term studies showed significant instability long term studies showed significant instability and progressive hyperopic shifts that led to and progressive hyperopic shifts that led to virtual abandonment of this surgical procedure virtual abandonment of this surgical procedure

in the late 1990sin the late 1990s. . Excimer laser which makes pulses of invisible Excimer laser which makes pulses of invisible

ultraviolet light of 193 nm ,each pulse of light ultraviolet light of 193 nm ,each pulse of light can removes a microscopic layer from the front can removes a microscopic layer from the front surface of the cornea , was introduced in surface of the cornea , was introduced in ophthalmology to reshape the anterior corneal ophthalmology to reshape the anterior corneal

surfacesurface . .

Early excimer laser was used in the PRK Early excimer laser was used in the PRK operation, establishing it's efficacy for the operation, establishing it's efficacy for the correction of myopia, hyperopia , and correction of myopia, hyperopia , and astigmatism .later excimer laser was used in astigmatism .later excimer laser was used in the operations of LASIK,LASEK and LTKthe operations of LASIK,LASEK and LTK..

The preoperative evaluation is of great The preoperative evaluation is of great importance in these circumstances , like patient importance in these circumstances , like patient selection ,motivation , selection ,motivation , contraindications ,physical and ocular contraindications ,physical and ocular examination ,cycloplegic refraction , and examination ,cycloplegic refraction , and screening tests like pachymetry , keratometry screening tests like pachymetry , keratometry

and computerized videokeratograohyand computerized videokeratograohy. .

We will discuss now the main refractive We will discuss now the main refractive procedures according to it's developmentprocedures according to it's development: :

11 ( (Radial Keratotomy (RK ): Refers to the Radial Keratotomy (RK ): Refers to the placement of deep paracentral and peripheral placement of deep paracentral and peripheral incisions in the cornea ,producing central incisions in the cornea ,producing central corneal flattening and thus reducing the central corneal flattening and thus reducing the central

refractive power and myopiarefractive power and myopia. .

RK is best for low myopia ( -2.00 TO -3.00 D.)RK is best for low myopia ( -2.00 TO -3.00 D.)The procedure has the advantage of being safe The procedure has the advantage of being safe

,with rapid results and high predictability in the ,with rapid results and high predictability in the low range of myopialow range of myopia. .

Incisions are ideally 80% to 90% of corneal Incisions are ideally 80% to 90% of corneal depth , and should not extend to Descement depth , and should not extend to Descement membrane to avoid the danger of mechanical membrane to avoid the danger of mechanical

instabilita and perforationinstabilita and perforation. . In general no more than eight radial cuts was In general no more than eight radial cuts was

done with a 3.0 mm central clear zonedone with a 3.0 mm central clear zone

22 ( (Astigmatic keratotomy : constitutes the Astigmatic keratotomy : constitutes the placement of transverse or arcuate incisions placement of transverse or arcuate incisions perpendicular to the steepest corneal meridian perpendicular to the steepest corneal meridian to correct astigmatism , the incised meridian to correct astigmatism , the incised meridian flattens while the meridian 90 degrees away flattens while the meridian 90 degrees away steepens by nearly the same amount .Incisions steepens by nearly the same amount .Incisions are ideally between 5 and 7mm from the pupil are ideally between 5 and 7mm from the pupil

centercenter. .

33 ( (Excimer laser PRKExcimer laser PRK: : Photorefractive keratectomy uses the cool Photorefractive keratectomy uses the cool

beam of the excimer laser to reshape the front beam of the excimer laser to reshape the front of the eye by treating the surface of the cornea of the eye by treating the surface of the cornea so that the rays focus more sharply on the so that the rays focus more sharply on the

retinaretina. . The outer surface of the cornea , called The outer surface of the cornea , called

epithelium , must be removed , this is epithelium , must be removed , this is accomplished by carefully scraping it awayaccomplished by carefully scraping it away. .

The laser is then applied directly to Bowman The laser is then applied directly to Bowman membrane and anterior corneal stroma to membrane and anterior corneal stroma to remove microscopic amounts of these tissues remove microscopic amounts of these tissues

measured in micronsmeasured in microns . .

The epithelium grows back over the treated The epithelium grows back over the treated area within several daysarea within several days. .

A (bandage ) contact lens is placed on the eye A (bandage ) contact lens is placed on the eye to minimize discomfort during this healing to minimize discomfort during this healing period . Complete healing and visual recovery period . Complete healing and visual recovery

can take as long as 3-6 months with PRKcan take as long as 3-6 months with PRK. .

RESULTS : In FDA Phase III trials for PRK in RESULTS : In FDA Phase III trials for PRK in low myopia (-1 to -6 D),88 to 92% of patients low myopia (-1 to -6 D),88 to 92% of patients had uncorrected vision of 20/40 or better at 1 had uncorrected vision of 20/40 or better at 1 year with 50 to 60% better than or equal to year with 50 to 60% better than or equal to 20/20, and 70 to 80% within 1.0 D of the 20/20, and 70 to 80% within 1.0 D of the

intended refractionintended refraction. .

Excimer laser PRK for higher levels of myopia Excimer laser PRK for higher levels of myopia is somewhat less predictableis somewhat less predictable. .

LASIK has virtually replaced PRK for the LASIK has virtually replaced PRK for the treatment of hyperopia and higher degrees of treatment of hyperopia and higher degrees of

myopiamyopia. .

44 ( (LASIK( Laser assisted in-situ KeratomileusisLASIK( Laser assisted in-situ KeratomileusisIs a refractive surgical procedure that results in rapid Is a refractive surgical procedure that results in rapid

recovery of vision and has the capability to benefit recovery of vision and has the capability to benefit patients with myopia , hyperopia , and astigmatism . patients with myopia , hyperopia , and astigmatism . Millions of people worldwide have already this exciting Millions of people worldwide have already this exciting and marvelous procedure . Candidates must be at and marvelous procedure . Candidates must be at

least 18 years of ageleast 18 years of age. . In this procedure the eye surgeon creates a thin In this procedure the eye surgeon creates a thin

surface flap of the cornea using a microkeratome to surface flap of the cornea using a microkeratome to expose the underlying tissues ( stromal bed ) in which expose the underlying tissues ( stromal bed ) in which the surgeon applies the excimer laser beam to create the surgeon applies the excimer laser beam to create

the refractive ablationthe refractive ablation . . Once the laser ablation is completed , the surgeon Once the laser ablation is completed , the surgeon

gently replaces the corneal surface flap to restore gently replaces the corneal surface flap to restore surface integrity of the eyesurface integrity of the eye. .

The results are often dramatic and very rapid , The results are often dramatic and very rapid , with most patients seeing well enough to drive with most patients seeing well enough to drive

a car without correction the very next daya car without correction the very next day. . However , the best post-operative visual acuity However , the best post-operative visual acuity

may not be obtained until 2 to 3 weeks , or in may not be obtained until 2 to 3 weeks , or in some cases , even a few months after the some cases , even a few months after the

procedureprocedure . .

Visual results with LASIKVisual results with LASIK: : LASIK nearly always results in improved vision LASIK nearly always results in improved vision

without correction .However LASIK is an without correction .However LASIK is an imperfect procedure , and does not always imperfect procedure , and does not always

result in 20/20 or even 20/40 visual acuityresult in 20/20 or even 20/40 visual acuity . .

Patients in the extreme range of myopia Patients in the extreme range of myopia generally have less favorable outcomes with generally have less favorable outcomes with

LASIKLASIK. . In a study results of the American Society of In a study results of the American Society of

Cataract and Refractive Surgery from 1736 Cataract and Refractive Surgery from 1736 eyes with myopia and myopic astigmatism that eyes with myopia and myopic astigmatism that underwent LASIK operation , they showed the underwent LASIK operation , they showed the

following resultsfollowing results: : Post-op 1 month 3 months 6 monthsPost-op 1 month 3 months 6 months

20/2020/20 or better 45% 46% 50%or better 45% 46% 50%20/4020/40 or better 87% 89% 93%or better 87% 89% 93%

The best candidate for LASIK is an individual The best candidate for LASIK is an individual who desires to be less dependant on glasses or who desires to be less dependant on glasses or contact lenses , is willing to accept the risk of the contact lenses , is willing to accept the risk of the procedure , and understands that an procedure , and understands that an enhancement procedure may sometimes be enhancement procedure may sometimes be requiredrequired. .

We now know that dry eye syndrome commonly We now know that dry eye syndrome commonly follows LASIK procedures , at least transiently . follows LASIK procedures , at least transiently . This make the patient feels dry or gritty or even This make the patient feels dry or gritty or even blurring vision . Many surgeons advise using non-blurring vision . Many surgeons advise using non-preserved artificial tears for the first few weeks preserved artificial tears for the first few weeks after LASIKafter LASIK. .

55 ( (LASEK(Laser Subepithelial Keratomileusis )LASEK(Laser Subepithelial Keratomileusis )

LASEK is a relatively new procedure that sits LASEK is a relatively new procedure that sits somewhat between LASIK and PRK ,is used somewhat between LASIK and PRK ,is used mostly for people with corneas that are too thin mostly for people with corneas that are too thin

or too flat for LASIKor too flat for LASIK. . It was developed to reduce the chance of It was developed to reduce the chance of

complications that occur when the flap created complications that occur when the flap created during LASIK is not of the ideal thickness or during LASIK is not of the ideal thickness or

diameterdiameter. . In LASEK instead of using a microkeratome , a In LASEK instead of using a microkeratome , a

blade called a trephine is usedblade called a trephine is used

LASEK is a procedure that takes about the LASEK is a procedure that takes about the same amount of time as LASIK . A topical same amount of time as LASIK . A topical anesthetic is applied to the eye , then the anesthetic is applied to the eye , then the trephine is used to create the epithelium flap . trephine is used to create the epithelium flap . After the flap is made , the surgeon covers the After the flap is made , the surgeon covers the eye with a dilute alcohol solution (20% ) . The eye with a dilute alcohol solution (20% ) . The

solution loosens the edges of the epitheliumsolution loosens the edges of the epithelium. . After the eye has been soaked for roughly 30 After the eye has been soaked for roughly 30

seconds , the surgeon uses a tiny hoe to peel seconds , the surgeon uses a tiny hoe to peel back the epithelium and fold it back so it is out back the epithelium and fold it back so it is out

of the wayof the way . .

At this point the doctor employs an excimer At this point the doctor employs an excimer laser in the same way as in LASIK or PRK ,and laser in the same way as in LASIK or PRK ,and

molds the corneal tissue to the desired shapemolds the corneal tissue to the desired shape. .

After the shaping is finished, the surgeon After the shaping is finished, the surgeon replaces the epithelium flapreplaces the epithelium flap. .

The recovery time for LASEK is slightly longer The recovery time for LASEK is slightly longer than it is for LASIK , as it takes approximately 4 than it is for LASIK , as it takes approximately 4 to 7 days to recover good vision .The flap itself to 7 days to recover good vision .The flap itself heals within a day , but the eye can still feel heals within a day , but the eye can still feel

irritated for up to three daysirritated for up to three days. .

66 ( (Thermokeratoplasty : Consists of heating the Thermokeratoplasty : Consists of heating the cornea to shrink the peripheral and paracentral cornea to shrink the peripheral and paracentral stromal collagen to produce a peripheral stromal collagen to produce a peripheral flattening and a central steepening of the flattening and a central steepening of the cornea to treat HYPEROPIA . Solid state cornea to treat HYPEROPIA . Solid state infrared lasers , such as the infrared lasers , such as the holmium:yttrium,aluminum , and garnet holmium:yttrium,aluminum , and garnet (Ho:YAG ) laser of 480-530nm,have been used (Ho:YAG ) laser of 480-530nm,have been used in a peripheral intrastromal radial pattern in a peripheral intrastromal radial pattern ( Laser Thermokeratoplasty ), to treat hyperopia ( Laser Thermokeratoplasty ), to treat hyperopia

of 2.50D.and lessof 2.50D.and less. .

77 ( (Another form of thermokeratoplasty is the so Another form of thermokeratoplasty is the so called ( Conductive Keratoplasty ) which used called ( Conductive Keratoplasty ) which used a handheld radiofrequency probe to shrink the a handheld radiofrequency probe to shrink the

peripheral collagenperipheral collagen. . The shrinkage temperature of the corneal The shrinkage temperature of the corneal

collagen is between 55-58 degreescollagen is between 55-58 degrees. . Despite the instability of corrections and Despite the instability of corrections and

regressions , laser thermokeratoplasty and regressions , laser thermokeratoplasty and conductive keratoplasty have the major conductive keratoplasty have the major

advantage of untouched the central corneaadvantage of untouched the central cornea . .

88 ( (Intracorneal ring segments (ICRS)Intracorneal ring segments (ICRS)::ICRS are placed in the peripheral cornea and ICRS are placed in the peripheral cornea and

act by compressing the peripheral cornea and act by compressing the peripheral cornea and changing the radius of curvature of the central changing the radius of curvature of the central cornea . When the anterior surface of the cornea . When the anterior surface of the cornea is lifted focally over the ring , a cornea is lifted focally over the ring , a compensatory flattening of the central cornea compensatory flattening of the central cornea occur for treatment of myopia .ICRS are occur for treatment of myopia .ICRS are threaded into a peripheral midstromal tunnelthreaded into a peripheral midstromal tunnel

A potential advantage of intracorneal segments A potential advantage of intracorneal segments over other refractive surgical techniques is over other refractive surgical techniques is

reversibilityreversibility. . The main drawback is the limited range of The main drawback is the limited range of

correction ( up to -3D )in myopia and ( up to correction ( up to -3D )in myopia and ( up to +2D ) in hyperopia+2D ) in hyperopia. .

There are another new approaches to refractive There are another new approaches to refractive surgery likesurgery like: :

11 ( (Refractive lensectomy : The extraction of Refractive lensectomy : The extraction of the clear lens in the correction of high myopia , the clear lens in the correction of high myopia , originally performed in 1890, was later originally performed in 1890, was later abandoned because of an unacceptable high abandoned because of an unacceptable high rate of complications . With more recent rate of complications . With more recent operative techniques, such as operative techniques, such as phacoemulsification , and better IOLs , there phacoemulsification , and better IOLs , there has been renewed interest in managing high has been renewed interest in managing high

refractive errors by clear lens extractionrefractive errors by clear lens extraction. . One drawback of this procedure is the loss of One drawback of this procedure is the loss of

accomodation .The use of accommodating or accomodation .The use of accommodating or multifocal IOLs could obviate this problemmultifocal IOLs could obviate this problem. .

22 ( (Phakic intraocular lensesPhakic intraocular lenses : : ----Anterior chamber phakic IOL , named as iris claw Anterior chamber phakic IOL , named as iris claw

lens to correct high myopia in phakic patients , lens to correct high myopia in phakic patients , enclaved in the midperipheral iris . Long term follow-enclaved in the midperipheral iris . Long term follow-up has reported progressive pupil ovalization with an up has reported progressive pupil ovalization with an older modelolder model..

-- --Posterior chamber phakic IOL , it must Posterior chamber phakic IOL , it must accommodate to the space between the posterior iris accommodate to the space between the posterior iris and the crystalline lens . If it vaults too much , pigment and the crystalline lens . If it vaults too much , pigment dispersion and even pupillary block glaucoma could dispersion and even pupillary block glaucoma could result .If it lies against the anterior surface of the result .If it lies against the anterior surface of the

crystalline lens , cataract could resultcrystalline lens , cataract could result. .

33 ( (Gel injection adjustable keratoplastyGel injection adjustable keratoplasty: : Consist in injecting gel in the paracentral Consist in injecting gel in the paracentral

corneal stroma in order to flatten the central corneal stroma in order to flatten the central cornea and reduce myopia . The gel was cornea and reduce myopia . The gel was extremely well tolerated with no evidence of extremely well tolerated with no evidence of inflammation .It can correct myopia above 5 inflammation .It can correct myopia above 5 or 6 diopters as well as astigmatismor 6 diopters as well as astigmatism. .

What is most exciting about this procedure is What is most exciting about this procedure is that it make it possible to adjust patients, that it make it possible to adjust patients, refractive errors throughout their lives . Gel refractive errors throughout their lives . Gel can either be added or removedcan either be added or removed

44 ( (Procedures that modify the axial length of the eye either by Procedures that modify the axial length of the eye either by resection of the sclera or by reinforcement of the posterior resection of the sclera or by reinforcement of the posterior pole in case of high myopia ,have had a greater role in the pole in case of high myopia ,have had a greater role in the management of staphyloma than in the management of the management of staphyloma than in the management of the

patient's refractive errorpatient's refractive error. .

55 ( (Customized corneal ablation through Wavefront mapping : Customized corneal ablation through Wavefront mapping : This is accomplished by mapping the profile of the whole eye This is accomplished by mapping the profile of the whole eye through wavefront sensing devices, this sophisticated method through wavefront sensing devices, this sophisticated method identifies abberations in the entire optical system and not only identifies abberations in the entire optical system and not only the corneal surface . With the use of advanced lasers and the corneal surface . With the use of advanced lasers and wavefront deformation measuring devices , the correction of wavefront deformation measuring devices , the correction of these distortions of the human eye will continue to gain these distortions of the human eye will continue to gain

widespread usewidespread use . .