INTRAOCULAR LENS IMPLANTS
Gözde Kerman
The eye has been called the most complex organ in our body. It’s amazing that something so small can have so many working parts.
And one of the working parts is LENS. This crystalline structure is located just behind the iris and in front of the jelly-like vitreous. It is normally clear, but becomes yellow as if ages.
Crystalline lens is made of a fibrous, jelly-like material which has an index of refraction of 1.44.
It has epithelium and fibers arranged inside a covering capsule.The central compactly arranged fibers of the lens form the “nucleus”, while the peripheric softer material is called cortex.Lens is suspended in its position by “suspensory ligaments” or “zonules”.The zonules are connected tothe ciliary body.So, ciliary body controls the tension in the zonules.Accordingly the lens capsule becomes relaxes, thus changing the thickness of the lens, thus eye becomes focused for distance or near. This is called “accomodation”.
3 To focus light onto the retina. Lens focuses light rays onto the retina by bending them.
3 Lens provides about one third of the eyes optical power.
3 Cornea does most of refraction and crystalline lens fine tunes the focus.
3 In healthy eye, accamodotion for providing clear vision at various distance.Accomodation is where lens changes its shape(Thickens), thereby changing its power, allowing us to focus on near objects.
The modern history of lens implantation began in 1949 with Harold Ridley in London. This followed the observation that intraocular fragments of PERSPEX seemed to cause little long-term inflammation in eyes of pilots who had suffered penetrating eye injuries from the shattered windows of aeroplanes during World War II. The original Ridley lens was made of PERSPEX(rigid polymethylmethacrylate (PMMA)) and implanted behind iris after extracapsular cataract surgery. Thousands were implanted and 15% have complications as uveitis, secondary glaucoma, hyphaema and dislocation. The weight of lens was 112mg in air.
Rigid lenses were developed by Strampelli who studied with a lens with four thin legs resting in chamber angle. First flexible anterior chamber lens was designed by Dannheim, who openned loops. Choice for lens is PMMA rather than silicate glass.
Major complication for lens is corneal endothelial decompensation. Nylon used for external fixation but this caused glaucoma and corneal decompensation. And also sharp edges that irritated eyes from within.
First iris-clip lens was developed in 1958. Loops of the iris-clip lens were designed to prevent frequent dislocation. Lenses were inserted horizontally but later vertical direction was preferred to minimise the corneal contact. These lenses were made of PMMA, loops were SUPRAMID/Polypropylene.
Because of optic lenses was large, the complications can also occur; for example untreatable glaucoma, corneal decompensation, oedema,...
In this period lenses have 3 types:
1. Single material lenses with haptics and optics made of PMMA e.g. Copeland, Pearce lenses
2. Two-material lenseswith haptics made of SUPRAMID or polypropylene e.g. iris-clip, sputnik, medallion-lenses
3. Three-material lenses e.g. platinum iridocapsular and medallion lenses
These have flexible open loop lenses made of PMMA. They have advantage of not requiring an intact posterior capsule for implantation and can be implanted into eyes evenafter posterior capsule rupture(occuring during complicated cataract surgery). They have better fixation.
This type of lens cause high incidence of cystoid macular oedema.
Advantage of posterior chamber IOLs is that they are placed in the position of original crystalline lens leading to a more physiological situation with optical benefits. And also posterior chamber IOLs are situated away from aqueous outflow channels, iris and ciliary body. This leads to a lower incidence of corneal problems.
Table 1: Five generations of lens implants
Type of IOL |
Date |
Characteristics |
Ridley posterior chamber IOL |
1950 |
Heavy PMMA |
Early anterior chamber IOLs |
1952 to 1962 |
PMMA, rigid design, closed loop |
Iris-supported IOLs |
1953 to 1973 |
PMMA |
Modern anterior chamber IOLs |
1970 to present day |
PMMA, Flexible haptics, open loop |
Modern posterior chamber IOLs |
1975 to present day |
Standard PMMA designs
Foldable lenses -silicone
-hydrogel
-acrylic
Scleral-sutured IOL
Multifocal IOLs |
Table 2: Advantages and disadvantages of IOL types
TYPE OF IOL |
ADVANTAGES |
DISADVANTAGES |
Ridley PC IOL |
Optical |
Uveitis
Secondary glaucoma
Hyphaema
Dislocation |
Early AC IOLs
(rigid, closed loop) |
Don’t require posterior capsule- capsule usu. removed therefore no Posterior Capsule Opacification (PCO) |
Corneal complications:
Decompensation, oedema, keratopathy, uveitis, subluxation,dislocation |
Iris-supported IOL |
don’t require posterior capsule |
Iris complicaitons:
erosion, pupil changes |
Modern AC IOLs
(flexible,open loop) |
don’t require posterior capsule
better fixation, corneal complications rare |
Cystoid macular oedema(CMO) retinal detachment |
Modern PC IOLs |
Less corneal problems |
Require intact zonules&posterior capsule
Less CMO
Less retinal detachment
Less pupil block |
Foldable IOLs |
Small incision
Less astigmatism
Quicker rehabilitation
Safer |
Expensive
Decentration
Spontaneous dislocation |
a)Polyamides(Nylons):
As a loop material according to the carbon situation 4-0 or 5-0 nylon was used in IOL. For iris fixation of IOLs and iris suturing 9-0 or 10-0 nylon was used until polypropylene displaced.
But then, material failure has been reported for nylon both as a loop material and IOL fixation sutures.
b)Polypropylene:
This is trademark name of Ethicon. It is used as loop material. Polypropylene isn’t susceptible to hydrolytic degeneration. No cases have yet been reported of in vivo loop degradation.
c)Metals:
In past platinum, platinum-iridium and titanium have been used for IOL haptics or clipping devices. Stainless steel wire was also advocated as a fixation suture for IOL.
Also iris fixated lens with metal loops were excessively heavy.
d)Glass:
Few years ago a company introduced an IOL with a glass optic and a polyamide haptic. Advantage of foldable IOLs are due to the smaller incision size required for their inseriton. They are usually self sealing and don’t require suturing. Smaller incisions produce less astigmatism, allow quicker visual rehabilitation.
Disadvantage of foldable IOLs is that they are more expensive than PMMA and have higher incidence of decentration.
IOL biocompatibility within human eye has 3 major aspects:
-effect on blood aqueous barrier
(changes can be assessed by amount of inflammation)
-cellular reaction on anterior surface of lens
(This can be examined using specular microscopy)
-effect on lens capsule
(consists of lens epithelial proliferaiton and metaplasia leading to anterior and posterior capsule opacification.
Many IOL manufacturers are concentrating their research on ways to prevent Posterior Capsule Opacification(PCO). There are 2 types of IOL available:
Ø nonfoldable lenses are made of PMMA and
hard plastic, type of incision is 5-7mm and
may require sutures for wound closure.
Ø foldable lenses are made of silicone, acrylic,
small incision(2,8-3,5mm) doesn’t require
sutures for wound closure.
Benefits of small incision:
ü less trauma to eye
ü little discomfort during/after surgery
ü often don’t require stiches
ü can aid in reducing astigmatism, provide bettervision
ü a faster postoperative recovery period and quicker reutrn to normalactivity
They are composed of highly cross-linked polysiloxane chains. They are compressible and can be inserted through a small incision by folding. These lenses are:
§ homogenous
§ heat resistant and autoclavable
§ moldable
§ 
compressible.
Lens is nearly weightless in aqueous , has excellent
tensile and tear strength. These have 3 pieces:
Ø open loop prolene
Ø polyamide/PMMA haptics
Ø plate haptic
Silicon is thicker than PMMA, so it is transarent to laser radiation.
Disadvantage for this is surface of silicone IOL is hydrophobic.(So cellular reactions can occur.)Another disadvantage is that they become slippery when wet and so, difficult to handle.
A recent silicone IOL design (CeeOn911(Pharmacia-Upjohn)) has been manufacturedwith square optic edge.
They are soft and resemble living tissues in their physical properties and smooth, hydrophylic nature minimises mechanical friction with ocular tissues and contributes to superior biocompatibility. This is important to produce less damage to the corneal endothelium after inadvertent touch on implantation than PMMA.
Hydrophylic acrylics have advantage of undergoing less damage during laser capsulotomy.
Examples for this lens are Hydroview lens, EasAcryl, Centerflex.
Ø Hydroview lenses provides outstanding vision with an excellent safety profile. Lens offers exciting new option in terms of its ease of
use and biocompatiblity. These lenses also has unique one piece design with PMMA haptics.
Ø 
Centerflex is an injectable IOL resistant to compression. The lens can be implanted using forceps or with a specially designed injector through a small incision of 2.85 mm to 3.00 mm. It is an acrylic hydrophilic lens for in-the-bag implantation made of RayAcryl (hydrophilic acrylic copolymer with 26%water content. Haptics of Centerflex have been developed to resist assymetrical capsular contraction. This provides benefit of increasing support for lens as capsule.
AcrySof(Alcon) is an example of hydrophobic
acrylic square optic edged IOL which has
become most commonly inserted IOL in USA.
Backbone for this lens is PMMA.Lens implants
made from AcrySof are thinner, facilitating
folding and insertion through a smaller incision.
Acrylic polymers change their mechanical properties with temperature, being hard and glassy at low temperature, and soft and fluid at high temperature. This kind of IOLs aren’t slippery when wet in contrast to silicone IOLs. Lens also improve reduces rates of PCO.
Square optic edge act as barrier to migration of LECs onto posterior capsule, reducing PCO.
An IOL may have excellent cytological biocompatibility.
The prevalance of lens materials in 1997 survey of American Society of Cataract and Refractive Surgery was 38% acrylic, 20% silicone and 40% PMMA.
Figure: LEC amounts for AcrySof, Silicone and PMMA IOLs
Table 3: Advantages and disadvantages of IOL types
IOL TYPE |
ADVANTAGES |
DISADVANTAGES |
PMMA |
Long-term experience
Good biocompatibility
Cheap
Timetested
Little inflammation |
Rigid so need large incision
High incidence of PCO
Woundsize>opticdiameter |
Silicone |
Foldable
Low incidence of PCO
İnjectable |
Thicker IOLs(first gen.)
Thinner IOLs(sec. gen.)
Rapid unfolding in the eye
More anterior capsule contraction
Slippery when wet |
AcrySof |
Foldable
Thin IOLs
Very low incidence of PCO
Biocompatible |
Short experience
Tacky surface
More difficult to fold
Cost |
Hydroview |
Foldable
Goodbiocompatibility-low inflammatory cell reaction
Controlled unfolding
Less endothelial cell damage with cornea touch |
Lens epithelial cell on anterior IOL surface
High incidence of PCO |
Standard IOLs are monofocal had so loss of accomodation which increases with age becomes absolute with surgery. Multifocal and Bifocal IOLs have been designed in an attempt to provide both distance and near vision without additional spectacle correction.
The goal of multifocal implants has been to enable patients to be less dependent on spectacle following surgery.
An example is ARRAY multifocal IOL by Allergan which has concentric rings of varying optical power around a central power for distance. One study compared 100 patients with a standard monofocal IOL implanted bilaterally. 41% of patients with ARRAY lens didn’t wear spectacles compared to 12% of patients with monofocal IOLs.
One of the diasadvantages of multifocal lenses is patients with these lenses were more bothered with glare and haloes from oncoming headlights at night and found night driving more difficult than the patients with monofocal IOLs. Another disadvantage of multifocal lenses is that they reduce contrast sensitivity. This results in loss of sharpness of vision particularly under low light of fog.
Therefore, patients who spend their lives in a twilight environment and night-time work conditions may be disturbed by this loss of contrast sensitivity.
One study removed lenses from a group of rabbits and primates, and refilled capsular bag with an inflatable endocapsular balloon. Accommodaiton could be demonstrated following this technique in primates,but incidence of PCO was repoted to be very high(94%). Postoperative amplitude of accommodation was small and decreased with time, which was likely to be due to increase in PCO.
When a soft injectabe liquid used for filling the capsular bag, phacoemulsification was occurred. Then silicone material was injected after, bag was closed with a silicone plug. Researchs have continued.
Compression Molding:
Precision Cosmet Company is the only company in U.S. using compresaion molding technique to manufacture intraocular lenses. This company uses Perspex CQ for its products.
ü Process begins with machining of an oversized blank of this material, which is then placed in a mold. This mold by compression and heat application, imparts the required shape and dioptric power to blank.
ü After sufficent time for dispersion of heat, blank is removed from the mold and placed on a lathe for the process known as “cut down”. In this step lens blank is held to lathe by suction as a diamond kniferemoves excess Perspex CQ from molded blank.
ü Various inspection steps are then performed, including verification of measurement and visual inspection with an industrial microscope.
ü Lens is buffed with silk cloth and inspected again.
ü For those intraocular lenses in which design incorporates bore holes and haptic loops, next maneuver is drilling of required holes. Bore holes, which are for surgeons convenience during surgery, are drilled through full thickness of lens or sometimes loop in the case of one-piece Perspex CQ lenses. The holes that will receive haptic loops, on the other hand are drilled to a preset depth in lateral edge of optic.
ü Another inspection is performed and any lenses with flawed or imprecise drillings are rejected. A manual cleaning followed by an ultrasonic cleaning is then performed.
ü In a separate process 5-0 polypropylene loops have been performed by heat to a desired shape. This is important that loops maintain shape and tension placed on loops during heat forming is crucial. These loops are now inserted into drilled holes and staked with a heat probe. Probe penetrates periphery of lens and bonds and loops to optic body. The lens is agan inspected a process which now includes verification of angulation of loops.
Lathe Cutting:
Several companies use lathe cutting for IOL manufacture Perspex CQ. High molecular weight Rohm Haas PMMA is also being used for lathe cut IOLs that have UV chromophores.Procedure:
Ø PMMA is supplied in 4´4 foot sheets of Perspex CQ one-eight inch in thickness. Blanks are cut to diameter specific for a given intraocular lens, by milling or lathing, depending on type of lens.
Ø Through posterior surface is flat because material is supplied as a sheet, posterior surface is recut to ensure uniform precision in its products.
Ø Some models being drilled for loops prior to cutting of optic.
Ø Forming of loops is similar to that of compression molded IOL.
Ø As a prelude to cutting anterior cut is made on PMMA blank giving it a cone-shaped appearance. Optic is cut by shaping anterior surface to desired dioptric power.
Ø Optic is finished by milling as required and is subjected to a tumbling and proprietary polishing process. Lenses with loops have them staked and inspected for dimensions ~loop angulation.
Ø A final cleaning and inspection is done and lenses are ready for packaging and sterilization.
Injection Molding:
Low molecular weight PMMA is required because polymer must have certain characteristics of flow which are precluded by viscosity of molten Perspex CQ and similar high molecular weight PMMA polymers. Rohm Haas PMMA products are used for injection molded IOLs.
In technique used by IOLAB,
Ø PMMA pellets are dried to remove any residual moisture, then melted.
Ø Molten PMMA is forced under hydraulic pressure into a highly polished lens mold, which imparts its shape to molten PMMA as polymer cools and solidifies.
Ø Lens or lens optic is then ejected from mold and requires no further polishing.
Ø Positioning holes and haptic loop bore holes are drilled as required and heat formed Prolene loops are staked into haptic body to complete lens.
Cast Molding:
This process uses purified methyl-methacrylate monomer and a chemical initiator. The MMA-initiator mixture is introduced into a mold and undergoes a curing cycle with two results, monomer is polymerized to PMMA and desired lens configuration and dioptric power are obtained from configuration of mold. Inspection processes and bore holes are made as with other techniques of manufacture. PMMA obtained with castmolding process is claimed to have a high molecular weight and to give good reproduciblity from lens to lens.
Ø Cast molding process flow.
Ø MMA monomer received as raw material.
Ø MMA is purified.
Ø Chemical initiator is added to MMA monomer to obtain prepolymer.
Ø Prepolymer is poured into molds and cured to form lens blanks.
Ø Lot tested for molecular weight, percent residual monomer, hardness.
Ø Blanks QA inspected for surface quality, optical accuracy, cytotoxicity.
Ø Loop haptics are attached.
Ø Finished IOL device.
Sterilization:
Ethylene-oxide sterilization is an approved technique. Because ethylene oxide is gas at ambient temperatures and forms an explosive mixture with air.
This type of sterilization doesn’t effect acrylic plastics of lenses or change physical and chemical properties of lens materials. Quarantine of ethyleneoxide sterilized lenses is required so residuals of gas and its by-products adhering to lens may decline to mandated levels.
A cataract isn’t a film over eye. A cataract occurs when lens become frosty-just like a frosty windshield in a car. Lens is made mostly of water and protein. Protein is arranged to let light pass through and focus on retina. Sometimes some of protein clumps together. This can start to cloud small areas of lens, blocking some light from reaching retina and interfering with vision.
Cataract development is a normal peocess of aging, but can also develop from eye injuries, medical problems(~diabetes), certain diseases of medications(~steroids). Your genes may also play a role in cataract development.
Symptoms of cataract:
ü Painless blurring of vision
ü Sensitivity to light and glare
ü Double vision in one eye
ü Poor night vision
ü Fading or yellowing of colors
ü Frequent changes in glasses or contact lens prescriptions
If only problem with eye is to do with frosty lens, then there is an excellent chance that vision can be restored by having a cataract operation to remove cataract, along with the intraocular lens implant which is meant to replace focusing power that is lost with removal of the lens during a cataract operation.
Following surgery you will need to
Ø use eyedrops
Ø be careful not to rub or press on your eye
Ø avoid strenuous activities
Ø ask your doctor when you can begin driving
Ø wear eye glasses or an eye-shield
Almost a million intraocular lens implants are used in United States each year. At least 90% of patients who have a cataract removed will have replaced with an IOL.
Posterior capsule opacification: Silicone plate-haptic versus AcrySof intraocular lenses
Kiran A. Abhilakh Missier MDa,, Rudy M. M. A. Nuijts MD, PhDa and Khiun F. Tjia MDb
a Department of Ophthalmology, Academic Hospital Maastricht, Maastricht, The Netherlands (Abhilakh Missier, Nuijts)
b Department of OphthalmologyIsala Clinics, Zwolle (Tjia), The Netherlands
Cataract&Refractive Surgery,2003
Abstract
Purpose
To evaluate posterior capsule opacification (PCO) in fellow eyes, 1 receiving a silicone intraocular lens (IOL) and the other, an acrylate IOL.
Setting
Department of Ophthalmology, Isala Clinics, Zwolle, The Netherlands.
Methods
This retrospective study comprised 107 patients (214 eyes). In each patient, 1 eye was randomly selected to have implantation of an acrylate IOL (AcrySof® MA30BA or MA60BM, Alcon) and the other eye, a plate-haptic silicone IOL (AA4203VF, Staar). Outcome measures were the total PCO index, percentage of neodymium:YAG (Nd:YAG) capsulotomies performed, and logMAR best corrected visual acuity (BCVA). The follow-up was 3 years.
Results
The total PCO index was significantly lower in the AcrySof group than in the plate-haptic silicone group (P<.0001). There was no significant difference in logMAR BCVA between groups (P>.05). The percentage of Nd:YAG laser treatments was significantly lower in the AcrySof group (2.8%) than in the plate-haptic silicone group (23.1%) (P<.05).
Conclusions
There was significantly less PCO and a lower Nd:YAG laser capsulotomy rate after AcrySof IOL implantation than after plate-haptic silicone IOL implantation. These results did not seem to affect the logMAR BCVA as there were no significant differences between groups in this parameter.
Article Outline
Patients and methods
Results
Discussion
References
Although a major goal of modern cataract surgery is to prevent or reduce the incidence of posterior capsule opacification (PCO), it is still the most frequent cause of decreased vision after cataract surgery, with a reported incidence between 10% and 50%.[1] The treatment for PCO is neodymium:YAG (Nd:YAG) laser capsulotomy, which is effective but can lead to serious complications such as vitreoretinal problems, increased intraocular pressure, and intraocular lens (IOL) damage. [2] In addition, today's cataract patient in the Western world is usually elderly but still active, with high expectations of visual rehabilitation after cataract extraction. [3] Because both the workload and costs in ophthalmology are increasing, innovations that may prevent PCO are important.
Regeneratory PCO is caused by the proliferation and migration of lens epithelial cells (LECs) from the lens equator. Transdifferentiation of LECs of the anterior capsule may lead to whitening and wrinkling of the capsule with subsequent visual distortion.[4 and 5]
Studies show that surgical factors such as meticulous cortical cleanup, consistent in-the-bag IOL fixation, and a continuous curvilinear capsulorhexis (CCC) that completely overlaps the IOL optic reduce or delay the incidence or onset of PCO.[1, 6, 7 and 8] In addition, the prevention of PCO has been attributed to IOL design and material modifications. A sharp-edged optic appears to be a major factor in the prevention of PCO. [9, 10 and 11] Other possible factors include adherence of the capsule to the surface of hydrophobic acrylic IOLs. [12, 13, 14 and 15] Numerous human and animal studies confirm that an acrylic IOL and a rectangular optic help prevent PCO. [13, 15, 16, 17, 18, 19, 20 and 21]
We evaluated PCO 3 years after cataract surgery in 107 patients who randomly received a sharp-edged hydrophobic acrylate IOL (AcrySof® MA30BA or MA60BM, Alcon) in 1 eye and a plate-haptic silicone IOL (AA4203VF, Staar) in the other eye.
Patients and methods
This retrospective study comprised 214 eyes of 107 patients who were examined 3 years after cataract surgery. All patients had phacoemulsification with IOL implantation between January 1995 and December 1997 by the same surgeon (K.F.T.). The surgeries were performed at the Department of Ophthalmology, Isala Clinics, Zwolle, The Netherlands.
In each patient, 1 eye was randomly selected to receive an MA30BA (n = 77) or MA60BM (n = 30) AcrySof acrylate IOL and the other eye, an AA4203VF plate-haptic silicone IOL. Randomization was performed using a computerized random number generator. Because of the smaller diameter of the optic and thus the incision for the MA30BA IOL, the MA60BM IOL was replaced during the study period.
Surgery was performed using a standardized phacoemulsification technique and in-the-bag IOL implantation. After the pupil was dilated, a scleral or corneal tunnel was made and the anterior chamber was reformed with sodium hyaluronate 3.0%–chondroitin sulfate 4.0% (Viscoat®). A 5.0 mm diameter CCC was made. Divide-and-conquer phacoemulsification of the nucleus and bimanual irrigation/aspiration of the cortex were performed. After the posterior capsule was polished, the capsular bag was reformed with sodium hyaluronate 1.0% (Provisc®) and the IOL was inserted.
Three years postoperatively, the patients were seen at the outpatient department for evaluation of PCO and the best corrected visual acuity (BCVA). The BCVA was measured using a standard Snellen chart, and PCO was classified using the Evaluation of Posterior Capsule Opacification (EPCO) system developed by Tetz et al.[22]
All follow-up visits were performed by the same observer (K.A.A.M.). The PCO evaluation was performed after pupil dilation with phenylephrine hydrochloride 2.5% and tropicamide 0.5%. The PCO was then clinically classified from 0 to 4 using the EPCO system (Table 1 and Figure 1).
Table 1. Posterior capsule opacification classification
LECs = lens epithelial cells
LECs = lens epithelial cells
Figure 1. (Abhilakh Missier) Left: Retroillumination image of an AcrySof IOL with grade 0 PCO 3 years after surgery. Right: Retroillumination image of the AA4203VF plate-haptic silicone IOL with grade 3 PCO 3 years after surgery.
The posterior capsule within the capsulorhexis was used for PCO scoring. The PCO was considered clinically significant if visual acuity had decreased more than 2 Snellen lines and the PCO was grade 3 or 4. In these cases, an Nd:YAG laser capsulotomy was performed. The percentage of cases with complete circumferential overlap of the optic by the capsulorhexis leaf and the percentage of decentered lenses were documented.
For statistical analysis, Snellen visual acuity was converted to logMAR values by taking the logarithm of the Snellen visual acuity. All results were analyzed using the Wilcoxon 2-sample test.
Results
Of the 107 patients evaluated, 35 (32.7%) were men and 72 (67.3%) were women. The mean age in both groups was 74 years ± 14 (SD). The mean follow-up was 3.09 ± 0.75 years in the AcrySof group and 3.06 ± 0.75 years in the plate-haptic silicone group. There were no significant differences in characteristics between the groups.
Ocular comorbidity was found in 47 eyes (22%), 25 (23.4%) in the AcrySof group and 22 (20.6%) in the plate-haptic silicone group. There was no significant difference in comorbidity between the groups (P>.05) (Table 2).
Table 2. Ocular comorbidities.
Of the 107 AcrySof lenses, 21 (19.6%) had grade 0 PCO; 57 (53.3%), grade 1; 18 (16.8%), grade 2; and 11 (10.3%), grade 3. Of the 107 plate-haptic silicone lenses, 7 (6.5%) had grade 0 PCO; 28 (26.2%), grade 1; 24 (22.4%), grade 2; and 48 (44.9%), grade 3. No eye in either group had grade 4 PCO (Figure 2). The total PCO index was significantly lower in the AcrySof group than in the plate-haptic silicone group (P<.0001).
Figure 2. (Abhilakh Missier) Posterior capsule opacification in the AcrySof and plate-haptic silicone groups.
Figure 3 shows the logMAR BCVA plotted against the PCO classification in each IOL group. For grade 1 PCO, the mean logMAR BCVA was 0.19 ± 0.29 in the AcrySof IOL group and 0.19 ± 0.49 in the plate-haptic silicone group. For grade 2 PCO, the mean logMAR BCVA was 0.18 ± 0.15 and 0.22 ± 0.22, respectively. For grade 3 PCO, the mean logMAR BCVA was 0.36 ± 0.23 and 0.31 ± 0.30, respectively. There was no significant difference in logMAR BCVA between the groups for any PCO grade (P>.05).
Figure 3. (Abhilakh Missier) Correlation of PCO with logMAR visual acuity for PCO grade 1, grade 2, and grade 3.
Figure 4 shows a Kaplan-Meier survival curve of the percentage of eyes that did not require an Nd:YAG laser capsulotomy during the follow-up. In the AcrySof group, no eye required a capsulotomy after 1 year; after 2 years, 2 eyes (1.9%) had a capsulotomy and after 3 years, 3 eyes (2.8%). In the plate-haptic silicone group, 10 eyes (9.3%) required a capsulotomy after 1 year, 19 eyes (17.7%) after 2 years, and 25 eyes (23.1%) after 3 years. There was a statistically significant difference in the incidence of Nd:YAG laser capsulotomy for PCO between the 2 groups (P<.05). There was no significant difference in the PCO rate between the MA30BA and MA60BM IOLs (P = .824).
Figure 4. (Abhilakh Missier) Kaplan-Meier survival curve of eyes that did not need Nd:YAG laser treatment after AcrySof versus plate-haptic silicone IOL implantation.
In 80 eyes (74.8%) in both groups, the IOLs were within 0.5 mm of the pupil center. The capsulorhexis leaf completely covered the IOL optic in 35.5% in the AcrySof group and 4.7% in the silicone plate-haptic group. Whitening of the capsulorhexis leaf occurred in 68.2% in the AcrySof group and 65.4% in the plate-haptic silicone group; the whitening did not correlate with PCO.
Figure: Haptic elongation between different company IOLs
Discussion
Our study shows that a hydrophobic acrylic IOL with a rectangular optic edge causes significantly less PCO and a lower Nd:YAG laser capsulotomy rate than a plate-haptic silicone IOL. Three years after surgery, clinically significant PCO necessitating a Nd:YAG capsulotomy occurred in 2.8% in the AcrySof group and 23.1% in the plate-haptic silicone group. This confirms earlier studies that show lower PCO rates for acrylic IOLs with a rectangular optic edge than for silicone IOLs.[1, 23 and 24] Other studies, however, show no difference in PCO and chronic inflammation between the AcrySof IOL and a second-generation silicone IOL with a round optic edge (SI-40, Allergan). [21 and 25]
It is well known that a rectangular edge prevents PCO formation. The mechanism appears to be the discontinuous capsule bend caused by the rectangular edge but that can also be created by a rectangular capsular tension ring.[9, 18 and 26] The tight wrapping of the posterior capsule around the sharp square edge creates a discontinuous sharp bend with little space between the IOL optic and the lens capsule. This prevents LEC migration in the post-optic space and hence reduces PCO. [27]
The plate-haptic silicone IOL we used is different from the AcrySof lens as it does not allow the formation of a capsule bend along the junction. A sharp, square-edged optic seems to be the most important parameter in the prevention of PCO, as demonstrated in a randomized study.[28] The study found that the sharp-edged Sensar® OptiEdge AR40e acrylic IOL (Allergan) caused 50% less PCO than an identical acrylic IOL except with a round edge (Sensar AR40, Allergan) 1 year postoperatively. Similarly, Kruger et al. [29] found that silicone lenses with a sharp optic edge (CeeOn® 911F, Pharmacia) led to significantly less PCO than an identical silicone lens except with a round optic edge (CeeOn 920, Pharmacia) 2 years postoperatively. In a study comparing 2 posterior chamber IOLs of similar design but different material with a 6.0 mm sharp-edged optic and poly(methyl methacrylate) haptics (AcrySof acrylic IOL versus CeeOn 911A silicone IOL), there was no difference in anterior capsule opacification (ACO) or PCO at 3 years. [30] In rabbit eyes, Nishi and
coauthors [31] found that implantation of IOLs with a sharp rectangular optic edge, whether acrylic or silicone, resulted in similar PCO prevention. From these studies, one may conclude that the rectangular design of the posterior optic is primarily responsible for the reduction in PCO.
Although the total PCO index in our study was significantly lower in the AcrySof group than in the plate-haptic silicone group, there was no significant between-group difference in logMAR visual acuity for any PCO grade. This may be because at lower PCO grades, the opacification had not reached the central posterior capsule. Moreover, at higher PCO grades, 23.1% of eyes with a plate-haptic silicone IOL had already had an Nd:YAG capsulotomy. In a 10-year follow-up study of the Staar AA-4203C plate-haptic lens with limited follow-up, the Nd:YAG capsulotomy rate was 10.5%.[32]
Some authors suggest that in addition to the optic edge design, lens material and surface properties may reduce the formation of PCO.[13, 14, 33 and 34] In a study of pseudophakic human autopsy eyes, fibronectin was the major extracellular protein responsible for the attachment of hydrophobic soft acrylate (AcrySof) to the capsular bag. It was suggested that a bioactive bond between the IOL and LECs or between the IOL and the capsular bag may be another reason for lower PCO and Nd:YAG capsulotomy rates. In vivo, this increased adherence of the posterior capsule to the acrylic IOL surface may lead to decreased migration of LECs by a barrier effect of the edge design. A recent study, however, showed that complete apposition to both the anterior and posterior capsules occurs significantly earlier with silicone IOLs than with acrylic IOLs. [35] These findings are unexpected in view of the better adhesiveness of acrylic optics than of silicone optics to the capsule. [36] However, numerous studies show that IOL material is probably less important than edge design in the prevention of PCO. [11, 18 and 37] In addition, most comparative clinical PCO reports study more than 1 variable (eg, optic edge design, material, haptics) between IOLs; therefore, the relative contribution of variables in the reduction of PCO is unknown.
The size of the CCC and the amount of anterior capsule overlap is important in reducing PCO. Unlike a small CCC, a large CCC leads to wrinkling of the posterior capsule, which enhances LEC migration and leads to PCO.[38] Small CCCs cause tight adherence of the capsular bag to the optic and reduce the space into which LECs can migrate. However, a CCC that is too small in eyes with a silicone IOL should be avoided because of the risk for inducing capsule contraction. [39 and 40] It has been suggested that complete anterior capsule overlap and more ACO cause the optic to place greater pressure on the posterior capsule, creating a discontinuous bend despite the absence of a square-edged optic. [25] Therefore, in the absence of a rectangular optic edge, complete anterior capsule overlap is more critical for PCO prevention. [25] This agrees with our results because even though overlap occurred in only 35.5% in the AcrySof group, the incidence of PCO was 2.8% 3 years postoperatively. Based on current knowledge, more emphasis should be placed on creating complete 360-degree anterior capsule overlap, which would probably further reduce the PCO rate.
We are aware our study had a drawback in that it compared 2 IOL types that had different designs and materials. Therefore, no definite conclusion can be made on whether the difference in PCO formation is mainly the result of IOL material or IOL design. However, the randomized intraindividual study design allows us to conclude that PCO development and Nd:YAG rates after implantation of the square-edged acrylate AcrySof IOL are significantly less than after implantation of the AA4203VF plate-haptic silicone IOL.
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REFERENCES:
Stark Walter J.,MD, Terry Arlo C.,MD, Maumenee A. Edward,MD: Anterior Segment surgery,1987 www.drfitterman.com/files/iochist.html
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Presentation advisor Proff. Dr. Pınar Aydın O’Dwyer
Figures from:
www.usiol.com
www.businesswire.com/webbox
www.changemakers.net
www.alconlabs.com
www.allaboutvision.com/resources/anatomy.htm
Conclusion for IOL materials:
IOL design has developed through years and now has become extremely successful with very few complications.
Complications of corneal decompensation, glaucoma, hyphaema and uveitis have largely been resolved with use of posterior chamber IOLs placed within the capsular bag. Developments in intraocular lens design are having an effect on reducing incidence of PCO.
In addition, in the future an intraocular lens which has less damage to endothelium, can send less UV to retina, doesn’t cause opacification in back capsule, can do accomodation should be improved.
