CATARACT IN MYOPIA

Previous Refractive Surgery

In the literature several papers discussed the association between cataract and refractive errors - specifically myopia- but not so many data were found between the age of manifestation of cataract and the different refractive groups.

McCarty CA, et al. in 1999¹ described the prevalence and risk factors for cataract in an Australian population aged 40 years and older. In the urban and rural cohorts, age, female gender, rural residence, brown irides, diabetes diagnosed 5 or more years earlier, myopia, age-related maculopathy, having smoked for greater than 30 years, and an interaction between ocular ultraviolet B exposure and vitamin E were all risk factors for nuclear cataract.

The rate of posterior subcapsular cataract was 4.08% (95%

confidence limits, 3.01%, 5.14%), whereas the overall rate of posterior subcapsular cataract including previous cataract surgery was 4.93% (95% confidence limits, 3.68%, 6.17%).

Wong et al in 2001²described the relation between refractive errors and incident age-related cataracts in a predominantly white US population: All persons aged 43 to 84 years of age in Beaver Dam, Wisconsin, were invited for a baseline examination from 1988 through 1990 and a follow-up examination 5 years later from 1993 through 1995. When age and gender were controlled for, myopia was related to prevalent nuclear cataract (odds ratio [OR], 1.67; 95% confidence interval [CI], 1.23-2.27), but not to cortical and posterior subcapsular cataracts.

Myopia was not related to 5-year incident nuclear, cortical, and posterior subcapsular cataracts, but was related to incident cataract surgery (OR 1.89; CI 1.18-3.04).

Hyperopia was related to incident nuclear (OR 1.56; CI 1.25-1.95) and possibly cortical (OR 1.25; CI 0.96-1.63) cataracts, but not to posterior subcapsular cataract or cataract surgery. Their data support the cross-sectional association between myopia and nuclear cataract seen in other population-based studies.

Younan C, et al³ in 2002 assessed whether an association exists between myopia and incident cataract and cataract surgery in an older population-based cohort study. Their epidemiologic data provided some evidence

of an association between myopia and incident cataract and cataract surgery.

Prevalence of Cataract in Myopia

Wong TY et al in 2003⁴ described the relationship of refractive errors and axial ocular dimensions and age-related cataract. In a Population-based, cross-sectional survey of ocular diseases among Chinese men and women aged 40 to 81 years (n = 1232) living in the Tanjong Pagar district in Singapore., nuclear cataract was associated with myopia (-1.35 D vs. -0.11 D, P

< 0.001, Cortical cataract was associated with thinner lenses (4.67 mm vs. 4.79 mm, P = 0.001, comparing right eyes with and without cortical cataract), but not with refraction and other biometric components. Posterior subcapsular cataract was associated with myopia. Their population-based data supported the associations between nuclear and posterior subcapsular cataracts and myopia reported in previous studies.

Chang MA et al⁵found significant associations between myopia and both nuclear and posterior subcapsular opacities. For nuclear opacity, the odds ratios (ORs) were 2.25 for myopia between -0.50 diopters (D) and -1.99 D (P<0.001), 3.65 for myopia between -2.00 D and -3.99 D (P<0.001), 4.54 for myopia between -4.00 D and -5.99 D (P<0.001), and 3.61 for myopia -6.00 D or more (P = 0.002). No association was found between myopia and cortical opacity. Their results confirm the previously reported association between myopia, posterior subcapsular opacity, and nuclear opacity.

Praveen MR, et al⁶compared the prevalence of different types and densities of age-related cataract in subjects with high myopia and emmetropia in an Indian urban clinic-based population, 800 healthy eyes in Ahmedabad, India.

Subjects with high myopia (axial length [AXL], >/= 26.0 mm; n = 400 eyes) and those with emmetropia (AXL, 21.0 to 23.99 mm) were examined (n = 400 eyes). In all the age groups nuclear cataract was encountered more often in subjects with high myopia; PSC and mixed cataracts were encountered frequently in subjects with emmetropia (P <

.001). Prevalence of nuclear cataract was higher in subjects with high myopia with increasing AXL when compared with other types of cataract (P < .001). Nuclear cataract was associated strongly with high axial myopia. The density of the cataract was higher in the high myopia group.

In conclusion: A definitive association is found in the literature between nuclear and subcapsular cataract and myopia.

Can Excimer Laser Surgery Cause Cataract Formation?

Is there any risk factor of 193 nm Excimer corneal surgery causing cataract formation?

I have found only a limited number of papers in the literature concerning this eventual relation. This year 2008 in a personal Theo Seiler stated that there is no risk at all of Excimer laser 193 nm as a cataractogenous factor.⁷

Two papers 1994-2000 mention and discuss the eventual risk. Their conclusion was that the exposure of the lens to secondary radiation generated by Arf 193 nm Excimer laser corneal surgery induces biochemical modifications which are known to be markers of cataractogenesis (Costagliola et al, 1994).⁸ Another paper -Wachtlin et al, 2000⁹ stated that the elevation of MDA in the lens of the rabbit microkeratome group was probably caused by the incision and not by the radiation of the Excimer.

Diagnosis: Decision to Perform Cataract Surgery The main indication and reason for surgery was of course visual loss. But in the hyperopic eyes we decided earlier for cataract surgery or refractive lens exchange.

For hyperopic eyes we would decide faster for lens surgery than in an eye with previous myopic surgery since we learned from experience that a retinal detachment after eventual Yag Laser Capsulotomy is seldom or inexistent in short hyperopic eyes and is more frequent than normally in myopic eyes.

Surgery was discussed and performed whenever we felt that this procedure could solve the problem of a patient coming in with visual complaints after previous refractive surgery or progressive refraction change with a decrease of his UCVA.

When all other reasons of visual deterioration were explored and the lens opacification was the only reasonable explanation for the complaints then the decision to replace the lens was made. A right approach, when in doubt, is of course to follow patients and exclude all other possible reasons after having performed Oct-Angiography –Topography-Careful fundoscopy- and visual field analysis. In some circumstances we also had to follow these patients for 3-6 months and repeat the topographies in order to make the exact clinical diagnosis In the eyes previously treated with myopic laser surgery we nearly always found a ongoing myopization reaching sometimes values as high as -9 dptr. Often these patients had still reasonably good objective visual acuity but of course a lot of subjective complaints as glare and halo’s

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caused by the change in lens index and the burden of a need to change spectacles frequently because of myopization caused by the nuclear sclerosis. It is interesting to mention that many of these patients with increasing myopia usually had no reading problems unless very late in the evolution.

IOL Choice

Most of the eyes in the study were operated before the area of aspheric and multifocal IOL’s. We performed our first cataract surgery after previous refractive surgery in 1999!

The majority had silicone or acrylic monofocal IOL’

implanted and the early cases even had 6 mm.Pmma IOL’s. These rigid 6 mm. IOL’s are of course obsolete now.

We would however not implant a multifocal IOL in a post RK eye with more than four incisions since they have too many aberrations. But I would not hesitate to implant a multifocal like the Tecnis MF in a post Excimer laser surgery cataractous eye but would warn the patient that they might need an enhancement.

The preferred lens in case a monofocal becomes the option would be an aspheric lens whenever possible; the choice of asphericity would be adapted according to the previous surgery and specifically in eyes with previous Hyperopic Lasik an aspheric neutral IOL would be the choice otherwise the AMO Tecnis monofocal or the Alcon Natural wave would be good choices.

Surgical Considerations of Cataract Surgery after Previous Refractive Surgery.

How to Proceed?

It is interesting to mention that in the literature not one article was found describing the surgical approach and eventual tricks to apply when performing surgery in this group of patients. In the whole group not one compli-cation or adverse effect occurred during or after surgery.

Radial Keratotomy

We performed phacosurgey in all eyes ,using a clear corneal 3.0 to 3.2 mm.incision exactly in between the two superiorly placed radial incisions. In 8 incisions RK eyes usually there is enough space to place a clear corneal incision between the RK incisions. After having entered the eye, routine phacoemulsification was performed and the appropriate IOL was implanted. In two eyes one of the radial incisions opened and we had two place two corneal sutures; these sutures were removed after 6 weeks without causing astigmatism.

In order to avoid an unstable wound or preoperative trauma we would advise a scleral tunnel approach in eyes treated with 16 or more radial incisions as the original procedure. This scleral tunnel incisions does not need suturing since we never applied more than 8 incisions as a primary procedure -eventually followed by a 4 incisions touch- up –we were never forced to use a scleral approach in our cohort.

One should of course remember that some of these RK eyes might have had unintentional or intentional (in order to increase the effect-which is a bad decision) micro perforations at time of the primary procedure. Specifically in these eyes, the incisions may open and the surgeon has to be prepared for that event.

We have never seen instability of the cornea during the procedure or some refraction change in the postoperative period that could have been attributed to the earlier surgical trauma. The healing was always similar to routine cataract cases.

Excimer Laser

In the group of corneal refractive Excimer laser surgery patients also a clear corneal incision with a 3.0 mm.size was the preferred way. Although we did not measure corneal thickness right before cataract surgery ,according to our subtraction the thinnest cornea of these eyes measured 400 mikron.We have never seen any abnormal reaction of the eye in these cases, except for the fact that these long eyes had a low rigidity and that focusing during surgery was very difficult in some cases. This was exactly the same as what happened in our group of myopic eyes without previous refractive surgery.

IOL Power Calculation after

Previous Corneal Refractive Surgery

Determining the IOL Power for a cataract patient has always been challenging, but has gotten a lot tougher lately. Thanks to refractive surgery, more and more individuals with cataracts have altered corneas that make it difficult to ensure an acceptable outcome for cataract surgery. Many surgeons are trying to solve this problem, but so far the result has been a proliferation of formulas and methods with no one solution rising to the top.

As said in the introduction is not the topic of this chapter to discuss formula’s but nevertheless it is interesting to say that we, in our local meetings, already from 2000 on highlighted the problem and the growing importance of IOL power calculations after previous refractive surgery for the future.

Now in the literature, around100 papers have been published and the predictability of IOL power calculation improved enormously. We are, however, still convinced that the routine cataract surgeon will not always find the right approach for this complicated problem.

Figure shows a nice example of the problems that could be encountered in earlier days when we had to rely on the “Clinical History Method”. Since most of the cataracts in these myopic eyes after previous Excimer laser surgery are nuclear cataracts, causing a myopization of the eye, it was not always easy to determine the endpoint of stabilization after the first Excimer laser surgery (Figs 26.1 and 26.2).

3. Many modern formulas predict IOL position using the axial length and corneal curvature.

Seitz et al¹⁰already in 1999 analyzed the sources of error and the validity correction methods of IOL power calculation after previous refractive surgery; they found an underestimation of the corneal flattening by 24% when using direct power measurements.

Lyle WA, and Jin GJ,¹¹concluded that corneal flattening effect caused by cataract surgery tends to occur in eyes that have undergone previous radial keratotomy.

The use of an average between the Binkhorst and Holladay formulas, aiming for -0.75 D with an adjusted K, seemed to be a more accurate and predictable method for IOL power calculation. This approach could reduce the chance of postoperative hyperopia.

Gimbel H, et al¹² described a case of bilateral cataract extraction with posterior chamber intraocular lens (IOL) implantation in a patient after previous photorefractive keratectomy, radial keratotomy (RK) combined with astigmatic keratotomy, and retreatment of RK. A significant hyperopic error was observed after cataract surgery, and the IOLs were eventually exchanged in both eyes.

Argento C, et al¹³ analyzed the results of phacoemulsi-fication cataract surgery in eyes that had had refractive surgery and compared the predictability of various methods of intraocular lens (IOL) power calculation. They concluded that: Post-phacoemulsification refraction in cases with previous refractive appeared to be predictable when the appropriate calculation method was applied.

When all the data were available, the CHM-Clinical History Method- provided the best results.

Latkany RA, et al,¹⁴ evaluated the effect of pre-refractive surgery refractive error on IOL deviation, and introduced a formula for IOL calculation for use after refractive surgery for myopia. They concluded that for IOL power selection in previously myopic patients, a predictive formula to calculate IOL power based only on the pre-refractive surgery SEQ (m) and current flattest keratometry readings was not statistically different from IOL (exact).

The IOL (HisKs), which was also not statistically different from IOL (exact), requires pre-refractive surgery keratometry readings that are often not available to the cataract surgeon.

Jin GJ et al¹⁵ evaluated the effectiveness of a manual keratometry (K) adjusted value for intraocular lens (IOL) power calculation in sixteen eyes of 14 consecutive patients who underwent cataract surgery after previous refractive surgery. They concluded that using an adjusted K with the Binkhorst II formula, aiming for -0.75 to -1.00 Fig. 26.1: Demonstrating the difficulty to rely upon clinical history

method. Outcome was excellent after Excimer PRK–starting with -16D-after enhancement PRK .Patient developed progressive cataract nuclear sclerosis and myopia increased to -6D.The refractive endpoint was 0.5 for the calculation and not the -6D.Using this value would have given a 4 Dptr.

hyperopia error.

Fig. 26.2: Clinical history method

Calculating IOL power after refractive surgery is tough for several reasons.

1. Most keratometers don’t measure the central cornea where the effective corneal power is.

2. LASIK and PRK change the index of refraction between the front and back surfaces of the cornea;

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D, and with the Holladay I formula, aiming for 0.50 to -1.00 D, and measuring K with a regular manual keratometer permits determination of an IOL power after myopic LASIK without the need of preoperative LASIK refractive data.

Awwad et al¹⁶ evaluated the most accurate method for corneal power determination in patients with previous radial keratotomy. They concluded that corneal refractive power after RK was best described by averaging the topographic data of the central 3.0 mm area. Applying this method, together with a double-K IOL formula, the authors achieved excellent IOL power predictability.

Randleman et al¹⁷ described a new strategy for intraocular lens power calculations after laser in situ keratomileusis (LASIK)-Consensus Method-they determined the accuracy of the method, and compared the results with those of previously described techniques.

. They concluded that the consensus method showed less variability and higher predictability than all other methods tested.

Shammas HJ and Shammas MC¹⁸prospectively evaluated the no-history method for intraocular lens (IOL) power calculation in 15 cataractous eyes that had previous myopic laser in situ keratomileusis (LASIK) and for which the pre-LASIK K-readings were not available.

The results of the Shammas post-LASIK formula compared favourably to the results obtained with the optimized Holladay 1, Hoffer Q, Haigis), and Holladay 2 formulas and were better than the results obtained with the optimized SRK/T formula (P = .0005). They concluded that the no-history method is a viable alter-native for IOL power calculation after myopic LASIK when the refractive surgery data are not available.

The problem was extensively discussed by several authors in “Review of Ophthalmology November 2007;

33-40”.¹⁹

Mark Packer mentioned that “Right now, there are more than 20 formulas and methods, and none of them is

‘the one. In reality, you can’t know for sure if a method works until you’ve actually done the surgery. Among the methods used to calculate IOL power, the historical method, which requires pre-refractive surgery data, is often thought of as the best approach.”

Jack T Holladay, recommended until recently using the historical and contact lens methods if you can. The historical method is simple: If the data is available, you subtract the refractive change caused by the earlier procedure from the original K-readings and get the new K-readings. Many methods currently used to calculate

corneal power are modifications of this approach, which he first published in 1992.”²⁰

Nevertheless, Dr. Holladay notes that even this approach has drawbacks. “This method assumes that the refractive changes that occurred between the pre-refractive-surgery measurements and the current refraction were solely due to the cornea, not the crystalline lens,” he says. Unfortunately we experienced that this is usually not true. A cataract growing inside the eye often changes the refraction. We have seen nuclear cataracts inducing myopia up to -10 D!!!: if one relies on the historical method in this situation, you end up with a refractive surprise.

Another, more common problem with the historical method is that the information is often not available. One does not always have the pre-surgery K-readings and how the patient’s refraction has changed unless it is your own patient. Given these caveats, of course direct measure-ments, when possible are the best way to proceed.

Dr Holladay is recently working with the Pentacam and found 98% accuracy in measuring post LASIK eyes if he used a 4.5 mm.optical zone. This approach is probably the best possible for the moment when one does not know the history of the patient.

Kenneth J. Hoffer, MD recently has created a spreadsheet containing all of the formulas that would automatically do the calculations for every formula incorporating the data the surgeon can provide.

According to Dr. Hoffer there are currently about 24 formulations in use. They can be divided into two major categories. “The first group tries to predict the true power of the patient’s cornea base on multiple factors. These formulas give you a different K-reading to plug into your IOL power calculation. The remaining methods say, ‘OK, your direct K-reading may not be accurate, but go ahead and calculate the IOL power; we’ll give you a way to fudge or adjust that power to make up for the error.’ Each of these groups can be subdivided into those that require some pre-op historical data and those that don’t.”

Even when all the pre-refractive surgery measurements are available, determining the correct IOL power with certainty can still be difficult or impossible. Since topographers and keratometers only measure the front surface of the cornea, “To calculate corneal power, you

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