Implanting an anterior chamber intraocular lens (IOL) in phakic high myopic eyes has been proposed as one of the most satisfactory surgical techniques for the correction of high myopia.13 Several models of anterior chamber lenses, mainly based on existing IOLs for aphakia, have been designed and implanted during the last few years with accurate refractive results.4"6 In 1986, Worst and Fechner modified the existing iris claw lens, used in cataract surgery, into a negative biconcave lens.7'8 Since that time, this biconcave Worst IOL has been successfully used and has provided accurate, predictable, and stable refractive results.9"13 In 1991, the optical part of the lens was altered into a convex-concave model. The new design of the lens was changed in two respects: 1) the optical part was increased from 4.5 to 5 mm, and 2) the somewhat prominent rim of the biconcave lens was lowered. The intention of the changes was to decrease possible danger to the endothelium, as well as subjective symptoms of glare and halos.
To perform intraocular surgery on eyes with extreme axial myopia raises many questions concerning the potential hazard to the fragile myopic eye. Therefore, we started a prospective study on this lens in 1991 to investigate these risks. In this article, we report the preliminary results of the implantation of the Worst myopia claw IOL in high myopic patients, performed by J. Worst in the JRefaja Hospital in Stadskanaal between September 1991 and March 1993.
All patients were operated in Stadskanaal and sent to the Department of Ophthalmology at the University Clinic in Groningen, for independent preoperative and postoperative examination. A total of 48 eyes in 25 patients were operated on, but for this report we excluded all patients with a follow-up period of less than 6 months and one patient with a previous corneal graft. Therefore, the final patient group we studied was comprised of 35 eyes in 18 patients (11 men and 7 women). Each patient was informed of the investigative nature of the procedure and received a detailed oral and written informed consent. Patient ages ranged from 17 to 52 years (mean, 35.4 years; SD, 9.7), with a preoperative refraction range from. -6.00 to -28.00 D, of which the majority had a myopia between -10.12 and -20.00 D (Table 1). The follow-up period was 6 months in 15 eyes and 12 months in 20 eyes.
WORST MYOPIA CUW I0L
The convex-concave Worst myopia claw IOL is made of one-piece CQ-UV absorbing polymethylmethacrylate, and manufactured by OPHTEC B. V. in Groningen, The Netherlands. The total length of the lens is 8.5 mm with an optic of 5 mm in diameter (Fig 1). The height of the lens does, regardless of power not exceed 0.96 mm. The lens power ranges from -5.00 to -20.00 D and is manufactured in 1.00-diopter steps. The two diamet- rically opposed haptics fixate the lens on the iris by enclavation of midperipheral iris stroma (Fig 2).
SURGICAL TECHNIQUE AND MEDICATION
Two days prior to surgery, indomethacin 0.1% was administered twice a day topically. One hour before surgery, pilocarpine 2% was instilled to constrict the pupil. Due to the relatively large size of the globe, the surgeon (J.G.F.W.) preferred general anesthesia, only performed upon a patient's request. When eyes were operated under local anesthesia, lidocaine 2%, with 1:80 000 adrenaline was used peribulbarly, with additional oxybuprocaine 0.4% in some eyes. The local anesthesia was given progressively through the eyelids and, if technically possible, retrobulbarly. Due to the thinness of the scleral wall, the risk of perforation had to be taken into account. Nine of the 18 patients were operated under general anesthesia.
Two episcleral traction sutures were placed at both sides of the rectus superior muscle. A large corneoscleral incision, which was a quarter of the circumference, was made at 12 o'clock. The anterior chamber was filled with the viscoelastic substance sodium hyaluronate (Healon, Kabi-Pharmacia) before implanting the IOL. The IOL was inserted in the anterior chamber with a special implantation forceps and was then released. One stainless steel suture was placed at 12 o'clock with one suture on each side to prevent extrusion of Healon from the anterior chamber. The lens was rotated into the horizontal position, bringing the enclavation sites to 3 and 9 o'clock. Small folds of iris tissue were enclavated with the iris "crochet" needle. Subsequently, a peripheral iridectomy was performed. All the viscoelastic material was carefully removed with Balanced Salt Solution, after which the incision was closed with interrupted stainless steel sutures.
Preoperative Refraction of the Total Patient Population
Gentamicin 40 mg with betamethasone 4 mg were injected subconjunctivally immediately after surgery. Postoperatively, tropicamide 1% eye drops and acetazolamide 250 mg tablets were administered in the first 2 days, timolol 0.5%, and cyclopentolate 1% during the first week, and prednisolone, neomycin, and indomethacin during the first 5 weeks topically.
Preoperatively, all eyes were carefully examined by slit-lamp microscopy and funduscopy. To determine the power of the IOL, we measured the subjective refraction, the corneal curvature with the Zeiss keratometer, and the anterior chamber depth with ultrasound. These three parameters are used in the Van der Heijde formula.14 To determine the predictability of the refractive outcome, we converted the Van der Heijde formula in such a way that we could calculate the expected correction for each implantation preoperatively. For the measurement of the visual acuity, we used the modified Bailey-Lovie chart,15 currently used in the Early Treatment of Diabetic Retinopathy Study and the Prospective Evaluation of Radial Keratotomy Study,16 which is placed in a box with standardized direct illumination.17 The visual acuity is expressed in the logarithm of the minimal angle of resolution (logMAR) and was converted into Snellen notation.
We assessed disability glare by measuring the intraocular light scatter with the straylightmeter by Van den Berg.18,19 With this instrument, the amount of forward scattered light is measured by a direct compensation method. The measurements are made in a dark room while the subject's head is positioned on a chin rest above a black screen. Four different ring-shaped straylight sources, with angles of 3.75°, 7.5°, 15°, and 30° between the optical axis and the middle of the rings are presented in front of the patient. A central light patch flickers in counterfase of 8 Hz with the eccentric rings. The disappearance point of the central flicker light was measured for each scattering angle and subsequently averaged. Because of their high myopia, patients wore a trial frame or spectacles during these measurements preoperatively. Otherwise they could not distinguish the central flicker light.
Figure 1: Schematic drawing of a -20.00 4 diopter convex-concave myopia claw lens.
For examination of the corneal endothelium, we used a Zeiss noncontact specular microscope in seven patients, and a Keeler Konan sp-3300 widefield contact specular microscope in all other patients, in combination with a video camera and a frame grabber. The specular images were analyzed semi-automatically with image processing software. We only examined the central cornea because of the arduous technique and the difficulty for patients to keep their eyes still while fixating one point. Three images were made of each eye during each session and all were processed. The weighted average of the three processed images are presented as the mean endothelial cell density.
Figure 2: The myopia claw lens after Implantation. Small folds of midperiphera! iris tissue are enclavated in the two haptics, by which the lens is fixated. A peripheral iridectomy is performed to prevent pupillary block.
All patients were asked to respond subjectively to their satisfaction with visual outcome, hindrance of night glare, distortion, and imbalance.
Statistical calculations were performed with Systat Software (Systat, Ine, Evanston, 111). A two-tailed probability of .05 or less was considered statistically significant. In 16 patients, both eyes were operated on. Because the Pearson correlation matrix with the Bonferroni-adjusted probabilities did not show any significant correlation for the variables we measured between the left and right eyes (1.0 > ? > .14), we will discuss the results of all eyes in this article.
Refraction and Visual Acuity
The mean preoperative spherical equivalent myopia was - 14.70 D (SD = 4.90 D), and the mean postoperative refraction was -0.93 D (SD = 2.90 D), measured at the last follow-up visit for the entire group. In Figure 3, we represented the individual refractive outcome in a scattergram. In 26 (74.3%) eyes, the postoperative spherical equivalent residual myopia was within 1.00 D of emmetropia (Table 2). Undercorrection of more than 2.00 D occurred in four (11.4%) eyes, while in three eyes an overcorrection was noticed. One severe overcorrection of 3.50 D was probably due to an incorrectly calculated IOL power. Because the IOL was available in diopter powers up to -20.00 D, eyes with a higher myopia could only be undercorrected. If we excluded the three "over 20 diopters" patients, the results would be: 81.3% of the eyes within 1.00 D of emmetropia and only one undercorrection of more than 2.00 D, and again three overcorrections.
In Figure 4, we plotted the time course of the mean postoperative refraction of the 20 eyes with a follow up of 12 months to demonstrate the stability in refractive outcome. The mean spherical equiva 7Elent refraction at 4 to 8 weeks was - 1.30 D; at 6 months -0.80 D; and at 12 months -0.98 D. The paired Student's t-test did not show any significant difference between these three periods (p > .05). In four eyes, the postoperative refraction changed by 1.00 D or more, to a maximum of 1.50 D, between 4 to 8 weeks and 12 months.
Figure 5 is a scattergram representing the deviation of the achieved correction from the calculated correction for each IOL. The mean deviation of the refractive outcome was 0.18 D (ranging from -3.62 to +3.77 D). Eleven eyes (ie, 31.4%) deviated by more than 10% of the calculated correction. The difference around the calculated outcome was within 1.00 D in 20 (57.1%) eyes (table 2). The 90-percent confidence interval of the deviation in predicted outcome was between - 0.34 and + 0.58 D.
Refractive Outcome After Worst Myopia Claw IOL
The mean spectacle-corrected visual acuity increased from 20/50 preoperatively to 20/40 postoperatively. However, the eye that was overcorrected with 3.50 D lost two lines (Fig 6). The mean uncorrected visual acuity postoperatively was 20/60. The cumulative number of eyes with an uncorrected visual acuity was: 20/20 or better in 1 (2.8%) eye, 20/25 or better in 3 (8.6%) eyes, 20/30 or better in 10 (28.6%) eyes, and 20/40 or better in 13 (37.1%) eyes. The spectacle-corrected visual acuity was 20/20 or better in 4 (11.4%) eyes, 20/25 or better in 9 (25.7%) eyes, 20/30 or better in 22 (62.8%) eyes, and 20/40 or better in 28 (80.0%) eyes. The visual acuity of these eyes was often affected by other pathological states such as myopic chorioretinal degeneration.
Glare and Halos
The straylight measurements did not show a significant increase postoperatively (Fig 7), even though some patients complained about occasional halos. At 6 months, 8 out of 18 patients did report halos, but were not disturbed by them. Six of those eight patients still perceived halos at 12 months. The visual acuity did not decrease in any of these eyes. The severity of halos and glare disappeared gradually within 6 months after surgery in the majority of patients.
We could only perform preoperative specular microscopy in 32 of the 35 eyes. Figure 8 represents a bar diagram of the endothelial cell densities at 0 and at 6 months in 32 eyes (group 1), and of the 17 eyes with a follow up of 12 months (group 2). The mean cell loss in all 32 eyes at 6 months was 5.3% (ranging + 6.3% from to - 22.6%). The mean celi loss at 12 months was 8.9% (ranging from +0.77% to - 23.5%) in 17 eyes, which was significantly different (p = .003) from the cell loss at 6 months. The two eyes with the highest cell losses, one at 6 months (22.6%) and one at 12 months (23.5%), did not show any sign of corneal edema.
Figure 3: Preoperative and postoperative spherical equivalent refraction (D) of 32 eyes with a Worst claw IOL. Refraction was between + 1 .00 and - 1 .00 D horizontal lines) in 26 eyes.
Figure 4: Mean (error bars, 1 SD) refractive outcome in 20 eyes with a Worst claw intraocular lens followed for 1 year.
The mean anterior chamber depth of these 32 eyes was 3.7 mm (ranging from 3.1 to 4.1 mm). We did not find any correlation between the anterior chamber depth and the amount of cell loss. Because nine patients wore contact lenses, we tested to determine if the cell loss was significantly different. At 6 months, the mean cell loss in contact lens wearers was 6.3% and in noncontact lens wearers 4.9%, which was not significantly different (p = .6). In three eyes, we could only examine the corneal endothelium postoperatively. The cell densities at 6 months were 2826, 2698, and 3025 cells/mm2, and at 12 months 2919, 2509, and 2844 cells/mm2, respectively. The mean cell loss between these two postoperative periods was 3.7%. One patient developed corneal guttata in both eyes (Fig 9). We performed preoperative specular microscopy on his left eye only, in which the mean cell loss was 11.8% after 12 months. The endothelial images of this eye did not show any guttata preoperatively.
Examination by slit-lamp microscopy did not reveal any apparent flare in the anterior chamber, nor did we see damage to the iris tissue. During surgery, we noticed corneal touch in one eye. In the same eye, the IOL had to be recentered 4 months after surgery, because of distorted images. Unfortunately, we could not perform endothelial cell count prior to the second surgical intervention, but the mean endothelial cell densities preoperatively and 6 months postoperatively were 3274 cells/mm2 and 3046 cells/ mm2. One patient received blunt trauma in his left eye, 4V2 months after surgery, without any obvious ocular damage. The endothelial cell counts in that eye were 3751 cells/mm2 preoperative, 3385 cells/ mm2 after 6 months, and 3332 cells/mm2 after 12 months. In the left eye of one patient, a severe inflammatory response was observed during the early postoperative period, which disappeared during the first week. The mean endothelial cell loss at 6 months was 18.7%.
Figure 5: Deviation of the achieved correction from the calculated refraction at the last follow-up visit. Results above or below the oblique lines deviate by more than 10% of the predicted correction.
In general, the patients were very satisfied with the results. For most of the patients, a new era has started. They felt less handicapped without spectacles or contact lenses. On a scale from 1 to 10, with 1 meaning very poor and 10 excellent, the mean score of satisfaction on the visual outcome in these patients was 7.5 (ranging from 5 to 10). On a scale from 1 to 10, where 1 means no disturbance and 10 means very much disturbed, the subjective response with respect to the disturbance of glare, distortion, and imbalance was 2.7 (ranging from 1 to 9), 1.1 (ranging from 1 to 3), and 1.0 (ranging from 1 to 3), respectively.
Despite a variety of surgical procedures to treat high myopia, no consensus exists on the optimum procedure yet. Keratorefractive surgical techniques to correct high myopia, such as epikeratoplasty and keratomileusis, have shown unpredictable results in refractive outcome and a delayed regression of lens power compared to phakic anterior chamber lenses.4,5 Excimer laser photorefractive keratectomy seems to be effective in correcting low to moderate myopia. However, with regard to correcting high myopia, several authors describe a significant increased rate of refractive regression and scar formation 1 to 2 years after surgery.20"22 The results of excimer laser keratomileusis, however, seem promising.22"24
Clear lensectomy to correct high myopia is still considered controversial,25-26 due to the increased incidence of retinal detachment in patients with high myopia. Even though a recent study27 did not reveal retinal detachment 1 year after clear lens extraction, other investigators28·29 described an incidence of 7.3%, and observed that 30% of the complications consisted of retinal detachment.
Figure 6: Change in spectacle-corrected visual acuity expressed in loss or gain of one or more Snellen lines. Most of the eyes showed an increase in visual acuity postoperatively.
Based on the preliminary results of the present study, we deduce that correcting high myopia with the Worst myopia claw IOL gives accurate refractive results. The high percentage of achieved nearemmetropia, as well as accuracy, stability, and predictability of the refractive outcome in our study confirm findings of other investigations on phakic anterior chamber lenses.4"13 We did not aim for emmetropia in all eyes to avoid aniseikonia. Consequently, some eyes were undercorrected intentionally. The mean increase in spectacle-corrected visual acuity that occurred in correcting high myopia with an IOL14 was ascribed to the increase in the retinal image by moving the myopic correction from the trial frame plane to the iris plane.30 The decrease in spectacle-corrected visual acuity in one eye of our series was possibly due to macular degeneration.
Figure 7: Stray light parameter values and standard error of the means as a function of light incidence angle preoperative and postoperative. Student's r-test did not show a significant difference (P=. 64).
Intraocular light scatter causes glare and can be measured with a straylight meter by Van den Berg.18 Although patients complained about halos occasionally, the straylight measurements did not show a significant increase postoperatively. The severity of halos and glare seems to diminish considerably during the first 3 to 6 months. But we must bear in mind that even if we were not able to measure the straylight scatter objectively, patients could suffer from decreased visual function under certain lighting conditions, when the pupils are dilated.31
Despite the effectiveness of correcting high myopia with a phakic anterior chamber lens, the longterm safety of this technique has yet to be determined.32'34 The potential hazard of the anterior chamber lens for the fragile surrounding ocular tissue in the anterior chamber has full attention in all of these studies. There is a significant concern for the long-term effect of phakic anterior chamber lenses on the corneal endothelium.
In our population group, the mean endothelial cell loss after 6 months was 5.3% and 8.9% after 12 months. This was in agreement with other investigators6·35 who found an acceptable mean endothelial cell loss of 5.3% and 7%, respectively. However, certain studies on other phakic anterior chamber lenses showed a marked decrease in cell density after 1 year with a mean cell loss of 16.6%, ranging from 0 to 53.2%.36·37 Fechner et al10·11 encountered severe endothelial cell loss in three eyes, which had to be treated with corneal transplantation. Bour et al38 found a mean endothelial cell loss of 8.2% at 6 months and 15.5% at 12 months (going up to 29% and 58%, respectively). In an experimental study on angle support phakic anterior chamber lenses in monkey eyes, Peiffer39 reported a mean cell loss of 31% after 1 year.
Figure S: Mean endothelial cell densities in all the eyes (group 1 , n =32) and in those eyes with a follow up of 12 months (group 2, n=17).
Various reports have been written on the longterm effect of cataract surgery on the corneal endothelium. The Oxford Cataract Treatment and Evaluation Team40 reports a mean cell loss ranging from 8.2% to 13.9% at 6 months and from 13.6% to 19.3% at 12 months, depending on the surgical technique. Psilas et al41 reported a mean cell loss of 26.6% at 6 months in anterior chamber IOLs and 23.8% in posterior chamber IOLs, whereas Schultz et al42 reported a mean cell loss of 7.5%. Werblin43 found a mean cell loss of the central corneal endothelium of 8,8% 1 year after phacoemulsification. A long-term study on these eyes showed plateauing of cell loss during the first 3 postoperative years at 11.5%, after which the total cell loss did not increase. In our study, we only examined the central corneal endothelium, which may not reflect the actual cell loss until the endothelium has equilibrated after several years. Therefore, we have to examine these patients for an extended period of time, until a plateauing of cell loss or an equilibration level is obtained.
Werblin43 has suggested comparison of the effect of a phakic IOL on the endothelium with the "acceptable" amount of cell loss seen with routine phacoemulsification surgery. After 1 year, we found a mean cell loss of 8.9%,which compared to the 8.8% of Werblin's3 study does not seem to be significantly different. If 50% of the total cell loss occurred in the first 3 months43 after intraocular surgery, then it follows that the mean cell loss at 3 years in our population would be 10.6%. Since we did not examine the endothelium at 3 months, we took the results at 6 months, 5.3%, as reference. Again, this was not significantly different from the 11.5% Werblin found in his study. Although some studies on phakic anterior chamber lenses showed a significantly larger endothelial cell loss than in cataract surgery, we may conclude that in our patient population the mean cell loss is not significantly different from the cell loss which occurs in phacoemulsification.
Figure 9: Specuiar microscopy of an eye 12 months after Worst claw IOL implantation shows corneal guttata and a mean cell density of 2844 cells/mm2.
We are aware that reporting on the mean cell loss alone does not reflect complete assessment of the vulnerability or functional reserve of the corneal endothelium. An accurate cell density, coupled with the coefficient of variation in cell area and the percentage of hexagonal cells would be more informative.44 However, we thought that an extensive study on the morphometry of the endothelium was outside the scope of this work. Furthermore, the references cited in this study did not perform such analysis, hence it would not have helped our comparative discussions.
Although we did not detect flare in our patients by biomicroscopy, anterior chamber lenses may lead to important blood-aqueous-barrier changes, producing subclinical uveitis, which may cause chronic endothelial cell loss.45 Recent studies46'47 on phakic anterior chamber lenses using cell flare photometry revealed increased flare and cell measurements both in angle supported IOLs (n = 947, and ? = 1746) and the biconcave Worst lens (n = 947), with a significant higher level in the latter,47 without clinically apparent inflammatory reactions. However, Strobel and Fechner48 retrospectively examined protein and cell concentrations in the anterior chamber of 68 eyes with a biconcave Worst lens. They found a slightly raised protein concentration which, compared to other IOLs, was situated between the capsular bag IOL and the sulcus fixated IOL. The concentrations of cells in the anterior chamber were also elevated, but 100 times less than one would expect in chronic or active iridocyclitis. Because we could not perform laser flare photometry, the concern about an ongoing inflammatory response creating chronic progressive endothelial cell loss in these phakic IOLs,39·43·45"47 can only be excluded in our patient population by a long-term study on the endothelium.
High myopia has a notorious reputation for causing blinding complications, even when such eyes are not operated on. One of the serious complications that has been related to phakic anterior chamber lenses is retinal detachment. Two reports49'50 on this subject have described retinal detachments in six eyes with a phakic anterior chamber lens, within 1.5 to 13 months after implantation. We do not know the exact incidence and prevalence of retinal detachment in phakic anterior chamber lenses. However, Fechner et al10*11 reported one case of a flat retinal detachment in their study of 123 eyes. Barraquer1 reported two detachments in 236 eyes, and Baikoff and JoIy4 1 in 163 eyes. In our entire group of 48 eyes, we did not encounter one retinal detachment; nor did we see cystoid macular edema, which might be considered in this type of lens.
Additional complications that have been described in other phakic anterior chamber lenses are early postoperative iritis, 10'u iridocyclitis,10·11 cystic wounds,10·11 temporary raised intraocular pressure,5·10·11 and Urrets-Zavalia syndrome.10·11 Saragoussi et al51 reported on specific complications in eyes with an angle supported lens, such as inflammatory reactions, pupillary deformations, and adherence of the iris to the implant. An early postoperative inflammatory reaction occurred in only one case of our series. We have not noticed any sign of iris atrophy or other abnormalities at the enclavation sites.
Our preliminary results on the myopia claw IOL confirm earlier findings on the effectiveness of the refractive results in phakic anterior chamber lenses.
Because of the general concern over the hazardous effect of a phakic anterior chamber lens, we must apply strict inclusion criteria. The patients operated on to date must be examined carefully in due course so that we may gain a better indication of the occurrence of possible complications and on the final endothelial outcome. It would also be of interest to conduct a more detailed study on the psychosocial findings because of the positive, subjective responses in these patients.
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Preoperative Refraction of the Total Patient Population
Refractive Outcome After Worst Myopia Claw IOL