Experimental evaluation of a phakic anterior chamber implant in a primate model. Part II. Pathology

Phakic Intraocular Lenses

An analytical review of the data available in the field of phakic intraocular lens implantation was conducted. Particular attention was paid to the more critical issues of intraocular lens sizing and safety guidelines. A comprehensive, competitive analysis of different implantation sites, intraocular lens model designs, and safety guidelines has been included. Specialized biometry techniques, such as very high frequency ultrasound and Scheimpflug imaging, have been reviewed, and a critical review of commercial claims regarding intraocular lens technologies has been included. Clinical studies of phakic intraocular lenses demonstrate increasing promise for the correction of refractive errors not amenable to mainstream excimer laser refractive surgery. The main issues currently revolve around adequate lens design (VHF ultrasound study suggests that custom-design and sizing may be the most effective and safest approach for every phakic IOL model), because these devices will be required to remain physiologically inert and anatomically compatible with internal ocular structures and relations for several decades. The possibility of safe removing or exchanging the IOL should remain a feasible option over time. It is of utmost importance that we continue to critically evaluate current encouraging short-term outcomes, which are being extrapolated to the longer term by ongoing high resolution imaging and monitoring of the anatomical and functional relations of implanted phakic IOLs.

Ocular biocompatibility testing of intraocular lenses: a 1 year study in pseudophakic rabbit eyes

PURPOSE

To evaluate the appropriate duration for conducting ocular biocompatibility studies with an intraocular lens (IOL) in the pseudophakic rabbit model.

SETTING

Alcon Laboratories, Inc., Fort Worth, Texas, USA.

METHODS

A single-piece biconvex poly(methyl methacrylate) (PMMA) IOL was implanted in the capsular bag of 18 eyes of New Zealand white rabbits; 8 eyes received sham surgeries. Rabbits were monitored clinically and then sacrificed 6 or 12 months after surgery for histopathological examination of ocular tissues.

RESULTS

Biomicroscopic examination revealed mild ocular changes in all surgical eyes during the first 3 months postoperatively. After that, there was a high incidence of posterior synechias, flare, and posterior capsule opacification (PCO) in eyes with PMMA IOLs. Posterior synechias and flare scores remained mild to moderate throughout the study, whereas PCO severity increased over time. Similar findings were observed in sham eyes. In addition, several eyes with PMMA IOLs developed IOL dislocation, hyphema, iris bombe, and a fibrous membrane covering the IOL. No discernible differences in biomicroscopic scores were observed in eyes at 6 or 12 months. Intraocular pressures and morphology of the corneal endothelium were normal in both groups. Results from histopathological analysis of the ocular tissues were consistent with observations from the biomicroscopic examinations.

CONCLUSION

The results suggest that IOL implantation studies in the pseudophakic rabbit eye should be conducted for 3 or fewer months. Regulatory guidelines requiring longer ocular implantation studies should be revised to reflect the inherently rapid and extensive ocular response in the rabbit model.

Retinal detachment in phakic eyes with anterior chamber intraocular lenses to correct severe myopia

PURPOSE

To analyze the incidence and characteristics of retinal detachment in patients with severe myopia corrected by implantation of phakic anterior chamber intraocular lenses.

METHODS

We studied retinal detachments in 166 consecutive eyes (98 patients) that underwent implantation of angle-supported phakic anterior chamber intraocular lenses (models ZB5M and ZB5MF; Domilens; Lyon, France) for the correction of severe myopia (follow-up +/- SD, 45.26 +/- 14.65 months; range, 20 to 84 months).

RESULTS

Retinal detachment occurred in eight eyes (4.8%); four eyes belonged to men and four to women. The time between implanting surgery and retinal detachment was 17.43 +/- 16.4 months (range, 1 to 44 months). In all cases, retinal detachment was spontaneous. In seven eyes, the retina was reattached successfully during the first retinal detachment surgery. Mean best-corrected visual acuity after phakic anterior chamber intraocular lens implantation and before retinal detachment development was 20/50 (range, 20/100 to 20/25). After retinal detachment repair, best-corrected visual acuity was 20/73 (range, 20/2000 to 20/33). In these seven eyes, differences between best-corrected visual acuity before and after reattachment were not statistically significant (P = .898, paired Student t test). In one eye, a proliferative vitreoretinopathy was observed, which required additional treatment by vitrectomy and explantation of the phakic anterior chamber intraocular lens. A refractive change was observed after retinal detachment repair, from -1.1 +/- 0.7 diopters (range, 0.00 to -2.50 diopters) before retinal detachment and -2.8 +/- 1.1 diopters (range, -1.00 to -4.50 diopters) after retinal detachment surgery (P = .03, paired Student t test).

CONCLUSIONS

The implantation of a phakic anterior chamber intraocular lens as a correcting procedure for severe myopia was followed by a 4.8% incidence of retinal detachment. Conventional scleral surgery was successful in most cases, without causing significant changes in the final best-corrected visual acuity. A significant increase in the myopic spherical equivalent was observed after retinal detachment repair in these patients.

Intraocular lens implantation in infant monkeys: clinical and histopathological findings

PURPOSE

To determine the long-term effects of intraocular lens (IOL) implantation in infant monkey eyes.

SETTING

Yerkes Regional Primate Research Center, Emory University School of Medicine, Atlanta, Georgia, USA.

METHODS

A 30.00 diopter (D), all-poly(methyl methacrylate) IOL with an overall diameter of 10.0 mm was implanted in the right eye of 11 infant monkeys. Seven monkeys developed postoperative complications and were not followed on a long-term basis. However, 4 monkeys were followed clinically for 4 1/2 years, after which their pseudophakic eyes were examined histopathologically.

RESULTS

The final refractive error in the four pseudophakic eyes with long-term follow-up ranged from -4.75 to +0.75 D. Three of the four eyes had a Soemmering's ring. Only one haptic was in the capsular bag. whereas five had eroded into the iris root/ciliary body. The corneas and posterior segments of the eyes were normal.

CONCLUSION

Two-thirds of the eyes having neonatal IOL implantation experienced significant postoperative complications. Haptic location was suboptimal in all four eyes followed for 4 1/2 years. The diameter of the IOLs implanted in these eyes was probably too large. Some of these complications might have been averted by implanting an IOL with a smaller diameter.

Correction of High Myopia With the Worst Myopia Claw Intraocular Lens

BACKGROUND

Phakic anterior chamber lenses is one of the modalities used to correct high myopia. We report the initial results of our prospective study on the Worst myopia claw intraocular lens (IOL) that is fixated to the anterior iris.

METHODS

We studied 35 eyes in 18 patients with a preoperative myopia ranging from -6.00 to -28.00 diopters (D). The follow up ranged from 6 months (n = 15) to 12 months (n = 20).

RESULTS

In 26 (74.3%) eyes, the postoperative spherical equivalent refractive error was within 1.00 D of emmetropia. The mean refraction was stable between 1 to 2 months and 12 months. The mean spectacle-corrected visual acuity improved from 20/50 to 20/40. The straylight measurements did not show a significant increase postoperatively (p = .64). The mean endothelial cell loss was 5.6% (range, +6.3% to -22.6%) at 6 months, and 8.9% (range, +0.77% to -23.5%) at 12 months. We did not encounter major complications.

CONCLUSION

Implanting a Worst myopia claw IOL in high myopic eyes resulted in a stable, reasonably accurate refractive outcome. This group of patients will be followed longer because of concern over ocular complications with this technique.

Refractive power calculations for intraocular lenses in the phakic eye

To correct a severe refractive error and obviate thick spectacles or contact lenses, an intraocular lens can be placed in the anterior chamber in front of the normal crystalline lens as an alternative to keratorefractive procedures. The power of the intraocular lens may be determined from the recipient's spectacle correction, its vertex distance, and the corneal power in diopters. These measurements, combined with an intraocular lens constant based on its location within the anterior chamber, provide the appropriate power of the intraocular lens. These formulas were applied to seven Baikoff anterior chamber lenses and three Momose anterior chamber lenses in phakic eyes. The mean absolute prediction error was 0.42 (standard deviation, +/- 0.60) for the Baikoff lenses and 0.57 (+/- 0.64) for the Momose lenses. The accuracy of the measurements is limited by the accuracy of the preoperative refraction, the measurement of the corneal power, and the restoration of the preoperative refractive power of the cornea.

Retinal detachment as a potential hazard in surgical correction of severe myopia with phakic anterior chamber lenses

Phakic anterior chamber lenses have been proposed as an effective refractive surgical procedure for the correction of severe myopias. We managed three cases of retinal detachment that complicated this operation. Two patients had retinal detachment in the immediate postoperative period at the fourth and sixth weeks, respectively. Both patients had preoperative equatorial lattice degeneration, which was prophylactically managed with argon laser in one case. The third patient developed retinal detachment at the eighth postoperative month and was associated with a severe fibrinoid uveitis and a combined exudative and rhegmatogenous retinal detachment. This third patient did not have any previous retinal degenerative lesion. Scleral buckling was successful in two of the patients, whereas the patient with preoperative inflammation required vitreous surgery because of proliferative vitreoretinopathy. The retinas were reattached in all three patients without explanting the phakic anterior chamber lens, but severe loss of visual acuity occurred in one patient. Retinal detachment should be regarded as a potentially important hazard in this type of refractive surgery.