Faculty Bibliography

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center, self-controlled clinical trial of a standardized technique of radial keratotomy in 435 patients who had physiologic myopia with a preoperative refraction between -2.00 and -8.00 diopters. The surgical technique consisted of eight incisions using a diamond micrometer knife with blade length determined by intraoperative ultrasonic pachymetry and the diameter of central clear zone determined by preoperative refraction. At one year after surgery, myopia was reduced in all eyes; 60% were within +/- 1.00 diopter of emmetropia; 30% were undercorrected and 10% were overcorrected by more than 1.00 diopter (range of refraction, -4.25 to +3.38 D). Uncorrected visual acuity was 20/40 or better in 78% of eyes. The operation was most effective in eyes with a refraction between -2.00 and -4.25 diopters. Thirteen percent of patients lost one or two Snellen lines of best corrected visual acuity. However, all but three eyes could be corrected to 20/20. Ten percent of patients increased astigmatism more than 1.00 diopter. Disabling glare was not detected with a clinical glare tester, but three patients reduced their driving at night because of glare. Between six months and one year, the refraction changed by greater than 0.50 diopters in 19% of eyes

Epikeratophakia is a simple and reversible form of refractive surgery for the correction of aphakia and myopia and for the treatment of keratoconus, perforation and pterygium. The tissue lenses are attached to the de-epithelialised cornea; no invasion of the central optical zone is required. The safety of this procedure makes it a potential solution to the problem of optical correction in infants and children with congenital and traumatic cataracts. With the advent of commercially prepared tissue lenses, this surgery should become accessible to many ophthalmic surgeons. In the future, the combination of epikeratophakia and alloplastic lenses may provide high plus powers and exchangeable dioptric corrections, if a plastic can be found that the cornea will tolerate on a long-term basis

The study of occlusion amblyopia and its therapy has involved animal models of stimulus deprivation achieved by various means, none of which closely simulates human congenital cataract. The authors used the Nd-YAG laser as a means of inducing cataracts in rabbit eyes. Twenty rabbit eyes were treated at various frequency and power settings. High energy YAG laser pulses of 10 mJ produced cataracts that at first resembled large bubbles. Over several days, these bubbles coalesced into smaller opacities. With multiple treatments (usually 150-200 pulses), the authors could create a cataract of a specific size and position. Six months later, 100% of these laser-treated rabbit eyes showed persistent cataracts that resembled human congenital cataracts. It appears that the YAG laser can provide a reproducible and reliable method of inducing specific types of cataracts in animal eyes without damaging other ocular structures

Three patients (a 13-year-old girl, a 25-year-old man, and a 22-year-old woman) who used daily-wear soft contact lenses, sterilized with saline made from distilled water and salt tablets, developed Acanthamoeba keratitis. Acanthamoeba was cultured from the contact lens solution of one patient. This patient, in whom the diagnosis was made by corneal biopsy early in the clinical course, was successfully treated with topical neomycin-polymyxin, miconazole, and propamidine isethionate. The other two patients underwent penetrating keratoplasty. One of these patients, who received a graft early in the clinical course, developed a recurrence of disease in the graft, whereas the other, who received the graft 18 months after the initial symptoms, has maintained a clear corneal transplant with useful vision

Epikeratophakia is based on the principles of the Barraquer refractive procedures, with modifications that simplify the surgical technique and eliminate the use of the microkeratome by placing the donor corneal tissue lens on the anterior surface of the cornea. Procedures developed to permit freeze-drying the preshaped lens for storage enable these lenses to be obtained from a central source, freeing the surgeon from the complexities of the computer and the cryolathe. The correction of theoretically unlimited amounts of myopia is possible with these lenses. In 12 eyes that underwent the final epikeratophakia procedure, the average desired correction achieved was 98%

Histological examination of primate corneas with hydrogel lenses implanted in intrastromal pockets showed the corneal lamella posterior to the implant protruding into the anterior chamber; these eyes had shown no increase in anterior corneal curvature. In an attempt to obtain a dioptric increase without removing a corneal lamella, relaxing incisions were made in Bowman's layer followed by intrastromal implantation of hydrogel lenses. However, no refractive increase resulted, although six of the seven eyes were optically clear eight months postoperatively

Two primate corneas were analyzed histologically 22 and 25 months after epikeratophakia surgery. Keratocytes had migrated from the host cornea into the lenticule through the surgical disruption of the host Bowman's membrane; the lenticule with the wider connection to the host cornea appeared to have more complete keratocyte repopulation. The lenticule stroma and host Bowman's membrane were continuously apposed along the interface, with a basement membrane-like material composed of collagen fibrils and amorphous matrix filling the interstices

Dimensional changes in the Barraquer cryolathe , resulting from contraction due to refrigeration, can exert a considerable effect on the dimensions of the lathed lenticule . We have devised a simple technique for re- zeroing the cryolathe after freezing. This procedure negates the effects of the dimensional changes and thereby improves the accuracy of shaping the lenticules

Epikeratophakia was performed in 61 children for the correction of aphakia after the removal of unilateral congenital or traumatic cataracts; 51 patients (54 grafts) have more than 6 months follow-up. In the first 27 grafts, 8 (30%) failed, but in the last 27 grafts, only 2 (7%) failed, largely due to improved surgical and tissue handling techniques. The average increase in corneal refractive power for the early patients was 12.68 +/- 4.63 D with an average overrefraction of +0.45 +/- 5.60 D. The last half of the patients showed an average increase of 14.83 +/- 4.83 D, with an average overrefraction of -0.00 +/- 5.20 D. Visual acuity results in patients with traumatic cataracts have been the most satisfactory, with the majority of patients obtaining useful vision. It also appears that in patients with congenital cataracts, the younger the patient at the time of surgery, the greater the chance for a good visual result. Some improvement in vision has been seen in all of the children with successful grafts, even those beyond the age when amblyopia therapy would be considered to have some potential for therapeutic effect. By attaching the correction permanently on the eye, epikeratophakia facilitates the vigorous occlusion therapy required after cataract extraction in these children