Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. Perk Study Group

The Prospective Evaluation of Radial Keratotomy Study is a nine-center clinical trial of a surgical technique to reduce simple myopia by making incisions in the cornea. There were 435 patients (one eye per patient is reported) enrolled in the study with a 91% follow-up rate at 4 years after surgery. After surgery, uncorrected visual acuity was 20/40 or better in 76% of eyes. Fifty-five percent of the eyes had a refractive error within +/- 1.00 diopter; 28% were undercorrected, and 17% were overcorrected by more than 1.00 D. The width of the prediction 90% interval for the refractive change was 4.42 D, indicating a lack of predictability. The refractive error was not stable in some eyes; between 6 months and 4 years after surgery, 23% of eyes had a continued effect of the surgery of more than 1.00 D. For 323 patients with both eyes operated on, 64% stated they wore no optical correction. There were few serious complications. Eleven eyes (3%) lost two or three lines of best corrected visual acuity. Two eyes developed delayed bacterial keratitis without significant loss in best corrected visual acuity.

Penetrating keratoplasty for keratoconus in Down's syndrome

Five patients with Down's syndrome underwent penetrating keratoplasty for keratoconus. In three patients, the indication for surgery was acute corneal hydrops, which had not resolved in the three months before surgery. The other two patients had corneal scars. Two patients had combined penetrating keratoplasty, cataract extraction, and intraocular lens insertion. Four of the five patients maintained clear grafts at their most recent follow-up examination. Two of the five patients had one or more graft reaction episodes; one graft was lost. Good results can be obtained in penetrating keratoplasty for keratoconus in patients with Down's syndrome who do not demonstrate a tendency toward excessive eye rubbing and for whom a single observant caretaker can be relied on to provide consistent postoperative care.

The corneal topography of epikeratophakia

Epikeratophakia is a surgical technique initially developed for the correction of aphakia, and later adapted for the correction of keratoconus and myopia. The concurrent development of color-coded computerized corneal topography has greatly assisted in the evolution of epikeratophakia. Corneal topography has demonstrated the importance of both accurate centration of the epikeratophakia lenticle over the visual axis and the size of the optical zone on the final refractive results. Corneal topographic changes associated with correction of aphakia are primarily the result of steepening of the anterior radius of curvature of the cornea, in contrast to myopic correction which results in flattening of the anterior cornea. Correction of keratoconus results from a physical compression of the cone thereby flattening both the anterior and posterior radii of curvature. Preoperative topography in patients with keratoconus permits the precise position and extent of both regular and irregular astigmatism mation may assist in designing the optimal lenticle size and amount of graft decentration necessary to achieve the maximal surgical effect. Corneal topographic mapping has also been helpful in the management of postoperative astigmatism following epikeratophakia. Topography identifies the location and extent of both regular and irregular astigmatism which assists in planning of both surgical and nonsurgical intervention. Corneal topographic mapping has also been extremely helpful in the management of postoperative astigmatism following epikeratophakia. Topography identifies the location and extent of both regular and irregular astigmatism which assists in planning of both surgical and nonsurgical intervention.

One-year refractive results of central photorefractive keratectomy for myopia in the nonhuman primate cornea

Photorefractive keratectomy for the correction of myopia was performed in 32 eyes of 16 green monkeys. The corneas healed satisfactorily, with normal formation of basal lamina and hemidesmosomal attachments visible in 14-week histologic specimens. No recurrent erosions were observed clinically. After a transient period of faint haze, all corneas were clear at 17 weeks and remained clear through the 1-year follow-up. In terms of accuracy, all corneas demonstrated a significant flattening compared with preoperative values, but no significant difference was seen between the groups with different intended corrections (1.5 and 3 diopters). The changes in corneal shape stabilized by 17 weeks, as measured by keratometry. The clinical results suggest that mechanical removal of the epithelium is preferable to laser ablation of the epithelium. Overall, the results demonstrate that excimer laser ablation of the corneal stroma can produce a stable diptric change in the primate cornea with good healing and long-term corneal clarity.

Topographic changes that occur with 10-0 running suture removal following penetrating keratoplasty

Twelve eyes undergoing penetrating keratoplasty with a double-running suture technique had corneal topographical analysis immediately before and one month after 10-0 suture removal. Substantial changes in astigmatism were evident following suture removal. Twenty five percent of eyes showed a decrease of 1 D, 33% of eyes showed a decrease of 3 D, 8.3% of eyes showed an increase of 1 D, 8.3% of eyes showed an increase of 2 D, 16.6% of eyes showed an increase of 3 D, and 8.3% of eyes showed an increase of 4 D of astigmatism following suture removal. The mean corneal astigmatism did not show a significant change from a mean of 5.3 D after suture removal. There was less individual variation of spherical corneal power following suture removal. Thirty three percent of eyes showed a decrease of 1 D, 33% of eyes showed a decrease of 2 D, 8.3% of eyes showed a decrease of 3 D, 18.3% of eyes showed an increase of 1 D, and 6.6% of eyes showed an increase of 2 D of spherical power following suture removal. The surface asymmetry index (SAI), a centrally weighted measure of corneal surface irregularity, decreased significantly (P less than 0.04) from a mean of 1.17 before suture removal to a mean of 0.93 after suture removal. These results suggest that surface irregularity may be decreased following the removal of a single running 10-0 nylon suture following penetrating keratoplasty.

A comparison of surgical keratometers

Surgical keratometers were conceived as an aid that would help anterior segment surgeons minimize postoperative astigmatism, a major obstacle along the road to rapid visual rehabilitation. Two classes of surgical keratometers are commercially available at present. The first class of devices produces a keratoscopic image from which the surgeon must make a qualitative assessment of both the amount and location of astigmatism based upon distortion present in the keratoscopic image. The second class of devices quantitates corneal power at a chosen meridian and providing the surgeon with either an analogue or digital readout. Usually it is up to the surgeon to identify the meridian of greatest corneal power based on qualitative alterations of the keratoscopic image. These keratoscopes are based either on the optical principles of the von Helmholtz keratometer, or on nonparallel electronic image digitization. In this article we critically review commercially available surgical keratometers emphasizing their attributes and limitations.

Results of penetrating keratoplasty after epikeratophakia for keratoconus in the nationwide study

In the Nationwide Study of Epikeratophakia, 22 eyes underwent penetrating keratoplasty (PKP) after epikeratophakia for keratoconus. Reasons for PKP included visual acuity unsatisfactory to the patients (6 eyes), recipient corneal scarring (4 eyes), recipient Descemet's folds (3 eyes), scarring in the tissue lens (2 eyes), vascularization of the tissue lens (2 eyes), astigmatism (2 eyes), failure of the tissue lens to reepithelialize (1 eye), corneal ulcer (1 eye), and scarring of the donor and recipient cornea (1 eye). After PKP, all patients had clear grafts and 20/40 or better visual acuity. Average follow-up was 17 months. Three of the 22 patients (13.6%) had graft reaction episodes, all of which were treated successfully, resulting in clear grafts. The authors conclude that previous epikeratophakia does not adversely affect the outcome of subsequent PKP for keratoconus.

Refractive results of hyperopic hydrogel intracorneal lenses in primate eyes

Hyperopic hydrogel intracorneal lenses were successfully implanted into 27 of 33 primate eyes. All eyes were evaluated preoperatively and postoperatively at monthly intervals for clinical appearance and refractive alteration. In a preliminary surgical series, several factors, such as tight sutures and implant design, resulted in a poor refractive yield. The final surgical series used a microkeratome with a pediatric microkeratome ring for smooth interface cuts, interrupted suturing with sufficient tension to align the wound without compression, a suture through the lens to prevent its dislocation, and intraoperative keratometry to reduce postoperative cylinder. The predicted vs measured refractive alteration for a range of 6 to 20 diopters had a correlation coefficient of .95. Keratometry changes correlated to the refractive changes with a coefficient of .97 but understand the change in refraction created by the surgery.

Symmetry of refractive and visual acuity outcome in the Prospective Evaluation of Radial Keratotomy (PERK) study

In the Prospective Evaluation of Radial Keratotomy (PERK) study, the symmetry of refractive and visual acuity outcome was analyzed in 269 patients with bilateral radial keratotomy with a single operation in each eye. Patients were required to wait 1 year after surgery on the first eye before having surgery on the second eye. At 1 year after surgery on the second eye, 98% of patients had 3.00 diopters or less difference between their two eyes in the spherical equivalent of the cycloplegic refraction (100% before surgery), and 96% of patients had 3.00 D or less difference between their two eyes in the amount of refractive power in the vertical meridian (100% before surgery). Thus, surgically induced refractive anisometropia was not a major complication in the PERK study. However, 14% of patients had four to eight Snellen lines difference in the uncorrected visual acuity between their two eyes (1% before surgery), emphasizing that induced asymmetry of refraction is a potential clinical problem for some patients.

Penetrating keratoplasty after epikeratophakia for keratoconus

Seven patients underwent penetrating keratoplasty after epikeratophakia for keratoconus. All seven patients achieved clear grafts and 20/40 or better best corrected visual acuity after penetrating keratoplasty. Three of the seven patients had one or more episodes of rejection after penetrating keratoplasty; all were treated successfully. No grafts were lost. The results in terms of graft clarity and visual acuity are comparable with those in patients undergoing penetrating keratoplasty for keratoconus with no previous ocular surgery. Whether the relatively high rate of rejection episodes (three [43%]) seen in this small number of patients indicates some relationship between previous epikeratophakia and subsequent rejection after penetrating keratoplasty remains to be seen.

The nationwide study of epikeratophakia for aphakia in older children

A nationwide study of epikeratophakia for aphakia in older children was conducted from March 1984 to March 1986. Sixty-three patients, 8 to 18 years of age, underwent this procedure in 65 eyes. Twenty-eight patients had congenital cataracts and 35 had traumatic cataracts. Fifty-one of the 65 eyes were aphakic at the time of surgery (secondary procedures). All surgeries were successful; no tissue lenses were lost or removed. Postoperatively, 73% of the patients were within 3 diopters (D) of emmetropia. The patients with congenital cataracts gained an average of one Snellen line of best-corrected visual acuity; patients with traumatic cataracts lost an average of one Snellen line of best-corrected visual acuity. In older pediatric patients, epikeratophakia appears to be a safe and effective procedure for the correction of aphakia.

Three-year results of the Prospective Evaluation of Radial Keratotomy (PERK) Study

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). The authors report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At 3 years after surgery, 58% of eyes had refractive error within 1.00 D of emmetropia; 26% were undercorrected and 16% were overcorrected by more than 1.00 D. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 D. Between 1 and 3 years after surgery, the refractive error changed by 1.00 D or more in 12% of eyes, indicating a lack of stability in some eyes. In the 435 eyes, there was a small number of complications including six eyes that lost two or three lines of best-corrected acuity, 16 that experienced vascularization of the incisions, 2 that had delayed bacterial keratitis, and 4 that had recurrent epithelial erosions.