Jenny Garbus

Corneal Sensitivity After Photorefractive Keratectomy

Corneal anesthesia or hypesthesia can complicate refractive surgical procedures such as epikeratophakia and radial keratotomy. An esthesiometer was used to measure the corneal sensitivity in unoperated-on corneas and fellow corneas after excimer laser photorefractive keratectomy. Decrease in corneal sensitivity was noted within six postoperative weeks, with mean sensitivity being 75.2% +/- 13.3% of normal. Within the first three postoperative months, the patients operated on for correction of compound astigmatism recovered 95.7% +/- 5.3% of the corneal sensitivity, whereas the patients operated on for correction of severe myopia recovered 86.2% +/- 11.2% (P = .07). None of the patients had delayed epithelial healing or recurrent corneal erosions during the time of decreased corneal sensitivity. In otherwise normal myopic eyes, photorefractive keratectomy measurably reduced corneal sensitivity for several postoperative weeks.

Clinical Follow-up of Phototherapeutic Keratectomy for Treatment of Corneal Opacities

We performed phototherapeutic keratectomy with a 193-nm excimer laser on 18 sighted patients (18 eyes) to treat corneal opacities. The corneal opacities were caused by corneal dystrophies in five patients; corneal scars secondary to corneal ulcers in six patients; corneal scar secondary to trauma in four patients; and band keratopathy, atopy, or corneal calcification in three patients. Mean follow-up was eight months (range, two to 18 months). Corneal clarity improved in 14 of the 18 eyes (77.7%). Four patients, three with band keratopathy or calcification and one with postinfectious corneal scar, did not improve. Uncorrected visual acuity improved in 11 patients, did not improve in five patients (including the four patients in whom treatment failed), and decreased in another two patients, apparently because of an increase in irregular astigmatism. A hyperopic shift was observed in ten patients. None of the successfully treated eyes developed surface problems or recurrence of the disease during the follow-up. Phototherapeutic keratectomy thus appears to be a safe and effective alternative to penetrating keratoplasty in some patients with selected anterior stromal opacities.

Photorefractive Keratectomy for Severe Postkeratoplasty Astigmatism

We performed cylindric corneal ablations with the excimer laser on 12 patients to correct severe, disabling astigmatism after keratoplasty. In some patients, an additional ablation was performed to correct myopia. Patients were followed up for an average of eight months (range, six to 14 months). Uncorrected visual acuity improved in nine patients, and nine of the 12 patients had a decrease in refractive cylinder at last follow-up. The mean preoperative refractive cylinder was 7.0 +/- 3.6 diopters, which decreased to a mean of 3.1 +/- 2.6 diopters at one month (P = .0003) and 4.3 +/- 2.9 diopters at last follow-up (P = .03). Keratometric astigmatism decreased from 7.5 +/- 3.9 diopters preoperatively to 5.2 +/- 3.9 diopters at the last follow-up (P = .001). Mean spherical equivalent was reduced from -7.4 +/- 4.2 diopters preoperatively to -3.3 +/- 4.4 diopters postoperatively (P = .003). Postoperative corneal haze, when present, did not reduce visual acuity. Excimer laser superficial keratectomy thus appears to be safe when used for postkeratoplasty ametropia, although substantial regression may limit its effectiveness in some patients.

Decrease in normal human corneal sensitivity with topical diclofenac sodium.

We tested the effect of topical diclofenac sodium on corneal sensitivity in the human eye. Corneal sensitivity was measured in ten adult subjects with the Cochet-Bonnet esthesiometer before, and immediately after, applying one drop of diclofenac sodium 0.1% in one eye and one drop of diclofenac vehicle in the other eye. Application was repeated every five minutes for 20 minutes; then no more drops were applied, and corneal sensitivity was measured every 15 minutes until sensitivity measurements returned to baseline levels. Diclofenac sodium decreased corneal sensitivity significantly (P = .0001) in all ten subjects, compared with eyes treated with the vehicle. The effect of diclofenac sodium increased as additional drops were administered. After the drug instillation was stopped, corneal sensitivity returned to baseline measurements within less than an hour in all the subjects. Diclofenac sodium substantially lowers sensitivity in normal, unoperated-on human corneas; the vehicle has no measurable effect on sensitivity.

Topographic analysis and visual acuity after radial keratotomy.

Using a computerized corneal topographic mapping system that allows detailed examination of the corneal curvature in the vicinity of the visual axis, we identified separate regions of differing corneal curvature in three of 11 eyes after radial keratotomy. In these eyes, the excellent uncorrected visual acuity appeared to be inconsistent with the postoperative spherical equivalent as determined by refraction and corneal curvature by standard keratometer measurements. The distinct regions of corneal curvature appeared to serve as alternative effective optical zones, thus allowing the patients to have excellent visual acuity. In essence, the cornea became a multifocal lens. Although degradation in the contrast of the image as well as monocular diplopia are possible, our patients had no significant complaints.

Mechanism of Corneal Topographic Changes

Pterygia induce irregular corneal astigmatism that sometimes necessitates surgical removal before the lesion has advanced close to the visual axis. This astigmatism may occur either due to traction generated by the pterygium mechanically pulling on and distorting the cornea, or by the pooling of tears in advance of the pterygium, or both. To evaluate the effect of localized tear pooling on pterygium-induced astigmatism, corneoscope photographs were obtained before and after absorbing excess tears at the pterygium-corneal interface with a cellulose sponge. Pterygia from these patients were then excised and examined with transmission electron microscopy for the presence of myofibroblasts. The absence of myofibroblasts in these lesions as well as the alterations in corneoscopy induced by localized removal of tears at the advancing edge of the pterygia suggest that corneal distortion in the presence of pterygia is caused in part by local changes in the tear film.

Corneal Wound Healing after Excimer Laser Ablation: Effects of Nitrogen Gas Blower

PURPOSE To examine the effects of blowing nitrogen gas over the cornea during photorefractive keratectomy. METHODS Excimer laser ablations for myopia were performed on rabbit corneas with or without the blowing of nitrogen across the surface of the cornea. All eyes underwent a 5-diopter myopic ablation; in 8 eyes, a ring was used to blow nitrogen gas across the cornea, and, in 8 eyes, the same ring was used, but no nitrogen gas was blown. RESULTS Epithelial healing occurred more rapidly in the eyes that were not treated with the gas (3.8 +/- 1.3 days) than in the gas-treated group (6.1 +/- 0.8 days; P = 0.0025). Corneal haze was greater in the group treated with gas. Results of histologic examination showed the ablated area to have a smoother surface when nitrogen was not blown across the cornea surface. CONCLUSION Superficial corneal deturgescence produced by the nitrogen gas appears to result in a rougher surface immediately postoperatively with undesirable effects on surface healing, but further studies will be necessary to determine the applicability of these results to humans.

Phototherapeutic Keratectomy for Granular and Lattice Corneal Dystrophies at 1.5 to 4 Years

BACKGROUND The capability of the 193-nm excimer laser to ablate the cornea and to remove opacities and various other corneal diseases in a procedure called phototherapeutic keratectomy (PTK) has been demonstrated. In this study we evaluated the long-term results of PTK for treatment of granular and lattice corneal dystrophies. METHODS Four eyes with granular or lattice corneal dystrophy were treated with a mean follow-up of 47.8 months (range, 36 to 58 months). Focal ablations of the central cornea with an ablation zone of 5.5 to 6.0 mm were performed. Ablation depth was 110 microns in three eyes and 140 microns in one eye. RESULTS Removal of corneal opacities allowed for improvement in corrected visual acuity in all patients. Mean corneal thickness in the area of pathology decreased from 0.583 mm before surgery to 0.449 mm after surgery. Spherical equivalent of the manifest refraction measurements increased by a mean of +5.09 D. There were no major complications, but all patients developed slight haze. There was a hyperopic shift in three eyes. CONCLUSION Our long-term results suggest that PTK is a safe and effective alternative to penetrating and lamellar keratoplasty in patients with granular or lattice corneal dystrophies.

Corneal Topography and Fluctuating Visual Acuity after Radial Keratotomy

A high-resolution photokeratoscope using computer graphics to model corneal topography was used on patients who had undergone radial keratotomy. After radial keratotomy, central optical zones are created that can be characterized as round, oval or band-like, or dumbbell-shaped or split. The dumbbell form of optical zone was associated with larger amounts of refractive and keratometric astigmatism than the round or band-like zones. The authors correlated the shape of the optical zone with the presence or absence of diurnal variation (fluctuation) in visual acuity. Of the 26 eyes studied, 11 experienced fluctuation and 15 did not. Of those 11 eyes with fluctuating visual acuity, 10 (91%) had dumbbell-shaped or split optical zones and 1 (9%) had a round optical zone. Of the 15 eyes without fluctuation, 12 (80%) had round optical zones and 3 (20%) had band-like zones. The presence of a split or dumbbell-shaped optical zone after radial keratotomy indicates that the patient is likely to experience diurnal fluctuation of visual acuity.

Computerized Analysis of Corneal Topography as an Aid in Fitting Contact Lenses After Radial Keratotomy

To select an appropriate base curve to use in fitting a contact lens in 16 eyes of 10 patients following radial keratotomy, we used a videokeratoscope that generates a 32-ring image, covering the entire cornea, to measure the midperipheral corneal curvature. We then based contact-lens selection on the curvature 3.5 mm superior to the visual axis. Photographic documentation of fluorescein patterns and subjective reports of the patients indicated a successful fitting in all cases.