Unsuccessful excimer laser phototherapeutic keratectomy. Clinicopathologic correlation.

A 46-year-old man underwent phototherapeutic keratectomy with a 193-nm excimer laser in an attempt to remove a superficial corneal scar that had been present for 36 years. The scar proved to be resistant to ablation with the laser, while relatively normal stroma was easily ablated. Histopathologic examination of the corneal button removed 3 months after excimer laser surgery revealed absence of Bowman's membrane in the area of ablation, superficial stromal disorganization and scarring, raised nodules of collagenous tissue extending into the epithelium, and no calcification within the lesion. Ultrastructural examination was remarkable for irregularly oriented collagen fibers within the scar. The resistance of this lesion to excimer laser ablation appears to have been the consequence of marked differences in rates of ablation between normal stroma and the very long-standing scar.

Diurnal variation of corneal topography after radial keratotomy.

A computerized videokeratography system was used to evaluate diurnal changes in corneal curvature of both untreated and surgically treated eyes of 11 patients who had undergone unilateral radial keratotomy. The mean postoperative interval was 34.5 months. Both corneas operated on and those not operated on steepened on average from morning to evening. For untreated eyes, this diurnal steepening was statistically significant at a distance of 0.5 mm from the corneal apex (mean +/- SE, 0.36 +/- 0.07 diopter) and in the inferotemporal quadrant (0.28 +/- 0.08 D); in eyes that had undergone radial keratotomy, steepening was significant at from 1.0 to 3.0 mm from the corneal apex (0.39 +/- 0.07 D) and temporal, inferotemporal, inferior, inferonasal, nasal, and superonasal to the corneal apex (0.42 +/- 0.08 D). The greatest steepening in the eyes treated with radial keratotomy compared with the untreated eyes occurred at 1.5 to 2.5 mm peripheral to the corneal apex in the inferonasal and nasal octants. Diurnal changes in intraocular pressure, corneal thickness, number of incisions, clear-zone size, postoperative period, and patient sex were not predictive of the magnitude of morning-to-evening change. Furthermore, diurnal changes in corneal curvature of untreated eyes were not predictive of diurnal changes in the fellow eyes after radial keratotomy.

Multifocal corneal topographic changes with excimer laser photorefractive keratectomy.

Excimer laser photorefractive keratectomy can flatten the central cornea, thereby eliminating myopic refractive errors; in older patients, however, presbyopia limits satisfaction. Computer-assisted topographic analysis of corneas after refractive surgery indicates that a minority of patients achieve a multifocal lens effect, such that they maintain reasonable acuity over a range of defocus. We have purposefully attempted to create a multifocal refractive effect and have analyzed the subsequent topographies quantitatively to determine if multifocality was achieved. In corneas not operated on and plastic hemispheres, a fairly small range of corneal powers is observed; the range of powers is increased after a monofocal ablation. After multifocal ablations, a greater spread of surface powers is observed, often with a bimodal distribution, indicative of an apparent multifocal effect. These observations suggest that in some patients undergoing photorefractive keratectomy for myopia, it may be possible to reduce symptoms of presbyopia, although a decrease in image contrast or monocular diplopia may complicate this approach.

Corneal sensitivity and burning sensation. Comparing topical ketorolac and diclofenac.

OBJECTIVES: To compare the effect of topical 0.5% ketorolac tromethamine and 0.1% diclofenac sodium on human corneal sensitivity and to assess the intensity of burning sensation at specific intervals after drop instillation. DESIGN AND SETTING: Double-masked parallel clinical study. PATIENTS: Eleven women and 4 men (8 white, 4 Hispanic, 3 Asian), 22 to 60 years of age (mean [ +/- SD], 34 +/- 10 years). INTERVENTIONS: Repeated instillation of either ketorolac and placebo or diclofenac and placebo at 5-minute intervals. MAIN OUTCOME MEASURES: Assessment of corneal sensitivity before instillation, immediately after instillation, and after termination of drop application; and subjective evaluation of burning sensation by asking participants to rate burning on a scale ranging from 0 (none) to 3 (severe) after each drop application. RESULTS: Both diclofenac (P < .01) and ketorolac (P < .01) decreased corneal sensitivity significantly, while the placebo had no measurable effect. After administration of additional drops over time, the effect of diclofenac and ketorolac increased. After termination of the drug instillation, corneal sensitivity returned to baseline significantly slower (P < .01) in participants receiving diclofenac than in those receiving ketorolac. Ketorolac (P = .01) and diclofenac (P < .05) were significantly more effective in whites than in nonwhites. Mean burning sensation was mild, and there was no statistically significant difference between the 2 drugs on this measure (P = .12). CONCLUSIONS: The decrease in corneal sensitivity in normal human corneas is more pronounced and longer lasting with diclofenac than with ketorolac. Both drugs are well tolerated topically and may be useful for pain reduction after refractive corneal surgery.

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.

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.

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.

Corneal topographic changes over time after radial keratotomy.

Radial keratotomy flattens the cornea, but in a nonuniform fashion. We used computer-assisted topographic analysis to examine curvature changes in different regions of the cornea. Within 45 days after surgery in human eyes, the central and midperipheral cornea flattens and the periphery steepens. Shortly after surgery, the central cornea (within 1-1.5 mm of the corneal light reflex) is steeper than the adjacent midperipheral cornea (1.5-3 mm peripheral to the light reflex). With time, however, the central cornea flattens more than the midperiphery, such that it is no longer relatively steeper. This regional variability in corneal curvature after radial keratotomy helps explain phenomena such as multifocal lens effect after radial keratotomy, and the changes with time account for the conflicting results observed clinically in human corneas and experimentally in human eye bank eyes.

Excimer laser myopic photorefractive keratectomy after undercorrected radial keratotomy.

Two patients, a 41-year-old female diabetic and a 37-year-old male, were undercorrected after radial keratotomy (spherical equivalents of -3.25 diopters in each eye). Because they were unable to wear a contact lens and had uncorrected visual acuities of 20/400 and 20/100, respectively, they elected to undergo excimer laser photorefractive keratectomy to reduce the myopia by 3.00 D and 2.75 D, respectively. Three months postoperatively, both patients were within 0.50 D of emmetropia. Videokeratography demonstrated a fairly uniform zone of central flattening. The previous radial keratotomy surgery and the diabetes (in one patient) did not appear to complicate the surgery. Excimer laser photorefractive keratectomy appears to hold promise as a means of correcting eyes left undercorrected by radial keratotomy.

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.

Corneal wound healing after excimer laser ablation in rabbits: expanding versus contracting apertures.

BACKGROUND: Photorefractive keratectomy for myopia can be performed using an expanding or contracting iris diaphragm, either of which allows for greater ablation centrally and less tissue ablation toward the edge of the treatment zone. METHODS: To compare the effects of these two strategies, eight rabbits underwent bilateral 5.00-diopter myopic ablations, performed with a contracting diaphragm in one eye and an expanding diaphragm in the other. RESULTS: The rate of epithelial healing and degree of anterior stromal haze, monitored by a masked observer, were similar for the two groups, as was the amount of corneal flattening. CONCLUSIONS: These results in rabbit corneas do not suggest a particular advantage of either the expanding or contracting apertures for achieving central corneal flattening in photorefractive keratectomy.

Computer-assisted study of diurnal variation in corneal topography after penetrating keratoplasty.

Diurnal changes in corneal topography have been documented to be greater in eyes following radial keratotomy that in normal eyes. To determine whether substantial changes of this nature result from corneal incisions in general or are a specific complication of radial keratotomy, we examined 12 corneas (10 patients) after penetrating keratoplasty for diurnal changes, using a computerized corneal topographic analysis system. Diurnal changes in keratometry readings, central corneal thickness, intraocular pressure, and refraction also were analyzed. From morning to evening, central corneal curvature flattened by an average of 0.74 +/- 0.18 diopters in eight eyes (67%), and steepened by an average of 2.00 +/- 0.53 D in four eyes (33%). Diurnal changes in central corneal thickness were correlated with diurnal changes in central corneal curvature (r = 0.63, P less than .05). These data suggest that changes in corneal thickness over the course of the day may partially account for the changes in corneal curvature demonstrated to occur following penetrating keratoplasty.

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.

Contact lens selection for keratoconus using a computer-assisted videophotokeratoscope.

We used the Corneal Modeling System, a digital videophotokeratoscope, as an aid in selecting the initial base curve and lens diameter for contact lenses in keratoconus patients. With this instrument we studied corneal topography in 24 keratoconus patients (33 eyes) who were being fit for the first time or who had not worn contact lenses for at least one month prior to our examination. For the purposes of fitting contact lenses, the corneas were classified according to the topographic patterns observed, and appropriate fitting strategies were adopted for each subgroup. Diagnostic lenses and their fluorescein patterns were analyzed for the desired cornea-lens relationship. Topographic analysis of the cornea provided a rational basis for selecting appropriate trial contact lenses for our patients.

Multifocal corneal topographic changes after radial keratotomy.

Quantitative analysis of the central corneal refractive powers of both eyes of three patients demonstrated that, after radial keratotomy, the corneas tended to have a greater range of refractive powers than preoperatively, and that the corneas with a multifocal effect had a wider distribution of refractive powers than the corneas of eyes without this effect. It may be possible to intentionally achieve a multifocal lens effect by designing a refractive procedure to predictably widen the distribution of central corneal refractive powers.

[Photorefractive keratectomy for correction of myopic astigmatism]. / Photorefraktive Keratektomie zur Korrektur von myopem Astigmatismus.

Nine eyes underwent superficial ablation with excimer laser for treatment of compound myopic astigmatism. In eight of the eyes, corneal cylinder was naturally-occurring, and in one eye the astigmatism had developed following retinal detachment surgery. All patients have been followed for 9 months. The pre- and postoperative cylinder was -2.7 +/- 0.4 diopters and -1.3 +/- 0.4 diopters, respectively, while the pre- and postoperative spherical equivalent was -4.7 +/- 0.4 diopters and -1.3 +/- 0.4 diopters, respectively. Uncorrected acuity improved from a preoperative mean of 20/300 to a postoperative mean of 20/40. Patients with a residual refractive error often demonstrated reasonably good unaided acuity. Toric ablations with the excimer laser can be performed at the same time as ablations for myopia, and appear to represent a promising strategy for correction of compound myopic astigmatism; the relative safety and efficacy of this procedure, and of combined radial and astigmatic keratotomy remain to be determined.