Vernon C. Parmley

Visual field defect associated with laser in situ keratomileusis

PURPOSE To report a case of visual field defect associated with laser in situ keratomileusis. METHODS Case report. A 28-year-old woman with high myopia (-10D) and a family history of normal tension glaucoma underwent bilateral laser in situ keratomileusis keratorefractive surgery. Preoperatively, both eyes had normal intraocular pressure and visual field. RESULTS At the first postoperative visit 1 day after apparently uncomplicated laser in situ keratomileusis, the patient reported a scotoma in the right eye. At 3-month follow-up, visual fields revealed the patient had developed a near-superior altitudinal visual field defect in the right eye. The defect did not progress over 1 year of follow-up examinations. CONCLUSION Increased intraocular pressure associated with the microkeratome vacuum ring used during laser in situ keratomileusis may have precipitated optic nerve head ischemia and visual field defect.

Combined Treatment of Acanthamoeba Keratitis With Propamidine, Neomycin, and Polyhexamethylene Biguanide

We developed an intensive treatment regimen of topical neomycin, propamidine, and polyhexamethylene biguanide that was tapered to a maintenance level over a 14- to 28-day period as toxicity developed. Since July 1991, we used this treatment on six eyes of five patients in whom Acanthamoeba keratitis was diagnosed clinically. All patients had positive cultures for microorganisms from their corneas or contact lens cases or had pathognomonic findings of pseudodendritic subepithelial infiltrates and radial keratone-uritis. After therapy, all patients improved within two to four weeks, with regression or resolution of neuritis and infiltrates, healing of epithelial defects, and lessening of pain. By three to four months, visual acuity had returned to 20/20 in all eyes. We believe the addition of polyhexamethylene biguanide to our treatment regimen in Acanthamoeba keratitis dramatically aided and hastened the clinical improvement in five consecutive patients and may, with early diagnosis, increase the number of medical cures.

The etiology of refractive changes at high altitude after radial keratotomy: Hypoxia versus hypobaria

OBJECTIVE Refractive changes at high altitude that occur after radial keratotomy (RK) may be caused by hypoxia or hypobaria. DESIGN A prospective study was performed to evaluate the effects of hypoxia on RK and non-RK corneas. PARTICIPANTS There were 20 RK and 20 control eyes. INTERVENTION These eyes were subjected to ocular surface hypoxia using an air-tight goggle system at sea level for 2 hours. MAIN OUTCOME MEASURES Keratometry, cycloplegic refraction, and pachymetry were evaluated using repeated measures analysis of variance. RESULTS A significant hyperopic shift (P < 0.0001) and corneal flattening (P < 0.0013) occurred in all subjects with RK compared with those of control subjects. Corneal thickening occurred symmetrically in both groups. CONCLUSIONS These results suggest that refractive changes in subjects with RK occur at high altitude as a direct result of corneal hypoxia.

Effects of simulated high altitude on patients who have had radial keratotomy.

BACKGROUND Previous studies documented diurnal myopic shifts in patients who have had radial keratotomy (RK). Recently, hyperopic shifts in these patients exposed to high altitude have been reported. A direct mechanical effect of reduced barometric pressure on surgically altered corneas has been theorized to cause this hyperopic shift. Another hypothesis implicates the effect of hypobaric hypoxia on the RK incisions. The authors examined the effect of a 6-hour exposure to decreased barometric pressure on 14 normal and 18 RK corneas. METHODS Cycloplegic refraction, keratometry, corneal pachymetry, and tonometry were performed on seven control subjects and nine patients who have had RK. Measurements were obtained over 8 hours at sea level on day 1 of the study. Measurements were repeated on day 2 which included a 6-hour exposure to 12,000 feet simulated altitude in a hypobaric chamber. Results were compared between subjects and control subjects to determine the effect of a 6-hour exposure to decreased barometric pressure. RESULTS There was no statistically significant difference in refraction or keratometry readings between control subjects and subjects who have had RK. Central corneal thickness decreased in the afternoon in RK eyes compared with control eyes. There was no clinically significant difference in intraocular pressure between subjects who have had RK and control subjects. CONCLUSIONS A measurable hyperopic shift in RK corneas exposed to high altitude requires more than 6 hours to develop. A direct effect on corneal shape due to barometric pressure alone should produce a sudden change in refractive error. This study supports the hypothesis that a slow metabolic process is responsible for the previously documented hyperopic shifts induced by altitude. However, a barometric pressure effect requiring more than 6 hours to occur cannot be ruled out with the methodology used in this study.

Infectious Crystalline Keratopathy Caused by Candida guilliermondii

PURPOSE To describe the manifestations of infectious crystalline keratopathy caused by Candida guilliermondii in a corneal transplant performed for pseudophakic bullous keratopathy. METHOD Case report. RESULTS Candida guilliermondii was identified as the causative organism of an indolent infectious crystalline keratopathy. Incisional lamellar biopsy provided diagnostic culture and histopathologic results. Histopathology showed aggregates of yeast elements between corneal stromal lamellae, without inflammation. The infection progressed despite a 6-week course of topical amphotericin B and an additional 6-week course of topical and oral fluconazole. Repeat penetrating keratoplasty resulted in clear graft, with no recurrent infection. CONCLUSIONS Fungal keratopathy should be included in the differential diagnosis of infectious crystalline keratopathy. Numerous Candida species have been isolated in addition to the most common causative bacterial organism, Streptococcus viridans. Candida guilliermondii is yet one more causative agent of infectious crystalline keratopathy. Candida guilliermondii, a rare human pathogen, was resistant to medical therapy in this case.

Refractive changes caused by hypoxia after laser in situ keratomileusis surgery

OBJECTIVE To determine whether hypoxia induces refractive changes in subjects who have had laser in situ keratomileusis (LASIK) refractive surgery. DESIGN Prospective paired eye clinical trial. PARTICIPANTS There were 20 LASIK subjects (40 eyes) and 20 myopic non-LASIK controls (40 eyes). INTERVENTION Each subject had one eye exposed to ocular surface hypoxia (humidified nitrogen) by use of an airtight goggle system at sea level for 2 hours. The other eye was simultaneously exposed to humidified, compressed air (21% oxygen) with the same airtight goggle system. MAIN OUTCOME MEASURES Keratometry, cycloplegic refraction, and pachymetry were compared before and after exposure by use of repeated measures analysis of variance. RESULTS A significant myopic shift (P: < 0.01) occurred in LASIK corneas exposed to hypoxia compared with myopic control subjects. A significant increase in corneal thickening occurred symmetrically in both LASIK and control subjects exposed to hypoxia. There was a trend toward corneal steepening (keratometry) in LASIK subjects, but this was not statistically significant. CONCLUSIONS These results suggest that ocular surface hypoxia induces a myopic shift in LASIK subjects.

Refractive corneal surgery with the Draeger rotary microkeratome in human cadaver eyes

BACKGROUND Instrumentation for performing a uniform lamellar keratoplasty has been undergoing various stages of refinement. Reliable reproduction and uniform thickness and diameter of lamellar resections is required before lamellar refractive keratoplasty can be considered safe and effective. METHODS The authors used the Draeger rotary microkeratome with mechanical blade advance for lamellar dissections in 61 human cadaver eyes prepared by injecting Swinger-Kornmehl (SK) solution into the anterior chamber to a pressure of 35 to 40 mm Hg and by soaking for 30 minutes in SK solution. Spacer sizes of 0.25 to 0.40 units were utilized using an anterior lamellar disc diameter estimate between 8.0 and 8.5 mm and a stromal lamellar disc diameter estimate between 5.5 and 6.5 mm. Preoperative pachometry, anterior and stromal lamellar disc thicknesses, and anterior and stromal lamellar disc diameters were measured. RESULTS The Draeger unit created anterior lamellar thickness between 100 and 268 microns. Stromal lamellar disc thicknesses were consistently between 90 and 161 microns. The continuous, unidirectional, rotary blade and the uniform mechanical advance of the instrument produced a generally uniform bed as evaluated by scanning electron microscopy, although undulations were still present. CONCLUSION The Draeger microkeratome produced regular lamellar dissections; however, predictability of the thickness of the lenticules varied 10% to 20%, and of the diameter, 1.5% to 15%. Predictability improved with experience. This variability may reduce predictability of refractive outcome.

Warm balanced salt solution for clearing tear film precipitation during cataract surgery

&NA; Adequate anterior segment visualization during cataract surgery can be hindered when excessive tear film secretions precipitate on the corneal surface before the initial corneal incision is made. In most cases, room‐temperature balanced salt solution applied to the corneal surface clears the debris. However, in cases in which tear film precipitates persist after the use of room‐temperature balanced salt solution, the application of warm balanced salt solution can provide rapid and sustained dispersion of the precipitates. We present our experience using this technique.

Penetrating Keratoplasty after Radial Keratotomy: A Report of Six Patients

BACKGROUND For more than 15 years, radial keratotomy has increased in popularity as an option for treating myopia in the United States. During this period of time, the procedure has been modified to improve results and decrease complications. Despite these changes, complications from radial keratotomy continue to occur. The authors report six cases of penetrating keratoplasty performed to correct significant loss of vision resulting from complications of radial keratotomy. METHODS The surgical records of one author (WR) were reviewed retrospectively for penetrating keratoplasties performed for complications of radial keratotomy. RESULTS Six cases of penetrating keratoplasty performed for complications of radial keratotomy were found. Severe loss of vision was the indication for surgery in each case, and was associated with aggressive and repeated incisional refractive attempts to correct astigmatism, hyperopic overcorrection, residual myopia, or refractive errors associated with keratoconus. Glare associated with subepithelial scarring and irregular astigmatism were the primary findings associated with loss of vision. CONCLUSIONS Despite advances in technique and instrumentation, radial keratotomy is limited in the amount of myopia it can correct. The risk for loss of vision increases with increasing number of incisions, intersecting incisions, very small optical zones, and keratoconus.