Stephen M. Cristol

Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium

PURPOSE To assess the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium. METHODS In a prospective study, the corneal endothelium of 98 eyes of 65 consecutive patients (mean age, 41 years; range, 22 to 66 years) was photographed before, 2 weeks after, and 12 weeks after LASIK for the correction of 2.75 to 14.5 diopters of myopia. Theoretical ablation depths were 200 to 330 microm below the corneal surface. Cell density, coefficient of variation, and percent of hexagonal cells were determined using 150 to 200 cells from each image. Eighty-eight eyes (91%) of 59 patients had a history of contact lens wear. RESULTS The mean+/-SD preoperative endothelial cell density was 2,549+/-365 cells per mm2, and the mean coefficient of variation was 0.35+/-0.06. There was no statistically significant change in the mean endothelial cell density or mean coefficient of variation of cell size at the 2-week (2,561+/-360 cells per mm2 and 0.35+/-0.06) or 12-week (2,541+/-364 cells per mm2 and 0.35+/-0.05) postoperative examinations. The percent of hexagonal cells was not significantly changed 2 weeks postoperatively; however, 12 weeks postoperatively (P=.0413, two-tailed t test), the percent of hexagonal cells was decreased by 1%. CONCLUSIONS Corneal endothelial cell density and morphology were unchanged 2 and 12 weeks after LASIK for the correction of up to 14.5 diopters of myopia. In this LASIK study, the correction of up to 14.5 diopters of myopia appears to cause no clinically significant effect on corneal endothelial cell density or morphology.

Results of large penetrating keratoplasty in microbial keratitis

Extensive corneal disease secondary to microbial keratitis can result in frank or impending corneal perforation requiring a large penetrating keratoplasty. In an 8-year period, 26 penetrating keratoplasties with recipient beds of > or = 9.5 mm were performed on 22 eyes: 11 for bacterial keratitis, 10 for fungal keratitis, and one for a mixed bacterial and fungal keratitis. The graft failed in 18 of 19 eyes (94.7%), with a median time to failure of 12.9 weeks in bacterial keratitis and 4.0 weeks in fungal keratitis. After large keratoplasty, 17 of 20 eyes (85.0%) maintained the structural integrity of the globe. The remainder became phthisical or required enucleation. With preservation of the structural integrity of the globe, a subsequent smaller optical penetrating keratoplasty is an option in some of these eyes.

Homozygous granular corneal dystrophy type II (Avellino corneal dystrophy): natural history and progression after treatment.

Purpose: To describe the clinical features of homozygous granular corneal dystrophy type II (GCDII) with age and with several kinds of treatment in 18 homozygous patients in several different conditions. Methods: Eighteen homozygous GCDII patients, confirmed with DNA analysis, of 13 families were enrolled. Their clinical features that include age at detection by parents, visual acuity, and disease progression were evaluated. We also studied the recurrence patterns for the 13 patients who underwent phototherapeutic keratectomy, penetrating keratoplasty, lamellar keratoplasty, or deep lamellar keratoplasty. Results: The age at detection by the parents ranged from 3 to 5 years; visual loss begins in childhood with progression into the 20s. All of the patients who had undergone surgeries acquired better vision immediately after surgery. Corneal deposits reappeared soon after treatments. Recurrences became progressively more rapid and severe with treatments. Conclusions: The clinical features of homozygous GCDII are characterized by a severe granular type of corneal dystrophy with an early onset and rapid progression. After surgical treatment, recurrence is rapid and severe.

Viscoelastic protection from endothelial damage by air bubbles

Purpose: To determine whether viscoelastic materials effectively protect the corneal endothelium from air bubbles. Setting: Department of Ophthalmology, Yonsei University College of Medicine, Seoul, Korea. Methods: Human eye‐bank and rabbit eyes had a standardized phacoemulsification procedure with or without viscoelastic material (Healon® [sodium hyaluronate 1.0%], Healon GV® [sodium hyaluronate 1.4%], or Viscoat® [chondroitin sulfate 4.0%−sodium hyaluronate 3.0%]). The integrity of the endothelium was examined after the procedure with F‐actin staining and scanning electron microscopy. Rabbit eyes with and without viscoelastic material (Healon or Viscoat) had a standardized irrigation/aspiration (I/A) procedure. The mucinous layer of the endothelium was examined after the procedure with transmission electron microscopy. Results: In the phacoemulsification experiment without viscoelastic material, with Healon, and with Healon GV, the endothelium of human and rabbit corneas had many areas of cell loss in a pattern consistent with air‐bubble damage. With Viscoat, endothelial cells remained intact. In the I/A experiment, the mucinous layer of Viscoat‐exposed rabbit endothelium appeared thinner. In the same experiments without viscoelastic material or with Healon, the mucinous layer of the endothelium appeared normal. Conclusions: Viscoat effectively protected the endothelium from air‐bubble damage. Viscoat appears to protect the endothelium by acting as a physical barrier. Its adherence is probably related to the way it interacts with the mucinous layer of the endothelium.

A Comparison of Corneal Stromal Edema Induced From the Anterior or the Posterior Surface

BACKGROUND Many differences between the anterior and posterior corneal stroma have been reported. The physiological and mechanical properties of the cornea are a summation of these properties across each of the corneal regions. This article investigates corneal stromal swelling that is experimentally induced through each surface. METHODS Corneal stromal swelling was induced in human and rabbit corneas through either the anterior or posterior surface. The rate of stromal swelling was analyzed with a linear regression model. RESULTS Swelling in the rabbit stroma was 3.65 x faster when induced through the posterior surface than through the anterior surface (p less than .0001), while the human stroma swelled 13.1 x faster through the posterior surface (p less than .0001). The hydration of the stroma increased during swelling through the posterior surface, but paradoxically decreased during swelling through the anterior surface. CONCLUSIONS These experiments showed that stromal swelling occurs more rapidly through the posterior corneal surface than through the anterior surface. These results may have implications for the refractive surgeon performing laser ablative procedures on the anterior surface of the cornea.

5-Fluorouracil after Trabeculectomy and the Iridocorneal Endothelial Syndrome

Nine patients (nine eyes) with iridocorneal endothelial (ICE) syndrome underwent trabeculectomy and received postoperative subconjunctival injections of 5-fluorouracil (5-FU) to enhance bleb formation (total 5-FU dose, 30-105 mg; mean, 53.8 mg). Eight eyes had undergone prior unsuccessful trabeculectomy. Four eyes had intraocular pressure (IOP) less than or equal to 21 mmHg on zero to two glaucoma medications after 6 to 54 months of follow-up (mean, 25.3 months). Five eyes required repeat surgery within 2 to 13 months and were considered failures. All five eyes that failed received a Molteno drainage implant. Progressive endothelial proliferation may explain late onset bleb failure and the relative ineffectiveness of 5-FU in this condition.

Prevalence of Granular Corneal Dystrophy Type 2 (Avellino Corneal Dystrophy) in the Korean Population

Purpose: This study investigates the prevalence of granular corneal dystrophy type 2 (GCD2; Avellino corneal dystrophy) in the Korean population. Methods: GCD2 homozygotes were identified through a collaboration of Korean referral centers for corneal disease. The genetic status of the patients and their immediate families were verified by DNA analysis. A lower bound for the gene prevalence was calculated using a model based on the Hardy-Weinberg principle. A second population-based model was developed to correct for known underestimation in the primary model. The corrected model used population data from the 2005 Korean census and fertility rates from historical Korean census data. Results: We identified 21 individuals homozygous for GCD2 (R124H mutation) from 16 Korean families. From this, we estimate that the overall prevalence (combining heterozygotes and homozygotes) is at least 8.25 affected persons/10,000 persons. Our corrected estimate for overall prevalence is 11.5 affected persons/10,000 persons. Conclusion: We present the first estimate of the prevalence of GCD2. Although uncommon, the prevalence of GCD2 in Korea is greater than anticipated. We believe that our approach could potentially be applied to estimating the prevalence of other rare diseases.

Bilateral acute angle-closure associated with systemic lymphoma: A report of 2 cases

Bilateral acute angle-closure is a rare occurrence. When the central anterior chambers are shallow, it is often associated with systemic disease. We present 2 patients with atypical bilateral acute angle-closure as the presentation of systemic lymphoma. In these patients, angle closure may be caused by a uveal effusion or swelling of the ciliary body. If an atypical bilateral acute angle-closure attack cannot be attributed to a drug reaction or a bilateral iatrogenic cause, the patient should be evaluated for an associated systemic disease. In some patients, the acute angle-closure cannot be fully resolved until the underlying disease is treated. This report discusses the spectrum of presentations and the various diseases that have been associated with bilateral acute angle-closure.

Endothelial protection: avoiding air bubble formation at the phacoemulsification tip

Purpose: To investigate the conditions under which bubbles form during phacoemulsification. Setting: Department of Ophthalmology, Yonsei University College of Medicine, Seoul, Korea. Methods: In the first part of the study, the partial pressure of oxygen (pO2) was used as a surrogate measure for the partial pressure of air. Irrigation solutions packaged in glass and plastic containers were studied. A directly vented glass bottle was also tested. The pO2 of the various irrigation solutions was measured as the containers were emptied. In the second part, phacoemulsification procedures were performed in rabbit eyes with different power settings and different irrigation solutions. Intracameral bubble formation during the procedure was recorded. Following the phacoemulsification procedures, the corneas were stained for F‐actin and examined for endothelial injury. Results: The initial pO2 in irrigation solutions packaged in glass bottles was about half that at atmospheric levels; in solutions packaged in plastic, it was at atmospheric levels. As irrigation solutions were drained from the container, the pO2 of the solution tended to rise toward atmospheric levels. The rate of pO2 increase was markedly reduced by using a directly vented glass bottle. In the phacoemulsification procedures, bubble formation was most likely to occur with higher pO2 and higher power settings. Observation of bubbles by the surgeon was highly correlated with endothelial damage. Conclusions: Keeping the pO2 low reduced the risk of endothelial damage, especially at higher phacoemulsification powers. The packaging of irrigation solutions was the most important factor in controlling the initial pO2 of the solution. The pO2 can be minimized throughout a phacoemulsification procedure by using a directly vented glass bottle.

Rates of Epithelial Ingrowth After LASIK for Different Excimer Laser Systems

PURPOSE To investigate the incidence of epithelial ingrowth after laser in situ keratomileusis (LASIK) using the VISX 20/20B and VISX Star S3 laser systems. METHODS A chart review of patients who had undergone LASIK between April 1999 and December 2001 was performed. Patients having known risk factors for epithelial ingrowth were excluded from the study. Both eyes of patients who were operated with both laser systems were included in a paired analysis. The first operated eyes of the remaining patients were included in an unpaired analysis. The outcomes studied were epithelial ingrowth (a region of epithelial growth under the flap that was contiguous with the flap edge and extended at least 0.7 mm in the radial direction) and epithelial ingrowth requiring treatment (extending into the pupillary zone, causing reduced vision, causing nighttime glare, or inducing any melting of the flap edge). RESULTS In the paired study, 11 (61.1%) of 18 eyes treated with the VISX 20/20B had epithelial ingrowth, and 7 (38.9%) eyes required treatment. None of the eyes treated with the VISX Star S3 had epithelial ingrowth. In the unpaired study, 39 (37.1%) of 105 eyes treated with the VISX 20/20B were noted to have epithelial ingrowth and 14 (13.3%) eyes required treatment. None of the eyes treated with the VISX Star S3 had epithelial ingrowth. The incidence of epithelial ingrowth was significantly different for the VISX 20/20B and the VISX Star S3 in both analyses (paired: P<.001, McNemars test; unpaired: P<.001, Fishers exact test). CONCLUSIONS The laser system used in LASIK is a risk factor for the development of epithelial ingrowth.