Hyaluronic acid in the rabbit cornea after excimer laser superficial keratectomy.

Hyaluronic acid (HA) is not normally found in the corneal stroma. Rabbit corneas were examined for the presence of stromal HA after excimer laser treatment. One eye in each of 28 rabbits received a 60 microns deep superficial keratectomy with the excimer laser. After 1, 8, 21, and 60 days, the corneas were analyzed by quantitative and histochemical methods specific for HA. A statistically significant increase in the HA concentration compared to the baseline amount in the untreated fellow eye was seen at 8, 21, and 60 days. HA was visualized histochemically in the anterior stroma of the excimer-treated eyes at all times tested. The presence of HA after excimer surgery may influence the hydration, thickness, and transparency of the cornea. The reactive production of HA in the stroma may represent a nonspecific corneal tissue response to injury.

Endogenous hyaluronan in corneal disease.

PURPOSE: Hyaluronan (HA) is a disaccharide polymer capable of binding considerable amounts of water. It is present in trace amounts on the cornea endothelium, and it is not normally found in the epithelium or stroma. A specific histochemical stain was used to test for HA in a wide variety of corneal disorders. METHODS. Eighty-six human corneal tissue specimens were examined histochemically for HA. The material consisted of 84 full-thickness corneal buttons, one epithelium scraping, and one pterygium. Cases were analyzed according to the patient's sex, age, diagnosis, and localization of HA staining. RESULTS: The corneal tissue specimens came from 47 women and 39 men, average age 59 years. Fifty-seven percent of the specimens displayed abnormal HA. HA was visualized in Fuch's dystrophy, keratoconus, infections, regrafts, mechanical and chemical trauma, post-excimer ablations, dystrophies, degenerations, pseudophakic bullous keratopathy, congenital opacities, Stevens-Johnson syndrome, and others. Staining was variously seen in the epithelium, stroma, and endothelium, with intensity of staining ranging from trace amounts to extremely heavy. CONCLUSIONS: Endogenous hyaluronan production is seen in virtually the entire spectrum of corneal disorders. The presence of HA was most often associated with dividing, migrating, or fibroblast-like cells and probably represents a nonspecific tissue response to wounding. Its production is biochemically distinct from that of normally present proteoglycans. The abnormal presence of HA may reduce corneal transparency by disrupting the normal spacing between collagen fibrils, creating focal changes in the index of refraction, and altering the normal flow of solutes through the cornea.

Steroid treatment of myopic regression: acute refractive and topographic changes in excimer photorefractive keratectomy patients.

We documented acute changes in corneal topography and refraction after readministration of topical steroids in five patients with myopic regression after photorefractive keratectomy (PRK). One was a high myope (-10.00 sphere); the others were moderate myopes (preoperative spherical equivalents -4.25 to -6). All patients had been off steroids for 3 to 8 months before reinstitution. The changes in refractive spherical equivalents ranged from +0.75 to +3.00 diopters, and were observed from 6 days to 4 weeks later. Refractive hyperopic shifts were accompanied by pronounced corneal flattening as measured by computer-assisted corneal topographic analysis. Two to seven months later, three patients have become even less myopic, and two patients have again become slightly more myopic. Topical steroid use can modulate refractive changes after excimer laser treatments in some patients.

Superficial keratectomy with the 193 nm excimer laser: a reproducible model of corneal surface irregularities.

Rough corneal surfaces may be smoothed by performing a superficial keratectomy with the 193 nm excimer laser. In order to smooth an irregular surface, a substance must be used during ablation to protect low corneal areas so that high spots are ablated preferentially. A simple, accurate, and reproducible method for modelling various corneal surface irregularities was developed. The technique uses the excimer laser to imprint the patterns of various metallic grids onto the stromal surface. The model was used to facilitate a comparison of three potential smoothing agents: 0.5% tetracaine, 2% hydroxypropylmethylcellulose, and a fluorescein-containing hyaluronate preparation. Preliminary results indicate that tetracaine may be the most efficacious smoothing agent.

Hyaluronan in the exfoliation syndrome.

PURPOSE: To histochemically analyze if the glycoseaminoglycan component of pseudoexfoliation material consists of hyaluronan. METHODS: The hyaluronan binding region of cartilage proteoglycans was utilized in a staining specific for hyaluronan. The technique has been described and employed previously. Human donor eyes with and without the presence of visible pseudoexfoliations were analyzed. RESULTS: Hyaluronan was found to coat the fibrillar exfoliation material on the lens, the zonules, the iris epithelium and the ciliary body. It was also found on a capsular bag following cataract surgery. CONCLUSION: In the anterior chamber hyaluronan constitutes one part of the exfoliation material. Abnormal findings of hyaluronan could be found in the cornea.

Risk for rabies transmission from encounters with bats, Colorado, 1977-1996.

To assess the risk for rabies transmission to humans by bats, we analyzed the prevalence of rabies in bats that encountered humans from 1977 to 1996 and characterized the bat-human encounters. Rabies was diagnosed in 685 (15%) of 4,470 bats tested. The prevalence of rabies in bats that bit humans was 2.1 times higher than in bats that did not bite humans. At least a third of the encounters were preventable.

Costs and benefits of a subtype-specific surveillance system for identifying Escherichia coli O157:H7 outbreaks.

We assessed the societal costs and benefits of a subtype-specific surveillance system for identifying outbreak-associated Escherichia coli O157:H7 infections. Using data from Colorado, we estimated that if it averted five cases annually, the system would recover all its costs.

Phototherapeutic keratectomy: long-term results in 166 eyes.

One hundred sixty-six eyes with corneal disease were treated with the excimer laser in order to ablate opacities, irregularities, or to improve wound healing. Postoperative follow up time was 15 months (range 6 to 28 months). An individual goal was set for each patient and 84% achieved the goal. The visual acuity change is given for each subgroup. Phototherapeutic keratectomy (PTK) was shown to be an advantageous surgical method, where the success is in the careful preoperative evaluation. One problem with the technique is the induced hyperopia.

Excimer laser photorefractive keratectomy for myopia. Clinical results in sighted eyes.

PURPOSE: To evaluate the refractive results of excimer laser photorefractive keratectomy (PRK) performed on normal, sighted myopic eyes; to assess the role of postoperative topical steroid treatment in patients with PRK; and to study the regression of effect. METHODS: An argon fluoride 193-nm excimer laser was used. Photorefractive keratectomy was performed on 420 eyes with preoperative refraction ranging from -1.25 to -7.50 diopters (D). Minimum follow-up time was 12 months, and 194 of the eyes were followed for 15 months. Postoperative treatment generally consisted of topical dexamethasone for 3 months, but in a sub-study, some eyes were treated for only 5 weeks. RESULTS: Mean refraction (spherical equivalent +/- standard deviation) at 12 months was -0.04 +/- 0.84 D and at 15 months -0.22 +/- 0.78 D. At 12 months postoperatively, 86% of the eyes were within 1.00 D of emmetropia, at 15 months 87%. At 12 months, 91% of the eyes had an uncorrected visual acuity of at least 20/40, at 15 months 87%. Eyes treated with dexamethasone for 3 months regressed significantly less than those treated for only 5 weeks (P < 0.01). Dexamethasone also was effective in reversing regression later in the postoperative course. Eyes with preoperative myopia up to 4.90 D had significantly better refractive results at 12 months than eyes with myopia ranging from 5.00 to 7.50 D (P < 0.01). CONCLUSION: These data show that excimer laser PRK can correct myopia with good predictability. Results at 12 and 15 months tend to suggest stability of postoperative refraction. Regression of effect was more common in higher myopes. Topical steroids postoperatively seem to play a crucial role for the refractive result.