Experimental globe rupture after excimer laser photorefractive keratectomy.

OBJECTIVE: To assess corneal weakening after photorefractive keratectomy. METHODS: Photorefractive keratectomy was performed in 16 human eye-bank eyes by means of a 193-nm excimer laser (range, 6 to 54 diopters [D]). Porcine eyes underwent either photorefractive keratectomy procedures (range, 30 to 93 D) with a 5-mm beam diameter or deep 5-mm plano disc ablations. Intraocular pressure was increased gradually with the use of nitrogen gas until the globe ruptured. RESULTS: Human eyes with less than 42 D of correction ruptured at the limbus or behind the insertions of the extraocular muscles. Two eyes showed initial leakage at the 42-D ablation site. Ablations greater than 46 D entered the anterior chamber during treatment. One porcine eye ruptured at the ablation site after a 42-D treatment. Other eyes ruptured at the equator with treatments up to 78 D. CONCLUSION: Excimer laser photorefractive keratectomy does not weaken the cornea after degrees of ablation commonly used in the clinical setting.

Glaucomatocyclitic crisis in a child.

PURPOSE: To report a case of glaucomatocyclitic crisis (Posner-Schlossman syndrome) in a child. METHOD: Case report. A 13-year-old boy presented with decreased vision, photophobia, halos, and pain in the right eye. RESULT: Findings in this child were consistent with a diagnosis of Posner-Schlossman syndrome. CONCLUSION: Glaucomatocyclitic crisis can occur in a child and must be included in the differential diagnosis of uveitis and glaucoma in pediatric patients.

Comparison of frequency doubling perimetry with humphrey visual field analysis in a glaucoma practice.

PURPOSE: To determine the sensitivity and specificity of frequency doubling perimetry with Humphrey visual field testing used as the gold standard. METHODS: Frequency doubling perimetry and Humphrey visual field testing (24-2) were performed on 29 consecutive patients in a glaucoma practice. Data for the right eye were used to calculate sensitivity, specificity, and receiver operating characteristic curves. RESULTS: For the frequency doubling perimetry in screening mode, and with an abnormal glaucoma hemifield test used as the gold standard, the area under the receiver operating characteristic curve was 89.3%, 81.5%, or 75.0% for the presence of mild, moderate, or severe relative defects, respectively. Similar results were found with the use of mean deviation (P <.05) to define Humphrey visual field defects. For frequency doubling perimetry in threshold mode, the area under the receiver operating characteristic curve was 93.4% with the presence of any defect (P <.05) used as the criterion for an abnormal case, and an abnormal glaucoma hemifield test as the gold standard. In all cases, the threshold mode detected defects better than the screening mode.

Photorefractive keratectomy following radial keratotomy.

BACKGROUND: Excimer laser photorefractive keratectomy (PRK) has been used to correct residual myopia in eyes that have had refractive keratotomy. METHODS: Nine eyes of eight patients were studied at a mean of 13 months after PRK. Previous procedures included radial keratotomy (9 eyes) and myopic keratomileusis (1 eye). PRK was performed using a Summit Technology excimer laser with a 5.0-mm diameter ablation zone. RESULTS: Uncorrected visual acuity improved in 7 of 9 eyes. The refractive outcome was within 1.00 diopter (D) of attempted correction for 3 of 9 eyes. Spectacle-corrected visual acuity decreased 2 or more Snellen lines in 2 of 9 eyes. Subepithelial corneal stromal haze was seen 1 month postoperatively in 6 of 8 eyes and was present in 4 of 6 eyes at 1 year. Stromal haze was associated with regression of the refractive effect of the PRK. CONCLUSIONS: PRK in eyes with previous radial keratotomy appears to be less predictable and may be associated with greater corneal haze and regression of refractive correction than in previously unoperated eyes. Activation of stromal fibroblasts in the previous corneal incisions may cause these findings.

Effect of oxidation of methionine residues in chicken ovoinhibitor on its inhibitory activities against trypsin, chymotrypsin, and elastase.

Oxidation of methionine residues of chicken ovoinhibitor with N-chlorosuccinimide resulted in a selective loss of its inhibitory activities. While trypsin inhibiting activity was not affected at all, half of the chymotrypsin-inhibiting activity and all of the elastase inhibiting activity were lost. Electrophoretic and affinity chromatography studies indicated that the 50% loss of the chymotrypsin-inhibiting activity resulted from the inactivation of one of its two chymotrypsin-inhibiting sites rather than from a decrease in the binding constants of both sites. Oxidation of ovoinhibitor-chymotrypsin and ovoinhibitor-elastase complexes with excess of N-chlorosuccinimide indicated that the complex formation in each case protected the site that binds the enzyme which participated in the complex, but did not protect the site that binds the other enzyme. Quantitative estimation of the number of oxidized methionine residues in the ovoinhibitor isolated from the complexes has shown that in each complex about one methionine residue was protected from oxidation. Nitrophenyl-sulfenylation of the single tryptophan residue of ovoinhibitor did not affect its inhibitory activities at all.

Selectivity of site of action and systemic effects of topical alpha agonists.

Clonidine hydrochloride, apraclonidine hydrochloride, and brimonidine tartrate constitute the three topical alpha agonists that are used in the treatment of elevated intraocular pressure. All the alpha agonists have prejunctional (alpha 2) as well as postjunctional (alpha 1) effects. Within the past year, questions have arisen about their local and systemic effects, and their effects upon the optic nerve. We will, therefore, attempt to clarify these points, to provide a greater understanding of the role of alpha agonists in glaucoma therapy.

Excimer laser phototherapeutic keratectomy. Surgical strategies and clinical outcomes.

PURPOSE: To assess the different strategies and analyze clinical outcomes of excimer laser phototherapeutic keratectomy (PTK) for a variety of superficial corneal disorders. METHODS: Twenty-eight eyes of 26 patients with one of five general categories of corneal disorders were treated with a variety of PTK techniques. Patients were assessed for preoperative and postoperative corneal thickness, uncorrected and best spectacle-corrected visual acuity, refractive changes, corneal topography and astigmatism, and results of a subjective patient questionnaire. Follow-up ranged from 6 to 30 months. RESULTS: The average number of laser pulses was 418, with a mean decrease in corneal thickness of 31 microns. Uncorrected visual acuity improved in 20 eyes and decreased in 5. Best spectacle-corrected visual acuity improved in 20 eyes and decreased in 5; two patients had two Snellen lines of best-corrected vision loss. Nineteen patients (21 eyes) noted symptomatic improvement. Corneal topography improved in 17 eyes and worsened in 1. The average refractive shift was +1.4 diopters; patients undergoing general PTK, PTK combined with mechanical superficial keratectomy, and superficial scar removal had greater degrees of hyperopic shift. Complications were rare. Two patients who did not appreciate adequate improvement in vision after PTK underwent subsequent penetrating keratoplasty. CONCLUSIONS: A number of PTK techniques are available to treat particular corneal disorders. Planning of surgical strategy is guided by careful patient selection which will minimize optical side effects and optimize visual outcome and subjective symptomatology after the PTK procedure.