[The IC3D classification of the corneal dystrophies]

BACKGROUND

The recent availability of genetic analyses has demonstrated the shortcomings of the current phenotypic method of corneal dystrophy classification. Abnormalities in different genes can cause a single phenotype, whereas different defects in a single gene can cause different phenotypes. Some disorders termed corneal dystrophies do not appear to have a genetic basis.

PURPOSE

The purpose of this study was to develop a new classification system for corneal dystrophies, integrating up-to-date information on phenotypic description, pathologic examination, and genetic analysis.

METHODS

The International Committee for Classification of Corneal Dystrophies (IC3D) was created to devise a current and accurate nomenclature.

RESULTS

This anatomic classification continues to organize dystrophies according to the level chiefly affected. Each dystrophy has a template summarizing genetic, clinical, and pathologic information. A category number from 1 through 4 is assigned, reflecting the level of evidence supporting the existence of a given dystrophy. The most defined dystrophies belong to category 1 (a well-defined corneal dystrophy in which a gene has been mapped and identified and specific mutations are known) and the least defined belong to category 4 (a suspected dystrophy where the clinical and genetic evidence is not yet convincing). The nomenclature may be updated over time as new information regarding the dystrophies becomes available.

CONCLUSIONS

The IC3D Classification of Corneal Dystrophies is a new classification system that incorporates many aspects of the traditional definitions of corneal dystrophies with new genetic, clinical, and pathologic information. Standardized templates provide key information that includes a level of evidence for there being a corneal dystrophy. The system is user-friendly and upgradeable and can be retrieved on the website www.corneasociety.org/ic3d .

UBIAD1 mutation alters a mitochondrial prenyltransferase to cause Schnyder corneal dystrophy

BACKGROUND

Mutations in a novel gene, UBIAD1, were recently found to cause the autosomal dominant eye disease Schnyder corneal dystrophy (SCD). SCD is characterized by an abnormal deposition of cholesterol and phospholipids in the cornea resulting in progressive corneal opacification and visual loss. We characterized lesions in the UBIAD1 gene in new SCD families and examined protein homology, localization, and structure.

METHODOLOGY/PRINCIPAL FINDINGS

We characterized five novel mutations in the UBIAD1 gene in ten SCD families, including a first SCD family of Native American ethnicity. Examination of protein homology revealed that SCD altered amino acids which were highly conserved across species. Cell lines were established from patients including keratocytes obtained after corneal transplant surgery and lymphoblastoid cell lines from Epstein-Barr virus immortalized peripheral blood mononuclear cells. These were used to determine the subcellular localization of mutant and wild type protein, and to examine cholesterol metabolite ratios. Immunohistochemistry using antibodies specific for UBIAD1 protein in keratocytes revealed that both wild type and N102S protein were localized sub-cellularly to mitochondria. Analysis of cholesterol metabolites in patient cell line extracts showed no significant alteration in the presence of mutant protein indicating a potentially novel function of the UBIAD1 protein in cholesterol biochemistry. Molecular modeling was used to develop a model of human UBIAD1 protein in a membrane and revealed potentially critical roles for amino acids mutated in SCD. Potential primary and secondary substrate binding sites were identified and docking simulations indicated likely substrates including prenyl and phenolic molecules.

CONCLUSIONS/SIGNIFICANCE

Accumulating evidence from the SCD familial mutation spectrum, protein homology across species, and molecular modeling suggest that protein function is likely down-regulated by SCD mutations. Mitochondrial UBIAD1 protein appears to have a highly conserved function that, at least in humans, is involved in cholesterol metabolism in a novel manner.

The IC3D classification of the corneal dystrophies

BACKGROUND

The recent availability of genetic analyses has demonstrated the shortcomings of the current phenotypic method of corneal dystrophy classification. Abnormalities in different genes can cause a single phenotype, whereas different defects in a single gene can cause different phenotypes. Some disorders termed corneal dystrophies do not appear to have a genetic basis.

PURPOSE

The purpose of this study was to develop a new classification system for corneal dystrophies, integrating up-to-date information on phenotypic description, pathologic examination, and genetic analysis.

METHODS

The International Committee for Classification of Corneal Dystrophies (IC3D) was created to devise a current and accurate nomenclature.

RESULTS

This anatomic classification continues to organize dystrophies according to the level chiefly affected. Each dystrophy has a template summarizing genetic, clinical, and pathologic information. A category number from 1 through 4 is assigned, reflecting the level of evidence supporting the existence of a given dystrophy. The most defined dystrophies belong to category 1 (a well-defined corneal dystrophy in which a gene has been mapped and identified and specific mutations are known) and the least defined belong to category 4 (a suspected dystrophy where the clinical and genetic evidence is not yet convincing). The nomenclature may be updated over time as new information regarding the dystrophies becomes available.

CONCLUSIONS

The IC3D Classification of Corneal Dystrophies is a new classification system that incorporates many aspects of the traditional definitions of corneal dystrophies with new genetic, clinical, and pathologic information. Standardized templates provide key information that includes a level of evidence for there being a corneal dystrophy. The system is user-friendly and upgradeable and can be retrieved on the website www.corneasociety.org/ic3d.

Genetic analysis of 14 families with Schnyder crystalline corneal dystrophy reveals clues to UBIAD1 protein function

Schnyder crystalline corneal dystrophy (SCCD) is a rare autosomal dominant disease characterized by progressive corneal opacification resulting from abnormal deposition of cholesterol and phospholipids. Recently, six different mutations on the UBIAD1 gene on chromosome 1p36 were found to result in SCCD. The purpose of this article is to further characterize the mutation spectrum of SCCD and identify structural and functional consequences for UBIAD1 protein activity. DNA sequencing was performed on samples from 36 individuals from 14 SCCD families. One affected individual was African American and SCCD has not been previously reported in this ethnic group. We identified UBIAD1 mutations in all 14 families which had 30 affected and 6 unaffected individuals. Eight different UBIAD1 mutations, 5 novel (L121F, D118G, and S171P in exon 1, G186R and D236E in exon 2) were identified. In four families with DNA samples from both affected and unaffected individuals, the D118G, G186R, T175I, and G177R mutations cosegregated with SCCD. In combination with our previous report, we have identified the genetic mutation in UBIAD1 in 20 unrelated families with 10 (including 5 reported here), having the N102S mutation. The results suggest that N102S may be a mutation hot spot because the affected families were unrelated including Caucasian and Asian individuals. There was no genotype phenotype correlation except for the T175I mutation which demonstrated prominent diffuse corneal haze, typically without corneal crystals. Protein analysis revealed structural and functional implications of SCCD mutations which may affect UBIAD1 function, ligand binding and interaction with binding partners, like apo E.

Comparison of Pentacam and Orbscan IIz on Posterior Curvature Topography Measurements in Keratoconus Eyes

PURPOSE

To compare the measurements of posterior elevation above the best-fit sphere and of pachymetry in established keratoconus patients using 2 different technologies--Scheimpflug imaging with the Pentacam and scanning slit combined with Placido imaging with Orbscan IIz.

DESIGN

Retrospective comparative case series.

PARTICIPANTS

Patients with confirmed keratoconus by biomicroscopy and Placido topography who had corneal topography scans by the Pentacam and Orbscan IIz on their visit from April 2004 to April 2005. These scans were obtained routinely for patient diagnosis, treatment, and progression.

METHODS

The mean difference, standard deviation (SD), and 95% limits of agreement (LOA) were calculated, and Bland-Altman plots were constructed for best-fit sphere radius of curvature, posterior elevation above the best-fit sphere, and pachymetry of the thinnest point.

RESULTS

Thirty-six eyes of 29 patients were analyzed. The average radius for posterior best-fit sphere was 5.97 microm (range, 4.69-6.79) for the Pentacam and 6.00 microm (range, 4.97-6.55) for Orbscan IIz. The mean difference (Pentacam - Orbscan IIz) for the radius generated for the best-fit sphere was -0.03+/-0.22 SD with a 95% confidence interval (CI) of -0.11 to 0.04 and a 95% LOA of -0.46 to 0.40 (P = 0.362). The mean posterior elevation by best-fit sphere fixed to the apex was 34.86 microm (range, 3-120) for the Pentacam and 48.50 microm (range, 11-118) for Orbscan IIz. The mean difference was -13.64+/-26.08 SD (95% CI, -22.46 to -4.81; 95% LOA, -64.75 to 37.48; P = 0.003). The average thinnest point for the Pentacam was 443.6 microm (range, 164-587), and that for Orbscan IIz was 445.9 microm (range, 204-597). The mean difference in the thinnest point for the Pentacam and Orbscan IIz was -2.28+/-35.55 (95% CI, -14.31 to 9.75; 95% LOA, -71.95 to 67.39; P = 0.703).

CONCLUSION

Both the Pentacam and Orbscan IIz determine similar thinnest points but have a measurable difference in posterior elevations above the best-fit sphere, despite similar radii of curvature. This difference may be important in the screening of patients for refractive surgery to avoid surgery on patients with early keratoconus. This study cannot determine if the Pentacam is underestimating the posterior vault or if Orbscan is overestimating this height, and further studies with a standardized test object are needed.

Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel

PURPOSE

To evaluate the safety, efficacy, and quality of vision after photorefractive keratectomy (PRK) in active-duty military personnel.

METHODS

Photorefractive keratectomy (6.0-mm ablation zone) was performed on 30 navy/marine personnel(-2.00 to -5.50 diopters [D]; mean, -3.35 D). Glare disability was assessed with a patient questionnaire and measurements of intraocular light scatter and near contrast acuity with glare.

RESULTS

At 1 year, all 30 patients had 20/20 or better uncorrected visual acuity with no loss of best-corrected vision. By cycloplegic refraction, 53% (16/30) of patients were within +/- 0.50 D of emmetropia and 87% (26/30) were within +/- 1.00 D. The refraction (mean +/- standard deviation) was +0.45 +/- 0.56 D (range, -1.00 to 1.63 D). Four patients (13%) had an overcorrection of more than 1 D. Glare testing in the early (1 month) postoperative period demonstrated increased intraocular light scatter (P<0.01) and reduced contrast acuity (with and without glare, (P<0.01). These glare measurements statistically returned to preoperative levels by 3 months (undilated) and 12 months (dilated) postoperatively. Two patients reported moderate to severe visual symptoms (glare, halo, night vision) worsened by PRK. One patient had a decrease in the quality of night vision severe enough to decline treatment in the fellow eye. Intraocular light scatter was increased significantly (>2S D) in this patient after the procedure.

CONCLUSIONS

Photorefractive keratectomy reduced myopia and improved the uncorrected vision acuity of all patients in this study. Refinement of the ablation algorithm is needed to decrease the incidence of hyperopia. Glare disability appears to be a transient event after PRK. However, a prolonged reduction in the quality of vision at night was observed in one patient and requires further study.

Observations on the natural history of herpes zoster ophthalmicus

We have studied certain aspects of the natural history of acute herpes zoster ophthalmicus in placebo-treated patients followed prospectively over one year as part of a therapeutic drug trial. Observations on the incidence of ocular complications relating to the efficacy of oral acyclovir in this disease have been previously published. This report provides supplemental observations on the natural history of frequently observed ocular complications of zoster ophthalmicus: corneal hypesthesia, episcleritis, dendritiform keratopathy, stromal keratitis, anterior uveitis, and post herpetic neuralgia. These ocular complications of zoster typically present within the first two weeks of the diagnosis. This report characterizes the onset of corneal hypesthesia, episcleritis, dendritiform keratopathy, stromal keratitis, and anterior uveitis as well as interrelationships amongst these sequellae of herpes zoster ophthalmicus. Post-herpetic neuralgia occurs in 52% of patients and persists beyond a year in 22% of those affected.

Oral acyclovir in the therapy of acute herpes zoster ophthalmicus. An interim report

A prospective, randomized, double-masked, placebo-controlled clinical trial was conducted to study the effects of oral acyclovir on 55 patients with acute herpes zoster ophthalmicus. Treatment with oral acyclovir resulted in more prompt resolution of signs and symptoms, particularly in patients treated within 72 hours after onset of skin rash (P less than 0.05), and shortened the duration of viral shedding (P = 0.02). Vesicular skin lesions involving other dermatomes (microdissemination) occurred in five (19%) placebo-treated patients but in no acyclovir-treated patients (P = 0.03). Interim analysis of this longitudinal study suggests that the incidence and severity of secondary ocular inflammatory disease was reduced by acyclovir. Prolonged observation of these patients is ongoing to determine if oral acyclovir reduces post-herpes zoster neuralgia or the late ocular complications of ophthalmic zoster.