Longitudinal study of the normal eyes in unilateral keratoconus patients.

PURPOSE: To determine the rate at which clinically normal eyes in unilateral keratoconus (KC) patients progress to KC and to identify the risk factors that might predict the development of KC in a longitudinal study. DESIGN: Prospective observational study. PARTICIPANTS: We recruited 778 patients with KC and 252 normal controls in Los Angeles, California. One hundred sixteen of 778 patients (14.9%) were diagnosed with clinically unilateral KC at baseline. METHODS: Both eyes of these unilateral KC patients were examined at baseline, and 85 patients were followed up with clinical evaluation and videokeratography for a period ranging from 6 months to 8 years. MAIN OUTCOME MEASURES: Progression to clinical KC from previously normal fellow eyes. Quantitative and qualitative videokeratography variables, contact lens wear, and demographic variables were analyzed as potential predictive factors for this progression. RESULTS: During the follow-up period, 30 of 85 (35.3%) clinically normal fellow eyes had KC develop, and 25 of these 30 (83.3%) had KC develop within the first 6 years after the initial KC diagnosis. By use of the time period from the patients' first diagnosis of unilateral KC to the end of the follow-up period (range, 6 months-41 years), the median time (estimated from the survival analysis) to the development of KC was 16.7 years (95% confidence interval, 11.34, 28.91). Fellow eyes with higher inferior-superior dioptric asymmetry value (I-S) or KC percentage index (logKISA) values had higher risk for KC developing (I-S, risk ratio [RR] = 1.348, P = 0.022; log(KISA), RR = 4.245, P = 0.003). Asymmetric patterns also showed an increased risk for KC developing (P = 0.03), especially the asymmetric bowtie with skewed radial axes (AB/SRAX) pattern. CONCLUSIONS: Approximately 50% of clinically normal fellow eyes will progress to KC within 16 years. The greatest risk is during the first 6 years of the onset. Quantitative indices (I-S and KISA values) and qualitative patterns (AB/SRAX) might predict this progression.

West African crystalline maculopathy.

OBJECTIVE: To describe the findings of a new crystalline maculopathy exclusively affecting elderly members of the Igbo tribe of southeast Nigeria. DESIGN: Retrospective, observational noncomparative case series. METHODS: Six patients referred over a 2-year period to the medical retina consultation service of the King/Drew Medical Center (Los Angeles, Calif) were identified as having a characteristic crystalline maculopathy. Each underwent detailed historical questioning and comprehensive ocular evaluation, including formal retinal examination. Color vision testing, fluorescein angiography, Humphrey visual field analysis, and electrophysiologic assessment were also performed. RESULTS: Each of the 6 patients was an elderly member of the Igbo tribe of southeast Nigeria and demonstrated a unique crystalline maculopathy. A central, superficial cluster of green or yellow, refractile, foveal crystals that were bilateral and asymmetric in distribution was noted in each case. The crystals were benign and unassociated with visual deficit. Retinal sequelae were notably absent and fluorescein angiography results were unremarkable. Additional ancillary testing was generally normal, although 1 patient demonstrated unexplained mild to moderate depression of the scotopic and photopic responses on electrophysiologic analysis. CONCLUSIONS: Elderly members of the Igbo tribe of southeast Nigeria may harbor characteristic bilateral but asymmetric foveal crystals, comprising a novel syndrome of crystalline maculopathy unassociated with obvious visual deficits or retinal sequelae. The etiology of this crystalline maculopathy remains unclear, although genetic, degenerative, and toxic causes are postulated.