Relationship between central corneal thickness and retinal nerve fiber layer thickness in ocular hypertensive patients

Purpose: To examine the relationship between retinal nerve fiber layer (RNFL) measurements obtained using scanning laser polarimetry with variable corneal compensation and corneal thickness measurements in ocular hypertension (OHT) patients. Design: Observational cross-sectional study. Subjects: The study included 1 eye each from 44 OHT patients and 48 healthy subjects, all of similar age. All subjects had normal optic discs and normal standard automated perimetry (SAP) visual fields. Ocular hypertension patients had intraocular pressure (IOP) measurements higher than 22 mmHg. Methods: All patients underwent imaging with the GDx VCC (Laser Diagnostic Technologies, Inc., San Diego, CA) scanning laser polarimeter. We examined the relationship between GDx VCC RNFL measurements and central corneal thickness, a risk factor for development of visual field loss among CHT patients. We also examined the relationship of GDx VCC measurements and age, IOP, SAP pattern standard deviation, and vertical cup-to-disc ratio. Main Outcome Measures: Central corneal thickness (CCT) and GDx VCC RNFL thickness parameters. Results: Central corneal thickness measurements in CHT patients were significantly higher than those in healthy subjects (575+/-30 mum vs. 555+/-32 mum; P = 0.002). Higher GDx VCC parameter nerve fiber indicator (NFI) scores, indicating thinner RNFL, were correlated significantly with thinner CCT measurements in OHT patients (r = -0.502; P = 0.001). Ocular hypertension patients with thinner corneas (n = 22; mean CCT, 553+/-21 Am) had significantly higher NFI scores than CHT patients with thicker corneas (n = 22; mean CCT, 598+/-18 Am) and healthy control subjects (NFI mean +/- standard deviation, 26.9+/-9.5, 20.7+/-9.8, and 19.7+/-7.0, respectively; P = 0.004, analysis of variance). The NFI values were not significantly different between OHT patients with thicker corneas and healthy subjects. In multivariate analysis, only age and CCT measurement were associated significantly with GDx VCC RNFL measurements in OHT eyes. Conclusions: Ocular hypertension patients with thinner corneas had significantly thinner RNFL than OHT patients with thicker corneas and healthy control subjects. These findings support the notion that RNFL defects as assessed by the GDx VCC may represent early glaucomatous damage in OHT eyes. (C) 2005 by the American Academy of Ophthalmology.