Effect of cataract and its removal on signal strength and peripapillary retinal nerve fiber layer optical coherence tomography measurements.

PURPOSE: To assess the effect of cataract on optical coherence tomography (OCT), signal strength (SS), and peripapillary retinal nerve fiber layer (RNFL) thickness measurements. METHODS: Peripapillary RNFL thickness measurements were obtained by Stratus OCT scans using the Fast RNFL thickness (3.4) acquisition protocol before and after cataract extraction in 45 patients with cataract, including 23 glaucoma patients. Cataracts were graded according to the Lens Opacities Classification System III. RESULTS: The postoperative RNFL thickness and SS were 9.3% (P=0.001) and 24.1% (P<0.001) higher than before surgery, respectively. There was greater postoperative change in RNFL thickness measurements in patients with lower preoperative RNFL measurements (r=-0.63, P<0.001) and SS (r=-0.59, P<0.001). Eyes with preoperative SS more than 6 had no significant difference between precataract and postcataract surgery RNFL thickness (P=0.14). There was no significant difference in RNFL thickness change between eyes with cataract only (10.9±20.8 µm) and those with cataract and glaucoma (7.0±14.7 µm; P=0.81). CONCLUSIONS: Cataracts may decrease peripapillary RNFL thickness measurements and the SS on OCT scans. Thinning of the peripapillary RNFL suggestive of glaucomatous progression may be the result of artifact from advancing cataract rather than actual structural changes in the peripapillary RNFL. Peripapillary RNFL thickness measurements should be interpreted with caution in glaucomatous eyes with significant cataract, particularly if the SS is attenuated.

Myopia affects retinal nerve fiber layer measurements as determined by optical coherence tomography.

PURPOSE: To determine whether increasing myopia is associated with thinner peripapillary retinal nerve fiber layer (RNFL) when measured by Stratus optical coherence tomography (OCT). DESIGN: Observational cross-sectional study. METHODS: Normal subjects with myopia underwent refractometry, axial length measurement (IOL Master), optic nerve examination, and OCT (12 fast RNFL scans/eye). The more myopic eye was chosen as the study eye. Correlation coefficients were calculated for demographic and optic disk characteristics, and degree of myopia. RESULTS: Mean age (n=27) was 34+/-8 years (range: 23 to 54). Mean cup-to-disk ratio was 0.38 with 41% large and 59% medium disk size. Eight subjects had peripapillary atrophy and 6 had disk tilt. Mean spherical equivalent was -5.40 D (range: -1.25 to -11.25), with mean axial length of 25.65 mm (range: 22.63 to 27.92). No significant associations were found between RNFL thickness and age (P=0.20), sex, disk size, cup-to-disk ratio, tilt, or peripapillary atrophy. RNFL thickness decreased with higher axial length (overall R=-0.70, P<0.001, superior R=-0.60, P=0.001, and inferior R=-0.60, P=0.001), and higher spherical equivalent (overall R=-0.52, P=0.005, superior R=-0.41, P=0.03, and inferior R=-0.45, P=0.02). Overall RNFL thickness decreased 7 mum/1 mm of axial length, and 3 mum/1 D sphere. CONCLUSIONS: Moderately myopic subjects tend to have thin peripapillary RNFL, mainly at the superior and inferior poles, as measured by Stratus OCT. This phenomenon should be considered when interpreting a glaucoma suspect's Stratus OCT measurements compared with the normative database.

Effect of lowering intraocular pressure on optical coherence tomography measurement of peripapillary retinal nerve fiber layer thickness.

PURPOSE: To assess, with optical coherence tomography (OCT), any changes in peripapillary retinal nerve fiber layer (RNFL) thickness in glaucoma patients after reduction of intraocular pressure (IOP). DESIGN: Prospective observational case series. PARTICIPANTS: Twenty-one eyes of 21 glaucoma patients who underwent medical or surgical intervention to lower IOP. METHODS: Patients with elevated IOP underwent fast peripapillary RNFL measurements with the Stratus OCT (model 3000, software version 4.04; Carl Zeiss Meditec, Dublin, CA) before and after the IOP was lowered by medical or surgical therapy. MAIN OUTCOME MEASURES: Changes in overall and quadrant RNFL thickness with respect to change in IOP. RESULTS: The OCT scans were performed before intervention (range, 0-38 days before; mean+/-standard deviation [SD], 9.8+/-9.3 days) and after intervention (range, 32-74 days; mean+/-SD, 46.8+/-11.2 days) to measure peripapillary RNFL thickness. Mean IOP (mean+/-SD) decreased from 31.5+/-8.2 mmHg to 12.8+/-4.6 mmHg with the intervention (P<0.001). Twenty of 21 eyes had an IOP reduction of more than 30%. There was no significant change in the overall RNFL thickness associated with the lowering of IOP (mean+/-SD, 1.02+/-10.3 microm; P = 0.653). Quadrant analysis did not show a significant change in the RNFL thickness of any of the 4 quadrants (superior, -1.71+/-14.5 microm, P = 0.593; inferior, 2.38+/-16.8 microm, P = 0.523; temporal, 2.19+/-9.50 microm, P = 0.303; and nasal, 1.24+/-12.5 microm, P = 0.655). No relationship was found between any of the changes in OCT parameters or percent change in OCT parameters and the extent of IOP reduction, or whether IOP was lowered medically or surgically, with or without adjusting for preintervention OCT measurements as an indication of disease severity (P values ranged from 0.331 to 0.985). CONCLUSIONS: No significant change in the RNFL thickness was associated with the lowering of IOP by medical or surgical therapy, as measured by OCT.