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J.-C. Mwanza, A. M. Bhorade, D. L. Budenz, J. J. McSoley, N. S. Sekhon, W. J. Feuer; Effect of Cataract and Its Removal on Signal Strength and Peripapillary Retinal Nerve Fiber Layer Optical Coherence Tomography Scans. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3332.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the effect of cataract before and following its removal on optical coherence tomography (OCT) signal strength and peripapillary retinal nerve fiber layer (RNFL) thickness.
Peripapillary RNFL thickness measurements were obtained by Stratus OCT scans using the Fast RNFL Thickness (3.4) acquisition protocol in 47 cataractous eyes of 47 patients of which 23 had open-angle glaucoma in addition. Lens opacities were graded according to the Lens Opacities Classification System III (LOCS III). The scans were taken 0 to 155 days (27.6 ± 33.3 days) prior to and 27 to 127 days (46.3 ± 24.1 days) following uneventful cataract extraction by phacoemulsification with intraocular lens (IOL) placement. Mean pre- and post-operative signal strengths and peripapillary RNFL thicknesses were compared.
The mean pre- and post-operative RNFL thickness values were 83.0 ± 22.9 µm and 91.9 ± 23.9 µm, respectively. The increase of 10.7% (9.0 ± 18.0 µm) was statistically significant; p = 0.001. In parallel, the post-operative signal strength (7.17 ± 1.37) significantly increased by 22.9% relative to the pre-operative value (5.83 ± 2.03); p < 0.001. There was a correlation between the magnitude of the RNFL thickness change and the pre-operative RNFL thickness (r = 0.34, p = 0.021), pre-operative signal strength (r = 0.52, p < 0.001) and post-operative change in signal strength (r = 0.53, p < 0.001). When considering only eyes with pre-operative signal strength ≥ 6, no significant change was observed between pre- and post-operative RNFL thickness (89.0 ± 17.7 µm vs 91.5 ± 18.7 µm); p = 0.1. There was no significant difference in RNFL thickness change between the group of eyes with cataract only (10.9 ± 20.8 µm) and that of eyes with cataract and glaucoma (7.0 ± 14.7 µm); p = 0.46. None of the cataract types was individually associated with pre-operative signal strength or change in RNFL thickness. In contrast, maximum LOCS scores correlated with degradation of pre-operative signal strength (r = 0.51, p < 0.001).
All types of cataracts may decrease RNFL thickness measurements on OCT scans. These measurements should therefore be interpreted with caution in eyes with significant cataract particularly if signal strength is attenuated. Thinning of the RNFL suggestive of glaucomatous progression may be the result of an artifact from advancing cataract rather than actual anatomic changes in the RNFL. Cataract removal with IOL implantation improves the signal strength and thereby results in a thicker OCT measurement of RNFL.
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