Calculation of Retinal Layer Thickness Considers Refractive Errors in OCT Measurements

Using a new formula, clinicians can account for refractive errors on measurements of peripapillary retinal nerve fiber layer (pRNFL), according to a study published in Optometry and Vision Science.

Investigators conducted a study to develop a method of interpreting average pRNFL values in eyes with refractive errors to help clinicians avoid false positive or negative diagnoses for patients with glaucoma. The researchers included 183 eyes of 183 healthy individuals and divided participants into the following age groups: 41 to 50 (n=46), 51 to 60 (n=46), 61 to 70 (n=57), and 71 to 85 (n=34). All participants were White. Axial length of the eyes ranged from 22.5 to 24.5 mm. Spherical equivalent of refraction ranged from -1.63 to 2.0 D. Glaucoma suspects and patients with serious ophthalmic diseases that could impact pRNFL thickness were excluded from the study.

Researchers performed OCT without pupillary dilation and only accepted scans with a signal strength of at least 6. They measured axial length and subtracted 0.14 mm to correct for optical biometry. They also performed a refraction and keratometry. 

The investigators found that average corneal power was associated with age, with a 1 D (P =.02) difference between younger and older groups. Mean average pRNFL thickness was inversely associated with age, with approximate decreases of 2.5 to 3.0 μm per decade (P <.001, analysis of variance). Mean standard deviation was 95.1±7.6, 92.4±7.9, 90.0±7.1, and 87.3±5.6 in the 41-50, 51-60, 61-70, and 71-85 age groups, respectively. 

“The results of this study make it possible to evaluate the average pRNFL data in eyes with refractive errors quickly and easily, without any calculations,” according to the researchers. “This is especially valuable in patients with refractive errors of high degree.”

Limitations of the study include the inability of researchers to measure pRNFL in quadrants and clock hours.

Reference

Shpak AA, Korobkova MV. Evaluation of average retinal nerve fiber layer measurement in eyes with refractive errors. Optom Vis Sci. 2021;98(12):1366-1370 doi:10.1097/OPX.0000000000001818