OCT Study Shows Some Structures Less Affected By Refractive Errors

A pair of new optic disc peripapillary spectral domain optical coherence tomography (SD-OCT) scan patterns appear to facilitate measurement of retinal nerve fiber layer (RNFL) thickness in young patients with myopia, according to a report in Photodiagnosis and Photodynamic Therapy.

Using conventional measurement techniques, children with myopia may present with RNFL thinning. However, it can be challenging to know whether thinning is due to structural changes, such as ganglion cell loss, or simply imprecise measuring technology, according to the investigators. So far, most research on RNFL thinning in myopia has been with adults. This current research gathers data on patients younger than 18 years of age, toward the goal of creating a normative database using new SD-OCT parameters; retinal nerve fiber layer acquired using an anatomic positioning system (APS-RNFL) and Bruch’s membrane opening-minimum rim width (BMO-MRW).

Investigators examined 378 healthy patients (378 left eyes) with myopia. The prospective, cross-sectional analysis gathered data from complete ophthalmic evaluations which included cycloplegic refraction, Goldmann applanation tonometry, confocal scanning laser ophthalmoscopy, and other tests. Peripapillary RNFL was assessed with standard SD-OCT imaging and with novel Spectralis® (Heidelberg Engineering Inc.) Glaucoma Module Premium Edition scans, including APS alignment for the axis, or angle, of the fovea to Bruch’s membrane opening center. Three groups were assigned, based on refractive error (RE):

• Group 1, n=141, control group, spherical equivalent (SE) -1.00 D to +1.00 D
• Group 2, n=189, SE -4.00 D to -1.00 D
• Group 3, n=48, SE greater than -4.00 D

The primary findings include a “relatively high” mean difference between groups when RNFL thickness is measured with the standard method, as compared with scans by BMO-MRW or APS-RNFL. In global averages, few differences were found among the groups with BMO-MRW (P =.089), and APS-RNFL (P =.563), compared with standard RNFL (P <.001) — demonstrating new methods are impacted less by level of myopia. 

In multiple regression analysis, the 3 techniques showed small statistically significant correlations between high myopia and thinner regions in the neuroretinal rim (NR) — greater correlations appeared for standard RNFL. Results also show moderately negative correlations between optic disc size and BMO-MRW in all 6 sectors (all P <.001). The investigators recommend utilizing BMO-MRW and APS-RNFL parameters for pediatric patients with myopia, but who are otherwise healthy, as they are less affected by the degree of RE, compared with standard RNFL measurements. This approach can also avoid the possible misdiagnosis of glaucoma, the study suggests.

RNFL changes were not tracked over time, and group 3 had fewer participants; thus limiting the study. Conversely, strengths included the prospective design, and a consistent set of healthy children with myopia. “Even if the rim may become thinner with increasing myopia, considering that these eyes are healthy (except for RE), since the weakest relationships exist between the novel methods and RE and groups, these findings suggest that first the BMO-MRW and then the APS-RNFL may provide a more accurate NR evaluation compared [with] standard RNFL in myopic eyes greater than -4.00  D,” the research explains. 

Reference

Gedik AC, Ozbilen KT, Bayraktar S, et al. Bruch membrane opening-minimum rim width and retinal nerve fiber layer thickness in myopic children. Photodiagnosis Photodyn Ther. Published online September 3, 2021. doi:10.1016/j.pdpdt.2021.102524