Optic Nerve Head Structural Changes May Be Tied to Axial Elongation

In eyes with non pathologic myopia, longer axial length (AL) may be associated with optic nerve head (ONH) structural changes, which include Bruch membrane opening (BMO) and anterior scleral canal opening (ASCO) misalignment, thinner choroid, thicker circumpapillary retinal nerve fiber layer (RNFL), and a larger peripapillary scleral angle, according to research published in the American Journal of Ophthalmology.

Researchers included 140 participants (eyes, 211; mean age, 46.7 years; 75 women; spherical equivalent [SE], -3.11 diopters [D]) with emmetropia (eyes, 96) and moderate (eyes, 83; AL, 24.5-<26.0 mm) or high myopia (eyes, 32; AL≥26.0 mm) from 8 sites in the  prospective, cross-sectional, observational study. Study participants underwent swept-source optical coherence tomography (SS-OCT) to evaluate ONH-derived parameters with the goal of assessing longer AL predictors. 

All parameters related to retinal pigment epithelium (RPE), BMO, and ASCO demonstrated excellent reproducibility. Intraclass correlation coefficient (ICC) ranged from 0.889 (region of peri-neural canal RPE atrophy) to 0.988 (BMO area) and 0.809 (ASCO/BMO offset direction) to 0.972 (BMO area) for intraobserver and interobserver reproducibility, respectively.

Significant predictors of long axial length included the BMO and ASCO offset (P <.0001), peripapillary scleral angle (P <.0001), circumpapillary RNFL thickness (P =.008), and circumpapillary choroidal thickness (P <.0001), according to the report.

A best fit model that included externally oblique choroidal border tissues and excluded ASCO and BMO offset magnitude revealed that the area of choroidal border tissues (P <.0001), ASCO area (P =.007), circumpapillary RNFL thickness (P =.04), and circumpapillary choroidal thickness (P =.0007) predicted longer axial length.

“[O]ur study revealed a greater misalignment between BMO and ASCO planes which resulted in a more oblique choroidal border tissue configuration, a thinner choroid, a more posteriorly bowed peripapillary sclera configuration, and a larger ASCO area are associated with longer axial length in healthy myopic eyes,” according to the study authors. “These findings are a foundation for future investigations to elucidate glaucoma specific optic nerve head changes that occur in glaucomatous myopic eyes.”

Study limitations include the exclusion of eyes with hyperopia. 

Disclosure: This research was supported by Topcon. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.