Higher axial length variation between two eyes tied to inter-eye glaucoma severity with quicker progression: Study

A new study published in the recent issue of Ophthalmology journal found that the glaucoma in the longer eyes tend to be more severe and to advance more quickly when there was an axial length variation of more than 1.0 mm, the findings of this study were .

Elevated intraocular pressure (IOP) can compress retinal ganglion cell axons at the lamina cribrosa, resulting in death and interrupting axonal transport. Long axial length (AL) is also independently linked to an elevated the risk of normotensive primary open angle glaucoma (OAG), and myopia is another well-known risk factor for glaucoma. Thus, Min Gu Huh and team sought out to determine if individuals with asymmetric axial length had a different inter-eye glaucoma development and severity.

The long-term observational research included patients over the age of 20 who were diagnosed with glaucoma at Seoul National University Hospital in Seoul, Korea, between 2010 and 2020. The patients who had an axial length difference of more than 1.0 mm and bilateral glaucoma were included. The paired test was used to compare baseline and follow-up clinical data after each individual's eyes and were classified as "longer eye" or "shorter eye." The main finding of this study was that those with asymmetric axial length had varied clinical characteristics.

The study comprised of a total of 190 eyes with unequal axial length from 95 glaucoma patients. The mean follow-up duration was 10.1 ± 3.9 years, and the mean age of these patients were 51.2 ± 12.3 years. The central corneal thickness (CCT) and baseline intraocular pressure (IOP) of longer and shorter eyes were the same. The ovality index, beta- and gamma-zone parapapillary atrophy (PPA) region, and other baseline disc characteristics were all higher in the longer eyes.

The ganglion cell-inner plexiform layer (GCIPL) and retinal nerve fiber layer (RNFL) thicknesses in the baseline OCT data were both thinner in the longer eyes. A baseline visual field (VF) test revealed that the longer eyes had considerably lower mean deviation (MD) and visual field index (VFI) values. The longer eyes had higher rates of change in superior GCIPL (-0.65 μm/yr, shorter eyes: -0.40 μm/yr), MD (-0.40 dB/yr, shorter eyes: -0.21 dB/yr), and VFI (-0.92%/yr, shorter eyes: -0.46%/yr) during glaucoma development. 

The rate of change of RNFL and GCIPL rises when the mean IOP and beta-zone PPA area vary between eyes. Also, the difference in rate of change between MD and VFI grew with the IOP fluctuation difference. When the axial length difference was more than 1.0 mm, glaucoma was more severe and progressed quicker in longer eyes. The inter-eye variation in glaucoma progression rate is proportional to both mean IOP and IOP fluctuations.

Reference:

Huh, M. G., Jeong, Y., Shin, Y. I., Kim, Y. K., Jeoung, J. W., & Park, K. H. (2024). Assessing Glaucoma Severity and Progression in Individuals with Asymmetric Axial Length: An Intra-Patient Comparative Study. In Ophthalmology. Elsevier BV. https://doi.org/10.1016/j.ophtha.2024.07.013