A report recently published in Ophthalmology by the Ural Eye and Medical Study in Russia evaluated the prevalence of non-glaucomatous optic nerve atrophy (NGOA) and associated symptoms in highly myopic patients.
Talk about this study.
In this population-based study, 5,899 ethnically mixed participants (ages +40) living near the Ural Mountains underwent an ophthalmological and general examination.
Based on patients’ medical records, NGOA was graded into five arbitrary stages and characterized by:
- Decreased visibility of the retinal nerve fiber layer (RNFL) on fundus photography and on red-free fundus photographs
- Neuroretinal rim pallor
- Abnormally thin retinal arteriole diameter
- Abnormally thin peripapillary RNFL as measured by optical coherence tomography (OCT)
How many patients were myopic?
Of 5,709 participants (96.9%) with axial length measurements, 130 patients (2.3%) were highly myopic; of this, 116 participants (89.2%) had available fundus photographs and OCT images and, consequently, were included in the study.
Findings?
The study authors noted a prevalence of NGOA of 29.3% (95% confidence interval [CI] 21.0-38.0) in this myopic cohort.
Further, increased NGOA severity correlated with the following:
- Longer axial length (95% CI 0.05-0.31, P=0.007)
- Wider temporal parapapillary gamma zone width (95% CI 0.20-1.06, P=0.005)
- Higher systolic blood pressure (95% CI 0.001-0.02, P=0.03)
What kind of impact did NGOA have?
A higher NGOA prevalence was associated with:
- Longer axial length (odds ratio [OR] 7.45, 95% CI 2.15-25.7, P=0.002)
- Wider temporal parapapillary gamma zone width (OR 6.98, 95% CI 2.61-18.7, P<0.001)
- Higher systolic blood pressure (OR 1.05, 95% CI 1.01-1.10, P=0.02)
For each millimeter of axial elongation and widening of the gamma zone, the odds for NGOA increased 7.45-fold and 6.98-fold, respectively.
Was there a connection to high systolic blood pressure?
The report outlined that the observed link between increased NGOA prevalence and higher systolic blood pressure—as well as higher prevalence of diabetes—potentially indicated a systemic component to the etiology of NGOA in highly myopic eyes.
Expert opinion?
The study authors noted that the gamma zone width increase associated with axial elongation caused an extension in the distance between the retinal ganglion cells (RGCs) and the optic disc, possibly leading to a lengthening and stretching of the RGC axons.
How would this impact the eye?
According to the investigators the retinal nerve fibers running in the papillomacular bundle in a primarily straight course to the optic disc cannot compensate for the increased distance to the optic disc.
As a result, they “may get stretched and potentially damaged in eyes with a large parapapillary gamma zone,” they wrote.
Take home.
This study demonstrated that high axial myopia has a relatively high prevalence of NGOA, which increases with longer axial length and wider temporal parapapillary gamma zone.
In highly myopic eyes, NGOA could potentially be a reason for visual field and central visual acuity loss that is unexplainable by myopic macular pathologies.