A recent study published in Ophthalmology assessed whether there is a difference in inter-eye glaucoma severity and progression in patients with asymmetrical axial length.
Give me some background.
Previous studies have demonstrated a positive relationship between myopia/axial length and glaucoma development and progression.
In fact: One study found that in highly myopic eyes, the lamina cribrosa was significantly thinner than in non-highly myopic eyes—notably increasing the risk of glaucomatous optic disc changes.
Talk about the study.
In this retrospective observational study, investigators included patients over the age of 20 who were diagnosed with glaucoma in both eyes and had an inter-eye axial length difference >1 mm.
Each participant’s eyes were classified into “longer eye” and “shorter eye,” and the baseline and follow-up clinical data were analyzed using paired t-tests.
- About a paired t-test: This is a statistical analysis that compares the means of two measurements taken from the same individual.
Findings?
In total, 190 eyes of 95 glaucoma patients (mean age 51.2±12.3 years) with asymmetric axial length were included in the study, with a mean follow-up period of 10.1±3.9 years.
There was no difference in the baseline intraocular pressure (IOP) or central corneal thickness (CCT) between longer and shorter eyes.
What traits were observed in the longer eyes?
The research team found that the ovality index and beta-zone and gamma-zone parapapillary atrophy (PPA) area were larger in the longer eyes.
In addition, the retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thickness was thinner in longer eyes.
- Meaning: In general, that glaucoma tended to be more advanced in the longer eye.
Based on the baseline visual field (VF) test, the mean deviation (MD) and visual field index (VFI) values were significantly lower in the longer eyes.
How did myopia impact glaucoma progression?
Results from glaucoma progression analyses indicated that three key parameters were larger in the longer eyes:
- Superior GCIPL
- Longer eyes: -0.65 μm/yr
- Shorter eyes: -0.40 μm/yr
- MD
- Longer eyes: -0.40 dB/yr
- Shorter eyes: -0.21 dB/yr
- VFI
- Longer eyes: -0.92 %/yr
- Shorter eyes: -0.46 dB/yr
As the inter-eye difference between the mean IOP and beta-zone PPA area increased, so did the difference in the rate of change of RNFL and GCIPL.
Further, the greater the difference in IOP fluctuation, the higher the difference in the rate of change between MD and VFI.
Why do these findings matter?
The study authors noted that, by understanding these differences in glaucoma manifestation within individuals with differing axial length, it “could aid in personalized treatment strategies and reinforce the importance of establishing an early treatment strategy in cases with notable structural disparities.”
Any limitations?
Notable limitations of this study included:
- A relatively narrow range of axial length difference values in the cohort (1-2 mm)
- Its retrospective and single-center design, which limited the generalizability of the findings
- Time of onset of glaucoma could not be clearly determined within the study, making it difficult to measure the progression rate from baseline
Take home.
These findings suggest that glaucoma patients with an inter-eye axial length difference of more than 1 mm tended to have more severe and faster-progressing glaucoma in the longer eyes.
- Longer eyes, characterized by structural variations at baseline and an accelerated rate of glaucomatous change, exhibited a higher susceptibility to disease severity and progression.
The inter-eye difference in glaucoma progression rate was related to both mean IOP and IOP fluctuation.