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A method employing steady-state pattern electroretinogram (ssPERG) may be useful in the diagnosis of glaucoma in patients with concurrent high myopia, according to an investigation published in Clinical Ophthalmology.
When compared with high myopia eyes, MagD/Mag ratio at 16° is significantly lower in glaucomatous eyes, with or without high myopia, investigators report.
A total of 48 participants (average age 59.4±7.6 years, and 29 men, 19 women) were divided into 3 groups: those with glaucoma (G, n=16), those with high myopia (HM, n=16), and those with glaucoma and high myopia (GHM, n=16). The participants were evaluated using visual field testing as well as ssPERG testing with both the Concentric Stimulus Fields (ConStim) and Contrast Sensitivity (ConSen) protocols.
“The pattern stimulus for the ConStim protocol evaluated either the central 16° or 24° field of vision and comprised 64 bar size black and white horizontal gratings with 100% contrast (mean luminance 102.1cd/m2) and a reversal rate of 15 reversals/second for 25 seconds per test per eye,” researchers explain. “The pattern stimulus for the ConSen protocol evaluated the central 24° of the macula and comprised 64 bar size black and white horizontal gratings with 85% contrast (mean luminance 112.3cd/m2) for the high contrast (Hc) and 75% contrast (mean luminance 128.2cd/m2) for the low contrast (Lc) tests, at a reversal rate of 15 reversals/second for 25 seconds per test per eye.”
Outcomes measured for each test included 4 parameters as noted by the study:
- Magnitude (Mag) — The average of the signal amplitude representing the RGC responses to the PERG stimuli.
- MagnitudeD (MagD) — The amplitude of the average signal across the frame, taking into account both magnitude and phase variability.
- MagnitudeD to Magnitude ratio (MagD/Mag ratio) — An indicator of the consistency of the response.
- Signal-to-noise ratio (SNR) — Compares the strength of the 15Hz signal and the average ambient electrical noise.
Mean Humphrey visual field mean deviation (VFMD) was -14.22±2.88 dB, -2.62±1.18 dB and -12.80±2.60 dB in the G, HM and GHM groups, respectively. Mean retinal nerve fiber layer (RNFL) thicknesses were 63.0±8.20 μm, 69.5±15.7 μm and 60.6±5.0 μm in the G, HM, and GHM groups, respectively.
For the 24° setting, researchers observed no significant differences for any of the parameters. For the 16° setting, the MagD was significantly lower in the GHM group compared with the HM group (0.29 μV vs 0.52 μV; P =.02).
The researchers also noted significant differences for the MagD/Mag ratio between HM and G groups (0.58 vs 0.40; P =.02) as well as between HM and GHM groups (0.58 vs 0.35; P =.002). There was a positive association between both MagD 16° and MagD/Mag ratio 16° with VFMD (r=0.37, P =.009; and r=0.44, P =.002, respectively) and RNFL (r=0.43, P =.002; and r=0.48, P =.001, respectively).
Of the different test protocols, MagD 16° and MagD/Mag ratio 16° were significantly lower in glaucomatous eyes compared with those with high myopia, according to the researchers. “Further validation studies with larger sample sizes and with varying severities of glaucoma and myopia are warranted in order to explore the possibility of differentiating glaucomatous from non-glaucomatous myopic changes using ssPERG.”
Limitations of the study include relatively small sample size and lack of a control group of participants without glaucoma or high myopia.
Reference
Lim XH, Nongpiur ME, Najjar RP, et al. Steady-state pattern electroretinography in eyes with glaucoma and high myopia. Clin Ophthalmol. Published online November 17, 2021. doi:10.2147/OPTH.S336903
