Next generation PERG system and method for human studies

Abstract

Purpose : To develop a novel PERG method with improved technology, signal to noise ratio, and analysis of signal dynamics.

Methods : The visual stimulus consisted of a black-white horizontal grating (1.6 cycles/deg, 15.63 reversal/s, 98% contrast, 800 cd/sqm mean luminance) generated on a 14 x 14 cm LED tablet developed with NEI support (R43EY023460) and presented binocularly at 30 cm viewing distance. Retinal signals were simultaneously recorded from both eyes with skin electrodes over the lower eyelids, amplified (100,000 x) filtered (1-300 Hz) and averaged over 1,024 epochs in 16 successive samples of 64 epochs each (~2 minutes recording time). The noise was simultaneously obtained with an even/odd sweep difference method. Response amplitude and phase were automatically assessed using Fourier analysis. Variance of the response and noise over recording time was also assessed. This paradigm (named PERGX) was compared with an established paradigm (PERGLA, Ophthalmology 2004, 111(1):161-8) in a mixed population of 20 subjects (40 eyes) including normal subjects and patients with early glaucoma to generate a range of amplitudes spanning the dynamic range of PERG signal. Subjects were tested with both paradigms in the same session, allowing 20 minutes pause between the two.

Results : Compared to PERGLA, PERGX had larger amplitude (+39.8%, P<0.001), lower noise (-67.9%, P<0.001) and higher (4.5 x) signal-to-noise ratio. PERGX phase (latency) was 16 ms shorter (P<0.001) than that of PERGLA. The variance due to noise accounted for 48% (95% C.I. 34-64%) of total amplitude variance, the residual variance being primarily due to progressive amplitude changes over recording time (adaptation).

Conclusions : The PERGX paradigm represents a substantial evolution in the PERG technique as its larger signal and lower noise extends the response dynamic range and allows monitoring of advanced stages of glaucoma and optic nerve disorders with low PERG signal. In addition, PERGX has the unique feature of quantifying the adaptive response component, which reflects metabolic changes and may be selectively altered in glaucoma and optic neuritis. Differences between paradigms can be explained by superior temporal characteristics and higher luminance of the LED display compared to standard CRT display and by differences in signal processing.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.