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2024
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Jesse Wang MS thesis final version_Jesse Wang.pdf
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"Purpose: To determine the pattern of the diurnal variations in retinal responses measured with the full-field scotopic and photopic electroretinogram (ERG).
Methods: Full-field flash ERGs were recorded with DTL electrodes after pupil dilation from 6 normal healthy subjects at 3AM, 9AM, 3PM and 9PM (one subject at 6AM, 12PM, 6PM, 12AM) on four separate days using a desktop ganzfeld ERG recording system (Diagnosys LLC). The test scotopic ERG test protocol consisted of 40 minutes of dark-adaptation followed by recordings with brief (<4ms) blue (440nm) test flashes in the range of 1x10-6 to 20 scot cd.s/m2. The photopic ERG test protocol consisted of 15 minutes of light-adaptation to 8 scot cd/m2 blue background followed recordings with brief red (690nm) test flashes in the range of 6x10-2 to 6.4 phot cd.s/m2 on the adapting background. The Scotopic Threshold Response (STR), scotopic and photopic b-waves and the Photopic Negative Response (PhNR) amplitudes were plotted as a function of test flash intensity and fit with the Naka-Rushton equation to extract the saturated amplitude (Vmax), slope (n) and semisaturation constant (K) parameters for each ERG measures. The fit parameters were plotted as a function of the time of the day when the recordings were performed to examine their diurnal variation. Saliva samples were collected and salivary melatonin was assayed (Salimetrics LLC) at 8 different time points during the day from each subject on one separate occasion and prior, during and after each ERG session.
Results: The Vmax of the ERG measures demonstrated statistically significant systematic diurnal variation. The Vmax of the Scotopic b-wave and the STR did not change appreciably from 3AM to 9AM but thereafter gradually increased to reach a maximum value at 9PM. The difference in the mean value of the Vmax between the 3AM and 9PM recordings was statistically significant for the scotopic b-wave (173uv and 338uv, p=0.0013) and the STR (15uv and 22uv, p=0.03). with the halfway point for this amplitude increase being 11AM. The Vmax of the photopic b-wave and PhNR showed a steep increase from 3AM to 9AM and thereafter a more gradual increase at 3PM to slightly reduce again by 9PM. The difference in the mean value of the Vmax between the 3AM and 3PM recordings was statistically significant for the photopic b-wave (60uv and 92uv, p=0.04) and the PhNR (36uv and 61uv, p=0.019) with the halfway point for this amplitude increase being 6AM. Salivary metalonin concentration on average started to show an increase around 9AM from daytime baseline value of 1 pg/ml to a peak of 16 pg/ml around 3AM and then reduced to 4 pg/ml by 9AM.
Conclusions: The maximal amplitude of the scotopic ERG parameters are achieved later during the day compared to the photopic ERG parameters that achieve maximal amplitudes at earlier times. The saturated amplitude of scotopic and photopic ERG measures have their lowest values around 3AM when salivary melatonin concentration is maximal. The relationship between the diurnal rhythms of melatonin and retinal function as measured by the ERG warrants further investigation.
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