Similarly, the average GCIPL thickness for each subject was determined for a 16° diameter circular region centered on the macula for both the 20° × 20° and 55° × 45° raster scans.Īfterward, an average thickness map for each of the three raster scan protocols was generated using data from all 30 animals. For comparison, circumpapillary RNFL thickness was determined for an interpolated 12° scan path from each widefield thickness map. Global RNFL thickness was determined for the circumpapillary scan, and thickness maps were generated for each of the raster scans using linear interpolation. Individual and Average Thickness Comparisons Images were exported as “*.vol” files and then read into Matlab (R2021, The MathWorks Inc, Natick, MA, USA), where images were segmented using custom programs, and thickness measures extracted. With this protocol, the 20 × 20° raster scans had twice the b-scan and a-scan density compared to the widefield raster volume. Widefield imaging included a 217 line raster scan covering 55 × 45°, with nine frames averaged. Scan density was reduced to 97 lines when excessive eye movement was present. With nine frame averaging, 20 × 20° raster scans with 193 b-scans were acquired centered on the optic nerve head and macula. For circumpapillary RNFL thickness, a standard 12° diameter circular scan with 100 frames averaged was used. Eyelids were held open using a pediatric speculum, and the cornea was protected from dehydration using a gas permeable contact lens, which covered the entire cornea.Īll scans were acquired using the Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany) system with high-resolution and small eye settings. Our study aimed to determine the utility of widefield scans in quantifying RNFL and macula ganglion cell inner plexiform layer (GCIPL) thickness in healthy rhesus macaques.įor imaging, the monkey was placed in a prone position, and their head stabilized using mouth and occipital bars. We hypothesized that inner retinal thickness measures from widefield scans are similar to those obtained using standard protocols and have similar repeatability. Nonhuman primates (NHPs) are a scarce resource, hence maximizing and standardizing data collected are important for comparability across studies. Widefield scans are commonly not acquired in this model, and normative data, including variability of thickness measures, have not yet been established. 12 – 16 As with the human condition, monitoring experimental glaucoma nominally involves two scans to assess optic nerve head and macula health. The rhesus macaque ( Macaca mulatta) has similar ocular and brain anatomy to humans, and experimental glaucoma in this model has provided valuable insights into disease pathophysiology and changes in visual function. These single wide-angle scans are valuable for detecting arcuate defects, 9 and segmented thickness measures correspond well to those from more standard scan protocols. In contrast, widefield OCT can scan areas routinely sampled for visual function. 7, 8 Although montaging is effective, scanning multiple regions with subsequent scan registration takes longer and adds an element of variability. 6 In fact, by montaging several raster scans, inner retinal thickness maps covering the entire area sampled by perimetry can be generated. Because there are often expected losses in both regions, combining the scanned areas with montaging algorithms has been shown to have added value. These include a volume or circular scan centered on the optic nerve head and a volume scan centered on the fovea. 3 – 5Īlthough there have been significant improvements in OCT resolution and speed, assessing RNFL and GCIPL thickness commonly requires two separate scans. 1, 2 In combination or independently, these measures demonstrate good repeatability and diagnostic value. For glaucoma management, retinal ganglion cell content is assessed using circumpapillary retinal nerve fiber layer (RNFL) thickness and macula ganglion cell inner plexiform layer (GCIPL) thickness. Optical coherence tomography (OCT) produces high-resolution images of ocular tissues and has become an essential tool for managing ocular pathologies.
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