Purpose: There are several indirect methods used to estimate retinal ganglion cell (RGC) count in an individual eye, but there is limited information as to the agreement between these methods. In this work, RGC receptive field (RGC-RF) count underlying a spot stimulus (0.43º, Goldmann-III) was calculated and compared using three different methods.
Methods: RGC receptive field (RGC-RF) count was calculated at a retinal eccentricity of 2.32 mm for forty-four healthy adult participants (aged 18-58 years, refractive error -9.75 DS to +1.75 DS) using (i) functional measures of achromatic peripheral grating resolution acuity (PGRA), (ii) structural measures of RGC-layer thickness (OCT-model, based on the method outlined by Raza and Hood), and (iii) scaling published histology density data to simulate a global expansion in myopia (Histology-Balloon).
Results: Whilst RGC-RF counts were, on average, similar from the OCT-model (median 105.3, IQR 99.6 to 111.0) and the Histology-Balloon model (median 107.5, IQR 97.7 to 114.6), PGRA estimates were ~65% lower (median 37.7, IQR 33.8 to 46.0). There was however poor agreement between all three methods (Bland Altman 95% limits-of-agreement; PGRA/OCT: 55.4; PGRA/Histology-Balloon 59.3; OCT/Histology-Balloon: 52.4). High inter-subject variability in RGC-RF count was evident using all three methods.
Conclusions: The lower PGRA RGC-RF counts may be a result of only targeting a specific subset of functional RGCs, opposed to the more coarse approach of the OCT-model and Histology-Balloon which include all RGCs and likely also displaced amacrine cells. In the absence of a ‘ground-truth’, direct measure of RGC-RF count it is not possible to determine which method is most accurate, and each method has limitations. However, what is clear is the poor agreement found between the methods prevents direct comparison of RGC-RF counts between studies utilising different methods and highlights the need to utilise the same method in longitudinal work.
|Journal||Ophthalmic and Physiological Optics|
|Publication status||Accepted/In press - 22 Jul 2022|
- Retinal Ganglion Cell Count
- Peripheral Grating Resolution Acuity
- Structure-Function Relationship