Examining the concordance of retinal ganglion cell counts generated using measures of structure and function

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 (0.43°, Goldmann III) was calculated and compared using three different methods. METHODS: RGC‐RF count was calculated at a retinal eccentricity of 2.32 mm for 44 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 average RGC‐RF counts from the OCT‐model (median 105.3, IQR 99.6–111.0) and the Histology‐Balloon model (median 107.5, IQR 97.7–114.6) were similar, PGRA estimates were approximately 65% lower (median 37.7, IQR 33.8–46.0). However, there was 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 intersubject variability in RGC‐RF count was evident using all three methods. CONCLUSIONS: The lower PGRA RGC‐RF counts may be the result of targeting only a specific subset of functional RGCs, as opposed to the coarser approach of the OCT‐model and Histology‐Balloon, which include all RGCs, and also likely 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 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 methodologies and highlights the need to utilise the same method in longitudinal work

Temporal summation in myopia and its implications for the investigation of glaucoma

Purpose We have previously demonstrated the upper limit of complete spatial summation (Ricco's area) to increase in non-pathological axial myopia compared to non-myopic controls. This study sought to investigate whether temporal summation is also altered in axial myopia to determine if this aspect of visual function, like in glaucoma, is influenced by reductions in retinal ganglion cell (RGC) density. Methods Achromatic contrast thresholds were measured for a GIII-equivalent stimulus (0.43° diameter) of six different stimulus durations (1–24 frames, 1.1–187.8 ms) in 24 participants with axial myopia (mean spherical refractive error: −4.65D, range: −1.00D to −11.25D, mean age: 34.1, range: 21–57 years) and 21 age-similar non-myopic controls (mean spherical refractive error: +0.87D, range: −0.25D to +2.00D, mean age: 31.0, range: 18–55 years). Measurements were performed at 10° eccentricity along the 90°, 180°, 270° and 360° meridians on an achromatic 10 cd/m2 background. The upper limit of complete temporal summation (critical duration, CD) was estimated from the data with iterative two-phase regression analysis. Results There was no significant difference (p = 0.90, Mann–Whitney U-test) in median CD between myopes (median: 44.3 ms; IQR: 26.5, 51.2) and non-myopes (median: 41.6 ms; IQR: 27.3, 48.5). Despite RGC numbers underlying the stimulus being significantly lower in the myopic group (p < 0.001), no relationship was observed between the CD estimate and co-localised RGC number (Pearson's r = −0.13, p = 0.43) or ocular length (Pearson's r = −0.08, p = 0.61). Conclusions Unlike spatial summation, temporal summation is unchanged in myopia. This contrasts with glaucoma where both temporal and spatial summation are altered. As such, perimetric methods optimised to test for anomalies of temporal summation may provide a means to differentiate between conditions causing only a reduced RGC density (e.g., myopia), and pathological processes causing both a reduced RGC density and RGC dysfunction (e.g., glaucoma)

Estimating the Critical Duration for Temporal Summation of Standard Achromatic Perimetric Stimuli

Purpose: To estimate the critical duration of temporal summation for achromatic Goldmann III stimuli under the conditions of standard automated perimetry (SAP) and quantify response variability for short duration stimuli. Methods: Contrast thresholds were gathered using the method of constant stimuli for seven circular (0.48° diameter) incremental stimuli of varying duration (sum-of-frames equivalent: 8.3-198.3 msec), at an eccentricity of 8.8° along the four principal meridians of the visual field in two healthy, psychophysically experienced observers. Stimuli were presented on a high-resolution CRT display with a background luminance of 10 cd/m2. Psychometric functions were fitted using a probit model and non-parametric local linear analysis. The critical duration was estimated using iterative two-phase regression analysis, the results also being compared with values produced using previously published methods of analysis. Results: The median critical duration estimated using iterative two-phase regression analysis was 27.7 msec (IQR 22.5-29.8). A slight steepening of the psychometric function slope (lower variability) was observed for longer stimulus durations, using both probit and local-linear analysis techniques, but this was not statistically significant. Conclusions: Critical duration estimates in this study are substantially shorter than those previously reported for a Goldmann III stimulus under the conditions of SAP. Further work is required to firmly establish the relationship between measurement variability and the degree of local temporal and spatial summation

Ageing changes in retinal outer nuclear layer thickness and cone photoreceptor density using adaptive optics-free imaging

Purpose: To investigate age-related changes of the outer nuclear layer (ONL) thickness and cone density, and their associations in healthy participants using a modified, narrow scan-angle Heidelberg Retina Angiograph (HRA2). Methods: Retinal cones were imaged outside the fovea at 8.8° eccentricity and cone density was compared to ONL thickness measurements obtained by Spectral-Domain Optical Coherence Tomography (SD-OCT) at the same locations. Fifty-six eyes of 56 healthy participants with a median age (interquartile range, IQR) of 37 years (29–55) were included. Results: Median (IQR) cone count was 7,472 (7,188, 7,746) cones/mm2 and median (IQR) ONL thickness was 56 (52, 60) µm for healthy participants. Both cone density and ONL thickness were negatively associated with age: cone density, R2 = 0.16 (F(1,54) = 10.41, P = 0.002); ONL thickness, R2 = 0.12 (F(1,54) = 7.41, P = 0.009). No significant association was seen between cone density and ONL thickness (R2 = 0.03; F(1,54) = 1.66, P = 0.20). Conclusion: Cone density was lower, and ONL thinner, in older compared to younger participants, therefore, image-based structural measures should be compared to age-related data. However, cone density and ONL thickness were not strongly associated, indicating that determinants of ONL thickness measurements other than cone density measurements, and including measurement error, have a major influence

Ophthalmology research in the UK’s National Health Service: the structure and performance of the NIHR’s Ophthalmology research portfolio

Purpose- To report on the composition and performance of the portfolio of Ophthalmology research studies in the United Kingdom’s National Institute for Health Research (NIHR) Clinical Research Network (UK CRN). Methods- Ophthalmology studies open to recruitment between 1 April 2010 and 31 March 2018 were classified by: sub-specialty, participant age, gender of Chief Investigator, involvement of genetic investigations, commercial/ non-commercial, interventional/observational design. Frequency distributions for each covariate and temporal variation in recruitment to time and target were analysed. Results- Over 8 years, 137,377 participants were recruited (average of 15,457 participants/year; range: 5485–32,573) with growth by year in proportion of commercial studies and hospital participation in England (76% in 2017/18). Fourteen percent of studies had a genetic component and most studies (82%) included only adults. The majority of studies (41%) enrolled patients with retinal diseases, followed by glaucoma (17%), anterior segment and cataract (13%), and ocular inflammation (6%). Overall, 68% of non-commercial studies and 55% of commercial studies recruited within the anticipated time set by the study and also recruited to or exceeded the target number of participants. Conclusions- High levels of clinical research activity, growth and improved performance have been observed in Ophthalmology in UK over the past 8 years. Some sub-specialties that carry substantial morbidity and a very high burden on NHS services are underrepresented and deserve more patient-centred research. Yet the NIHR and its CRN Ophthalmology National Specialty Group has enabled key steps in achieving the goal of embedding research into every day clinical care

Investigating the spatiotemporal summation of perimetric stimuli in dry age-related macular degeneration

Purpose. To measure achromatic spatial, temporal and spatiotemporal summation in dry age-related macular degeneration (AMD) compared to healthy controls, under conditions of photopic gaze-contingent perimetry.Methods. Twenty participants with dry AMD (mean age, 74.6 years) and 20 healthy controls (mean age, 67.8 years) performed custom, gaze-contingent perimetry tests. An area-modulation test generated localized estimates of Ricco’s area (RA) at 2.5° and 5° eccentricity along the 0º, 90º, 180º, and 270º meridians. Contrast thresholds were measured at the same test locations for stimuli of six durations (3.7-190.4 ms) with a Goldmann-III stimulus (GIII, 0.43º) and RA-scaled stimuli. The upper limit (critical duration) of complete temporal (using GIII stimulus) and spatiotemporal summation (using RA stimulus) was estimated using iterative two-phase regression analysis. Results. Median (interquartile range [IQR]) RA estimates were significantly larger in AMD participants (2.5°: 0.21 [0.09 – 0.41] deg2; 5°: 0.32 [0.15 – 0.65 deg2]) compared to healthy controls (2.5°: 0.08 [0.05 – 0.13] deg2; 5°: 0.15 [0.08 – 0.22] deg2) at all test locations (all P&lt;0.05). No significant difference in median (IQR) critical duration was found in AMD participants with the GIII stimulus (19.6 [9.9 – 30.4] ms) and RA-scaled stimuli (22.9 [13.9 – 40.3] ms) compared to healthy controls (GIII, 17.0 [11.3 – 24.0] ms; RA-scaled, 22.4 [14.3 – 33.1] ms) at all test locations (all P &gt; 0.05). Conclusions. Spatial summation is altered in dry AMD, without commensurate changes in temporal summation. Translational Relevance. The sensitivity of perimetry to AMD may be improved by utilising stimuli that probe alterations in spatial summation in the disease.<br/

Quantifying the signal/noise ratio with perimetric stimuli optimised to probe changing spatial summation in glaucoma [Abstract]

Purpose : Guided by changes in spatial summation in glaucoma, we undertook a cross-sectional prospective study to compare disease signal, response variability, and signal/noise ratio (SNR) between perimetric stimuli varying in area, contrast, and both simultaneously, in patients with glaucoma and age-similar healthy controls. Methods : Participants were 30 glaucoma patients (median [interquartile range] age: 70.4 years [66.2, 73.5], MD: -4.04dB [-9.65, -2.85]) and 20 controls (age: 69.3 years [66.1, 77.8], MD +0.38dB [-0.36, +0.91]). Using a 3-stage approach (1: staircase procedure; 2: short Method of Constant Stimuli (MOCS, 180 presentations); 3: extended MOCS (640 presentations)), threshold (50% seen) and response variability (slope) were measured for 200ms achromatic spot stimuli, presented at 4 diagonal locations (9.9° from fixation). Stimuli were: A - fixed contrast (ΔI: 0.5, starting within Ricco’s area), varying in area; C1 - fixed area (0.02deg2, within Ricco’s area), varying in contrast; AC - varying in both area and contrast simultaneously (starting within Ricco’s area); C2 - fixed area (0.15deg2), equivalent to Goldmann III, varying in contrast. Stimuli were defined by a common scale (energy: luminance x area x duration). Step size and visibility were equated across all stimulus forms. Total deviation (TD, calculated from healthy subjects for each stimulus form), slope, and SNR (TD/slope) were compared between stimuli per hemifield in three TD strata (upper, middle, lower, according to TD for the C2 stimulus). Results : Overall, the greatest disease signal was found with A and AC stimuli (Fig.1A). Response variability was least dependent on depth of defect with the A stimulus, and most for the C2 stimulus (Fig.1B). The SNR was greatest for the A stimulus, and the difference from that for the C2 stimulus was statistically significant in the superior hemifield in the middle (p=0.04) and lower (p=0.049) strata (Fig.2). Conclusions : Area-modulated stimuli likely offer benefits for measuring glaucomatous changes in spatial summation, in the form of greater disease signal and least dependence on depth of defect than conventional fixed-area, contrast-modulated stimuli. This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017

The UK clinical eye research strategy: refreshing research priorities for clinical eye research in the UK

Objectives To validate and update the 2013 James Lind Alliance (JLA) Sight Loss and Vision Priority Setting Partnership (PSP)’s research priorities for Ophthalmology, as part of the UK Clinical Eye Research Strategy. Methods Twelve ophthalmology research themes were identified from the JLA report. They were allocated to five Clinical Study Groups of diverse stakeholders who reviewed the top 10 research priorities for each theme. Using an online survey (April 2021-February 2023), respondents were invited to complete one or more of nine subspecialty surveys. Respondents indicated which of the research questions they considered important and subsequently ranked them. Results In total, 2240 people responded to the survey (mean age, 59.3 years), from across the UK. 68.1% were female. 68.2% were patients, 22.3% healthcare professionals or vision researchers, 7.1% carers, and 2.1% were charity support workers. Highest ranked questions by subspecialty: Cataract (prevention), Cornea (improving microbial keratitis treatment), Optometric (impact of integration of ophthalmic primary and secondary care via community optometric care pathways), Refractive (factors influencing development and/or progression of refractive error), Childhood onset (improving early detection of visual disorders), Glaucoma (effective and improved treatments), Neuro-ophthalmology (improvements in prevention, diagnosis and treatment of neurodegeneration affecting vision), Retina (improving prevention, diagnosis and treatment of dry age-related macular degeneration), Uveitis (effective treatments for ocular and orbital inflammatory diseases). Conclusions A decade after the initial PSP, the results refocus the most important research questions for each subspecialty, and prime targeted research proposals within Ophthalmology, a chronically underfunded specialty given the substantial burden of disability caused by eye disease