Investigating the Linkage Between Mesopic Spatial Summation and Variations in Retinal Ganglion Cell Density Across the Central Visual Field: Mesopic Spatial Summation with Eccentricity

Aoife Hunter, RS Anderson, Tony Redmond, David F. Garway-Heath, Padraig Mulholland

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The relationship between perimetric stimulus area and Ricco's area (RA) determines measured thresholds and the sensitivity of perimetry to retinal disease. The nature of this relationship, in addition to effect of retinal ganglion cell (RGC) number on this, is currently unknown for the adaptation conditions of mesopic microperimetry. In this study, achromatic mesopic spatial summation was measured across the central visual field to estimate RA with the number of RGCs underlying RA also being established.

Achromatic luminance thresholds were measured for six incremental spot stimuli (0.009–2.07 deg2) and 190.4 ms duration, at four locations, each at 2.5°, 5° and 10° eccentricity in five healthy observers (mean age 61.4 years) under mesopic conditions (background 1.58 cd/m2). RA was estimated using two-phase regression analysis with the number of RGCs underlying RA being calculated using normative histological RGC counts.

Ricco's area exhibited a small but statistically insignificant increase between 2.5° and 10° eccentricity. Compared with photopic conditions, RA was larger, with the difference between RA and the Goldmann III stimulus (0.43°) being minimised. RGC number underlying RA was also higher than reported for photopic conditions (median 70 cells, IQR 36–93), with no significant difference being observed across test locations.

Ricco's area and the number of RGCs underlying RA do not vary significantly across the central visual field in mesopic conditions. However, RA is larger and more similar to the standard perimetric Goldmann III stimulus under mesopic compared with photopic adaptation conditions. Further work is required to determine if compensatory enlargements in RA occur in age-related macular degeneration, to establish the optimal stimulus parameters for AMD-specific microperimetry.
Original languageEnglish
Number of pages11
JournalOphthalmic and Physiological Optics: the Journal of the College of Optometrists
Early online date28 Apr 2023
Publication statusPublished online - 28 Apr 2023

Bibliographical note

Funding Information:
This study was supported by a PhD studentship from the Macular Society, United Kingdom (AMLH), and in part by the National Institute for Health & Care Research (NIHR) Biomedical Research Centre based at Moorfields Eye Hospital NHS Foundation Trust and University College London (UCL) Institute of Ophthalmology (RSA, DFG‐H, PJM). DFG‐H's chair at UCL is supported by funding from Glaucoma UK. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.

Publisher Copyright:
© 2023 The Authors. Ophthalmic and Physiological Optics published by John Wiley & Sons Ltd on behalf of College of Optometrists.


  • Spatial summation
  • Microperimetry
  • Hill-of-vision
  • Perimetry
  • Ricco's area
  • Partial summation
  • hill-of-vision
  • spatial summation
  • partial summation
  • microperimetry
  • perimetry
  • mesopic


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