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The optics of comparative ophthalmoscopy.
Abstract: One factor peculiar to the practice of comparative ophthalmoscopy is the very large variation in ocular size of the animals examined, a factor which is ignored in current textbook treatments of the subject. We have computed values of lateral magnification, axial magnification, angular field of view and linear field of view for 19 species of terrestrial vertebrates. The dimensional value of a 1 diopter change in direct ophthalmoscopic focus was also determined. The anterior focal length of the eye in air and the vitreal refractive index were the intrinsic optical parameters of the animal's eye necessary for these calculations. Where these values were not available from the literature, the vitreal refractive index was assumed to be 1.336 and the anterior focal length was estimated as two-thirds of the axial length using a regression equation we derived from data in the literature. The angular field of view in ophthalmoscopy was shown to be invariant in the emmetropic eye and equal to the angular subtense of the ophthalmoscopic beam. The lateral field of view and retinal depth corresponding to a 1 diopter change in direct ophthalmoscopic focus varied directly with the anterior focal length of the eye. The remaining parameters of lateral and axial magnification varied inversely with the anterior focal length of the animal's eyes. These findings provide a basis for evaluating the relative size and significance of ophthalmoscopically viewed features in terrestrial vertebrate eyes.
Publication Date: 1987-01-01 PubMed ID: 3660621DOI: 10.1016/0042-6989(87)90045-9Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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This research discusses the impact of ocular size diversity among animals on comparative ophthalmoscopy, a specialized medical procedure used for examining the eye’s interior. Researchers calculated key parameters, including lateral and axial magnification, field of view and the impact of a 1 diopter change in focus, across 19 species of terrestrial vertebrates to offer improved insight and evaluation of ophthalmoscopically viewed eye features.
Study Background and Objectives
- The objective of this study was to investigate the effect of variations in animal eye size on comparative ophthalmoscopy, a procedure that examines the interior structures of the eye.
- Standard textbook treatments of comparative ophthalmology tend to overlook this variable, prompting this detailed research.
- The research aimed to compute the lateral and axial magnification, angular and linear fields of view, and values related to a 1 diopter alteration in direct ophthalmoscopic focus across 19 species of land vertebrates.
Methodology
- The researchers made use of two intrinsic optical parameters: the anterior focal length of the eye in air and the vitreal refractive index for their computations.
- When data were missing, the investigators used assumed values for the vitreal refractive index (1.336) and used a regression equation to estimate the anterior focal length as two-thirds of the axial length.
Findings
- The study revealed that the ophthalmoscopic field of view’s angularity remains constant in the emmetropic eye and corresponds to the subtense of the ophthalmoscopic beam.
- The lateral field of view and the retinal depth corresponding to a 1 diopter adjustment in direct ophthalmoscopic focus were found to have a linear relationship with the eye’s anterior focal length.
- In contrast, the parameters for lateral and axial magnification showed an inverse relationship with the anterior focal length of the eyes.
Significance
- The findings from this research provide a foundation for interpreting the relative size and significance of features viewed through ophthalmoscopy in terrestrial vertebrate eyes.
- This work contributes to a more comprehensive understanding of comparative ophthalmology, particularly regarding how differences in eye size may affect ophthalmoscopic examination results
Cite This Article
APA
Murphy CJ, Howland HC.
(1987).
The optics of comparative ophthalmoscopy.
Vision Res, 27(4), 599-607.
https://doi.org/10.1016/0042-6989(87)90045-9 Publication
Researcher Affiliations
- Section of Ophthalmology, Veterinary Medical Teaching Hospital, University of California, Davis 95616.
MeSH Terms
- Animals
- Horses
- Humans
- Ocular Physiological Phenomena
- Ophthalmoscopes
- Optics and Photonics
- Refraction, Ocular
- Vitreous Body / physiology
Grant Funding
- EY-02994 / NEI NIH HHS
Citations
This article has been cited 7 times.- Mutti DO, Sinnott LT, Zadnik K. Compensation for Vitreous Chamber Elongation in Infancy and Childhood. Optom Vis Sci 2023 Jan 1;100(1):43-51.
- Ausprey IJ. Adaptations to light contribute to the ecological niches and evolution of the terrestrial avifauna. Proc Biol Sci 2021 May 12;288(1950):20210853.
- Iwaniuk AN, Heesy CP, Hall MI, Wylie DR. Relative Wulst volume is correlated with orbit orientation and binocular visual field in birds. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2008 Mar;194(3):267-82.
- Shupe JM, Kristan DM, Austad SN, Stenkamp DL. The eye of the laboratory mouse remains anatomically adapted for natural conditions. Brain Behav Evol 2006;67(1):39-52.
- Kijas JW, Cideciyan AV, Aleman TS, Pianta MJ, Pearce-Kelling SE, Miller BJ, Jacobson SG, Aguirre GD, Acland GM. Naturally occurring rhodopsin mutation in the dog causes retinal dysfunction and degeneration mimicking human dominant retinitis pigmentosa. Proc Natl Acad Sci U S A 2002 Apr 30;99(9):6328-33.
- Chue-Sang JJ, Peralta XG, Clary JE, Smith A, Peterson A, Macasadia ME, Tijerina AJ, Noojin GD, Hart MV, Schwarten CF, Kinerk WT, Ferris LM, Boice EN. Corneal dose response from exposure to a Q-switched laser at a central wavelength of 1645 nm using a rabbit model. J Biomed Opt 2026 May;31(5):054703.
- Kaiser KP, Bucur J, Jandewerth T, Kohnen T, Lwowski C. Fellow eye data for intraocular lens calculation in eyes undergoing combined phacovitrectomy. Acta Ophthalmol 2025 Feb;103(1):e31-e37.
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