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Mohamed Belmouhand, Simon Rothenbuehler, Michael Larsen; Investigation of the origin of the specular fundus reflex. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6122.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate to origin of the specular fundus reflex seen on conventional fundus photographs in healthy children and young adults.
Comparison of conventional color fundus photographs and en-face swept-source optical coherence tomography scans (OCT; Topcon Triton, Topcon, Tokyo, Japan) of the vitreoretinal interface region in 7 healthy subjects aged 7-60 years.
The distribution of specular reflexes over the fundus varied between fundus photographs and en-face OCT scans captured in a combined fundus imaging procedure. The specular reflex varied from procedure to procedure in the same seating. In a stack of en-face images averaged over a thickness of 2.6 µm and fitting the contour of the inner surface of the retina and presented in steps of 2.6 µm, the specular reflex reached its maximum intensity at a nominal depth of 7.8 µm and spread to a depth 26 µm or more. The B-scans showed the specular reflex at the inner surface of the retina, corresponding to the internal limiting membrane (ILM). In subjects where the posterior hyaloid was separated from the ILM, if only by a small distance, there was no evidence that the posterior hyaloid contributed to the specular fundus reflex. The results were consistent in all 7 subjects.
Our observations indicate that the source of the specular fundus reflex is the ILM, not the posterior hyaloid membrane of the vitreous. The term posterior hyaloid reflex should therefore be avoided. We found no evidence to suggest that the specular fundus reflex is fundamentally different between conventional fundus photography and en-face OCT. The apparent peak of the specular fundus reflex being found at a nominal distance of 7.8 µm inside the retina may result from the segmentation algorithm having set the retinal surface where it detected only by the tip of the OCT sampling volume, the Z-axis length of which is determined by the coherence length of the OCT system. The results are relevant for the interpretation of abnormalities of the specular fundus reflex and for the development of methods that can limit its interference with the imaging of deeper retinal structures, such as retinal vessels, especially in children.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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