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M. F. Marmor, S. S. Choi, J. S. Werner, R. J. Zawadzki; Role of the Foveal Pit: Adaptive Optics and mfERG of Foveal Hypoplasia in Albinism. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3708.
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© ARVO (1962-2015); The Authors (2016-present)
To relate visual acuity and the absence of a foveal pit to the structure and function of foveal cones. In an albino subject, with good visual acuity and no nystagmus, we obtained images of central cones with adaptive optics (AO) and assessed cone function with multifocal ERG (mfERG).
The study subject was a 20 year-old male with partial oculocutaneous albinism, and no fundus pigmentation except a dusting in the macula and around the disc. Stratus OCT measurements were made through multiple central slices. VERIS mfERG recordings were made according to ISCEV guidelines, using a matrix of 103 pixels. Two AO imaging systems, AO- flood illumination and AO- high resolution Fourier domain OCT, were used to acquire images of cone photoreceptors in the central retina. High resolution Fourier domain OCT was also used to reconstruct the retina in 3D volume which allows visualization of all layers.
Visual acuity measured 20/25. OCT images showed no foveal depression, but prominent lengthening of foveal cones. The mfERG responses were normal, including the central foveal pixel, with amplitudes near the median for his age. Central cone images showed relatively normal cone diameter at 1-2 degrees of eccentricity, and only mild disorganization.
This study poses a dilemma: How can acuity be quite good without a foveal pit? The absence of a pit traditionally signifies poor vision, and poor visual acuity from macular dysfunction is typically associated with reduced mfERG. However, our data indicate that a pit is not required for foveal cone anatomic specialization nor for normal electrical responsiveness. The critical factors for visual acuity may be neither the anatomic pit nor cone numbers alone, but the degree to which direct cone-to-bipolar transmission is preserved in order to allow resolution and produce a local ERG response. These data give insight into the interrelationship of fundus pigmentation, foveal specialization, foveal pit, and visual acuity.
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