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        Foveal Dark Adaptation by Albert J. Hofeldt, MD.

 

​​    Can you imagine, using your iPhone to measure your foveal function?  Foveal Dark Adaptation (FDA) is a new measurement of photoreceptors behavior to light bleaching and recovery.  The iPhone, iPad and MacBook are the first to detect disease of the macula using FDA.

    FDA of the fovea could not be detected in the late 1800s when ERG (electroretinalgram) became able to measure the peripheral rods and cones with slower function.  The cones of the fovea were thought to be too fast to measure.

     In 1921, Selig Hecht, PhD at Columbia University in NYC was the first to measure the foveal function, called Foveal Dark Adaptation, which measured 7.1 seconds in duration using a red-cross target. Testing averaged 1.5 hours per test and that the pupil and room luminance were important variables.

In 2021, 100 years after Dr Hecht’s report, Albert J. Hofeldt, MD, was granted the US patent: Relative Focal Photo-Stress, US Patent 9,089,257. Hofeldt studies focused on the psychophysical properties of the bullseye target having a white center and a peripheral white annulus.  While the subject observes the bleaching light on the iPhone which is aligned with the center disc of the bullseye, changed the subject’s fovea from active to passive function (places the foveal cones to passive function). After 30 seconds of bleaching, the view expands to the diameter that allows the subject to see the complete bullseye target, the center fovea and the surrounding non-foveal rod and cones. Upon bleaching, the center disc turns dark and the peripheral annulus remains white. As the fovea recovers, the center starts turning whiter while the annulus starts turning darker, the moment the center appears whiter than the annulus is the endpoint.  Shifting the white balance from the peripheral annulus to the center disc is in accordance to Weber’s law, “There is only one bright object per visual field”.

     Foveal dark adaptation opens a numerical function for study in health and disease. The test is easy and precise, which makes it applicable for identifying macular disease by iPhone or iPad at home, the first test for screening macular disease.  The app has two models, MacHealth (99¢ for 30 tests) for all people and MacDx® for professionals ($99.00/month), both available from The Apple Store.

     The first article published in EYE, Nature’s Magazine: Relative Foveal Dark Adaptation: A Potential Method for Assessing Macular Health. 2024, J S Kane, M Gaspich, A Gold, H Pichardo, S A Kane. (Eye; https://doi.org/10.1038/s41433-024-03201-2) This study describes a novel method for measuring dark adaptation of primarily foveal cones relative to perifoveal rods and cones that utilizes the shift of a visual anchor on an iPhone as the endpoint after a relatively brief period of foveal bleaching. Relative foveal dark adaptation was studied in 6 normal subjects ranging in age from 20 to 81 years and across differing testing conditions. Testing times in normal subjects were typically less than a minute. An anchor shifting endpoint from surround to center of a bullseye stimulus following 30 s of foveal bleaching was reproducible and unaffected by ambient room lighting, pupil size, and light attenuation. Repeat, sequential testing was similarly reproducible except after long bleaching times. This paradigm more directly assesses macular health than currently available methods of dark adaptation that assess peripheral retinal health. It is intuitive and reproducible, and testing times are brief, requiring only an iPhone screen positioned at reading distance. Relative foveal dark adaptation may be a useful tool to assess macular health. One case of cystoid macular edema post-cataract was detected and treated. 

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