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Michael G. Quigley, John V. Lovasik; Higher Intensity Retinal Light Levels In Spectacle Corrected Hyperopia Vs Myopia May Be Linked To The Increased Incidence Of Armd In Hyperopia. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4405.
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Age-related macular degeneration (ARMD) is more frequently associated with hyperopia than myopia. Inasmuch as spectacle lenses correcting myopia and hyperopia have opposing effects on the vergence of light entering the eye through the pupil, any refractive based differences in retinal illumination may be related to the patho-physiology of ARMD. Last year we reported that spectacle correction of ocular refractive errors between -6.00D and +6.00D resulted in a linear increase in retinal illumination originating from a light source of 5 white LEDs forming a 20 mm circular array 40 cm from the cornea. The objective of the present study was to determine whether a luminous patterned stimulus also placed a corrected hyperopic eye at greater risk to photic damage due to higher light intensities at the retina.
A model eye was built with adjustable refractive components, anterior chamber depth and axial length to create a range of refractive errors using population-based ocular biometric values from the Reykjavík Eye study. The anterior chamber depth and pupil were fixed to 3.2 mm and 3.0 mm respectively. A finger-type camera with a 7mm2 2 megapixel CCD was affixed to the eye through its back wall using a water-tight rubber bushing that provided a water tight seal and allowed the camera to be displaced along the A-P axis into the retinal plane for eyes with refractive errors between -3D and +3D. White luminous letters on a black background (iSnellen visual acuity chart for the iPad) served as the test object imaged at 2.4m and 0.4m. A J64 image analysis program from the NIH was used to provide grey level plot profiles for each image, as well as histograms providing the number of pixels for each grey level bin between 0 and 255.
Grey level plot profiles for space-averaged retinal light levels confirmed that spectacle correction of hyperopia vs myopia increased the mean retinal illumination. The space averaged retinal illumination for a corrected +3D hyperopic eye was ~4.72 % greater than a corrected -3D myopic eye. In addition, the pixel density histograms revealed that the hyperopic retina had ~6.87 times the number of maximal brightness pixels then did a corrected -3D myopic retina.
The increase in retinal light intensity following spectacle correction of hyperopia is an important factor associated with the higher incidence of ARMD in hyperopia.
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