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D Poinoosawmy, J Tan, DF Garway-Heath, FW Fitzke, R Hitchings; Does Change in Lens Refraction Affect the Size of Images in Scanning Laser Tomography? . Invest. Ophthalmol. Vis. Sci. 2002;43(13):268.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study the effect of changing 1) refractive ametropia and 2) scanning distance on the image size of the optic disc in scanning laser tomography. Methods: A simulated optic disc in a model eye was imaged using the Heidelberg Retina Tomograph. Lens power in this model eye was alterable by exchanging intraocular lenses (IOLs) to mimic refractive changes caused by the lens. IOLs were positioned in a holder at the normal lens plane of the eye and made of PMMA and rigid (+16D to +25D; diameter=7 mm). We determined the IOL power and axial length for emmetropia then kept axial length constant. The model eye’s optic disc was imaged through IOLs of different strengths. This was then repeated with the scanner positioned at different distances from the model eye for each lens’ strength. Image size was represented by the transverse distance in a topography image as measured by pixels. Results: Image size increased as IOL power increased with their relationship roughly linear (r=0.97, p<0.0001), although the strength of this relationship tended to differ at different scanning distances. The effect of scanning distance on magnification was very small in emmetropia but increased with induced myopia (more positive IOLs). With increasing myopia, longer scanning distances caused increasingly more magnification than shorter distances. For a given scanning distance, a +2D increase in IOL power relative to emmetropic lens power resulted in image size increasing by about 5%. Conclusion: Changing lens power can affect the size of optic disc images in scanning laser tomography. Possible causes of this are cataract and accommodation. Scanning distance can also influence magnification, especially with increasing degrees of myopia associated with lens change. These should be noted when monitoring the optic disc to detect sequential glaucomatous change.
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