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Rony R. Sayegh, Claes H. Dohlman, Eli Peli; Evaluation of the Through-focus Curve of the Boston Keratoprosthesis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1395.
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To measure the through-focus curve for eyes implanted with a Boston keratoprosthesis (KPro) and compare it to that of pseudophakic controls with a fixed pupil sizes.
Autorefraction and subjective refractions were obtained. The through-focus VA curve was plotted in reference to the BCVA by spectacle defocus ranging from +5.0D to -5.0D in 0.5D increments. Ten KPro-implanted eyes and 3 pseudophakic control eyes were included. Through-focus curves were obtained on the KPro eyes, and undilated controls as well as dilated controls fitted with black painted contact lenses with a 3mm and 2mm pupil respectively.
Good agreement was noted between the subjective refractions and autorefraction (possible in 6 eyes), with a mean difference of 1.0±1.0D. The average depth-of-focus curve of the KPro was flatter than all three controls curves. For an error in correction of 0.5D we found a drop in acuity of 0.13 (6), 0.09 (4), and 0.08 (4) logMAR (letters), for the undilated, 3mm pupil and 2 mm pupil control subjects, respectively and only 0.05 (3) logMAR (letters) for the KPro eyes. Similarly for a 1.0D error, acuity dropped by 0.25 (13), 0.18 (9), and 0.15 (8) logMAR (letters) , for the undilated, 3mm pupil and 2mm pupil control subjects, respectively and only 0.10 (5) logMAR (letters) for the KPro eyes. Higher steepness of the KPro through-focus curve was noted in patients with better BCVA and younger age.
Known factors (pupil size, age and VA) influence the through-focus curve of a KPro eye similarly to a non-KPro eye. The KPro’s wide depth-of-focus makes it less dependent on an exact refractive correction and counters the necessity of 0.1D increments in manufacturing; the manufacture of 0.5D increments appears sufficient. The autorefraction, when possible, provides a good estimate of the refraction. It is interesting that cylinder was observed in some cases, possibly due to tilting of the device.
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