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Nika Priest-Allen, Rominder Momi, Bret Hughes, Chaesik Kim, Justin Tannir, Kresge Eye Institute/Wayne State University; Evaluation of Keratometry Measurements by IOL Master with Variable Degrees of Eccentric Fixation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2557.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effects of eccentric fixation on keratometry readings and axial length during IOL Master measurements in adults in order to quantify the degree of fixation loss causing a clinically significant amount of incorrectly measured astigmatic error when using the IOL Master.
Subjects: 29 eyes from 17 volunteers recruited from Kresge Eye Institute residents and faculty. Age range 26 to 65 years, mean 38. Exclusion criteria: visual acuity <20/60, stereopsis >80 seconds of arc, monocular status, strabismus, history of strabismus surgery and/or patching, known corneal or macular disease.Measurements of keratometry and axial length were obtained with the IOL Master. Baseline measurements served as the control for each eye. Testing was performed 45 minutes after instillation of cycloplegic eye drops for paralysis of accommodation, which was necessary to induce the desired gaze deviation with prisms while suppressing convergence. Eccentric deviation was induced using 2,5,10 diopter prisms placed base-in over the non-test eye. Axial length and keratometry measurements were obtained for each prism. Raw values K1, K2, and meridian given by IOL Master were used to calculate Kh (horizontal component) and Kv (vertical component) for each measurement obtained using equations for calculating points on an ellipse (see figure). x=ab /√b^2+a^2(tan^2θ), y=ab(tanθ)/√b^2+a^2(tan^2θ), Kv,h=x/cosθ=y/sinθ.
T-test, ANOVA, regression analysis of data comparing baseline Kh, Kv, axial length to Kh, Kv, axial length obtained with 2, 5, 10 diopter prisms. R^2 values show no statistically significant difference in keratometry values from baseline.
There was no statistically significant change in keratometry and axial length values measured by the IOL Master when a deviation of 2, 5 and 10 prism diopters was induced. The study demonstrates that eccentric fixation of up to 10 prism diopters does not significantly alter the keratometry and axial length measurements obtained by the IOL Master. However, there appears to be a trend toward decreased axial length with increasing deviation, which has the possibility of greatly changing the spherical IOL power.
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