Total corneal astigmatism in older adults taking into account posterior corneal astigmatism by ray tracing

• Autores: Alvaro Rodríguez Ratón, Xavier Orbegozo, Iñaki Basterra
• Localización: Journal of Emmetropia: Journal of Cataract, Refractive and Corneal Surgery, ISSN-e 2171-4703, Vol. 4, Nº. 4, 2013, págs. 179-184
• Idioma: inglés
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• Resumen

  • PURPOSE: To study the composition of corneal astigmatism in older adults, evaluating the difference made by the inclusion of posterior corneal astigmatism in a ray tracing calculation of total corneal astigmatism.

    SETTING: Ophthalmology clinic.

    METHODS: One hundred consecutive patients aged between 60 and 80 years were included in a prospective descriptive study. Their right eye was analysed by an integrated Placido disk and rotating Scheimpflug camera topographer (CSO™ Sirius). Several parameters were measured: anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA), total astigmatism based on anterior topographic data (simK) and total corneal astigmatism (TCA) by merging anterior and posterior astigmatism using ray tracing.

    RESULTS: Mean ACA was 1.51 diopters (D) and PCA was 0.38D. ACA was aligned 47% with-the-rule and PCA 87% against-the-rule. Cases with against-the-rule ACA showed low magnitude correlation between anterior and posterior surfaces. TCA had a mean deviation of 0.30D @ 3 over SimK in a vector calculation. Eighteen percent (18%) of cases differed by 0.50 D or more between SimK and TCA magnitude, and 53% had 10 or more degrees of axis discrepancy, the difference being higher at lower magnitudes of astigmatism.

    CONCLUSIONS: Anterior WTR astigmatism tends to be compensated by posterior ATR astigmatism in older patients. Nevertheless, the high number of cases largely justifies the use of tomographic technology that takes into account the posterior corneal surface for managing individual total corneal astigmatism.