Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation

Abstract

Measurements of posterior cornea have on average only a small but significant impact on the outcome of toric IOL calculation, however, they are nevertheless recommended to detect outliers in which corneal irregularities (e.g. beginning keratokonus) may be overlooked.

Age‐related changes in with‐the‐rule and oblique corneal astigmatism

“…Conversely, for the 80-89 years old with average keratometric ATR astigmatism, TCA was larger than KA. This discrepancy between TCA and KA has practical significance in toric IOL calculation, where measurements based on TCA are recommended (Koch et al 2013;Ueno et al 2014;Preussner et al 2015;Savini & Naeser 2015).…”

New regression formula for toric intraocular lens calculations

“…These findings correlate well with the finding by Koch at el., 9 who reported a steep posterior corneal meridian aligned vertically (WTR) in 86.6% of 715 corneas of 435 consecutive cases, as well as with findings in other studies. 11,18 Because the posterior cornea acts as a negative lens, the effect of the posterior cornea will cause anterior corneal measurements to underestimate the total corneal astigmatism on the horizontal meridian. Thus, using anterior corneal measurements for toric IOL calculations tends to lead to ATR prediction errors of the postoperative residual astigmatism, which could result in overcorrection of eyes with WTR astigmatism and undercorrection of eyes with ATR astigmatism.…”

Toric Intraocular Lenses in the Correction of Astigmatism During Cataract Surgery

“…54 Thus, the ratio between anterior and posterior corneal curvature is not constant throughout life. Although the contributions from the posterior corneal curvature are small, they are significant 55 and the main cause for astigmatic refractive errors after toric IOL implantation. 56 This calls for individual preoperative evaluation of the posterior corneal curvature.…”