Refractive, anterior corneal, and internal astigmatism in the pseudophakic eye

Session Details

Session Title: Imaging

Session Date/Time: Tuesday 16/09/2014 | 08:00-10:30

Paper Time: 09:33

Venue: Capital Hall B

First Author: : K.Næser DENMARK

Co Author(s): :    J. Bregnhøj   P. Mataji           

Abstract Details

Purpose:

To evaluate the correlation between refractive astigmatism (RA) and anterior corneal astigmatism (ACA), and determine the internal astigmatism (IA) in 184 pseudophakic eyes.

Setting:

Department of Ophthalmology, Randers Regional Hospital, Denmark

Methods:

The study was a prospective non-masked single-centre study. Patients were examined 8 weeks after phacoemulsification with implantation of aspheric one-piece monofocal, non-toric IOLs. Examination included autokeratometry and subjective refraction. All refractive data were converted to the corneal plane. The corneal refractive index, taken to be 1.376, was used to estimate the ACA. All astigmatisms were converted to Næsers polar values with the steeper corneal plane as the reference meridian. The internal astigmatism (IA) was calculated as the difference between RA and ACA. In the pseudophakic eye the IA largely represents the posterior corneal astigmatism.

Results:

The refractive astigmatism could be described as a function of anterior corneal astigmatic magnitude and direction α by the multiple linear regression equation: RA= -0.09 + 0.61*ACA + 0.33*cos2α, (r2 = 0.59, p < 0.0001). The average internal astigmatism amounted to 0.47 D inclined 92 degrees relative to the steeper anterior corneal meridian. The magnitude of internal astigmatism depended on the angle α of the steeper anterior corneal meridian, averaging 0.86 D @ 91 degrees for with-the-rule, 0.37 D @ 95 degrees for oblique, and 0.17 D @ 97 degrees for against-the-rule corneal astigmatisms. All directions are relative to the direction of the anterior corneal meridian.

Conclusions:

The internal astigmatism varies as a function of the direction of the anterior steeper corneal meridian. In patients candidates to surgical correction of astigmatism, measuring only the curvature of the anterior corneal surface and neglecting that of the posterior corneal surface can lead to inaccurate evaluation of total corneal astigmatism.

Financial Interest:

NONE