Posters

Refraction in keratoconus: subjective refraction vs automated refraction

Poster Details

First Author: A.Daxer AUSTRIA

Co Author(s):                        

Abstract Details

Purpose:

The measurement of the spherical and cylindrical refractive error in keratoconus is often difficult but of great importance for the determination of the preoperative status and the evaluation of the treatment success after surgical procedures. In this regard it is important to know how reliable different methods for the determination of the refractive errors in keratoconus are.

Setting:

Private practice and university hospital.

Methods:

We measured sphere, cylinder and cylinder axis in 200 keratoconic eyes and 200 normal controls by different methods (autorefractometer, wavefront analyzer and subjective manifest refraction) and compared the results via statistical evaluation (mean, standard deviation) of the different groups. The automated refraction measurments included Autorefractometer ARK-1 (Nidek Co.,Ltd, Japan), RK-F2 (Canon Inc., Japan) and ORK Wavefront (Schwind, Germany). All subjective manifest refraction measurements were performed by the Author.

Results:

The refraction (sphere, cylinder, cylinder axis) obtained from automated measurments showed an insignificant deviation from subjective manifest refraction in normal controls. In all examined cases (keratoconus, controls) the subjective refraction resulted in the best corrected visual acuity. The deviation of the automatic measurements from subjective refraction in keratoconus was significant for all devices. In more than 90% of the automated measurements deviated by more than 1 diopter in both, sphere and cylinder in all devices. In many cases the visual acuity tested by means of the refraction obtained by automatic measurements is even worse than the uncorrected visual acuity.

Conclusions:

While automated refraction measurements give excellent results in normal eyes with only minimal deviations from the subjective refraction this is not the cases in keratoconic eyes. In many cases of keratoconus these deviations are dramatic and it may even happen that the uncorrected visual acuity is even better than the corrected visual acuity with glasses obtained by automated refraction measurement. Automated refraction in keratoconus is not reliable at all.

Financial Disclosure:

None