Regional EuroTimes
Date Posted 14/09/2009
Mydriatic drops can skew aberrometry readings
Mydriatic drops can skew aberrometry readings
Wavefront analysis carried out in eyes treated with mydriatic eye drops can yield refraction values that differ by as much as +1.5 D from the values obtained in miosis, according to a study presented by Suphi Taneri MD, Augenkinik am St Franziskus Hospital, Münster, Germany
“The cycloplegic effect of mydriatic eye-drops of up to 1.5 D should be taken into account when interpreting aberration measurements and planning a wavefront-guided ablation to avoid refractive surprises.
The study involved 200 myopic eyes which were measured in miosis and pharmacologically induced mydriasis with the Zywave aberrometer and automated refraction. In 100 eyes the researchers induced mydriasis with were dilated with tropicamide 0.5 per cent +phenylephrine 2.5 per cent eye drops, the other 100 eyes with tropicamide 0.5 per cent. They compared the phoropter-predicted-refraction (PPR) for a pupil of 3.5mm in miosis and mydriasis and then correlated those to the values obtained with automated refraction.
They found that the PPR values obtained in mydriasis were significantly less myopic than in miosis. The sphere of PPR differed by an average of +0.23 D (range:-1.5 D to +0.8 D) when using tropicamide 0.5 per cent plus phenylephrine 2.5 per cent. With tropicamide 0.5 per cent eye drops alone the mean difference was +0.27 D (range: -1.3 D to +0.6 D). In both groups the cylinder and the axis remained unchanged. The age of the patient had no influence on the amount of the cycloplegic effect of the drops, Dr Taneri said.
Automated refraction yielded a smaller mean spherical difference of about +0.16 D and +0.11 D but had a similar range of about 2.0 D. Dr Taneri noted that mydriatics affected the aberrometer measurements more in terms of sphere and the autorefraction measurements more in terms of cylinder.
Dr Taneri pointed out that in eyes with insufficient natural pupil dilation wavefront-guided ablations are based on wavefront sensing over a pupil after the application of mydriatic eye-drops.
“Based on our findings, we conclude that ideally pharmacological pupil dilation should be avoided. This is what I call a silent revolution there are algorithms now to expand measured wavefront information without using mydriatic eye drops and thereby avoiding their influence on aberrometry measurements,” he concluded.
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