Abstract
Purpose: :
To evaluate the performance of monofocal, bifocal and multifocal contact lenses that could provoke an increment of intraocular scattered light under glare conditions. Two different psychophysical methods have been used in order to test their capacities to be used in clinical measurements.
Methods: :
Two different methods were evaluated. In one of them we measured contrast sensitivity with and without a glaring source. In this case we determined contrast threshold of sinusoidal gratings of 1 c/d with a QUEST method and an orientation discrimination task. The glare source produced an illuminance of 500 lx on the pupil and the mean luminance of the display was 70 cd/m2. Light Scattered Factor (LSF) was calculated for each evaluated condition. In the other method subjects compared the brightness of a standard patch presented under transient glare conditions (E = 60 lx and 30 lx) to the brightness of a test with the glare source turned off. The matching luminance value was used to evaluate the scattered light. Both methods were applied to test the three hydrogel contact lens designs: monofocal, multiconcentric bifocal (Acuvue Bifocal) and asymmetric aspheric multifocal (Proclear Multifocal). Four subjects wearing monofocal, bifocal, multifocal lenses and with naked eyes (control) performed both kinds of measurements.
Results: :
LSF shows that the performance of monofocal lenses is better than bifocal and multifocal lenses under glare conditions. Also there is a weakly advantage in the performance of multifocal lenses compared with bifocal lenses, but this difference could depend on the specific design of the lens. The presence of different transition zones in the contact lens design should increase the intraocular scattered light. Results with the brightness comparison experiment showed the same trend.
Conclusions: :
Both test methods show an acceptable sensitivity to discriminate the effects of different designs of contact lenses on the intra ocular scattered light. In future work, we will improve different methodology aspects in order to discriminate which technique is more appropriated to be implemented in clinical measurements.
Keywords: contact lens • contrast sensitivity • perception