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Aixa Alarcon, Rosario G. Anera, José R. Jiménez, Luis Jiménez del Barco, José J. Castro, Carolina Ortiz; Visual Evaluation Of Different Multifocal Corneal Models For The Correction Of Presbyopia With Laser Ablation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5758.
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To evaluate the visual quality of two multifocal corneal models designed to correct presbyopia by corneal photoablation, taking into account the effects of decentring and pupil size.
Two multifocal corneal surfaces were analysed: center near (CN) model (with a central zone for near vision and a peripheral zone for distance vision), and center distance (CD) model (with a central zone for distance vision and a peripheral zone for near vision).To assess the visual quality, we calculated the Neural Sharpness (NS) determined by the Point Spread Function. The analysis was made using the Liou-Brennan eye model and ray tracing with the commercial optical-design software ZEMAX.
We have compared the visual quality in near and far vision for the two corneal models as a function of the diameter of the central zone obtaining the best quality with 2.5 mm of central zone diameter. Regardless of the size of the central zone, the visual quality is overall better in the CN model.Figure 1 represents the NS for the two models (central zone diameter: 2.5mm) for different pupil sizes. It can be noted that considering a certain degree of miosis when focusing on a near object, the center near model provided better visual quality both for near and far vision.
Considering a decentring towards the nasal side when the pupil size decreases, we found that for pupils smaller or equal to 3 mm, the visual quality provided by the peripheral zone was appreciably favoured by the decentring of the pupil, as opposed to what occurred in the central zone. The effect was not significant in larger pupils.
This work shows that decentring and pupil size are decisive for choosing a certain design that offers multifocality. Comparing the two multifocal models, we found that the multifocal cornea with the central near zone appears to be the most effective alternative to provide the presbyopic subject good visual quality both in near as well as in far vision.
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