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Optimum centration of small aperture corneal inlays

Session Details

Session Title: Intracorneal inlays for correction of presbyopia

Session Date/Time: Tuesday 08/10/2013 | 08:00-10:30

Paper Time: 08:48

Venue: Main Lecture Hall (Ground Floor)

First Author: : P.Artal SPAIN

Co Author(s): :    P. Artal   S. Manzanera   J. Tabernero   P. Prieto   A. Vilupuru   J.

Abstract Details


Quality of vision in patients with small aperture corneal inlays to correct for presbyopia depends on its proper centration. In practice, the inlay is usually positioned on the 1st Purkinje image but theoretically the optimum centration would be the achromatic axis. To compare these two references, we developed a new instrument to simultaneously determine both the 1st Purkinje image and the intersection of the achromatic axis with the pupil plane.


Laboratorio de Optica, Universidad de Murcia, Murcia, Spain


The novel instrument records images of the eye’s pupil and the 1st Purkinje reflection when illuminated with a semicircle of infrared LEDs. A second optical path permits patients to perform a subjective task to determine the achromatic axis. A liquid crystal spatial light modulator produces a small aperture conjugated to the subject’s pupil plane with a location that can be controlled by the subject. A chromatic stimulus (inner red and outer blue cross) is then projected into the eye. Subjects perform a Vernier-type alignment task by moving a 1-mm aperture over the eye’s natural pupil to align a red target to a blue grid. Both the positions of the 1st Purkinje reflection and the achromatic axis intersection are determined simultaneously. Series of data in 33 eyes with a range of +/- 4 D refractive errors were obtained.


The standard deviation in the measurements was below 0.18 and 0.04 mm for the achromatic axis and 1st Purkinje positions respectively. The average location of the achromatizing pupil was: x = 0.29 ± 0.19 mm (nasal); y = 0.09 ± 0.19 mm (superior). The location of the 1st Purkinje image was: x = 0.34 ± 0.19 mm; y = 0.07 ± 0.07 mm. The differences in the two locations were smaller than 0.4 mm for both directions in all the measured eyes.


To determine the optimum centration of small aperture inlays, we have measured simultaneously both the locations of the 1st Purkinje image and the achromatic axis intersection with the pupil plane. On average, both locations coincide within the measurement errors. Although there is individual variability, the maximum differences in location of both marks did not exceed 0.4 mm in any eye. Even in those patients, this relative de-centration would induce a modest amount of transverse chromatic aberration. This indicates that centration of the inlay on the 1st Purkinje image should be adequate for most patients.

Financial Interest:

... is employed by a for-monetary company with an interest in the subject of the presentation, ... receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented

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