Pupil size and its effect on vision

Pablo Artal PhD   Because depth of focus increases with decreasing pupil size, there has been growing interest in developing approaches for creating a small pupil to correct presbyopia. However, it is important to understand that pupil size also affects multiple other parameters influencing vision.These issues were discussed by Pablo Artal, PhD, Murcia, Spain. Dr Artal said that findings from research performed in his laboratory show that compared with the use of monovision or induction of asphericity for the correction of presbyopia, a small-aperture approach is associated with similar binocular depth of focus. Unlike monovision, however, a small aperture technique does not significantly decrease stereoacuity. As another benefit, having a small aperture provides some tolerance to residual astigmatism, and with unilateral implantation of small aperture devices, binocular contrast sensitivity is not significantly reduced. A small aperture does reduce retinal illuminance, which raises concern about the potential for problems in dim light. However, it appears that patients with small aperture inlays or IOLs adapt relatively quickly to this issue. Although aberrations decrease and image quality improves with decreasing pupil size, Dr Artal emphasised that obtaining good image quality using small-aperture IOLs and inlays depends on precise positioning of the device. Natural pupil size is also an issue that should be considered when choosing patients for the annular aperture inlay, realising that light will enter the eye from around the outer margin of the inlay if the diameter of the pupil is larger than that of the device.