Intraocular Straylight (Glare) After LASIK Surgery

Intraocular straylight (glare) can occur after LASIK surgery

To date, for most post-LASIK surgery patients, the assessment of visual performance involves no more than the measurement of Snellen acuity. However, despite the advances in laser technology, a minority of patients still suffer a permanent reduction in visual quality (contrast sensitivity), most commonly associated with an increase in higher order aberrations and/or intraocular straylight. An assessment of visual performance in the contrast domain is, therefore, an essential part of any post-refractive surgery eye examination. Intraocular straylight is considered as one of the side effects or patients’ complaints after LASIK that are known to have an impact on visual performance. This article focuses primarily on visual outcome after LASIK surgery which is commonly expressed in terms of corneal morphology which can possibly lead to the phenomenon of intraocular straylight.

What is intraocular straylight?
In the simplest terms, an abnormally increased intraocular straylight can be defined as a “disability glare” which occurs due to light scatter in the optic media of the eye, which results in a veil of straylight over the retinal image. In an ideal eye there, there would be no light scattering at all, but the eye media are not optically ideal. Some of the rays entering the eye are dispersed by optical imperfections of the refracting elements. These dispersed rays spread over the retina with decreasing densities at distances farther away from the focal point of the eye.

It must be remembered that the levels of intraocular straylight found in a normal eye under average lighting conditions do not tend to have any impact on vision. Straylight, however, is increased in the presence of an intense glare source, which can lead to a reduction in visual performance (disability glare). The effect is much more dramatic in those suffering from an increase in baseline intraocular light scatter (e.g. post-LASIK) and is one of the side effects of refractive surgery such as LASIK. It causes reduction in the contrast of the retinal image, thus decreasing quality of vision in such people and patients may experience blinding from oncoming traffic lights at night.

What can cause intraocular straylight after LASIK?
Currently, LASIK is by far the most popular refractive procedure undertaken in the world and the speed of visual recovery is a major factor in its popularity with patients. Stabilization of the refraction occurs in the majority of eyes by around six months post-LASIK. From this point forward, following conventional LASIK, the percentage of eyes achieving 6/6 or better unaided, ranges between 83- 100%. However, in some rare cases, reduced quality of vision resulting from the abnormally increased intraocular straylight has been reported.

One major source that contributes to the total amount of intraocular straylight is the cornea and it is now well known that corneal light scatter may increase after refractive surgery (LASIK), mainly after surface ablation, due to the healing process. With Laser in-Situ Keratomileusis (LASIK) currently being one of the most widely used laser refractive surgeries, it is necessary to assess the quality of vision as well.

It is now widely believed that both the flap formation during LASIK and the wound healing process after surface ablations contribute to the final optical properties of the eye and both situations may interfere with the intraocular straylight.

All in all, based on the above observations and findings, the vast majority of LASIK patients has no complications and maintains their visual quality as judged by visual acuity, contrast sensitivity and intraocular straylight after LASIK. With advanced ablation techniques, there seem to be even a potential to have improved visual quality post operatively. Therefore, it can be concluded that various advances in refractive surgical techniques have resulted in a higher proportion of patients achieving functional unaided vision following surgery. Thus, it can be said that the modern LASIK procedure is safe and effective. However, it is essential that practitioners incorporate suitable tests into their assessment in order to obtain a full picture of any visual problems and hence select the correct management strategy.

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