Project Gullstrand: Ocular biometry and straylight

September 14, 2009

Soft contact lenses can induce greater straylight issues in long-term users but those effects appear to be improved by LASEK surgery.

Barcelona-Soft contact lenses can induce greater straylight issues in long-term users but those effects appear to be improved by LASEK surgery, Dr. Joz Rozema told delegates of the European Society of Cataract and Refractive Surgeons.

Revealing some of the first results of the Project Gullstrand, Dr. Rozema presented data that showed preop LASEK patients demonstrated greater degrees of straylight, but after surgery they returned to the norm.

“We postulate that this might be caused by LASEK, because of course LASEK removes the epithelial surface which could be damaged by wearing contact lenses, and also anterior stroma, which might be damaged as well,” said Dr. Rozema.

This is one of the first results from the Project Gullstrand, an attempt to establish baseline data for common biometric results of vision quality tests currently available. It is a multicentre study with 1850 volunteers and uses both biometric and visual function tests to look for correlations between biometry and visual experience, in what Dr. Rozema termed as 'benchmarking' for the human eye.

In his address, Dr. Rozema showed how the project developed new biometric baselines for straylight. The straylight study had a cohort of 518 eyes and first tracked the effect of straylight on age.

From this the team could establish a measure they term Straylight BAC, or baseline age corrected. Next they turned their attention to the effect of spherical equivalent which showed a correlation between increasing myopia and increased incidence and severity of straylight. However, there was insufficient data to see any particular hyperopic effect.

When the team turned to pre- and postop LASEK patients they found a surprising result. Preop LASEK patients were systematically higher than the age model, but postop the patients followed the age model.

Further study revealed that the degree of correction did not impact the change in straylight, neither did retinal image size. However, the team argued that LASEK patients wish to be spectacle-independent, which would lead to greater contact lens use.

The group was divided into those using rigid contact lenses (RCL), soft CLs (SCLs), those who used spectacles after a period of using CLs and those who always used spectacles.

After correcting the straylight baseline for age and spherical equivalence (BASEC), the researchers discovered that BASEC straylight increases with contact lens wear and that this decreses postop for SCL users, but increases somewhat for RCL users.

The results are an early demonstration of the insights promised by the Gullstrand project.