Developing glare tests

Oliver Stachs PhD

The importance of testing glare disability in patients is increasing as surgical technology and patient expectations advance, Oliver Stachs PhD told delegates attending a Clinical Research Symposium on Dysphotopsia at the XXXIII Congress of the ESCRS in Barcelona, Spain.

“Clinicians and researchers need to understand the principles behind halo and glare measurement in order to be able to use available measures,” he said.

Prof Stachs, University of Rostock, Germany, noted that simply defining glare and halos is fraught with difficulty, as the terms have many different meanings to different people.

“When a patient states that they have problems with glare or halo, there are many distinct visual effects that they may be describing. In order to address the problem we first need to find exact definitions for glare and halo, identify methods for objective quantification and define baseline values. My personal opinion as a physicist is that it is difficult to give exact definitions for halo and glare due to the overlap between neural and intraocular light scattering effects,” he said.

NEURAL COMPONENT

The standard example of glare disability is caused by oncoming headlights, said Prof Stachs, with two main reasons for the discomfort: firstly, the neural component related to the period of light adaptation required by the photoreceptors; and secondly, the reduction of contrast in the retinal image.

Dysphotopsia – defined as the introduction of unwanted patterns on to the retina after intraocular lens implantation – takes two main forms: positive and negative, said Prof Stachs.

Approaches to quantifying glare include subjective methods such as score charts or patient questionnaires, or objective methods using any one of a number of devices currently available such as the halometer, glaremeter, stray light meter, brightness acuity tester, Berkeley glare test and straylight meter. While there is a wide range of commercial devices on the market purporting to objectively measure dysphotopsias, the lack of agreed standards and definitions makes it difficult to assess their efficacy, said Prof Stachs.

Going forward, Prof Stachs said there was a need for some universally agreed method to quantify halos and glare. “Successful glare tests that are cheap, accessible, valid and reliable are required,” he added.

Oliver Stachs:

oliver.stachs@
uni-rostock.de