Visual symptoms and aberrations

Researchers study the relation between the two.

Map of patient after wavefront
retreatment with reduced spherical
aberration and coma, though some
coma is still present.
Source: Brian Boxer Wachler, M.D.

While researchers often discuss higher-order aberrations (HOAs) and whether they lead to visual symptoms, it is also worthwhile to understand which visual symptoms are related to which aberrations.
Maria Regina Chalita, M.D., The Cole Eye Institute, Cleveland, and colleagues published a study in the March 2004 issue of Ophthalmology that correlated HOAs with symptoms such as glare, halos, and double vision. It is a study, also co-authored by Ronald K. Krueger, M.D., medical director of refractive surgery, The Cole Eye Institute, which HOA researchers continue to find valuable and use today.
“This is a good study to use,” said Brian S. Boxer Wachler, M.D., director, Boxer Wachler Vision Institute, Beverly Hills, Calif. “It shows correlations of aberrations with symptoms, which is important.”
Scott MacRae, M.D., professor of ophthalmology and visual science, University of Rochester (N.Y.) Medical Center, agreed.
“This is an interesting study,” Dr. MacRae said. “It’s the first study that really looks at the effect of higher-order aberrations on subjective symptoms.”

Conducting the study

In the study “Wavefront analysis in post-LASIK eyes and its correlation with visual symptoms, refraction, and topography,” researchers analyzed 105 eyes (58 patients) to make their correlations.
Measurements were taken with the LADARWave (Alcon, Fort Worth, Texas). All patients had LASIK surgery sometime between 1995 and 2001. Wavefront maps were assessed using three different pupil sizes. Those included the 5 mm, 7 mm, and the scotopic pupil size. Coma aberration also was divided into vertical and horizontal components.
Four optical symptoms were studied: halo, glare, double vision, and starburst. Patients were asked whether they had such symptoms and whether they considered them to be significant.
Researchers found 69 eyes with halos, 66 eyes with glare, 32 eyes with double vision, and 35 eyes with starburst.
Those symptoms then were compared with vertical, horizontal, and total coma; spherical aberration; other HOA terms; and total aberration measurements for the pupil sizes studied.
“An interesting observation of our data is the strong correlation of most of the reported visual symptoms with one or more of the higher-order aberrations when analyzed with the scotopic pupil size,” Dr. Chalita wrote in her study.

X aberration means Y symptom?

While the scotopic pupil size turned out to be an important factor in the correlation between aberrations and symptoms, it wasn’t the only size that mattered.
“Double vision was associated with horizontal coma at all pupil sizes analyzed, and total coma was associated with double vision for a 5-mm and 7-mm pupil size,” Dr. Chalita wrote in her study. However, vertical coma did not appear to yield optical symptoms in the study, “showing that not only is the amount of coma important but also its orientation.”
Dr. Boxer Wachler said that his experience is similar with coma in that it leads to monocular double vision.
“The reason it does is that it is like a ‘mini-keratoconus’ pattern where one area on topography is relatively steeper than the area 180 degrees opposite to it,” Dr. Boxer Wachler said.
Halos were associated with spherical aberration for the scotopic pupil size.
“I find this as well,” Dr. Boxer Wachler said. “The reason is that if you look at the very center of the topography and look towards the periphery, the corneal power gets steeper. If the steeper power transition occurs relatively close to the center of topography – as in higher myopes, and/or smaller laser optical zones – this causes more spherical aberration.”
Glare also was significantly correlated with spherical aberration and total aberration. Starburst was associated with spherical aberration and total aberration for the scotopic pupil size.
“Less intuitively, for the 7-mm pupil size, starburst was inversely associated with total coma,” Dr. Chalita concluded.

Challenges in methodology

This study was a very difficult one to perform, said Dr. MacRae, who has considering putting his own analysis together to correlate HOAs and symptoms.
“I think they did an excellent job of probing a very challenging area because it’s hard to get good objective data from subjective questionnaires,” Dr. MacRae said. “Everybody has a different idea as to what double vision is versus blurred vision versus starbursting. It’s very interesting to try to tease out the aberration patterns relative to the subjective symptoms.”
Dr. Boxer Wachler agreed, saying that some patients use “glare,” “halo,” and “starburst” interchangeably.
Nonetheless, Dr. MacRae said, just by having a large patient group respond to a questionnaire, researchers can get patterns of data that are meaningful.
“Even though it’s an imperfect science, it evens out in the sense that you are getting the popular opinion about what is considered starburst or what is considered halo,” Dr. MacRae said.

Editors’ note: Dr. MacRae is a consultant for Bausch & Lomb (Rochester, N.Y.). Dr. Boxer Wachler is a consultant for Alcon. Dr. Chalita has no financial interests in her study. Dr. Krueger receives travel and research support from Alcon.

Contact Information
Boxer Wachler: 310-860-1920, bbw@boxerwachler.com
Chalita: +55-61-344-0507, mrchalita@hotmail.com
Krueger: 216-444-8159, krueger@ccf.org
MacRae: 585-341-7817, Scott_MacRae@urmc.rochester.edu