A new quantitative model can determine a patients visual acuity based on wavefront aberration measurements, according to a study in the April 22 issue of Journal of Vision. Potentially, this would allow a machine to automatically produce optimal prescriptions for corrective lenses.

Until now, data generated by an aberrometer could not help assess visual clarity without subjective questioning and input from both the practitioner and the patient.
However, with this metric and model a wavefront aberrometer can generate an automated, objective measurement of visual acuity, which may then be used to automatically produce optimal prescriptions for corrective lenses, say the studys authors (who are NASA physicists).

For this study, the authors compiled and evaluated the performance of more than 30 metrics that predict visual acuity based on calculated refractive error and neurological image processing.

Then, they developed their own simple metric and model, which predicts visual acuity using both wavefront measurements and automated simulations of specific acuity target identification from the Sloan letter set.
The authors believe this predictive model could be used internationally because the metric will still work with other symbol/letter sets, such as Chinese characters.

So, will robots soon take over refraction? While this objective, automated model may have great utility in the future, several O.D.s believe that the technology is many years away from being applied in routine clinical practice.

There will always be an element of subjective evaluation of refractive error, and certainly practitioner judgment [when prescribing lenses], says Brian Chou, O.D., of Carmel Mountain Vision Care in San Diego. For example, specific eye diseases and conditions, such as age-related macular degeneration and amblyopia, will likely throw off visual acuity predictions in metrics and models.

Also, The authors seem to underestimate the significance and the patient-to-patient variability of neural effects in vision correction, says Lou Catania, O.D., of Jacksonville, Fla. They do not fully address the need to accurately measure and control contrast sensitivitythe most sensitive measurement of neuro-adaptationin predicting final acuities, nor do they propose an adequate method of quantifying such effects on acuity and its corrective potential.

Finally, could this technology ultimately reduce the need for O.D.s in prescribing corrective lenses? Not anytime soon, says Dr. Catania. Until a model is created to effectively replace optometrys good old mantra, Which is betterone or two?, optometrists will continue to have a role in refracting and prescribing. To date, this is the single most effective way to subjectively measure cortical influences on vision and visual acuity.

Watson AB, Ahumada AJ Jr. Predicting visual acuity from wavefront aberrations. J Vis 2008 Apr 22;8(4):17.1-19.

Vol. No: 145:06Issue: 6/15/2008