CLINICAL APPLICATIONS & DISEASE - Refractive Surgery

Clinical Applications & Disease > Refractive Surgery

Summary from: "Functional vision should be documented before and after refractive surgery." (In references, see: Functional vision should be documented before and after refractive surgery).

How good is the functional vision of a patient before refractive surgery? Which laser system and refractive surgical procedure offers the best result for the patient? If the anticipated results of the refractive surgery are not achieved, how good is the functional vision of the patient? How are the patient's expectations managed?

At the International Society of Refractive Surgery meeting in 1996, Dr. Arthur P. Ginsburg of Vision Sciences Research Corporation (VSRC) showed how a battery of functional vision tests help answer these types of questions. Functional vision testing includes visual acuity, contrast sensitivity, VSRC's EyeView® pictorial analysis, corneal topography, daily activities questionnaire, lifestyle considerations and driving simulation results.

Personal Expectations Patients who choose refractive surgery have varied personal expectations. If those expectations are not met, serious complaints can be voiced. One common complaint is the loss of quality of vision, such as walking or driving at night. It is necessary to manage patient expectations before and after surgery. It is also important to determine if the visual complaint is functionally significant. Functional vision is more easily understood when combining visual acuity results with contrast sensitivity, illustrating and relating the results with processed pictures and night driving.

It is well established that visual acuity alone cannot describe the functional vision of patients nor does visual acuity accurately distinguish important differences between different lasers and refractive surgical procedures. Additional information is needed.

Contrast Sensitivity Contrast sensitivity is initially used for proper patient selection by establishing a baseline and by determining whether eye disease, vision disorders or effects from drugs may affect outcomes. A post-op contrast sensitivity test measures the effectiveness of the surgery by comparing the results to pre-op contrast sensitivity. Tracking the results of refractive surgery with contrast sensitivity helps to determine the optimum laser system and surgical procedure.

Sine-wave grating contrast sensitivity testing using the FACT chart, shown below, is used rather than low contrast letter acuity charts because gratings have the highest sensitivity and specificity to contrast loss. Contrast sensitivity is directly related to the optical transfer function of the eye and relates more strongly to the functional visibility of everyday objects. Patients with higher contrast sensitivity before surgery will have more of a functional vision reserve after less optimum results than will patients having lower contrast sensitivity.

FACT Sine-wave Grating Test Chart

EyeView simulations, as shown below, explain what visual acuity and contrast sensitivity curves mean in terms of pictures. EyeView pictures document the patient's vision before surgery without correction, show the patient how they may see after surgery, and their improved vision after surgery. Thus the patient can compare uncorrected pre- and post- surgical EyeView pictures to target correction pictures to appreciate the outcome. Contrast sensitivity and EyeView pictures can be used to track and show improved vision from procedures over time.

This graph and picture analysis was generated by EyeView®, an image processing software developed by Vision Sciences Research Corporation.

Night driving capabilities of these patients are understood from the VSRC Night Driving Simulator, shown below, which was developed using FDA protocol guidelines. Sine-wave contrast sensitivity using the FACT chart is related to the detection and identification of road message signs, warning signs and pedestrian hazards for rural and city driving scenes under clear, fog, and glare visibility conditions. Similar to previously published research by Dr. Ginsburg and others, the peak area of the contrast sensitivity curve (which is only measured accurately by sine-wave gratings) best relates to this driving task. Decreased sine-wave contrast sensitivity measures decreased detection and identification distances of these targets. These data are used to determine the night driving capability of patients who may have complaints but are not functionally compromised.

VSRC's Night Driving Simulator (NDS)

This approach provides outcome measures that can determine which laser and refractive procedures are optimum for different optical problems and offer unique patient selection and management tools and information.

Clinical Applications & Disease > Refractive Surgery

 

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