Interval Visual Acuity Decay (IVAD) Test

The Interblink Interval Visual Acuity Decay (IVAD) test provides a precise measurement of visual function shown in real time.


Performing certain tasks that normally involve a protracted interblink interval can cause some problems for patients with ocular surface dysfunction. Ocular surface dryness and irritation can be exacerbated by these types of activities because of their association with a lower blink rate. For example, a prolonged visual task like working on a computer is associated with a prolongation of the interblink interval to as long as 12 seconds. For a dry-eye patient with a tear-film breakup time of three seconds, such long intervals are likely to lead to ocular discomfort. As the minutes tick by, ocular surface conditions can worsen, and keratitis may increase as a result of these successive, extended interblink intervals.

In terms of the interblink interval, it can often be difficult to measure a decrease in visual acuity. To counteract this, a test validated by researchers here at Ora was specifically developed to provide an accurate measure of visual function. The interblink interval visual acuity decay (IVAD) test provides a necessary measurement of visual function shown in real time. (Walker PM et al. IOVS 2007;48: ARVO E-Abstract 422)

A computer-based system presents the optotype Landolt C at the patient’s best-corrected visual acuity, and then visual acuity decay results are measured in milliseconds. The patients are instructed to track the orientation of the C by pressing a button on a keypad. During the patient’s interblink interval, his BCVA declines as the size of the stimuli decreases. (Visual function indisputably includes more than static visual acuity.) All in all, the capability of measuring visual acuity over time, in real time, is vital to obtaining precise information on everyday visual task performance.