Ocular Motility and Binocular Vision Assessment

The doctor and technicians will perform simple tests of your eye movements, depth perception and measurement of the gross alignment of the eyes. The doctor will evaluate how your well eyes work together. Do you have binocular vision? Do both eyes work efficiently together with excess effort and fatigue? Do you have a full range of movement of your eyes? Is there double vision present or the potential for double vision when fatigued?  Do you have depth perception?

Is depth perception essential for driving?

Pure ocular depth perception is a high order skill. It requires good vision in each eye and both eyes working together with good binocular vision. Any reduction in visual acuity even in one eye immediately reduces depth perception. The maximum limit of ocular depth perception is based on far apart our eyes are which is about 58 to 70 mm. This eye separation limits our pure ocular depth perception in an automobile traveling at 55 miles an hour to only about one to two blocks ahead. And a Navy pilot landing a jet on an aircraft carrier cannot depend only pure ocular depth perception due to the speed and distanced at which his decision must be made.

Depth perception is often impaired in low vision patients. However other cues in the environment can be used to judge depth. While we test ocular depth perception in clinical settings with careful controls on other cues, in the real world our drivers use many cues both monocular and binocular to judge depth.

Artists understand and utilize many of these cues to show depth in a painting on a flat canvas. The first is relative size where objects farther away are smaller or perspective where lines of the road converge the farther from the viewer. Another cue is distance atmospheric fog, which causes a far object to be fainter than a near object. The artist paints distant mountains much fainter than closer mountains.

We may also judge depth by motion parallax, our observation of relative movement in the environment of stationary objects while we are driving. As you pass a sign it appears to move by you quickly while the sign a block away appears to move slowly.

Although vision loss can interfere with some of these cues, and some visually impaired drivers may lack binocular vision, bioptic drivers quickly learn to compensate just like the thousands of people who drive successfully with only one eye throughout there life.

The answer to our question “Is depth perception essential for driving?” is  no. It is preferred to have good ocular depth perception but not essential to operate an automobile.