Visual Performance in Dry Eye Patients
Visual Performance in Dry Eye Patients
By Gary N. Foulks, MD, FACS
We now know with certainty that dry eye disease affects vision, so that, in addition to ocular discomfort and red eyes, patients may also suffer functional impairment. Dry eye disease can produce visual symptoms by two mechanisms. Fairly early in the course of the disease, growing tear film instability can lead to tear film breakup between blinks, with a concomitant decrease in vision. Patients often compensate for this by blinking frequently, which restores the continuity of the tear film, and clears vision for a few seconds.
Patients with an unstable tear film often experience changes in vision when they are doing intense close work, such as reading or using the computer, or when they become tired—as all of these conditions reduce blink rate. Because the patient can blink while looking at a Snellen chart (and get an instant boost in vision), this form of acuity loss is often missed in standard testing.
In later stages of the disease there can be physical alteration of the ocular surface that affects vision. Epithelial damage or breakdown can produce ocular surface irregularity that can’t be corrected by blinking. The specific problems may range from adherent mucus or filaments on the corneal surface to punctate keratopathy. This type of visual impairment doesn’t significantly improve on blink, so it can often be detected in routine Snellen acuity or contrast sensitivity testing.
Quantifying Vision Impairment
How significant is the visual disturbance in dry eye? To quantify visual disturbance, Japanese researchers have developed a functional visual acuity test system. This test platform employs a rapid projection system that requires patients to react quickly to a projected image. In this way, the device is able to measure changes in vision in the brief space between blinks. The interblink interval visual acuity decay (IVAD) test, a newer system developed in the US, works on a similar principle. While these devices will likely find application in clinical trials, they are too expensive and too cumbersome for routine office practice.
It is, however, important for eyecare practitioners to determine qualitatively whether a patient is experiencing visual symptoms related to dry eye disease—even if the extent of the impairment is not quantified. When patients understand that their visual function is being reduced by their dry eye disease—that the condition causes more than just discomfort—they are more likely to comply with treatment recommendations. The goal is to get patients to be proactive with the interventions we have available, and not wait until symptoms are bad before, for example, instilling a lubricant drop.
Interventions To Restore Visual Function
Interventions for dry eye disease-related visual impairment fall into two main categories: environmental/behavioral modifications and therapeutic agents. Environmental modifications, which are designed to reduce evaporation from the tear film, may include repositioning a computer monitor so that it is at or below eye level, increasing ambient humidity with a humidifier, and avoiding air currents from air conditioners, heaters, and fans.
Therapeutic treatments include lubricant eye drops, which aim to restore the integrity of the tear film, thus restoring clear vision. Very viscous drops have the advantage of remaining on the eye, but their downside is that they blur vision (precisely the opposite of what is wanted). Some newer lubricant eye drops employ shear reducing polymers that help stabilize the tear film without significantly increasing blur.
Patients should be counseled to incorporate both environmental modifications and therapeutic treatments into their daily routine. The greatest effect comes when lubricating drops are taken proactively on a schedule, rather than by reacting to symptoms after they become noticeable.
When surface damage is present, contact lenses may improve the integrity of the ocular surface and improve vision. Bandage soft contact lenses or scleral lenses of high oxygen permeability can be helpful in managing both the surface problem and visual function.
Gary N. Foulks, MD, FACS, is the Arthur and Virginia Keeney professor of ophthalmology, University of Louisville, Louisville, KY, and is editor-in-chief of The Ocular Surface.