Diagnostic Focus

Measuring Adaptation to Dark

Head-mounted testing device fits much like virtual reality goggles

The “Diagnostic Focus” column presents an optometrist’s firsthand experiences with a new device, via answers to questions posed by OM.

What is the AdaptDx Pro?

The AdaptDx Pro (MacuLogix) is a dark adaptation testing instrument. Dark adaptation delay was shown in the ALLSTAR study to be a biomarker for macular degeneration. The device works by testing a patient’s eyes’ ability to adapt from light to dark. A delayed dark adaptation time indicates the earliest stages of macular degeneration.

The AdaptDx Pro is unique because it is a head-mounted testing device — much like virtual reality goggles. It also has an on-board instruction voice that walks the patient through the testing.

For whom is it indicated?

Because the device aids in identifying the earliest changes in macular degeneration, it is indicated for anyone who is at risk for macular degeneration or who is starting to have symptoms related to early macular degeneration. Those at greatest risk include: smokers, people with a family history of macular degeneration, people over the age of 50 and people who have poor overall systemic health. The earliest symptom of macular degeneration is a reduction in night vision.

Additionally, the testing also is used as functional testing for patients who have active macular degeneration. Their rod intercept can indicate disease progression.

Image courtesy of MacuLogix

For whom is it contra-indicated?

The test can be taken by anyone. It has no contra-indications. However, it is not likely a younger person, under age 40, who has normal eye health will have delayed dark adaptation.

What does the device measure?

The device measures dark adaptation time and gives optometrists a value called “rod intercept.” This value is the time it takes rods in the macula to recover from light exposure.

What procedure do you follow?

We test every patient who is older than age 60 and those younger than age 60 who have AMD risk factors. Patients who have no evidence of AMD undergo the rapid version of the test as part of their pre-testing. The rapid test stops when the patient’s rod intercept is reached faster than 6.5 minutes. Otherwise, the test stops at 6.5 minutes and reports a failed screening. A failed screening prompts a return visit one to two weeks out for threshold testing. The threshold test does not stop at 6.5 minutes, but continues until the patient’s rod intercept is reached, for example, at 8.3 minutes. After rod intercept time is established, the patient reviews the testing with the O.D., who creates a treatment and follow-up plan.

How do you discuss the testing with the patient?

I explain that the macula is critical to their detailed vision and show them an image of their macula. I tell them the testing will determine whether their macula is showing the earliest signs of macular degeneration. I explain that during the test, they will see a small flash of light and then they will push a button when they see little circles show up where the small flash occurred. I explain what the test is assessing and that a healthy retina will recover in less than 6.5 minutes.

What staff involvement is there?

Our team explains to patients that we are going to do a screening test for AMD prior to their visit with the doctor. Generally, the team does not need to elaborate more. They do, however, have to explain that the instrument goes on the head, that it will test one eye and that there will be instructions provided by an on-board voice. MacuLogix does a good job of working with the team on communication. OM