Early, dry AMD does not get the attention it deserves. In fact, it is a topic that many eye care providers do not get too excited about. In my opinion, there are a few reasons why some clinicians are so dispassionate about early AMD, but the two biggest are lack of patient symptoms and a perceived lack of treatment options. Here, I will explain why early AMD deserves more attention and describe what we can do to help patients in a meaningful way.
AMD Is a Huge, Expensive Problem
To begin, AMD is not a small problem that affects only a handful of our patients. On the contrary, in the UK, AMD affects one in 12 patients over age 40, one in six people over age 60, and one in three patients over age 75. This represents more cases than glaucoma and diabetic retinopathy combined.
Fortunately, there are some excellent treatments for late stage wet AMD, but these are extremely expensive, costing billions per year. The longer we can keep patients healthy, the less this disease will cost. Similarly, if we refer patients for injection therapy before significant vision is lost, outcomes can be vastly improved.
How Good Is Your Diagnostic Acumen?
We should be amazing at detecting this disease. We should be able to nail the diagnosis every time. But how good are we? A study of 1,288 eyes (644 adults) published in JAMA Ophthalmology revealed that optometrists and ophthalmologists miss AMD about 25% of the time. Importantly, the doctors in this study were not taking a laid-back approach nor were they too busy to take a really good look. On the contrary, they were all aware that their findings would be double-checked by trained graders.
How does this translate into patient
outcomes? Simply put, as many as 78% of AMD patients seek their first treatment after having already suffered irreversible vision loss in one eye, and nearly half of them have an acuity of 6/60 or worse, which means they are essentially self-diagnosing, even though we should be the ones taking the lead and directing care.
When you consider the poor outcomes that result from delayed diagnoses, there is no question that early AMD matters quite a bit. We must be more willing to take a serious look at early disease and improve our diagnostic acumen to prevent patients from falling off the visual cliff. In all this we are aiming to ‘flatten the curve’ – we cannot cure AMD yet but by intervening early we can slow the progression of the condition and delay loss of vision flattening the curve as long as we can.
AMD Is Easier Than Glaucoma
Glaucoma is complex and it is exceedingly difficult to determine who will progress and who will not. Even IOP can sometimes be a false indicator. Nonetheless, we follow suspects closely, though it is very likely their disease will progress quite slowly. Conversely, patients with small drusen can, and often do, convert to CNV between annual visits. This was an unavoidable consequence of this disease until about four years ago when a very straightforward diagnostic technology, called automated dark adaptometry, demonstrated that a simple test could provide clear evidence about whether or not small drusen were actually early AMD. Dark adaptometry also helps us identify progression of AMD despite stable visual acuity, making disease management far simpler than it used to be.
Importantly, dark adaptometry does not tell us that a patient is at risk of developing AMD – it tells us that a patient already has AMD, even though we may not be able to detect it clinically for years. Armed with this knowledge, we can follow these patients more closely, examine them more regularly, and hopefully save precious lines of vision along the way. In other words, AMD is a high-stakes condition, but it is much easier to manage than glaucoma.
Rethink AMD Symptoms
By the time a patient develops what we commonly think of as classic symptoms of AMD, such as distortion on the Amsler grid or noticeable loss of central vision, it is too late. We do not wait for glaucoma patients to develop tunnel vision before we start managing them very closely, so why is this so often the case with AMD care? We have a duty to do far better than what we achieve when we rely on advanced disease symptoms.
Interestingly, despite our tendency to cling to symptoms as harbingers of disease, we write off certain complaints, such as night vision difficulties. Older patients routinely present with night vision challenges, but more often than not we automatically assume these are due to cataracts. Make no mistake, chucking night vision difficulties into the cataract box is a dangerous choice, since this is a leading sign of early AMD that should prompt dark adaptation testing.
Can You Classify AMD?
We all know how to find drusen, but no matter how skilled we are, measuring the size of drusen is not practical in a typical clinical setting. Our estimates are best guesses. We cannot say for sure how many microns a druse may be. Furthermore, AMD is present well before drusen are clinically visible. Histopathological studies have shown that the retinal pigment epithelium (RPE) cells deposit locally generated cholesterol beneath the RPE cell layer and in Bruch’s membrane before drusen are formed. The cholesterol accumulation creates oxidative stress and inflammation that impedes the normal transport of nutrients, including that of vitamin A, from the choriocapillaris across Bruch’s membrane. This in turn affects photoreceptor health and creates a localised vitamin A deficiency. Even though these cholesterol deposits are invisible to us and cannot be detected by any current imaging technology, they eventually grow into visible drusen. This process can take several years, during which the patient already has subclinical form of AMD, yet neither us nor the patient is aware of the damage happening to their macula.
The modified Backman AMD Classification that includes subclinical AMD
Functional Testing Is Essential
In the absence of our ability to accurately stage disease by looking at it clinically, we must consider other options – namely functional testing in the form of dark adaptometry. Several peer-reviewed studies have shown that dark adaptation function is impaired from the earliest stages of AMD, with increasing impairment as the disease progresses. In fact, impaired dark adaptation is the earliest biomarker of the disease and identifies it at least three years before structural changes can be observed using OCT or fundus photography.
The first commercially available automated dark adaptometer, called the AdaptDx, measures a patient’s Rod Intercept (RI) time. The RI reflects the amount of time it takes the rod cells in a patient’s retina to adjust to darkness. The AdaptDx test provides a clear and objective measurement of retinal function with 90% sensitivity and specificity. An RI of less than 6.5 minutes indicates normal dark adaptation consistent with healthy photoreceptor function. An RI greater than 6.5 minutes indicates impaired dark adaptation, most often due to AMD in patients over age 60, unless there is a pre-existing hereditary retinal degeneration or significant vitamin A deficiency, which is rare. This gives clinicians a clear yes or no answer regarding the patient’s AMD status.
The AdaptDx is a straightforward adjunct to OCT, fundus photography and standard clinical examination. In this way, it is much like the visual field in glaucoma, because here too functional impairment can be detected before clinically evident structural impairment. Quite often in glaucoma, the nerve changes are too subtle to discern without additional diagnostic testing; and so the first sign of damage that we discover is in the visual field. We do not look exclusively at the visual field in glaucoma, just as we do not look exclusively at dark adaptation in AMD; but in both cases, the functional test is an essential, irreplaceable adjunct.
The Future of Dark Adaptation
The original AdaptDx automated dark adaptometer was introduced in 2014 and has since been used by more than 1,000 eye care professionals worldwide to identify and monitor AMD. Earlier this year, a second-generation dark adaptometer, the AdaptDx Pro, was introduced. As a rather extraordinary self-contained wearable headset, the AdaptDx Pro requires no dark room or external computer and features an artificial intelligence-driven onboard technician named Theia. After the in-office technician selects the testing protocol and places the device on the patient’s head, Theia takes over to facilitate a reliable, consistent testing experience by using automated instructions and adaptive feedback spoken directly to the patient.
Years of development went into creating this one-of-a-kind medical device to improve the testing experience and make modern AMD management practical in almost any optometry or ophthalmology office. Importantly, the medical grade hardware withstands all necessary disinfection and the consumables that make contact with the patient’s face are single-use disposable items, offering a greater level of patient confidence in this new era of point of care testing.
By embracing this new technology and our role in detecting, managing and treating AMD at its earliest stages, we can most certainly make a significant impact on our patients’ quality of life. In doing so, we can reduce the overall burden of late AMD treatment – both financially and
emotionally.
Ian Cameron is an independent therapeutic optometrist based in Edinburgh.