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BLOG: New monitoring app for maculopathy
Age-related macular degeneration has been a daily part of my practice since starting in Arizona in 1993. In my early years, I dreaded hearing about the phone call that went something like this: “Mrs. Jones is coming over, as she says her vision in her right eye is suddenly blurry.”
A quick look at the chart and seeing the patient had dry AMD usually established the diagnosis before the patient walked through the door: she had developed choroidal neovascularization (CNV). Sudden vision loss in these patients was really not so sudden. Studies show that a typical CNV lesion when first forming grows at an average rate of 26 microns per day, and the lesion size at the time of diagnosis is 3,300 microns. This equates to a lesion being detected after it has been present for a little over 4 months.
The Amsler grid was introduced in 1947 and has been used with limited success. One of the biggest reasons for this is that it is not fully self-explanatory. Unsupervised, only 10% of patients appreciate a new visual distortion. This percentage rises substantially under the guidance of a trained observer; however, who will fill this role for testing patients on a daily or even biweekly basis?
Other reasons for the poor sensitivity of the Amsler grid are that it does not force central fixation. Additionally, there are also the phenomena of crowding and completion. Crowding refers to the averaging in of crowded stimuli; the surrounding lines on the chart mask a scotoma caused by CNV. Completion refers to the cortically driven filling in of the missing part of the picture. Visually, we do not see an image projected on our retina; we see the image created by the brain. This is why we are not aware of our physiologic blind spot, as our brain ignores this retinal “defect.”
In everyday practice, we use visual acuity to document a patient’s level of vision. Visual acuity represents the smallest discernable visual feature – think of this as recognition of shape.
On the other hand, you may recall from optometry school the principle of Vernier acuity, which is also referred to as hyperacuity. Our resolution with hyperacuity is five to 10 times greater than visual acuity. This is due to the arrangement of our retinal photoreceptors, which allows for discrimination of relative position. In other words, we are better at lining objects up in space than discerning what they actually are.
For example, Snellen visual acuity of 20/20 represents 1 minute of arc. Hyperacuity allows resolution of 0.03 minutes of arc. This equates to the width of a pencil viewed from a distance greater than three football fields.
The Preferential Hyperacuity Perimeter (PHP), now distributed by Reichert, became commercially available in the early 2000s, and I started using it in clinic in 2004. It was light years ahead of the Amsler grid in terms of sensitivity and specificity for detecting new CNV. Over the years we have monitored hundreds of patients with PHP and have detected quite a few cases of CNV at an early, treatable stage. It is incredibly rewarding to be able to save an eye based on testing I have prescribed.
Distribution of the office-based PHP changed a few times over the years. In early 2013 my unit died, and because it was one of the original units, there was no bringing it back. I did start prescribing home PHP for my patients, but many of them were unable to do the test correctly and could not qualify for home monitoring. Other patients have complained about the monthly fee associated with the monitoring service and have opted out of testing. Over the past year I have gotten away from prescribing the home PHP device.
I have become more dependent on following patients in-office based on genetic risk and have implemented detailed instructions for them on testing their visual acuity at both distance and near each day at home. However, based on my above discussion on hyperacuity, this has given me a bit of an uneasy feeling. This all changed a couple of months ago.
Perusing the morning news, I came across an article about a new vision monitoring service for patients with maculopathy from AMD or diabetes (or any maculopathy). The company had received its second FDA clearance for its iPhone-/iPad-based app, as well as a provider dashboard to monitor results. The app uses shape discrimination hyperacuity for home monitoring of vision. What? How did I not know about this company?
I immediately contacted them and was fortunate enough to be accepted as a beta-prescriber. While a full commercial rollout of the app has not yet started, recruitment for a large clinical trial has begun. I am sure you will see much more about this in the near future.
I have been prescribing this app to my AMD and diabetic patients since early April, with enthusiastic acceptance from patients. In a word: it is really cool. In fact, I also prescribed it for a gentleman that had suffered a branch retinal vein occlusion who at the time of diagnosis and referral had vision of 20/40. After treatment with Avastin (bevacizumab, Genentech) he regained vision of 20/20 and is now on a treat-and-extend protocol. I am confident that if he does start to develop macular edema prior to his next scheduled visit or injection, I will know about it and get him in sooner. And my good friend and local retinal specialist is thrilled as well.
From a broader perspective, I feel that this app will become a cornerstone of practice as optometry implements the medical model for the coming changes associated with health care reform. Consider a pay-for-performance/outcome reimbursement model. Let’s say a diabetic patient presents for exam reporting poorly controlled blood sugar. Upon examination, minimal retinopathy is present without macular edema. While advising the patient to follow up with their doctor regarding blood sugar control, what if they continue with poor control of their blood sugar and develop macular edema prior to their next scheduled eye exam? We could very well have a tool to monitor the patient’s vision for just such a scenario. In fact, it is entirely possible that patients monitoring their vision three times per week with an app will actually increase their compliance with blood sugar control.
Studies show that diabetics are fearful of losing their eyesight. Armed with a tool for self-monitoring of vision, will this make them more compliant with treatment recommendations for controlling their blood sugar? Time will tell, but the answer may well be yes.
While some of the news regarding the future of our profession can be unsettling, such as self-refraction, technology such as this app will help secure our role as primary eye care providers in the future. Keep an eye out: more on this to come.
References:
Alster Y, et al. Ophthalmology. 2005;112(10):1758-1765.
Crossland M, et al. Br J Ophthalmol. 2007;91:391–393.
Fine AM, et al. Arch Ophthalmol. 1986;104(4):513–514.
Liu TYA, et al. Ophthalmology. 2013;131(3):335-340.
Olsen TW, et al. Ophthalmology. 2004;111(2):250-255.