During the last decade, treatment options and management strategies for age-related macular degeneration have advanced on many fronts. Not only have numerous medical breakthroughs improved therapy for wet AMD, but cutting-edge technologies have also been developed to support monitoring and early detection of subtle changes in macular function. Most importantly, several diagnostic instruments have emerged recently, which have been adapted for home use or are portable. 

Effective home monitoring of AMD can play a role in expediting detection and intervention, particularly considering the speed with which a choroidal neovascular net may develop. Instrument portability may enable eye care providers to access or acquire sophisticated equipment that can be shared between multiple offices or practices. Early detection of AMD and relative risk evaluation enable eye care providers to build the value of the practice, enhance the value of their services and serve the public at a higher standard of care.

Foresee PHP
The Foresee Preferential Hyperacuity Perimeter (PHP, Reichert Ophthalmic Instruments) is approved by the U.S. Food and Drug Administration to detect the formation of drusen associated with dry AMD and to monitor for conversion to wet AMD.1 In clinical trials, Foresee PHP provided excellent detection of choroidal neovascularization (CNV), demonstrating 82% sensitivity and 88% specificity.1-3 The technology also has the potential to detect metamorphopsia due to other macular disturbances, such as pigment epithelial detachment, histoplasmosis, epiretinal membranes and central serous retinopathy.4

Foresee’s technology is based on the visual skill of hyperacuity. Humans are particularly capable of detecting whether an object is out of place in relative comparison to its surrounding counterparts. Indeed, hyperacuity is so named because it exceeds visual acuity thresholds by a factor of 10. Additionally, hyperacuity is well maintained in the presence of image degradation resulting from media opacities; reductions in visual acuity and contrast sensitivity do not diminish an individual’s capacity to detect whether objects are out of alignment.

Foresee’s test has a very simple, user-friendly design. The test presents either a horizontal or vertical line of white dots on a black background. The patient must identify artificial distortions created in the line. These distortions are designed to imitate the appearance of visual distortions that are caused by macular lesions. The patient reports the area of greatest perceived distortion. Defect depth can be quantified by comparing the size of a clinical distortion with artificial distortions. Generally, the patient will choose the area of greater displacement. Repeated comparisons can be used to determine the amplitude threshold of the macular disturbance.

The patient uses a stylus on a touch-sensitive screen to indicate the area of disturbance. Fixation is controlled by smoothly guiding the patient’s fixation from the point at which he or she touched the screen back to a central location with a single white dot moving against the black background. The fixation dot pauses briefly at the center before the next test stimulus is presented.

Test parameters, including unit size (dot size), gap (inter-dot spacing), spatial resolution of results, stimulus duration (160ms, which is shorter than the 250ms required to execute a saccade), and extent of visual field tested, are displayed on the printout. Test distance is controlled by chin placement on the examination cup. Testing takes less than five minutes per eye.

Frequent testing is recommended to facilitate early detection, depending on the severity and relative risk of the AMD.3 As with any perimeter, a baseline test is recommended. If the first test is within normal limits and reliable, monitor the patient every three months. If the initial test is normal but unreliable, a retest is recommended within two weeks. Keep in mind that even if the initial test is outside normal limits, the measurement may still be used as a baseline. Careful evaluation and/or related testing, such as optical coherence tomography, is recommended if reliable retesting reveals repeatable defects. A retrospective study evaluating the influence of Foresee PHP and optical coherence tomography on clinical decisions to treat CNV found that in cases where the CNV lesion was “previously stable,” the Foresee PHP was more sensitive to change than OCT. Thus, Foresee PHP may be particularly useful in the detection of CNV reactivation post-treatment.5

The Foresee PHP is compact, but not conveniently portable, as it is assembled from two components: a computer and an integrated monitor. The unit has a 20” x 12” monitor, and a 16” x 16” base and chin rest that sits adjacent to the monitor. The overall footprint is 28” deep x 20” wide, and the unit weighs 40lbs. 

The ForeseeHome (Notal Vision) received FDA approval in December 2009.
ForeseeHome (Notal Vision) is based on Foresee PHP technology, and includes several hardware, software and customer support modifications. In late December 2009, the device obtained FDA clearance, and the company plans to introduce it to the market during the first quarter of 2010.

The ForeseeHome has been evaluated in contrast to Amsler grid (AG) testing as a home monitoring device, and has demonstrated significantly greater sensitivity than AG among patients with CNV and intermediate AMD.6

In a study that evaluated frequency of ForeseeHome usage, 15 subjects with AMD were followed for seven months, and were told only to use the device at their convenience at home, as frequently as possible. The subjects elected to use the device an average of 3.7 ± 1.7 times/week. Half of the subjects were “organized,” using the ForeseeHome at regular intervals (4.9 ±1.4 times/week). The other half of the subjects tended to use the device more spontaneously (2.1± 0.8 times/week).7 Testing several times per week is recommended to monitor for early changes in vision, particularly in active CNV cases.

The ForeseeHome is designed to be user friendly––from unpacking and installation to test monitoring and usage. It is more compact than Foresee PHP, and uses a projection screen that is viewed through an un-occluded ocular. The patient uses a mouse pointer to identify the disturbance. The user must guide the mouse to a central fixation point to initiate each subsequent presentation.

Thus, the ForeseeHome device permits a self-paced assessment. The test takes three to four minutes per eye. Along with quality of results, patient compliance data (testing frequency) is available. Testing is recommended “at one’s convenience, as frequently as possible.” But, testing at least twice-a-week is sufficient for early detection of macular changes.7

After each test, the results are automatically transmitted to a data-monitoring center. The data-monitoring center evaluates all test results for a significant change in performance. If a change is detected, the monitoring center issues an urgent notification to the patient’s clinician so he or she will not have to wait until the patient’s follow-up visit to evaluate the results. Additionally, the patient can view a simplified version of his or her results.

The ForeseeHome collects data in three phases:8

• Phase 1. During the first several days of testing, the results are used to establish a baseline reading.

• Phase 2. Consistent retesting performance is used to statistically strengthen the baseline. If, however, there is a change in performance during this period (the next three weeks), the data-monitoring center will be alerted.

• Phase 3. The third phase is termed the “usage period.” During this ongoing phase, any statistically significant change in the pattern of the test results relative to the first two phases will generate an alert. Once the data-monitoring center is alerted, the clinic associated with the patient is notified so that an emergency follow-up visit can be scheduled with the treating clinician.

Costs and coverage for the ForeseeHome device and remote monitoring service are not yet available.

Exploring HFP and MPOD in Depth
Heterochromatic flicker photometry (HFP) is a psychophysical test that requires the patient to observe a small, flickering, blue-green light centrally. Then, he or she reports when the flickering slows or stops. In actuality, the test alternately shows two spots of monochromatic light.

HFP measures a patient’s macular pigment optical density (MPOD) level. Macular pigments are comprised of lutein and zeaxanthin, and protect against the oxidative stress of ultraviolet (UV) radiation and free radical activity.

Several major studies, including the Lutein Antioxidant Supplementation Trial (LAST), have documented the efficacy of nutritional supplements in not only enhancing MPOD, but also reducing the progression of AMD.12-17 It is worth noting that nutritional supplementation with lutein and zeaxanthin does not have a uniform effect on MPOD. Various studies indicate that a patient’s ability to absorb these nutrients and convert them into macular pigment may vary.15,17-19 In fact, Meike Trieschmann, M.D., and associates at the Institute of Ophthalmology, St. Franziskus Hospital, in Muenster, Germany, found that patients with a low MPOD who took lutein and zeaxanthin supplements could be categorized into two groups: They either experienced a dramatic rise in MPOD, or they were non-responders who showed no rise in MPOD.19 These findings indicate that some individuals lack the ability to convert serum levels of carotenoids into macular pigment deposits.19

HFP takes advantage of the anatomical presence of pigment at the macula lutea. This pigmented area creates the entoptic phenomenon known as “Maxwell’s spot.” Maxwell’s spot can be seen when viewed through a cobalt blue filter. Upon viewing, the central few degrees will appear darker than the periphery because the yellow macular pigments filter out blue light at the macula. This presentation can be accentuated by first bleaching the retina with a green light before viewing through the cobalt blue filter.

The patient’s macular pigment absorbs the test wavelength of 460nm. HFP compares this with a reference wavelength of 550nm, which is not absorbed by macular pigment. Next, the luminance of the reference wavelength is modulated. When the luminance of the two wavelengths matches, the flickering appears to stop or diminish. The lower the luminance of the reference wavelength at the macula, the more macular pigment is present, reducing the perceived brightness of the test wavelength.

The same luminance comparison is then made at a parafoveal point, several degrees beyond the macula lutea. With a lower amount of macular pigment blocking the parafoveal point, the reference wavelength should require a higher luminance level to match the perceived brightness of the test wavelength.

The subtractive difference between the two luminance levels is compared against a normative database and categorized as low, average or high. The larger the difference between the foveal and parafoveal luminance levels, the denser the patient’s macular pigment is at the fovea. And, the denser the patient’s macular pigment, the more macular protection it affords.

MacuScope and QuantifEye
• MacuScope. The MacuScope (MacuChek) is a psychophysical test that uses heterochromatic flicker photometry (HFP) to measure the patient’s macular pigment optical density (MPOD). The test indicates whether the patient has a low, average or high optical density of macular photopigment.

Proper use of the MacuScope requires a great deal of patient-technician communication, as well as a high level of discrimination and fixation control. It is best to perform the test on the patient’s dominant eye first. In case of difficulty discriminating, it is not necessary to perform the test on both eyes, because the deposition of macular pigment is assumed to be symmetric.

The MacuScope has been evaluated recently in clinical research. One study indicated that subjects found the task of identifying “minimum flicker” to be conceptually difficult.5 This study also documented that the greater a patient’s macular pigment density, the more variability he or she demonstrated in test-retest responses.9 This is because at higher MPOD levels, a more intense test wavelength is required to minimize the flicker. At greater light intensities, incremental intensity changes make a smaller impact, resulting in several possible machine settings that give the same appearance of minimized flicker.10 Software updates might assist with result repeatability by accounting for each subject’s sensitivity to flicker and compensating for various test conditions.11 However, it appears that clinically significant changes in MPOD would be rather difficult to detect with the current instrument design.9-11

• QuantifEYE. The QuantifEYE (ZeaVision) performs the same function as the MacuScope, except in this case, the patient self-adjusts the luminance while assessing the flicker rate, rather than notifying the technician when the constant or minimal flicker rate has been reached. This may be an advantage over the MacuScope, because the flicker rate will begin to increase again once the luminance of the test stimulus is adjusted too low. So, if an individual is self-adjusting the controls, he or she may recognize the increasing flicker rate and reverse the direction to minimize the flicker. Working with a technician who adjusts the luminance on behalf of the patient creates a time lag between patient report and technician response.

Additionally, the QuantifEYE can help determine a patient’s chances for AMD development with its “risk assessment” software. The software includes a subjective patient questionnaire.

 Currently, both the QuantifEYE and MacuScope are only available for in-office use. If nutritional supplements are initiated, a change in the MPOD is expected within six months, which is the recommended follow-up schedule.

Portability makes it possible to share these devices between offices. The QuantifEYE is smaller and lighter than the MacuScope, weighing 11lbs, with an 11” long x 8” wide footprint. The MacuScope is nearly four times heavier, weighing 40lbs; however, it has a narrow 21” long x 10” wide footprint. Some practitioners prefer to advertise risk screening for AMD as a supplementary, billable service, while others offer it as a value-added service to a comprehensive eye exam.

These non-invasive, portable technologies provide eye care professionals with valuable tools for early monitoring of AMD. The office version of Foresee PHP may supplant all other forms of functional macular assessment, offering a fast, interactive, subjective test of great sensitivity and specificity. The ForeseeHome unit has the potential to mark a new era in early intervention, offering daily monitoring and data review.

Additionally, QuantifEYE and MacuScope offer patients an opportunity to identify the potential benefits of lifestyle modifications and nutritional supplementation of macular pigments. In this era of evidence-based medicine, HFP technology takes a front seat in validating and documenting a patient’s progression status.

Dr. Slotnick is a behavioral optometrist who practices in Dobbs Ferry and Mahopac, N.Y. She also participates in vision research with Manhattan Vision Associates. She has no financial interest in any of the companies or technologies mentioned. 

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2. Loewenstein A. Macular perimetry for diagnosing neovascular AMD. Paper presented at the 2002 Retina Congress. San Francisco: September 28-October 3, 2002.
3. Goldstein M, Loewenstein A, Barak A, et al. Results of a multicenter clinical trial to evaluate the preferential hyperacuity perimeter for detection of age-related macular degeneration. Retina. 2005 Apr-May;25(3):296-303.
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12. Richer S, Stiles W, Statkute L, et al. Double-masked, placebo-controlled, randomized trial of lutein and antioxidant supplementation in the intervention of atrophic age-related macular degeneration: the Veterans LAST study (Lutein Antioxidant Supplementation Trial). Optometry. 2004 Apr;75(4):216-30.
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