Spotlight ON TECHNOLOGY & TECHNIQUE

The Foresee PHP: Designed to Detect Conversion from Dry AMD to Wet AMD

By Leslie Goldberg, Assistant Editor

The Foresee PHP, a preferential hyperacuity perimeter developed by Notal Vision and distributed exclusively in the United States by MSS, monitors the progression of agerelated macular degeneration (AMD) and is a clinically validated diagnostic device for improved early detection of choroidal neovascularization (CNV). The Foresee, the second-generation follow-up to the Preview PHP (Carl Zeiss Meditec, Dublin, Calif.), features a number of improvements based on customer feedback.

About the Foresee PHP

The Foresee PHP is a non-invasive, easy-to-perform eye exam that has been proven to be highly effective in identifying elevations in the retinal pigment epithelium (RPE) consistent with conversion from an intermediate to an advanced stage, or "wet" AMD.¹ Its diagnostic capability is based on hyperacuity, the inherent human ability to visually detect the misalignment of objects relative to other objects in space. Hyperacuity is 10 times more sensitive than standard visual acuity and is characteristically stable regardless of a patient’s age or physical condition.²

The Foresee PHP from Notal Vision/MSS.

Importance of Early Detection

"The Foresee PHP is able to detect recent-onset CNV resulting from AMD and can differentiate patients with recent-onset CNV from patients with intermediate-stage dry AMD," says Ingrid U. Scott, M.D., M.P.H., Professor of Ophthalmology and Health Evaluation Sciences at the Penn State College of Medicine.

"This is important because there are various treatment options which have proven efficacy in treating CNV associated with AMD, and treatment outcomes are better if the CNV is diagnosed and treated at an earlier stage. Thus, the earlier patients with CNV are sent to the retina specialist for evaluation and management, the better. Currently, many patients are diagnosed with wet AMD at a stage when the CNV is already subfoveal and already large in size."

How Does the Foresee PHP Work?

Preferential hyperacuity perimetry uses a form of perimetry that is similar to visual field testing, but instead of using white-on-white stimuli, it uses Vernier hyperacuity —the ability to perceive minute differences in the relative spatial localization of two objects in space.

The Foresee PHP maps defects within a patient’s visual field by analyzing responses to "dot deviation signals" flashing on a screen. A signal, consisting of a series of closely spaced dots in a single straight line with one or more dots out of alignment, is displayed on the screen for 160 milliseconds. The patient uses a stylus pen to touch the screen to identify the most prominent distortion in the line.

A typical 3-to-5 minute test measures 500 retinal data points covering the central 14° of the macular visual field. The response patterns are recorded, analyzed and compared to the normative database, producing a report revealing the relative location of the defects in the macular area.

By utilizing a phenomenon called "preferential looking," the Foresee can determine abnormalities that may indicate RPE elevation. The patient’s attention will always be drawn to the greatest distortion they see, so if a visual defect causes the patient to see a bend in the line that appears greater than the one presented by the instrument, the patient will select the physiological distortion. The dot deviation signals show differing magnitudes and locations of distortions to measure the extent and location of defects consistent with CNV, explains Yair Alster, M.D., CEO of Notal Vision.

"The test provides the examiner with the patient’s hyperacuity deviation map for the central 14° of visual field and provides information as to whether similar visual field findings are found in the population of intermediate-stage dry AMD patients in the normative database and in the population of patients with CNV in the normative database," says Dr. Scott.

"Reliability indices, such as the frequency of false-positive and false-negative responses, are also provided. If the examiner has any doubt about whether a patient has wet AMD, referral to a retina specialist is recommended."

A Comprehensive Patient Report

The Foresee PHP report features data on the history of examinations, whether the visual field map is outside normal limits, test reliability, relative location of defects in the macular area and the likelihood of each visual field defect being a true defect vs. noise (Figure).³

The hyperacuity deviation map plots all visual field hyperacuity disturbances. Each point in the map has a color corresponding to the level of disturbance at this point — darker colors correspond to larger disturbances. During analysis, an engine defines areas that are suspected as being related to conversion to wet AMD. These areas, called hyperacuity defect zones, are marked on the map, and the four largest areas are described in a table. The table lists the following properties for each hyperacuity defect zone:

■ Zone. Location identification on the map.

■ Cluster consistency. A value indicating the intentionality of the abnormal response in this region. The higher the value, the higher the likelihood that this abnormality was caused by a genuine visual field defect.

■ Estimated retinal location. Presumes the anatomical location of the zone in the retina.

The result section represents the average deviation of the patient’s overall field compared to a normal reference. There are also two indices that determine the reliability of the report’s result.

Figure. A screenshot of Foresee PHP test results.

The examination history chart helps to track and monitor patient results over time. The comments section includes a recommendation of next steps in patient management and is based on the test result and baseline protocol.

Physician Feedback

"The most important aspect of the Foresee PHP is its potential to identify patients who can benefit from treatment at an earlier stage of their disease process and, thereby, it may play an important role in optimizing visual outcomes for our patients with wet AMD," says Dr. Scott.

Dr. Scott counsels all her patients and their families regarding the risk factors for AMD development and the strategies aimed to reduce the risk or progression of the disease (such as dietary factors, sun protection, no smoking, optimal control of serum cholesterol and blood pressure and the findings of the AREDS Study). For patients who meet study inclusion and exclusion criteria, she discusses the option of participating in the AREDS II study. In addition, she gives patients an Amsler grid and explains to them how to monitor their visual status using an Amsler grid.

"The Foresee PHP was designed to overcome many of the potential limitations of the Amsler grid, such as cortical completion, the crowding phenomenon, the potential for incorrect use of the grid, and inability to maintain fixation," concludes Dr. Scott. OM

For additional information about the Foresee PHP call MSS at (800) 728-9615 or e-mail info@ms-services.com.

References

1. Preferential Hyperacuity Perimetry Research Group. Results of a multicenter clinical trial to evaluate the preferential hyperacuity perimeter for detection of age-related macular degeneration. Retina. 2005;296-303.

2. Enoch JM, Williams RA, Essock EA, Barricks M. Hyperacuity perimetry: assessment of macular function through ocular opacities. Arch Ophthalmol. 1984;1164-1168.

3. Nataloni R. New technology allows for earlier detection of pre-CNV. Retinal Physician. 2006;73-83.