Strategies for improving early detection and diagnosis of neovascular age-related macular degeneration

Figures & data

Table 1 Techniques and diagnostic tools for the early detection and diagnosis of neovascular age-related macular degeneration

Test	Description	Comments
Amsler chart (classical)	Evaluates the 20° of visual field centered on fixation.^Citation31 The complete set of Amsler charts consists of seven plates, each consisting of a 10 cm square with a central spot for fixation. Each chart is held at approximately 30 cm, and the patient is asked to fixate on the central dot, reporting any distortion, blurred areas, or blank spots anywhere on the grid.	Although widely used with patients with AMD since at least the 1960s, sensitivity and specificity for the detection of AMD is low.^Citation31 This poor performance is related to such factors as cortical completion (“filling in”) and crowding phenomena, as well as poor patient compliance.
Amsler chart (automated, threshold)	Standard Amsler chart testing is a suprathreshold stimulus, and thus relative scotomas may go undetected. In “threshold” Amsler chart testing, the subject is asked to view a white-on-black version of the chart through cross-polarizing filters.^Citation42 An automated, computerized version of the threshold Amsler test has also been developed; patients are instructed to map any observed distortion of scotomas using a standard Amsler grid displayed on a touch-screen computer display at different contrast levels. A three-dimensional depiction of the visual field defect is then produced.^Citation44	High reproducibility for detection of central visual field defects on repeat testing in patients with AMD.^Citation45 Quantitative analyses may also allow differentiation between neovascular and nonneovascular forms of AMD.^Citation50
Preferential hyperacuity perimetry (PHP)	The patient is presented with a pattern of dotted lines projected for 160 ms to the central 14° of their visual field. Any geometric shift in retinal morphology occurring in the stimulated area will lead to a hyperacuity defect, and thus the perception of distortion.^Citation37 Each dotted line also contains an artificial distortion of varying magnitude. This serves as a competitive stimulus to any pathologic distortion, if present. The point at which a test subject becomes aware of a pathologic distortion over an artificial distortion provides a measure of its magnitude.	Initial studies demonstrated that PHP can detect recent-onset choroidal neovascularization with high sensitivity (82%), and can differentiate these patients from those with intermediate AMD only with high specificity (88%).^Citation54 The ForeseeHome device was evaluated in the HOME study, a Phase III randomized clinical trial. This study provided the first definitive evidence of efficacy for a device allowing early detection and treatment of patients with neovascular AMD.^Citation57
Shape-discrimination hyperacuity (SDH)	An alternative form of hyperacuity measurement involves discrimination of shapes (eg, a perfect circle compared to one that has a distorted contour).^Citation60 Successful completion of such tests requires global shape-detection mechanisms, something that is impaired in patients with AMD but not in age-matched controls.^Citation61	A handheld SDH test (MyVisionTrack) has recently been implemented for use with smartphones.^Citation63 Health Management Tool, a remote monitoring system that utilizes the MyVisionTrack app, has recently been tested in a pilot clinical trial, but the results are not yet publicly available.
Macular mapping test (MMT)	The MMT is a software program used in conjunction with a desktop computer.^Citation66 Letters are briefly displayed in the central visual field (8° radius) on the computer display. A constant background pattern in a wagon-wheel shape aids the test subject in maintaining fixation on the center of the display area.	Designed primarily for quick assessment of residual vision in patients with maculopathies. Considerable test–retest variability may be a limitation.^Citation67
Entoptic perimetry	When patients with an acquired scotoma stare at images of random visual noise (eg, video static), they often perceive an inhomogeneous region corresponding to their scotoma.^Citation68 Once the scotoma is perceived in this manner, it is often possible to map it, a procedure referred to as entoptic perimetry.	Although not very effective in eliciting scotomas from postchiasmal lesions or from the physiological blind spot, variations of this technique have been successfully used to screen for visual field defects caused by prechiasmal ocular diseases, including AMD.^Citation70
Optical coherence tomography (OCT)	OCT is an imaging modality that provides cross-sectional imaging of the retina in a noninvasive manner.^Citation71 Due to its extremely high resolution, OCT may allow early detection of neovascular AMD disease features (eg, subretinal fluid) before patients become symptomatic.^Citation73	Initial studies with time-domain technology suggest that OCT has a greater specificity than PHP or Amsler chart testing for the detection of new-onset neovascular AMD. However, using this older technology, OCT was found to be less sensitive than conventional fundus fluorescein angiography.^Citation74 Newer “swept source” laser-light sources may allow OCT systems to become handheld and portable. Binocular OCT designs may allow comprehensive eye examination to be performed by patients themselves without the need for skilled personnel to acquire images.^Citation72 Commercially available OCT devices are now capable of performing retinal and choroidal angiography in a noninvasive manner.^Citation72

Abbreviation: AMD, age-related macular degeneration.

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