Landmark-driven fundus perimetry using the scanning laser ophthalmoscope.

Visual field measurement provides important information regarding the diagnosis, progression, and management of many ocular diseases. Most notably, visual fields are extremely important in glaucoma to diagnose and evaluate the progression of disease, in neuroophthalmologic disorders to aid in the determination of the site of involvement in the eye, optic nerve, or brain, and in some retinal diseases, such as retinitis pigmentosa, to assess the extent of involvement and visual disability. These evaluations are well served by our current methods of visual field determination, herein referred to as conventional visual field testing, which include Goldmann kinetic perimetry, Humphrey static perimetry, and similar techniques. However, conventional visual field determination is inadequate for the accurate evaluation of macular disorders or any retinal disorder in which foveal vision is compromised and the patient may have unstable fixation or extrafoveal fixation. Accuracy of the conventional visual field relies on the assumption that fixation is foveal and stable. If fixation is not foveal, the conventional visual field will still be mapped as though fixation is at the center (0°) of the field, so that all points tested will be shifted relative to their true retinal location. (A perimeter that uses the blind spot to test fixation may register fixation losses, but it is unable to correct for these.) If central fixation is unstable and there is significant eye movement during testing, scotoma size will be incorrect. Often, eccentric fixation and unstable fixation coexist, and there is a combination of these errors in scotoma location and size. In addition, there is often perceptual “filling in” of the area of the scotoma so that even the Amsler grid, used as a screening test for changes in central vision, may not detect the presence of a scotoma.1,2 Pericentral fixation lines to facilitate a patient’s centering on the fovea often still result in eccentric fixation. 3,4 Fundus perimeters are devices that provide for visualization of the fundus and the precise location of the stimulus on it. One can then see the exact test site on the retina and can correlate visual field defects to their true retinal positions.5 Several fundus perimeters have been designed and used in the past 30 years.6–14 The scanning laser ophthalmoscope (SLO) is the most recent and well-known fundus perimeter. It has allowed us to gain new information regarding the nature of visual loss in various macular diseases, including age-related macular degeneration and macular holes.1,6,7,15–25 However, because of difficulties in dealing with the additional data provided by SLO testing, methods of performing fundus perimetry have not used and have even ignored the advantage of viewing the fundus during testing. These difficulties include how to evaluate data correctly when the stimulus does not fall on the desired retinal location because of eye movement, how to ensure that the desired retinal areas are tested, and how to summarize the data. An additional problem is how to test for scotomas that might not correspond to observable lesions rather than simply testing over or at borders of retinal lesions. A number of investigators have shown that in diabetes26–28 and other macular diseases,29 scotomas may be present that do not correspond to observed retinal lesions; this is undoubtedly true in other retinal diseases, and these areas would be missed by testing only over observed retinal lesions. Finally, there must be a reliable method to test over the same retinal points when testing is repeated, even if fixation has shifted, to assess change over time.