Psychophysical Testing
Douglas J. Rhee
Tara A. Uhler
L. Jay Katz
INTRODUCTION
The goal of this chapter is to show representative visual field patterns for glaucoma rather than provide a comprehensive discussion of perimetry. There are several texts dedicated solely to the extended description of perimetry and atlases dedicated to just perimetric findings.
The broad term psychophysical testing refers to the subjective testing of vision of an eye. In clinical terms for the glaucoma patient, this involves perimetry to assess the peripheral vision of an eye. Because the pathophysiology of glaucoma affects the paracentral and peripheral vision before affecting central acuity, there are both diagnostic and therapeutic benefits to assessing the patient’s visual field. It is important to note that usage of the term peripheral vision does not necessarily mean far periphery. In fact, most glaucomatous visual field defects occur paracentrally (within 24 degrees of fixation). Our use of the term peripheral refers to anything beyond central fixation (i.e., greater than the central 5 to 10 degrees).
Contrast sensitivity is not routinely tested in glaucoma patients. Contrast sensitivity is affected in even early glaucoma (but not ocular hypertension, that is, an elevated intraocular pressure [IOP] without the presence of optic nerve damage), and progressively worsens with continued optic nerve damage. Contrast sensitivity highly correlates to the perceived visual problems in patients with glaucoma (Fig. 8-1A). The Pelli Robson chart is the most commonly used (Fig. 8-1B and C), but other charts have been developed. When testing, it is important to use standard illumination.
Ishihara color plates are not generally affected in glaucoma until very advanced stages of disease. Even patients with very small central islands have minimal defects on color plate testing. Using techniques with more refined color discrimination, patients with even early glaucoma can have decreases primarily in the blue-yellow axis which is exploited by the short-wave automated perimetry (SWAP) test.
BIBLIOGRAPHY
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 FIGURE 8-1. Contrast sensitivity. A. Photoshop simulation of the effect of worsening levels of contrast. The original image without manipulation is the top left. Down the left-hand column is decreasing contrast by 50% (middle left) and 75% (bottom left). The right-hand column increasing contrast by 25% (top right), 50% (middle right), and 75% (bottom right). (Figure from: https://commons.wikimedia.org/w/index.php?curid=750555.) Pelli Robson Contrast Sensitivity Chart (B) letters in triplet with decreasing contrast as one moves from left to right and down each row. The testing distance is 1 m using an illumination of 85 cd/mm2. The score of the test is recorded by the faintest triplet, out of which at least two letters are correctly identified. The log CS value for this triplet is given by the number on the scoring pad. |
 FIGURE 8-1 (continued) C. Shows sample letters (different from A) without fading and the log values next to the triplet. Grossly, normal contrast perception is being able to see 6 to 7 lines (12-14 triplets), moderate loss is seeing 4 to 5 lines, severe loss is being able to see 2 to 3 lines, and profound loss would be to only see 1 line. |
PURPOSE OF TEST
Diagnosis
• As part of the initial evaluation of a patient suspected of having glaucoma, automated monochromatic visual field testing is an important aspect of the diagnostic determination of glaucomatous optic nerve damage. Visual field abnormalities have localizing value for lesions along the entire visual tract, which extends from the retina to the occipital lobes. Glaucomatous visual field defects are those that are typically found with lesions localizing to the optic nerve.
• It is important to note that the presence of a so-called optic nerve field (i.e., defects that localize to the optic nerve) is not solely diagnostic of glaucoma. This must occur in the presence of a characteristic optic nerve appearance (covered in Chapter 6) and history.
• Other findings, such as IOP, gonioscopic appearance, and anterior segment findings, may help categorize the specific type of glaucoma. All optic neuropathies (e.g., anterior ischemic optic neuropathies, compressive optic neuropathies, etc.) demonstrate “optic nerve” visual fields.
• It is also critical to note that the absence of an optic nerve field does not exclude the diagnosis of glaucoma. Although in the year 2002, automated achromatic static visual field (AASVF) testing was the gold standard for the evaluation of optic nerve function, its threshold of sensitivity to detect ganglion cell loss is still limited. Clinicopathologic and experimental evidence indicates that the earliest visual field defect detectable by AASVF corresponds to approximately 40% ganglion cell loss.
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