Glaucoma is the leading cause of irreversible blindness globally. It is estimated that the prevalence of glaucoma will increase to over 110 million in 2040.¹ It may occur in any age group, but is common especially after 40 years of age. Elevated intraocular pressure is the most important causal risk factor for glaucoma, but high intraocular pressure is not necessary for glaucomatous damage to occur. The physical impact of glaucomatous optic neuropathy includes an irreversible loss of retinal ganglion cells that is clinically manifested as optic nerve head (ONH) cupping and localized or diffuse defects of the retinal nerve fiber layer (RNFL). Because glaucomatous damage is irreversible but largely preventable, early and accurate diagnosis and progression detection are important.

Evaluation of the optic nerve and nerve fiber layer includes examinations that test their structure and function. Glaucomatous retinal ganglion cell loss results structurally in RNFL and optic nerve defects, and functionally in visual field changes that can be assessed by automated perimetry and electrophysiology testing. Glaucomatous visual field defects include nasal steps, arcuate defects, localized paracentral scotomas, and, more uncommonly, temporal defects (Fig. 7-1). The most common location of visual field defects related to glaucoma is within an arcuate area commonly referred to as Bjerrum’s region, which extends from the blind spot to the median raphe.

Standard automated perimeters (SAPs) test the visual field by presenting static stimuli of constant size and varying light intensity at specific locations for a short period of time while recording the patient’s response at each location. The Humphrey field analyzer 24-2 standard achromatic examination (Humphrey Systems, Dublin, CA) uses a white stimulus with white background illumination; similar programs are present on other automated perimeters. Standard achromatic automated perimetry, along with clinical examination, has been the gold standard for following glaucoma; however, this automated testing strategy is time consuming, often resulting in patient fatigue and patient errors with high short-term and long-term variability. Advances in automated perimetry have aimed at reducing testing time and at developing strategies for earlier detection of visual damage in glaucoma. The SAP provides global indexes, such as the mean deviation, pattern standard deviation, and visual field index that are commonly used for diagnosis and monitoring disease progression. Glaucoma hemifield test is a parameter that compares specified regions of the visual field above and below the horizontal midline¹ (Fig. 7-2). These parameters are present in most automated perimeters.

The most commonly used test strategy is the Swedish interactive threshold algorithms (SITAs; Figs. 7-3 and 7-4). SITA uses information gained throughout the program to determine the threshold strategy for adjacent points. This allowed shortening the test duration in comparison with earlier iteration of the test without scarifying test reliability.²,³

Supported in part by NIH R01-EY13178.

Guided progression analysis (GPA) is progression analysis technique available in the Humphrey visual field report.¹,² GPA includes both event- and trend-based analysis to identify progression (Fig. 7-5). Event-based analysis identifies a point as progressing when it changed from the level at the baseline tests beyond the change that was detected in the population. Trend analysis is using linear regression to determine if the slope at any visit exceeds the no progression rate. When the change occurs in the same location over two consecutive tests, the GPA flags “possible progression.” “Likely progression” is flagged when change is detected in three consecutive tests.

The functional evaluation of glaucoma is prone to important limitations, such as subjectivity and marked variability. Electrophysiology tests eliminate most of these shortcomings and provide an objective testing. Devices such as pattern electroretinogram can assess the ganglion cell layer and inner retina; electroretinogram assesses the retinal function and visual evoked potential of the entire visual pathway¹,²,³ (Figs. 7-6 and 7-7). Glaucoma is predominantly a disease of localized damage; thus, multifocal electrophysiology modalities that evaluate specific areas in the retina offer a better potential for correspondence with structural evaluation of the retina. To this date, despite the high diagnostic potential, no electrophysiology examination has been incorporated into the standard clinical practice of glaucoma.⁴