Structure and Function Relationship
It is important to correlate changes in the visual field (function) with those in the optic nerve (structure). If such correlation is lacking, the ophthalmologist should consider other causes of vision loss, such as ischemic optic neuropathy, demyelinating or other neurologic disease, or pituitary tumor. This consideration is especially important in the following situations:
The patient’s optic nerve head seems less cupped than would be expected for the degree of visual field loss.
The pallor of the optic nerve head is more impressive than the cupping.
The rate of visual field loss seems too rapid for a patient with treated glaucoma.
The pattern of visual field loss is uncharacteristic for glaucoma—for example, it respects the vertical midline.
The location of the cupping or thinning of the neural rim does not correspond to the location of the visual field defect.
It should be noted, however, that progressive visual field loss may sometimes be seen in the absence of optic nerve head changes and vice versa. In cases of early disease, progressive structural changes of the optic nerve and retinal nerve fiber layer can frequently be seen despite lack of apparent visual field progression. Conversely, in cases of more severe disease, progressive visual field losses tend to occur despite a lack of detectable structural change. This apparent disagreement may be explained by the different characteristics of the tests, including scaling, variability, and presence of floor/ceiling effects. Therefore, follow-up of patients with glaucoma should be performed using both structural and functional assessments.
Recent studies have suggested that early glaucomatous visual field defects may sometimes be seen in the macular area and detected with central 10-2 testing in the absence of defects detected with the 24-2 pattern. This has led to the suggestion that central tests be incorporated into the regular management scheme of patients with glaucoma or in those suspected of disease. However, the benefit of adding more 10-2 pattern tests in these cases needs to be weighed against the increased patient burden and the missed opportunity of obtaining another regular 24-2 pattern test. The Humphrey perimeter offers a combined perimetric strategy that tests the 24-2 pattern along with 10 additional locations in the central 10°, the 24-2C pattern; its utility is under investigation.
Medeiros FA, Zangwill LM, Bowd C, Mansouri K, Weinreb RN. The structure and function relationship in glaucoma: implications for detection of progression and measurement of rates of change. Invest Ophthalmol Vis Sci. 2012;53(11):6939–6946.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.