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Editors Selection IGR 16-4

Structure and Function: Factors leading to lack of concordance

Comment by David Greenfield on:

53999 Accuracy of Matching Optic Discs with Visual Fields: The European Structure and Function Assessment Trial (ESAFAT), van der Schoot J; Reus NJ; Garway-Heath DF et al., Ophthalmology, 2013; 120: 2470-2475

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Measures of structure and function often disagree in glaucomatous eyes, particularly in patients with mild and advanced disease severity. Both are essential in order to monitor disease progression over time but it is widely recognized some patients may develop isolated changes in a single measurement that correlates poorly with other measurements. In the present study, Van der Schoot and colleagues conducted a study among European ophthalmologists to determine their ability to match stereoscopic optic disc photographs to visual fields of varying severity. Sixty percent of cases were correctly matched; the severity of visual field damage was more commonly overestimated rather than underestimated. Not surprisingly, physicians with fellowship training in glaucoma performed better than general ophthalmologists.

Not surprisingly, physicians with fellowship training in glaucoma performed better than general ophthalmologists

Many factors contribute to the lack of concordance between structural and functional damage in glaucoma including disease severity and disc size. There is considerable evidence that early glaucomatous optic disc and retinal nerve fiber injury often precedes functional loss detected using standard visual field testing. In the United States, the current ICD-9 glaucoma staging scale has defined mild or earlystage glaucoma (365.71) as optic nerve abnormalities consistent with glaucoma but no visual field abnormalities on white-on-white visual field test, or abnormalities present only on short-wavelength automated perimetry or frequency-doubling perimetry. Small optic discs may not demonstrate typical glaucomatous features such as neural rim thinning or cupping until the development of advanced stage disease. Lastly, many eyes with visual field loss confined to a single hemifield have been reported to exhibit diffuse rather than localized retinal nerve fiber layer atrophy.

Glaucomatous changes in structure and function often disagree and contribute to the matching inaccuracy reported by Van der Schoot and colleagues in this interesting study. In routine clinical practice other commonly observed non-glaucomatous variables that may contribute to a mismatch between the appearance of the optic disc and visual field include unreliable visual field examinations, the influence of comorbid conditions such as refraction scotoma in eyes with high myopia, and retinal pathology such as AMD or retinal vein occlusion.

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