Functional field score: the effect of using a Goldmann V-4e isopter instead of a Goldmann III-4e isopter

PURPOSE: To investigate the underestimation of field loss in functional field score (FFS) between the Goldmann isopters III-4e and V-4e in visually impaired patients, in order to develop a predictive model for the FFS(III-4e) based on FFS(v-4e) that adjusts for possible confounders. Although the visual field is generally evaluated using Goldmann isopter III-4e, it has the disadvantage that not all low-vision patients are able to see the stimulus corresponding to this isopter.

METHODS: Goldmann visual fields were obtained from 58 patients with a variety of eye diseases. Eligibility criteria were age of 18 years or older and valid results of a Goldmann III-4e and V-4e visual field test in at least one eye. Linear regression was used to develop the model, setting FFS(III-4e) as the dependent variable and FFS(V-4e) as the independent one.

RESULTS: The FFS(V-4e) was higher than the FFS(III-4e), the mean difference being 14.56 points (95% CI, 12.48 -16.64). Multiple linear regression analysis showed that age, functional acuity score, primary eye disease, and central-peripheral loss were not confounders for the prediction of FFS(III-4e). FFS(III-4e) was estimated with the following equation: FFS(III-4e) = -19.25 + 1.063 x FFS(V-4e).

CONCLUSIONS: The relationship between FFS(III-4e) and FFS(V-4e) is linear, and the FFS(V-4e) can be used to estimate the FFS(III-4e). In practice, just subtracting 19.25 points of the value of FFS(V-4e) will be sufficient to estimate the value of FFS(III-4e). This model should give confidence about using the bigger isopter for determining the visual impairment of a person by the FFS.