Agreement amongst consultant ophthalmologists on levels of visual disability required for eligibility for certificate of sight impairment: Sight impairment registration using binocular composite visual fields

Background Registration as sight impaired allows access to services important for patients. The rates of sight impairment due to visual field loss are underestimated. Previous work has shown that evaluation of visual field defects in both eyes produces poor agreement among ophthalmologists for categorisation of patients as eligible for sight impairment registration. Aim To evaluate the impact of binocular summation of both eye glaucomatous visual field defects on agreement for sight impairment registration. Methods Thirty consultant ophthalmologists (Graders), graded 50 glaucomatous visual field sets. Each consisted of both monocular fields and summated binocular plots. Graders classified the visual field sets as sight impaired (SI), severely sight impaired (SSI) or neither. Trichotomous, (SI, SSI or no sight impairment) and dichotomous (any sight impairment versus no sight impairment) concordance values were estimated for the group of graders as a whole and for glaucoma and non-glaucoma experts. Results For trichotomous analysis the overall kappa agreement rate was 0.29; for dichotomous analysis it was 0.40. There was no material difference between glaucoma experts and non-experts. Conclusion Overall agreement was modest. Grading for SI showed the poorest levels of agreement. Using binocular fields does not appear to improve concordance for sight impairment registration. Moreover, there is no difference in agreement between glaucoma and non-glaucoma experts. An overall score for visual disability using mean deviation may be a more pragmatic approach.