Assessing Gender- and Race-based Differential Item Functioning with the National Eye Institute Visual Functioning Questionnaire for Patients with Glaucoma

Abstract

Purpose : To evaluate whether The National Eye Institute Visual Functioning Questionnaire-25 (NEI VFQ-25) can serve as a generic measure for quality-of-life (QoL) assessment in patients with glaucoma across race and gender.

Methods : This was a cross-sectional study of data sourced from the Duke Glaucoma Registry. Patient level diagnosis of glaucoma was classified by the presence and topographic correspondence of functional and structural damage assessed by spectral-domain optical coherence tomography (SDOCT) and standard automated perimetry (SAP) parameters in the worse eye. The NEI VFQ-25 graded scale was collapsed for all items to have three categories going from extreme and moderate difficulty, slight difficulty, to no difficulty. Only items of visual functioning components were studied. Gender evaluated females and males while race studied African Americans and Caucasians as focal and reference subgroups, respectively. The multiple group analysis and differential item functioning (DIF) of the R package, mirt, were used for item-wise analysis. A five-item anchor selection strategy was employed prior to final DIF detection. Expected score standardized differences (ESSD) were calculated and the effect for each item was classified as small (|ESSD| <0.200), moderate (|ESSD| 0.200 to 0.800), or large (|ESSD| ≥0.800).

Results : 258 glaucoma patients were evaluated in the study of which 82 were self-identified as Black or African American and 176 as White or Caucasian. Gender included 138 females and 120 male subjects. Racial DIF was observed for items pertaining to difficulty reading ordinary newspaper print (p=0.008), going downstairs or curbs in low light (p<0.001), seeing how people react to things the patient says (p=0.026), and picking out and matching ones’ own clothes (p=0.044). The respective item-level ESSD values were 0.214, -0.672, 0.290, and -0.190. Gender DIF was observed for items pertaining to difficulty in seeing how people react to things patient says (p = 0.033) and driving in difficult conditions (p=0.011) with low to moderate effect (ESSD of 0.196 and -0.484, respectively).

Conclusions : In assessing QoL in glaucoma patients using the NEI VFQ, racial and gender subgroups demonstrated to have different probabilities of endorsing responses for certain activities of daily living with small to moderate effect sizes for clinical utility.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.