• Written By: Gail F. Schwartz, MD

    The authors of this study examined the structure-function relationship in glaucoma using spectral-domain optical coherence tomography (SDOCT)-derived structural measurements and evaluated this relationship using a linear model. They found the strongest structure-function associations using SDOCT for retinal nerve fiber layer (RNFL) measurements at arcuate areas and inner retinal thickness measurements at the macula.

    This was a cross-sectional study that determined structure-function relationships for all of the participants in the Diagnostic Innovations in Glaucoma Study (DIGS) and the African Descent and Glaucoma Evaluation Study (ADAGES) who had undergone standard automated perimetry (SAP) and SDOCT within six months of each other. The authors analyzed results of 579 SAP and SDOCT examinations from 47 control subjects (80 eyes), 130 patients with suspected glaucoma (199 eyes) and 146 patients with glaucoma (213 eyes).

    The coefficient of determination (R2) for the association between SAP total deviation and SDOCT variables ranged from 0.01 (P=.02) for the nasal rim area to 0.30 (P < 0.001) for inferior inner retinal thickness at the macula. The linear model fit the data well.

    Overall, the relationship between structure and function in the present study was weak to moderate. Different factors have been proposed to explain the imperfect relationship between structure and function; important among them are eyes that show a lag in either the structural or the functional test during the disease course.

    The study's finding could be related to improvements in software analysis of SDOCT compared with time-domain OCT (TDOCT) macular thickness data, which now concentrates on the inner retinal layers instead of on all retinal layers at the macula. Such improvement has been made possible by the higher resolution of SDOCT compared with TDOCT, enabling better identification of the different retinal layers.

    Optic nerve and retinal imaging are at the forefront of developing strategies for gaining knowledge about disease state with the goal of earlier detection of damage. Weak correlation with visual fields was not surprising. Continued study of RNFL parameters will enhance our ability to detect disease and monitor progression.