This study shows a good agreement between RNFL bundle defects and perimetric loss in patients with glaucoma. Photo: Brian Fisher, OD, April Stursma, OD, Austin Lifferth, OD, and Stephanie Carter, OD.  Click image to enlarge.

Many studies have assessed structure-function relations in glaucoma but most without topographical comparison across the central 30°. In a recent study, researchers presented a method for assessing structure-function relations with en face images of retinal nerve fiber layer (RNFL) bundles allowing topographical comparison across much of this retinal area and found a good agreement between structural and functional measures in patients with glaucoma, which was consistent with other studies.

Forty-four patients with glaucoma with a median age of 61 years old were tested with OCT and perimetry. Six rectangular volume scans were gathered and montaged to provide en face views of the RNFL bundles. En face images of the RNFL bundles covering most of the 24-2 perimetric locations were used to establish the spatial structure-function comparison. A perimetric defect for a location was defined as a total deviation value equal to or deeper than -4dB.

The team found that the median number of locations with abnormal RNFL bundle reflectance that also had abnormal total deviation was 78%, and for locations with abnormal total deviation that also had abnormal RNFL bundle reflectance, it was 75%. “We demonstrated a potential approach for structure-function assessment in glaucoma by presenting a topographic reflectance map, confirming results of previous studies and including larger retinal regions,” the authors wrote.

“En face images enable the visualization of the extent and locations of the structural defects, despite a wide range of glaucomatous defects included in this study. The extent and distribution of structural defects are two critical features to assess the agreement between structural and functional defects in patients with glaucoma, as demonstrated in a prior study from our lab using customized perimetric locations.”

The authors suggest more research is needed to investigate accurate assessment of structure-function relations in early to moderate cases of glaucoma.