Structure–function assessment in glaucoma based on perimetric sensitivity and en face optical coherence tomography images of retinal nerve fiber bundles

Abstract

Many studies have assessed structure–function relations in glaucoma, but most without topographical comparison across the central 30°. We present 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. Forty-four patients with glaucoma (median age 61 years) were recruited and tested with Optical Coherence Tomography (OCT) and perimetry. Six rectangular volume scans were gathered, and then montaged to provide en face views of the RNFL bundles. We calculated the proportion of locations showing a perimetric defect that also showed an en face RNFL defect; and the proportion of locations falling on an RNFL defect that also showed a perimetric defect. A perimetric defect for a location was defined as a total deviation (TD) value equal to or deeper than -4 dB. We found that the median (IQR) number of locations with abnormal RNFL bundle reflectance that also had abnormal TD was 78% (60%) and for locations with abnormal TD that also had abnormal RNFL bundle reflectance was 75% (44%). 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.

Predicting perimetric defects from en face maps of retinal nerve fibre layer reflectance

“…The first exploratory analysis used data from Group 1, from a prior study conducted in Indiana 24 : 15 patients with glaucoma, aged 59–79 years, median 67 years, interquartile range (IQR) 64–73 years; 15 controls aged 56–79 years, median 67 years, IQR 63–72 years. The first evaluation analysis used data from Group 2, from a prior study conducted in Saudi Arabia 25 : 23 patients with glaucoma aged 35–70 years, median 53 years, IQR 49–60 years; 10 age‐similar controls aged 39–63 years, median 54 years, IQR 51–58 years. The second exploratory analysis used data from all the controls from Groups 1 and 2, and all but one of the patients (data for one patient from Group 2 were removed for this analysis).…”

“…Details of inclusion and exclusion criteria have been published elsewhere 25,26 . Briefly, all participants were required to have clear ocular media, corrected monocular distance visual acuity of at least 6/12 at the study visit, refractive correction between +3.00 and −6.00 dioptre spherical equivalent and cylindrical correction <3.0 dioptres.…”

“…Details of inclusion and exclusion criteria have been published elsewhere. 25,26 Briefly, all participants were required to have clear ocular media, corrected monocular distance visual acuity of at least 6/12 at the study visit, refractive correction between +3.00 and −6.00 dioptre spherical equivalent and cylindrical correction <3.0 dioptres. Participants were required to be under the care of an eye care practitioner and to have had a recent clinical examination with normal retinal findings (except those associated with glaucoma in the diagnosed patients); patients with glaucoma were also required to have glaucomatous perimetric defects.…”

“…Details of spectral-domain optical coherence tomography (SD-OCT) imaging were given in prior studies. 24,25 Briefly, a Spectralis OCT2 (Heidelberg Engineering, heide lberg engin eering. com) was used for SD-OCT imaging of the RNFL.…”

“…For these patients, AOSLO found that if RNFL reflectance defects were due to loss of fibres, then the corresponding perimetric defects were usually deep. The optimal criterion developed on these carefully selected patients was then evaluated with an independent dataset gathered from newly‐recruited subjects in a different clinic 25 . Subsequently, a second exploratory phase performed an expanded analysis that combined these two datasets and finally a second evaluation was conducted on a third dataset.…”