UC San Diego

Purpose

To evaluate the relationship between intraocular pressure (IOP) and rates of retinal nerve fiber layer (RNFL) thickness change over time measured by spectral-domain (SD) optical coherence tomography (OCT).

Design

Observational cohort study.

Participants

The study involved 547 eyes of 339 patients followed up for an average of 3.9±0.9 years. Three hundred eight (56.3%) had a diagnosis of glaucoma and 239 (43.7%) were considered glaucoma suspects.

Methods

All eyes underwent imaging using the Spectralis SD OCT (Heidelberg Engineering GmbH, Heidelberg, Germany), along with IOP measurements and standard automated perimetry (SAP). Glaucoma progression was defined as a result of "Likely Progression" from the Guided Progression Analysis software for SAP. Linear mixed models were used to investigate the relationship between average IOP during follow-up and rates of RNFL thickness change, while taking into account potential confounding factors such as age, race, corneal thickness, and baseline disease severity.

Main outcome measures

The association between IOP and rates of global and sectorial RNFL thickness loss measured by SD OCT.

Results

Forty-six eyes (8.4%) showed progression on SAP during follow-up. Rates of global RNFL thickness change in eyes that progressed by SAP were faster than in those that did not progress (-1.02 vs. -0.61 μm/year, respectively; P = 0.002). For progressing eyes, each 1-mmHg higher average in IOP during follow-up was associated with an additional average loss of 0.20 μm/year (95% confidence interval [CI]: 0.08 to 0.31 μm/year; P < 0.001) of global RNFL thickness versus only 0.04 μm/year (95% CI: 0.01 to 0.07 μm/year; P = 0.015) for nonprogressing eyes. The largest associations between IOP and rates of RNFL change were seen for measurements from the temporal superior and temporal inferior sectors, whereas the smallest association was seen for measurements from the nasal sector.

Conclusions

Higher levels of IOP during follow-up were associated with faster rates of RNFL loss over time measured by SD OCT. These findings support the use of SD OCT RNFL thickness measurements as biomarkers for the evaluation of the efficacy of IOP-lowering therapies to slow down the rate of disease progression.