The Relationship between intraocular pressure and progressive retinal nerve fiber layer loss in glaucoma

Abstract

Purpose: To evaluate the relationship between intraocular pressure (IOP) and progressive retinal nerve fiber layer (RNFL) loss, as measured by scanning laser polarimetry with enhanced corneal compensation (GDx ECC), in a cohort of glaucoma patients and individuals suspected of having the disease followed over time.

Design: Observational cohort study.

Participants: The study included 344 eyes of 204 patients recruited from the Diagnostic Innovations in Glaucoma Study (DIGS). There were 98 eyes (28%) with a diagnosis of glaucoma and 246 (72%) were considered glaucoma suspects at baseline.

Methods: Images were obtained annually with the GDx ECC scanning laser polarimeter, along with stereophotographs and SAP. The study included a total of 1211 GDx ECC visits with an average of 3.5 visits per eye. Progression was determined by the Guided Progression Analysis software for SAP and by masked assessment of stereophotographs performed by expert graders.

Main outcome measures: Random coefficient models were used to evaluate the relationship between IOP and RNFL thickness measurements over time in progressors and nonprogressors. Models were adjusted for baseline diagnosis and central corneal thickness.

Results: For all 344 eyes, the overall rate of change for the GDx ECC average thickness at an average IOP of 17 mmHg was -0.25 microm per year (P = 0.002). Each 1-mmHg higher IOP was associated with an additional loss of 0.05 microm per year of RNFL (P = 0.001). Twenty-nine eyes (8%) showed progression on SAP and/or optic disc stereophotographs. These eyes had a significantly higher rate of RNFL change (-0.95 microm/year) than nonprogressors (-0.17 microm/year; P = 0.001). For progressors, each 1-mmHg higher IOP was associated with an additional loss of 0.13 microm per year of RNFL.

Conclusions: Higher levels of IOP during follow-up were significantly related to higher rates of progressive RNFL loss detected by the GDx ECC. These findings suggest that the GDx ECC may be helpful in monitoring progression and estimating rates of change in patients with glaucoma or suspected of having the disease. Also, they may contribute to a better understanding of the relationship between IOP and structural deterioration in glaucoma.

Financial disclosure(s): Proprietary or commercial disclosure may be found after the references.

Figure 1

Distribution of average intraocular pressure (IOP) measurements during follow-up for all 344 eyes included in the study.

Figure 2

Scatterplot illustrating the relationship between rates of change in the scanning laser polarimetry with enhanced corneal compensation parameter temporal–superior–nasal–inferior–temporal (TSNIT) average and intraocular pressure (IOP). Rates of change are shown for eyes that progressed by visual fields and/or stereophotographs (progressors) as well as for eyes that did not (nonprogressors). RNFL = retinal nerve fiber layer.

Figure 3

Radar plot illustrating the rates of change in scanning laser polarimetry with enhanced corneal compensation retinal nerve fiber layer measurements according to the sectors around the optic disc. Eyes that showed progression on visual fields and/or optic disc stereophotographs had greater loss of the RNFL in the inferior and superior sectors. I = inferior; N = nasal; S = superior; T = temporal.

Figure 4

Scatterplots illustrating the relationship between intraocular pressure (IOP) and rates of change in the scanning laser polarimetry with enhanced corneal compensation for the inferior temporal (A, S13), superior temporal (B, S4), and temporal sectors (C, S16). Rates of change are shown for eyes that progressed by visual fields and/or stereophotographs (progressors) as well as for eyes that did not (nonprogressors). RNFL = retinal nerve fiber layer.

Figure 4

Scatterplots illustrating the relationship between intraocular pressure (IOP) and rates of change in the scanning laser polarimetry with enhanced corneal compensation for the inferior temporal (A, S13), superior temporal (B, S4), and temporal sectors (C, S16). Rates of change are shown for eyes that progressed by visual fields and/or stereophotographs (progressors) as well as for eyes that did not (nonprogressors). RNFL = retinal nerve fiber layer.

Figure 5

Scanning laser polarimetry with enhanced corneal compensation measurements in an eye that showed progression on optic disc stereophotographs with an average intraocular pressure (IOP) of 27 mmHg during follow-up. The optic disc photographs (middle row) show progressive development and enlargement of an inferior temporal localized retinal nerve fiber layer (RNFL) defect (blank arrows). The standard automated perimetry Guided Progression Analysis (SAP GPA; bottom row) shows corresponding progression on the superior nasal portion of the visual field (red arrows), however, as only 2 points showed repeatable change by this method, it was not sufficient to be flagged as likely progression. The scanning laser polarimetry with enhanced corneal compensation retardation maps (upper row) show progressive loss of the RNFL in the corresponding location. Avg = average; GHT = glaucoma hemifield test; GPA = Guided Progression Analysis; Inf = inferior; Sup = superior; TSNIT = temporal–superior–nasal–inferior–temporal.