Invest Ophthalmol Vis SciOctober 20179 citations

Patients With Normal Tension Glaucoma Have Relative Sparing of the Relative Afferent Pupillary Defect Compared to Those With Open Angle Glaucoma and Elevated Intraocular Pressure.

Lawlor Mitchell, Quartilho Ana, Bunce Catey, Nathwani Neil, Dowse Emily, Kamal Debbie, Gazzard Gus

View on PubMed DOI: 10.1167/iovs.17-21688

AI Summary

Normal tension glaucoma patients show less relative afferent pupillary defect for a given visual field loss than high-pressure glaucoma patients, suggesting differing damage mechanisms and potentially mitochondrial involvement in NTG.

Abstract

Purpose

We determined whether there is relative sparing of pupil function in glaucoma patients with normal pressures compared to those with high pressures.

Methods

A cross-sectional study was done of 68 patients with primary open angle glaucoma (POAG): 38 had normal IOPs on all-day phasing before treatment (never >21 mm Hg), with confirmed progression of glaucomatous optic neuropathy (NTG) and 30 had glaucomatous optic neuropathy associated with elevated intraocular pressures (>25 mm Hg; HP-POAG). The relative afferent pupillary defect (RAPD) was quantified with the RAPDx device, and mean deviation of visual field loss was obtained from reliable Humphrey visual fields. Outcomes measures evaluated were difference in slope between NTG and HP-POAG when plotting: (1) RAPD score against difference in mean deviation (MD) between eyes, and (2) RAPD score against difference in RNFL thickness between eyes.

Results

The slopes for magnitude of RAPD versus difference in MD were -0.06 (95% confidence interval [CI], -0.076, -0.044) for patients with NTG and -0.08 (95% CI, -0.109, -0.067) for those with HP-POAG. Fitting the interaction term showed a statistically significant difference between the slopes (0.023; 95% CI [0.0017, 0.0541]; P value = 0.037; HP-POAG reference group). Thus, for difference in MD, the slope for patients with NTG was flatter than the slope for those with HP-POAG.

Conclusions

Glaucoma patients with NTG have a lesser RAPD for a given level of intereye difference of HVF MD, compared to patients with high IOPs. This suggests that damage to intrinsically photosensitive retinal ganglion cells (ipRGCs) differs between the normal and high-pressure forms of open-angle glaucoma (OAG), and supports the theory that mitochondrial optic neuropathies may have a role in the group of diagnoses currently termed normal tension glaucoma.

MeSH Terms

AgedCross-Sectional StudiesDark AdaptationFemaleGlaucoma, Open-AngleHumansIntraocular PressureLow Tension GlaucomaMaleMiddle AgedOcular HypertensionPupilPupil DisordersTonometry, Ocular

Shields Classification

Ch. 2Intraocular Pressure and Tonometry

Ch. 4Optic Nerve, Retina, and Choroid

Ch. 11Chronic Open-Angle Glaucoma and Normal Tension Glaucoma

Key Concepts4

The slopes for magnitude of relative afferent pupillary defect (RAPD) versus difference in mean deviation (MD) were -0.06 (95% confidence interval [CI], -0.076, -0.044) for patients with normal tension glaucoma (NTG) and -0.08 (95% CI, -0.109, -0.067) for those with high-pressure primary open angle glaucoma (HP-POAG) in a cross-sectional study of 68 patients.

PrognosisCross-sectionalCross-sectional studyn=68 patientsCh6Ch12

The interaction term showed a statistically significant difference between the slopes of RAPD magnitude versus difference in MD (0.023; 95% CI [0.0017, 0.0541]; P value = 0.037; HP-POAG reference group) in a cross-sectional study of 68 patients with primary open angle glaucoma (POAG).

Comparative EffectivenessCross-sectionalCross-sectional studyn=68 patientsCh6Ch12

Glaucoma patients with normal tension glaucoma (NTG) have a lesser relative afferent pupillary defect (RAPD) for a given level of intereye difference of Humphrey Visual Field (HVF) Mean Deviation (MD), compared to patients with high intraocular pressures (IOPs), suggesting that damage to intrinsically photosensitive retinal ganglion cells (ipRGCs) differs between normal and high-pressure forms of open-angle glaucoma (OAG).

MechanismCross-sectionalCross-sectional studyn=68 patientsCh5Ch12

The finding that glaucoma patients with normal tension glaucoma (NTG) have a lesser relative afferent pupillary defect (RAPD) compared to patients with high intraocular pressures (IOPs) supports the theory that mitochondrial optic neuropathies may have a role in the group of diagnoses currently termed normal tension glaucoma.