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. 2001 Nov;85(11):1352–1356. doi: 10.1136/bjo.85.11.1352

Hypercapnia invokes an acute loss of contrast sensitivity in untreated glaucoma patients

S Hosking 1, D Evans 1, S Embleton 1, B Houde 1, J Amos 1, J Bartlett 1
PMCID: PMC1723756  PMID: 11673305

Abstract

BACKGROUND/AIM—It is widely accepted that hypercapnia results in increased retinal, choroidal, and retrobulbar blood flow. Reports of a visual response to hypercapnia appear mixed, with normal subjects exhibiting reduced temporal contrast sensitivity in some studies, while glaucoma patients demonstrate mid-peripheral visual field improvements in others. This suggests that under hypercapnic conditions a balance exists between the beneficial effects of improved ocular blood flow and some other factor such as induced metabolic stress; the outcome may be influenced by the disease process. The aim of this study was to evaluate the contrast sensitivity response of untreated glaucoma patients and normal subjects during mild hypercapnia.
METHODS—10 previously untreated glaucoma patients and 10 control subjects were evaluated for contrast sensitivity and intraocular pressure while breathing room air and then again during mild hypercapnia.
RESULTS—During room air breathing, compared with normal subjects, glaucoma patients had higher IOP (p = 0.0003) and lower contrast sensitivity at 3 cycles/degree (cpd) (p = 0.001). Mild hypercapnia caused a significant fall in contrast sensitivity at 6, 12, and 18 cpd (p < 0.05), only in the glaucoma group.
CONCLUSION—Glaucoma patients with early disease exhibit central vision deficits as shown by contrast sensitivity testing at 3 cpd. Hypercapnia induces further contrast loss through a range of spatial frequencies (6-18 cpd) which may be predictive of further neuronal damage due to glaucoma.



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Figure 1  .

Figure 1  

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Contrast sensitivity outcomes measured at 3, 6, 12, and 18 cycles per degree (cpd) for glaucoma patients and normal subjects. Measurements were taken at baseline (BL), in room air through a breathing mask (RA), and while breathing carbon dioxide (CO2 ). Significant differences between groups are noted by the plus symbol, and differences due to conditions are noted by an asterisk.

Figure 2  .

Figure 2  

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Histogram showing end tidal carbon dioxide levels (ETCO2 )in room air and in hypercapnia for normal subjects and glaucoma patients. Significant differences from baseline are indicated by an asterisk.

Figure 3  .

Figure 3  

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Oxygen saturation levels measured by pulse oximetry in room air and hypercapnia for normal subjects and glaucoma patients. Significant differences from baseline are indicated by an asterisk.

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