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

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 eVects 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. (Br J Ophthalmol 2001;85:1352-1356

Retrobulbar haemodynamics and contrast sensitivity improvements after CO2 breathing

“…Two other studies used CO 2 and room air for the gas perturbation to achieve an isoxic hypercapnia (Roff et al. 1999; Hosking et al. 2001).…”

“…1997). Hypercapnia invokes an acute loss of contrast sensitivity in untreated glaucoma patients (Hosking et al. 2001).…”

Ocular haemodynamic responses to induced hypercapnia and hyperoxia in glaucoma

“…This is consistent with previous reported findings. 28 The IOP drop was greater in normal subjects than in glaucoma patients, a difference which may be accounted for by the previous pressure lowering treatment in the glaucoma group.…”

The effect of hypercapnia on the sensitivity to flicker defined stimuli

“…More recently, it has been shown that changes in retinal and choroidal blood flow as a result of hypercapnia or hypocapnia significantly improved or reduced visual acuity, respectively, with a significant correlation with increased arterial blood flow during hypercapnia 24. Finally, Hosking et al 25 reported lower contrast sensitivity during hypercapnia in patients with untreated glaucoma compared with controls, possibly caused by an impaired circulation. These findings suggest that improved ocular blood flow has a significant positive effect on visual function.…”