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


CONCLUSIONS
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.
Hosking
S L
SL
Neurosciences Research Institute, School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK. s.l.hosking@aston.ac.uk
Evans
D W
DW
Embleton
S J
SJ
Houde
B
B
Amos
J F
JF
Bartlett
J D
JD
D016022:Case-Control Studies; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D005901:Glaucoma / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D006935:Hypercapnia / Q000150:complications / Q000503:physiopathology*; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods; D014792:Visual Acuity / Q000502:physiology