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

Background/aim-It is widely accepted that hypercapnia results in increased retinal, choroidal, and retrobulbar blood flow. Reports of a visual respons e to hypercapnia appear mixed, with normal subjects exhibiting reduced temp oral contrast sensitivity in some studies, while glaucoma patients demonstr ate mid-peripheral visual field improvements in others. This suggests that under hypercapnic conditions a balance exists between the beneficial effect s of improved ocular blood flow and some other factor such as induced metab olic stress; the outcome may be influenced by the disease process. The aim of this study was to evaluate the contrast sensitivity response of untreate d glaucoma patients and normal subjects during mild hypercapnia. Methods-10 previously untreated glaucoma patients and 10 control subjects w ere evaluated for contrast sensitivity and intraocular pressure while breat hing 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 cy cles/degree (cpd) (p = 0.001). Mild hypercapnia caused a significant fall i n contrast sensitivity at 6, 12, and 18 cpd (p < 0.05), only in the glaucom a group. Conclusion-Glaucoma patients with early disease exhibit central vision defi cits as shown by contrast sensitivity testing at 3 cpd. Hypercapnia induces further contrast loss through a range of spatial frequencies (6-18 cpd) wh ich may be predictive of further neuronal damage due to glaucoma.