Patients with severe sleep apnea have several differences in their corneal makeup compared with healthy eyes, a team of Spanish researchers report. 
Their study, published in Cornea, enrolled 25 patients recently diagnosed with severe obstructive sleep apnea-hypopnea syndrome (with an apnea-hypopnea index above 30) and a paired control group of 25 healthy subjects. The investigators gave all patients a complete eye exam to look at topographic, anatomic and biomechanical variables.
The majority of patients in both groups were men (23 in each group) with an average age of 64. The study reported no differences in keratometry, cylinder, refractive indexes or pachymetry. 
However, the investigators found that the mean corneal volume for those with sleep apnea was 58.64 ± 3.05mm compared with 60.48 ± 3.33mm for healthy patients. Additionally, the mean minimum radius for sleep apnea subjects was 7.49 ± 0.31 and 7.36 ± 0.30 in the controls. The study found the apex readings between the groups was 8.46 ± 5.18 in sleep apnea patients and 2.38 ± 2.36 in the controls. In the apnea group, researchers noted two eyes were given a topographic diagnosis of keratoconus, and imaging detected subclinical keratoconus in another six.
Many of the corneal topographic and biomechanical variables in patients with severe obstructive sleep apnea-hypopnea syndrome present different values from the general population with a trend toward keratoconus, the researchers said in their study.