Acquired pits of the optic nerve (APONs) are an area of focal loss of neural tissue associated with a discrete area of depression/excavation within the optic cup at the level of the lamina cribrosa. It is commonly associated with glaucoma and can be seen on the optic disc when examining the back of a patient's eye. It causes a characteristic visual field defect in the central 5-10 degrees of vision which has a significant impact of a patient's daily activities. There is no treatment to restore vision once it has formed.

Previous studies suggest mechanical stress across this part of the eye may have role in the formation of APONs. The investigators therefore hypothesise that if a patient has a more elliptical shaped optic disc, which would have more irregular mechanical stress across it, it may have a higher risk of an APON forming.

Patients with glaucoma attending the ophthalmology department at University Hospital of Wales have regular photographs taken of the optic nerve/optic disc as part of their routine clinical care in order to monitor the condition. The research team, who are all practicing ophthalmologists in the department, will review anonymised photographs to find optic discs with APONs, and another group with glaucoma but no APONs to use as a control. The research team will then measure the dimensions of the optic disc to determine if APONs are more common in optic discs with a more elliptical shape. The patients' clinical notes will then need to be accessed to collect data on the age, sex and diagnosis. This data will be anonymised using ID numbers once collected.

The final outcomes of the study will the average measured dimensions of the optic disc in each group, and the position that the APON occurs.

Inclusion Criteria:

• Documented diagnosis of primary open angle glaucoma (POAG) or normal tension glaucoma (NTG)
• Under the care of the ophthalmology department at University Hospital of Wales
• Available optic disc photograph
• Presence of an APON for disease group, no APON for control group

Exclusion Criteria:

• No documented diagnosis of POAG/NTG
• Other form of glaucoma - e.g. traumatic glaucoma/juvenile glaucoma
• Poor photograph quality
• Optic disc tilted so that the margin is obscured and cannot be demarcated
• Coexisting disc pathology, e.g. congenital optic disc pit

Patients under the care of University Hospital of Wales Ophthalmology Department with optic nerve head photographs taken as part of routine clinical care for monitoring of glaucoma.