A New View of Normal Tension Glaucoma: Autoregulation and Systemic Blood Pressure

Glaucoma is an eye disease that leads to damage of the optic nerve, visual field loss and can progress to blindness. Traditionally, glaucoma and its treatment have been closely linked to intraocular pressures. In normal tension glaucoma, damage to the optic nerve occurs without any increase in intraocular pressure. Normal tension glaucoma most often occurs in the elderly and can lead to loss of sight and significant disability. Subjects with progressive visual field loss are often a highly motivated group of subjects, ready to take an active part in the treatment of their condition. Investigating the risk factors that contribute to the development of normal-tension glaucoma may shed light on the progression of the disease.

Subjects with normal tension glaucoma will have their demographic and clinical characteristics recorded and their eyes examined at baseline, 6-months and 12 months. Subjects will wear an external blood pressure cuff for 48 hours that will record blood pressure every 30 minutes. This same blood pressure recording procedure will be performed at baseline, at 6 months, and at 12 months. At these same time intervals, visual fields will also be measured, as per routine clinical care, by the treating ophthalmologist. The results of the visual field testing will be recorded. The primary outcome of the study will be visual field abnormalities and their relationship to dips in systemic blood pressure. Results will be published and will be used as a base for future projects that may impact treatment and the understanding of risk factors of normal tension glaucoma.

Inclusion criteria

• The IOP must be less than or equal to 21 mmHg without treatment and must have never been higher than 24 mmHg, without treatment.
• Gonioscopically open angles.
• Typical glaucomatous optic disc changes, including: rim thinning, cupping, rim notching, disc hemorrhage, nerve fiber layer defect, vertical cup/disc asymmetry ≥0.2.
• A reproducible visual field defect must have been demonstrated on at least three prior visual fields, as observed using standard automated perimetry with Swedish Interactive Threshold Algorithm (SITA-STANDARD) from the Humphrey Visual Field Analyzer using the 24-2 test pattern.
• There must have been progression of glaucomatous loss with the past 36 months, specifically, two or more adjacent non-peripheral points changed by 10dB relative to the average baseline value for the points, confirmed by two subsequent fields.

Exclusion criteria

• Subjects with a visual field defect attributable to conditions other than glaucoma, such as a history of intra-cranial or ENT mass lesion.
• Occludable narrow angles.
• Subjects with intermittent elevation of intraocular pressure associated with another form of glaucoma, including intermittent angle closure, inflammatory glaucoma, old pigmentary glaucoma, psedoexfoliation or uveitis.
• Subjects who cannot complete follow-up testing every six months for any reason.
• Subjects who are unable to provide informed consent or who refuse or whose physicians do not wish for the subjects to participate for any reason.