Gonioscopy is an important technique that enables viewing of the iridocorneal angle and allows assessment and diagnosis of different eye conditions.
Best practice standards for accurate diagnosis of Glaucoma are detailed in the National Health and Medical Research Council (NHMRC) guidelines. These include a comprehensive medical history (to identify risk factors), a full eye examination (including gonioscopy), an assessment of visual function (visual field analysis) and measurement of intraocular pressure.
Reasons for performing gonioscopy – what am I looking for?
Open-angle Glaucoma versus Closed-angle Glaucoma
Gonioscopy is important to perform in both patients with Glaucoma and patients that are considered Glaucoma suspects. It is a crucial box that needs to be ticked on your Glaucoma work-up checklist, to determine if an angle is wide open, narrow or closed. It can also detect the presence of peripheral anterior synechiae (PAS), a sign of chronic angle closure, and in certain instances can be used to break these aberrant connections of iris to anterior angle structures.
An angle is considered to be occludable when the pigmented trabecular meshwork (PTM) is visible in less than 90 degrees of the angles’ circumference. This is determined using gonioscopy with the patient in primary gaze. If a patient is deemed to have an occludable angle, this is an indication for laser peripheral iridotomy (LPI).
Gonioscopy allows for the identification and appreciation of subtle findings such as pigmentation within the angle. Secondary glaucomas like Pigment Dispersion Glaucoma (PDG) will demonstrate very dark pigmentation of the trabecular meshwork (even, tiramisu pattern). In Pseudoexfoliation Glaucoma (PXG), white fluffy material can be seen in the trabecular meshwork. Sampaolesi’s line can be present in both PDG and PXG and is visualised as a dark pigmented line situated anterior to Schwalbe’s line.
Angle recession occurs due to rupture of the longitudinal and circular ciliary muscle fibres following ocular trauma. With gonioscopy, this appears as a localised area of iris bending posteriorly instead of running flat and can also be seen as widening of the scleral spur. Since patients can develop Glaucoma secondary to angle recession after days, months and even years, it is important to perform gonioscopy in cases where there has been ocular trauma both recently and in the past.
Neovascularisation of the angle
Gonioscopy can be used to detect growth of new blood vessels in the anterior chamber angle. These abnormal vessels are leaky and can cause inflammation. It can also lead to scarring and narrowing of the angle. Gonioscopy should be performed in patients at risk including those with a history of Central Retinal Vein Occlusion, proliferative Diabetic Retinopathy, or other retinal ischaemic conditions.
Helpful Gonio Acronym
Corneal or conjunctival inflammation or infection
Lacerated or perforated globes.
Significant corneal abrasions or erosion
Significant epithelial basement membrane dystrophy
NHMRC Guidelines for the screening, prognosis, diagnosis, management and prevention of glaucoma 2010 https://www.nhmrc.gov.au/_files_nhmrc/publications/attachments/cp113_glaucoma_1204 04.pdf
Herschler J. Trabecular damage due to blunt anterior segment injury and its relationship to traumatic glaucoma. Trans Am Acad Ophthalmol Otolaryngol .1977;83:239