There are many ways to classify glaucoma. It can be classified based on the status of drainage angle of the eye (‘open’ vs. ‘closed’) and whether glaucoma occurs as a primary disease or secondary to other disease processes such as inflammation, pseudo-exfoliation and diseases affecting the retina. Most glaucoma occurs in older adults, but congenital (from birth) and early-onset forms can occur.
Most people affected with glaucoma are unaware that they have glaucoma. The disease tends to be asymptomatic until very late stages. As the peripheral vision is affected more than central vision in glaucoma, only specialised clinical examination and diagnostic methods can pick up early cases. In addition, as one eye tends to be more affected than the other, the better eye may compensate. It is crucial to detect glaucoma as early as possible because the vision that has been lost from glaucoma is unfortunately lost permanently. Treatment of ocular hypertension may reduce the chance of developing glaucoma.
Diagnosis of glaucoma is based on clinical examination of the eye and additional testing. Clinical exam involves a complete examination of the eye comprising measurement of intraocular pressure, gonioscopy (exam of the drainage angle of the eye) and formal assessment of the optic nerve. Additional tests performed in the clinic include a computerised assessment of the optic nerve (OCT scan) and a visual field test (evaluation of peripheral vision). All these parameters are considered collectively before a diagnosis of glaucoma can be made or excluded. Sometimes it is not possible to say whether one has glaucoma and these patients require ongoing monitoring. It is important to monitor patients with glaucoma to ensure that the intraocular pressure is sufficiently low to offset optic nerve damage and increasing peripheral vision loss. In late disease, central vision loss may ensue (blindness) but this is rare with today’s treatments.
The main aim of treatment is to prevent vision loss from glaucoma. The only modifiable factor that is targeted in glaucoma treatment is the intraocular pressure. Lowering of intraocular pressure can be performed in many ways. All these approaches have different side-effects and safety profiles and can be discussed with your specialist.
Medications (and tablets) lower eye pressure by either decreasing fluid production in the eye or increasing fluid drainage from the eye. These can be given alone or in combination with other drops. Eye drops are limited by side effects and problems with adherence and compliance.
Laser surgery has a key role in glaucoma management. Laser iridotomy (making a small hole in the coloured part of the eye) is used if a patient has a ‘closed’ drainage angle to allow another passage of fluid towards the drainage angle. Selective Laser Trabeculoplasty (SLT) allows a laser to be directed at the drainage angle to improve the drainage of fluid which then lowers eye pressure. SLT is very safe and effective and can be repeated if necessary. Cyclodiode laser reduces the amount of fluid produced by the eye and is typically performed when glaucoma doesn’t respond to other treatments.
A trabeculectomy is the most traditional surgical method to treat moderate-advanced glaucoma. It works by lowering eye pressure through the making of a channel in the eye wall that allows fluid to escape from the eye. Anti-scarring medication (mitomycin-C) is used to stop the hole from healing over, and special stitches control the amount of fluid escaping the eye. A glaucoma drainage tube (e.g. Baerveldt tube) is used in special cases of secondary glaucoma and also when traditional surgery has failed.
Several new procedures have been developed that are quicker and safer than the trabeculectomy and have been termed minimally-invasive glaucoma surgery (MIGS). Two of these devices (I-stent inject™ and Cypass™) must be performed with cataract surgery and typically reserved for mild-moderate glaucoma cases. I-stent inject™ comprises two 0.4mm titanium stents that are implanted through the drainage angle (trabecular meshwork) through a micro-incision. Cypass™ is a 6.3mm tube with 64 fenestrations made of a special plastic (polyimide) that is inserted into a different part of the drainage angle (supraciliary space). When performed with cataract surgery, both I-stent inject™ and Cypass™ lower eye pressure compared to cataract surgery alone and reduce reliance on eye pressure-lowering medications. The XEN™ implant is a 6mm gelatine stent that can be performed as a solo-procedure or with cataract surgery for moderate-advanced glaucoma. XEN™ lowers intraocular pressure by draining fluid from inside the eye to the space under the eye coat (conjunctiva) with mitomycin-C, similar in principle to a trabeculectomy.
Further information on glaucoma and glaucoma surgery can be found here:
Glaucoma Australia: https://www.glaucoma.org.au/
I-stent inject: https://www.glaukos.com/au/treatment-options/micro-invasive-glaucoma-surgery-migs/
XEN Implant: www.xengelstent.com/