GLAUCOMA

Open Angle Glaucoma

Open angle glaucoma is a prevalent condition in Canada, particularly among people in their sixties and beyond. In OAG, there is a gradual loss of vision-carrying nerve fibres passing from the retina into the optic nerve. This results from either high pressure within the globe, or increased vulnerability to pressure of the very small blood vessels that feed the optic nerve at this entry point. Loss can be due to the excessive pressure or unhealthy optic disc vessels alone, but more often is a combination of the two.

Loss of vision in OAG is gradual and imperceptible, with the inessential peripheral vision first affected. It often takes years or even decades for significant loss to develop. Regular follow up visits and elaborate testing measures need to be carried out to pick up earliest evidence of loss, as well as progression, in patients felt to be at risk. At VRV, in addition to standard pressure measurement, peripheral visual field assessment and high definition imaging (Ocular Coherence Tomography (OCT), The Diopsys instrument is used to measure the electrical signal produced and transmitted by the retina in response to light, which has been shown to be impaired in glaucoma years before damage to the retina or to the visual field can be detected.

At the present time we are unable to directly treat the site of the damage, the optic disc, but can only manage open angle glaucoma by lowering the intraocular pressure. For this, eyedrops and sometimes oral medications can be used to reduce the output of aqueous humour, the fluid that inflates the eye and nourishes its internal lining cells. Other eyedrops can be used to increase the outflow from the uptake channel which carries this liquid back out to the bloodstream, through a filter known as the trabecular meshwork.

At VRV, Selective Laser Trabeculoplasty (SLT) may be used to painlessly, and with a high degree of safety, make small perforations in this filter. SLT can achieve the same end, increasing outflow of aqueous humour. It can also be used in conjunction with eyedrops for additional pressure lowering effect.

Finally, numerous surgical drainage procedures can be employed to divert fluid from the internal eye environment to the space underneath the surface membrane covering the front of the eye, the conjunctiva, where it is returned to the general circulation.

Management of open angle glaucoma is a long-term process and requires commitment from both patients and their doctor, but with proper care and attention to instructions, blindness from this condition is now quite rare.

Angle Closure Glaucoma

At VRV, patients with risk of angle closure glaucoma are managed on a referral basis. Treatment involves performance of laser peripheral iridotomy (LPI) which can often be curative. For this the YAG laser is used to creat a small hole in the iris, allowing aqueous humour to pass freely from the posterior chamber where it is produced, into the anterior chamber where it can pass out of the eye through a filter, the trabecular meshwork, located in the angle between the cornea and iris peripherally. This angle narrows with age, and in some people can block completely with a condition known as angle closure glaucoma. This can occur gradually over years, but more typically occurs as a rapid onset event accompanied by considerable deep eye pain, halos around lights and ultimately vision loss, in an acute angle glaucoma attack. This is a medical emergency, and can be broken with LPI if treated in time.