Glaucoma Characterisation and Diagnosis

Glaucoma Characterisation

Glaucoma is the leading cause of irreversible blindness in the world, as defined by best-corrected central visual acuity of less than 3/60 or a visual field of less than 10° in the better seeing eye ¹⁰.

Several lines of thought regarding Diabetes-related Glaucoma development suggest:

• Micro-vascular injuries caused by diabetes reduce blood flow to the retina and optic nerve areas resulting in reduced nutrient and oxygen supply to the Retinal Ganglion Cell (RGC) axons. Ultimately this is likely to induce the degeneration of the RGCs.
• Hyperglycaemia and lipid anomalies induced by diabetes could increase the risk of neuronal (nerve fibre) injury, indicating that the RGCs were more likely to be killed in the patients with diabetes. 
• The hyperglycaemia of aqueous humour in the eyes of  patients with diabetes would stimulate the formation and accumulation of a substance called fibronectin in the trabecular meshwork to promote depletion of trabecular meshwork cells, which could impair the outflow system of the aqueous humour and finally result in POAG ⁸.

Primary open angle glaucoma (POAG) is the most common type of glaucoma in individuals with diabetes, with nearly 70 million affected worldwide. Type 2 diabetes is a risk factor for primary open-angle glaucoma. This has been demonstrated by large epidemiologic studies including the Los Angeles Latino Eye Study and the Blue Mountains eye study in Australia. In patients with diabetes who have primary open-angle glaucoma, the glaucoma is treated the same way as for  patients without diabetes with open-angle glaucoma by lowering the eye pressure with medications, laser, and surgery if needed.

Neovascular glaucoma is another type of glaucoma for which patients with diabetes are at higher risk. In this type of glaucoma, patients usually have a severe form of diabetes-related retinopathy, in which new vessels exhibit abnormal growth which can extend to the iris and over the drainage angle which is the part of the eye where the aqueous humour drains, preventing aqueous humour outflow and may cause scar formation and a form of angle-closure glaucoma. The treatment plan includes treating the Diabetes-related Retinopathy, typically by a laser applied to the retina and injections of medications. Both treatments are intended to stop these abnormal new vessels from growing.  However, even if these vessels regress (die off or become less developed), the drainage angle may be so compromised that the eye pressure is uncontrolled even with eye drops. Some Laser treatments cannot be performed in these closed angles, so patients will sometimes require surgery to manage the neovascular glaucoma. Most ophthalmologists will choose to implant a glaucoma drainage device for immediate eye pressure control.

Steroid-induced glaucoma is a secondary open-angle glaucoma that is caused by steroid eye drops or injections for the treatment of Diabetes-related Macular Edema. Treatment for steroid-induced glaucoma includes eye drops, laser to the drainage system, or surgery such as a glaucoma drainage device to lower the eye pressure. Sometimes it is difficult to balance a treatment (steroids) that can improve your macular edema, uveitis, and ocular surface conditions and vision with the unwanted side effects (high eye pressure).