Glaucoma screening in fundus image

What is glaucoma?

Glaucoma is a disease that damages your eye’s optic nerve (which transmits images to your brain).

It usually happens when fluid builds up in the front part of your eye. That extra fluid increases the pressure in your eye called intraocular pressure, damaging the optic nerve. If the damage continues, glaucoma can lead to permanent vision loss.
Glaucoma is a leading cause of blindness for people over 60 years old. But blindness from glaucoma can often be prevented with early treatment.

How many types of glaucoma exist?

There are 2 types of glaucoma: primary open-angle glaucoma and angle-closure glaucoma.

Open-angle glaucoma

This is the most common type of glaucoma. It happens gradually, where the eye does not drain fluid as well as it should (like a clogged drain). As a result, eye pressure builds and starts to damage the optic nerve. This type of glaucoma is painless and causes no vision changes at first.

Angle-closure glaucoma (also called “closed-angle glaucoma” or “narrow-angle glaucoma”)

This type happens when someone’s iris is very close to the drainage angle in their eye. The iris can end up blocking the drainage angle. When the drainage angle gets completely blocked, eye pressure rises very quickly. This is called an acute attack. It is a true eye emergency, and you should call your ophthalmologist right away or you might go blind.
Signs of an acute angle-closure glaucoma attack are blurry vision, severe eye pain, headache, nausea, vomit, you can also see rainbow-colored rings or halos around lights.
Many people with angle-closure glaucoma develop it slowly. There are no symptoms at first, so they don’t know they have it until the damage is severe or they have an attack. 

The Cup-to-disc ratio
The CDR is a measurement used to assess the progression of glaucoma.

The optic disc is the anatomical location of the eye's "blind spot", the area where the optic nerve and blood vessels enter the retina. The optic disc can be flat or it can have a certain amount of normal cupping.

But glaucoma, which is in most cases associated with an increase in intraocular pressure, often produces additional pathological cupping of the optic disc.

The pink rim of disc contains nerve fibers. The white cup is a pit with no nerve fibers. As glaucoma advances, the cup enlarges until it occupies most of the disc area.
The cup-to-disc ratio compares the diameter of the "cup" portion of the optic disc with the total diameter of the optic disc.

The normal cup-to-disc ratio is 0.4. A large cup-to-disc ratio may imply glaucoma or other pathology.

However, cupping by itself is not indicative of glaucoma. Rather, it is an increase in cupping as the patient ages that is an indicator for glaucoma.

What are the symptoms of glaucoma?

Most people with open-angle glaucoma do not notice any change in their vision until the damage is quite severe.

This is why glaucoma is called the “silent thief of sight.” Having regular eye exams can help your ophthalmologist find this disease before you lose vision. Your ophthalmologist can tell you how often you should be examined.