Symptoms: Blurred vision, Floaters, Dark areas in the field, Sudden vision loss

Diabetes affects the small blood vessels and also causes nerve damage (neurodegeneration). Rich in both nerve and vascular cells, the retina is the tissue most affected by this disease.

The early (non-proliferative) stage usually has no symptoms; microaneurysms and small haemorrhages form in the vessels. In the advanced (proliferative) stage, abnormal new vessels grow that can bleed and pull, leading to severe vision loss and retinal detachment. When fluid collects in the macula (diabetic macular oedema), central vision drops markedly.

Treatment rests on controlling blood sugar, blood pressure and cholesterol; laser, intravitreal anti-VEGF injections and, in advanced cases, vitrectomy are used as needed. Everyone diagnosed with diabetes should have a retinal exam at least once a year.

Symptoms: A spot or gap in the centre, Straight lines looking wavy, Faded colours

The dry type is the most common form (about 80% of patients) and progresses slowly. Deposits called drusen form under the retina, the macula thins and central vision gradually declines.

The wet type is less common but faster and more serious. Abnormal vessels growing under the retina leak and bleed; left untreated they can cause permanent damage.

In the wet type, intravitreal anti-VEGF injections suppress the growth of abnormal vessels. In the dry type, certain vitamin and mineral supplements (AREDS) have been shown to slow progression. Quitting smoking and eating well reduce the risk.

Symptoms: Sudden flashes of light, Many floaters, A curtain over the vision

From the moment the retina starts to separate, nerve cells begin to be lost; the detached area loses its blood supply and oxygen. Left untreated it leads to permanent vision loss.

It usually develops after a retinal tear, when intraocular fluid seeps beneath the retina. High myopia, eye trauma, previous eye surgery and diabetic retinopathy all raise the risk.

In early, limited cases the area around the tear can be secured with laser or cryotherapy. In advanced cases the retina is repositioned with surgery such as vitrectomy or scleral buckling. Treatment should begin as soon as possible.

Symptoms: Sudden flashes, New floaters, Shadowing at the edge

With age the vitreous gel shrinks, sticks to the retina and tugs on it; this traction can create a tear. High myopia, trauma and previous eye surgery raise the risk.

Seeking care as soon as symptoms appear is critical. Laser (photocoagulation) or cryotherapy applied around the tear can prevent fluid from seeping underneath and stop a detachment from developing.

Symptoms: Sudden painless vision loss, A dark area in the field, Blurred vision

Nerve cells are very intolerant of oxygen loss; if a blockage is not relieved quickly, permanent retinal damage follows. Vein occlusions (central CRVO, branch BRVO) cause leakage and oedema; artery occlusions (CRAO, BRAO) cause a sudden loss of blood flow.

The main risk factors are high blood pressure, diabetes, high cholesterol, smoking and arteriosclerosis. Treatment involves controlling the underlying vascular disease, anti-VEGF or corticosteroid injections and laser. Artery occlusions need emergency assessment.

Symptoms: Distorted or wavy vision, Reduced central vision

It usually develops with age or after minor damage to the retina. Thin at first, it may cause no symptoms; over time it tugs on the macula, distorting its shape, or thickens and reduces vision.

Mild cases can be monitored. With significant vision loss, peeling the membrane during vitrectomy aims to improve vision; it is surgery that requires experience.

Symptoms: A spot in the centre, Bending of straight lines, Difficulty seeing detail

It usually forms when the vitreous pulls on the macula with age; trauma and other retinal diseases can also cause it. It progresses through three stages, and central vision loss grows as the hole enlarges.

The most common treatment is vitrectomy: the vitreous is removed and a gas bubble is placed inside the eye to help the hole close. Head positioning afterwards may matter; visual recovery can take a few months.

Symptoms: Blurred vision, Dark spots in the field, Vision loss in advanced stages

High blood pressure narrows and hardens the retinal vessels; in advanced stages bleeding, fluid leakage and swelling of the optic nerve (papilloedema) can appear. It is usually classified into four stages.

The first step in treatment is bringing blood pressure under control. Because it often causes no symptoms, regular eye exams are important; advanced cases may need laser or injections.

Symptoms: Night blindness, Tunnel vision, Narrowing visual field

Because the rod cells are affected first, the earliest sign is usually night blindness. As it progresses, peripheral vision is lost and tunnel vision develops; in late stages central vision can be affected too.

There is no definitive cure yet; care aims to slow progression and preserve quality of life. Research continues in areas such as gene therapy, stem cells and the bionic eye. People with a family history should have regular check-ups.

Symptoms: Floaters, Flashes of light, Sudden blurring

With age the vitreous shrinks and separates from the retina (vitreous detachment). This is usually harmless, but it can pull on the retina and cause a tear or detachment. Bleeding into the vitreous (vitreous haemorrhage) can cause sudden vision loss.

Mild floaters usually need no treatment. When the vitreous pulls on the macula (vitreomacular traction) or there is heavy bleeding, an intravitreal injection or vitrectomy may be considered.