The Four Principal
Causes of Blindness

Worldwide, some 285 million people suffer from vision loss that interferes with daily activities; 39 million of them are totally blind. Multiple diseases can afflict the same eye. Three common and treatable diseases occur in the front of the eye. There currently is no cure for age-related macular degeneration, which occurs in the back of the eye near the retina.

Global estimates of the causes

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This is how you see with

Healthy Vision

Each of your eyes is about the size of a Ping-Pong ball. Impairment is caused by eye disease and conditions like structural abnormalities and aging. Some 80 percent of cases are preventable or treatable.

This is how you see with

Refractive Errors

Nearsightedness, farsightedness, and astigmatism are types of refractive errors, flaws that keep the eye from focusing light sharply on the retina. Absent lenses or surgery, they’re the most common causes of impairment.

Farsighted eye
Nearsighted eye
This is how you see with


The world’s leading cause of blindness, cataracts are caused when proteins in the lens clump together, blocking and distorting light to the retina. Surgery can restore sight.

This is how you see with


Glaucoma is caused by fluid buildup in the eye, resulting in pressure that can damage the optic nerve. If it’s caught early enough, surgery and medication may slow its advance.

This is how you see with

Age-Related Macular

Caused by an alteration of the underlying layers of the retina’s macular area, AMD affects photoreceptors that process images. There is no cure.

New Technologies
for the Retina

Vision may account for nearly half the activity in the brain. Failures in the retinal layers, which sense light and transmit signals, can lead to blindness that’s at present untreatable. This prognosis may change, however, if retinal treatments currently being tested (described below) prove effective.

Cell Patch

A patch coated with stem cell–derived epithelial cells is set behind deteriorating photoreceptors, replacing dead cells to slow or reverse age-related macular degeneration.

Cell Injection

Retinal progenitor cells are injected into the eye’s vitreous cavity, where they release factors to slow the progression of hereditary degeneration and blindness.

Subretinal Implant

A microchip that converts light into currents is implanted amid dead photoreceptors in the retina’s macular region, allowing the optic nerve to pick up electronic signals.

Retinal Implant

The Argus implant, now approved, bypasses damaged photoreceptors with the help of glasses, an external camera, a video processor, and an electrode array.

Gene Therapy

Step 1

A solution carrying a benign virus laden with the RPE65 gene—which provides instructions for a protein essential to vision—is injected near damaged photoreceptor cells.

Gene Therapy

Step 2

The virus delivers healthy RPE65 genes, and the protein products of these genes allow the photo­receptors to translate light into sight.

Manuel Canales and Daniela Santamarina, NGm Staff; patricia healy. art: Emily M. Eng. Photo: design pics inc, National Geographic Creative; Manipulations by NGM staff.
Sources: Vision Loss Expert Group; silvio paolo mariotti, World health organization; united nations Development Programme; Mark S. Humayun, University of Southern California; Henry Klassen, University of California, Irvine; Robert MacLaren, University of Oxford; Jean Bennett, University of Pennsylvania.