What Vision Loss Looks Like

Different eye conditions damage vision in different patterns, and the pattern tells your doctor where the problem is. Trouble at the front of the eye (the cornea or the lens) blurs the whole picture. Trouble at the center of the retina takes the middle of the view. Glaucoma takes the edges. A stroke can remove one whole side. The simulator below applies each of these to an everyday scene so you can see the difference, and so family members can understand what someone they care for is experiencing.

Two things the pictures cannot show. First, the simulator shows one eye at a time. With both eyes open the fields overlap, so damage in one eye is often hidden by the other, which is one reason eye disease goes unnoticed. Second, missing areas are not experienced as black holes. The brain fills them in with its best guess, so a person with advanced glaucoma sees a complete picture with pieces quietly absent from it. The "filled in" rendering is the realistic one; the black rendering is there because it makes the extent of the loss easier to appreciate.

These simulations are approximations for understanding, not a diagnosis or a measurement. If any of them look like your own vision, make an appointment; if you have a new curtain, shadow, or shower of floaters, call the same day.

Glaucoma

Glaucoma damages the optic nerve, usually from eye pressure the nerve cannot tolerate. It takes side vision first, typically in arcs above or below the center that start toward the nose, and it spares the center until late. Because the loss is slow, painless, and filled in by the brain, most people feel nothing until a large part of the field is gone. That is why glaucoma is found by testing, not by symptoms, and why the treatment (drops, laser or surgery) is aimed at protecting what remains rather than restoring what is lost.

The "Paint your own" pattern lets you mark cells to match a visual field printout. Dr. Katz can set it up in the exam room and send it to your phone with the QR code so you can show family what your test means.

Cataract

A cataract is clouding of the eye's natural lens. Because the lens is in the path of all the light entering the eye, everything is affected at once: the picture softens, contrast drops, colors turn yellow or brown, and lights at night grow halos and glare, which is often what makes night driving hard first. Reading needs more light than it used to. Unlike glaucoma, this damage is reversible: cataract surgery replaces the cloudy lens with a clear implant, and the color and sharpness come back.

Macular degeneration

Age-related macular degeneration (AMD) affects the macula, the small central area of the retina responsible for reading, recognizing faces and seeing fine detail. Side vision is kept, so people with even advanced AMD walk around safely but cannot read or make out faces.

• Dry AMD is slow. The center fades, print needs more light and magnification, and a blank or grey spot may appear in the middle of the view.
• Wet AMD is sudden. Abnormal blood vessels leak under the macula, so straight lines look bent or wavy and a dark spot can appear over days. It is treated with injections of medicine into the eye, and the sooner the better, so a new distortion in one eye should be seen within days.

Checking each eye separately against straight lines (a door frame, a grid, lines of print) is the simplest way to catch a change early.

Diabetic retinopathy

High blood sugar damages the small blood vessels of the retina. They leak and bleed, and in advanced disease new fragile vessels grow. Vision can be normal for years while damage builds, then blur patchily where the retina has swelled or bled; swelling of the macula (diabetic macular edema) blurs the center; bleeding into the gel of the eye causes dark floaters or a sudden fog. Yearly dilated eye exams catch retinopathy before it threatens sight, and keeping blood sugar, blood pressure and cholesterol under control slows it. Treatments include injections and laser.

Retinal detachment

The retina can pull away from the back wall of the eye, often after a tear. The warning signs are a sudden shower of new floaters, flashes of light like a camera flash at the edge of vision, and then a dark curtain or shadow moving in from one side. This is an emergency. A detachment repaired before it reaches the center of the retina usually keeps good vision; once the center detaches, some loss is permanent. Call the office the same day, or go to an emergency department if it is after hours.

Stroke and the visual field

Half of what each eye sees is processed on the opposite side of the brain. A stroke, tumor or injury on one side of the brain can remove the same half of the field in both eyes (a hemianopia). People bump into things on that side, miss the beginning or end of lines when reading, and may not be aware of the loss at first. The eyes themselves are healthy, so eye drops or surgery do not help; some of the field can recover in the first months, and training and prism glasses help people adapt.

Needing glasses: nearsightedness, astigmatism and presbyopia

These are not diseases. The eye is simply focusing light in front of, behind, or unevenly across the retina.

• Nearsightedness (myopia) blurs distance evenly while near is clear.
• Farsightedness (hyperopia) does the reverse, with near blurring first.
• Astigmatism means the front of the eye is curved more like a football than a basketball, so the image is smeared or doubled in one direction. Lights streak and letters have ghosts.
• Presbyopia is the stiffening of the lens with age, so near focus is lost in the 40s and reading glasses are needed.

Glasses, contact lenses, or refractive surgery correct all of these fully. Very high nearsightedness does carry a higher lifetime risk of glaucoma and retinal detachment, so regular eye exams still matter.

Dry eye

The tear film is the first surface light crosses, and when it is thin or breaks up quickly the picture blurs between blinks, then clears for a moment after one. Dry eye causes fluctuating blur, burning, grittiness, and, paradoxically, watering. It is more common with age, screen use, some medicines, and after eye surgery, and it can make glaucoma drops sting. Artificial tears, warm compresses and lid care help most people; prescription drops are available for more severe disease.

Floaters and flashes

Floaters are shadows of clumps and strands in the vitreous, the gel that fills the eye. They drift when the eye moves and settle when it stops, and are easiest to see against a bright page or sky. Most are harmless, and the brain learns to ignore them. A sudden shower of new floaters, especially with flashes of light or a shadow at the edge of vision, can mean the gel has pulled on and torn the retina, and needs a dilated exam the same day.

Color blindness

Color vision depends on three types of light-sensing cells in the retina. When one type is missing or shifted, usually from birth and most often in men, certain colors blend together. Red–green deficiency is by far the most common; blue–yellow is rare. Vision is otherwise sharp, and most people adapt without noticing much. Acquired changes in color vision, on the other hand, can be a sign of optic nerve or retinal disease and are worth mentioning to your doctor.

Call the same day if

• A curtain, shadow or dark area appears in part of your vision
• A sudden shower of new floaters, with or without flashes of light
• Straight lines suddenly look bent or wavy in one eye
• Sudden loss or blurring of vision in one eye
• Eye pain with nausea, halos around lights and a red eye (possible acute angle-closure glaucoma)

Scene photographs are public domain (CC0): "Nighttime Traffic" by Anthony Delanoix; "Family Breakfast" by Direct Media; "Newspaper Magazine" by Patryk Dziejma; "Crosswalk Intersection" by Peter Miranda; kitchen by rawpixel. Color vision matrices from Machado, Oliveira and Fernandes (2009).