Learn how DNA health testing can detect eye diseases

Not just the color of your eyes may be all in the family. Genes also can influence how clearly you see — and whether you could go blind.

“If you have a family member with eye disease, it’s worth getting a routine eye exam and sometimes a more extensive one,” says Dr. Michael Lin, M.D., an ophthalmologist at Massachusetts Eye and Ear and a Harvard Medical School instructor in Boston.

Ophthalmologists, optometrists and ocular genetic counselors agree on several points: 

— General eye exams are essential to screen for conditions that threaten 20/20 vision.

— Usually, the more common the eye condition, the less likely it’s caused by a single gene. That factor helps determine whether genetic screening is worth your while.

— The frequency of eye disease among your ancestors and the age of onset suggest whether you should be concerned about suffering the same fate.

“Genetic screening is less likely to be helpful for many conditions first detected at an older age,” Lin says. “But if someone in your family gene pool was born with or developed a serious eye disease in childhood, your doctor may recommend genetic testing after an eye exam.”

THE BEST WAY TO STAY ON TOP OF VISION ISSUES: Find an eye doctor near you and book an eye exam.

Here’s what else you need to know about inherited eye traits — and whether genetic tests can help you save your sight:

Glaucoma

Under pressure? More than a David Bowie lyric that stays with you, glaucoma is a condition that runs in families. 

What glaucoma is: Elevated intraocular pressure harms the optic nerve, which helps ship images from your eye to your brain, Lin says.

When glaucoma is likely: Usually glaucoma strikes after age 60 and worsens gradually with time. 

Who gets glaucoma: With age comes unwelcome eye disease, including glaucoma. Latinos and those of African or Caribbean descent are more vulnerable.

Contributory negligence, such as smoking or not protecting your eyes from sunlight, also can be a factor. And yes, genes can be a factor, though they’re a small part of the blame game — unless you’re diagnosed earlier in life. 

Some folks don’t have the tell-all of high eye pressure. They may be diagnosed with “normal tension” glaucoma, and up to one-fifth of these people have a family history of the disease.

How glaucoma is diagnosed: Yearly eye checkups should include a moment when eye pressure is gauged with a puff of air or a specialized tool. Since glaucoma typically is painless, eye exams are particularly valuable to detect the disease before vision loss, which is permanent.

Those with a predisposition to glaucoma also may need visual field testing to see whether vision loss has occurred and map out where it is. Doctors also may measure the thickness of the retinal nerve fibers that feed into the optic nerve with OCT or optical coherence tomography, Lin says.

“Eye doctors examine the back of the eye. The optic nerve usually looks like a circle inside another circle, like a doughnut with a hole. The larger the doughnut hole gets, the likelier a person has glaucoma.”

Slashing intraocular pressures helps thwart future glaucoma damage.

Genetic testing for glaucoma? Genetic testing usually is reserved for those whose glaucoma first appears in childhood or under age 40, because these cases — called congenital or juvenile open-angle glaucoma — may have a stronger identifiable genetic link. 

Indeed, a single gene may distort the eye’s drainage system. “That’s when genetic testing may be helpful,” says Kari Branham, MS, CGC, director of ophthalmic genetic counseling at University of Michigan Kellogg Eye Center in Ann Arbor.

But as Lin points out, “so many genes out there could be associated with it, and age is a much larger contributor, so it’s typically not worth gene testing for people beyond younger adulthood. And gene testing doesn’t change treatment.” 

Age-related macular degeneration

What age-related macular degeneration (AMD) is: Yellow deposits, called drusen, form in the center of the retina, that is the macula. These drusen can spur cell death, swelling or bleeding. This can lead to blurriness and vision loss. Over time, the loss can widen or become more severe, Lin says.

When AMD strikes: As the name indicates, most macular degeneration occurs in later years, starting usually between age 60 to 80.

Who gets AMD: Advanced age is the main culprit, but European ancestry, a variety of genes and harmful habits contribute, including smoking, excess sun exposure and a diet lacking in antioxidant vitamins or minerals, Branham says.

How AMD is diagnosed: Yearly eye exams with dilation can catch AMD deposits earlier, delaying vision loss. Swelling and bleeding occur in wet AMD, for which regular, even monthly, shots in the eye of medications called anti-VEGF can help the body absorb extra fluid that accumulates in the retina, thus slowing vision loss.

In another form, dry AMD, cells waste away in the retina, including photoreceptors that detect light and the cells that support them. “Your doctor may recommend a cocktail of vitamins and minerals that have been shown to slow damage due to dry AMD, converting it into wet AMD,” Lin says. 

OCT imaging of the retina, along with dilated eye exams can help monitor damage.

Genetic testing for AMD? Most people don’t get genetic tests with AMD. But if the drusen deposits are atypical or arise at an unusually young age, genetic testing can confirm other causes of retina changes, such as Stargardt's juvenile macular dystrophy. 

Studies suggest that someday gene therapy may help the retina make anti-VEGF on its own, so that injections in the eye won’t be needed. 

Cataracts

What cataracts are: The naturally clear lens inside your eye may become cloudy, blocking light and blurring vision, as if you were peering through a dirty window, Lin says.

When does one get cataracts? Cataracts occur mostly in the late 60s and beyond. But the connection between the eye and brain may not develop properly in young children. Such cataracts run in families and can cause lazy eye or amblyopia, in which eyes don’t perform equally. 

Who gets cataracts? Live long and you’re likely to form cataracts, but the good news is surgery often can restore sight. 

How cataracts are diagnosed: Standard eye exams reveal clouding of the lens of the eyes — and so do personal photos. “Sometimes you see red eyes in photos, which is caused by light bouncing off the back of the eye,” Lin says. “If you notice the reflection is white, not red, it may indicate something’s blocking vision, like cataracts.”

A white pupil in kids can be due to a cataract — or something more serious, meriting a prompt eye exam.

Genetic testing for cataracts? Genetic testing doesn’t alter treatment, which is always surgery.

DO CONDITIONS LIKE GLAUCOMA OR CATARACTS RUN IN YOUR FAMILY: Find an eye doctor near you and book an eye exam.

Nearsightedness and farsightedness

What are nearsightedness and farsightedness? The shape of the eye and curve of the cornea affects how the eye focuses light. It determines whether one has 20/20 eyesight by changing how, and whether one has 20/20 eyesight at any distance or can see clearly only close up but not far away, Lin says.

When does one become nearsighted or farsighted? Any age, but nearsightedness (also called myopia) is rapidly increasing in children worldwide. Experts believe more time spent in front of screens and less time spent outside playing in the sun at least partly explains the booming population of young myopes.

Nearsightedness, farsightedness and genes: Such vision issues run in families, with many genes and environment playing a part.

How nearsightedness and farsightedness diagnosed: Eye exams reveal how the eyes focus light onto the retina, which is like the camera film — pre-digital — in the back of the eye. Glasses or contact lenses can restore focus. New research suggests that drugs, such as diluted atropine eye drops can thwart extreme nearsightedness in young tykes.

Genetic testing for nearsightedness or farsightedness? Too many genes are involved in myopia (nearsightedness) or hyperopia (farsightedness) — and treatment remains the same — to make genetic screening worthwhile.

SEE RELATED: Is there a cure for nearsightedness? Learn about myopia control.

Astigmatism

What is astigmatism? An eyeball may be more oblong, like an American football, rather than round, like a British football (AKA soccer ball). This changes the direction of light as it hits the eye.

When does does astigmatism hit?: At birth, or it can develop over time. 

Who gets astigmatism? Genes play a part, but “most people have some degree of astigmatism, and it’s generally mild,” Lin says.

How is astigmatism diagnosed? Routine eye exams reveal it, and adjusting eyeglass or contact lenses prescriptions usually fixes it.

Genetic testing for astigmatism? The score doesn’t change, so there’s no win to genetic tests.

Color blindness

What is color blindness? A decreased ability to distinguish colors, most commonly red and green.

When does color blindness strike? You’re usually born with it, though not everyone realizes they have it.

Color blindness and genes: The inability to see a full range of colors typically is passed down via mothers and more commonly affects men, Lin says. 

That’s because the pertinent genes are linked to X chromosomes, of which women have two and men only one (along with a Y chromosome). This gives women double the chance to have normal genes. But if a mother has one normal X chromosome and one with a color blindness gene, her sons have a 50-50 chance of being color blind.

Less than 1 percent of women but roughly 8 percent of men see the world with a limited color palette.

How is colorblindness diagnosed? A routine eye exam can include a test called an Ishihara color plate, in which the viewer looks at a circle made up of smaller dots, formed into numbers in different colors. Those with normal vision spot the numbers easily, while the color blind cannot. 

Recently, spectacles that block certain light waves have become available to help the color blind see better. “Your mileage may vary: Some people are thrilled with them, while others don’t get much benefit,” he says. “Their particular mutation affects results.”

Genetic testing for color blindness? Genetic screening won’t change the outcome, so why bother? 

Crossed eyes (strabismus)

What are crossed eyes, wall eyes and lazy eyes? Crossed or wandering eyes point in different directions, which is called strabismus. 

A child also may favor one eye more than the other, which strengthens that eye’s connection to the brain while preventing proper development of the connection to the less favored eye.

This can cause lazy eye, also called amblyopia, Lin says. Unlike adults, kids could lose some vision permanently if their brain stops reading signals from the weaker eye.

When does strabismus strike? Early childhood. 

Does strabismus run in families? When one or more of the half-dozen muscles surrounding the eye positions the eyes incorrectly, causes are varied. “It certainly runs in families,” he says. Children with strabismus often have parents or siblings with the condition.

How is strabismus diagnosed: The child with crossed eyes should see an eye doctor regularly — and promptly, if eyes cross suddenly or pupils are white in flash photos. 

Surgery can reposition eyes. Eye drops or a patch over the favored eye for a few hours daily can strengthen the weaker eye. A pediatric ophthalmologist may recommend this for a few months or longer.  

Genetic testing for strabismus? Early detection of eyes that point in differing directions can lead to prompt treatment and prevention of poor vision due to amblyopia.

SEE RELATED: How Down Syndrome Affects Eyes and Vision

Retinoblastoma

What is retinoblastoma? Retinoblastoma is a rare eye cancer in children. It can threaten life if it spreads beyond the eye.

Who gets retinoblastoma? Young children. The cancer may first be noticed because of crossed eyes or a pupil appearing white instead of pink in flash photos.

Retinoblastoma and family history: Parents with a history of retinoblastoma should get their children checked since the disease is highly inheritable.

How retinoblastoma is diagnosed: Children should get an urgent eye exam if one or both pupils appear white in flash photos. Though many causes for white pupils are possible, retinoblastoma should be ruled out. If the cancer is discovered, the eye may need to be removed.

Genetic testing for retinoblastoma? Retinoblastoma is highly though not exclusively inherited, Lin says. But genetic knowledge is power: If either parent carries a faulty gene, their child has a 50 percent chance of inheriting that gene. Early and frequent eye exams can monitor for cancer, sparing sight and life.

Single gene, rare genetic eye diseases

All it takes is a single faulty gene and you (or more likely your child) risk extremely rare multi-syllabic ailments.

“One-gene eye diseases are rare,” Lin says. “For instance, fewer than 1,000 cases of retinal dystrophy are detected yearly.”

What are some of these rare genetic eye diseases? Retinitis pigmentosis, Usher’s syndrome, Best disease, juvenile X-linked retinoschisis, Stargardt's juvenile macular dystrophy, Leber congenital amaurosis, Leber hereditary optic neuropathy, Apert syndrome, ocular albinism, Pfeiffer syndrome and others stem from a sole gene. 

When do these rare genetic eye diseases strike? Birth through early adulthood. Symptoms may be as minor as involuntary eye motion or poor night vision. A child may be born blind, or signs may worsen slowly.

Who gets these rare genetic eye diseases? Those who have the misfortune of inheriting the gene from ancestors. 

More than 60 percent of blindness among infants is hereditary.

 “Strong family history and early age of onset are red flags for which a referral to a genetic counselor might be appropriate,” says Meghan DeBenedictis, MS, LGC, MEd, Licensed Certified Genetic Counselor at Cleveland Clinic Cole Eye Institute in Ohio.

How rare genetic eye diseases affect vision: Some or all vision may be lost. None of these illnesses are reversible, though damage may be stopped or slowed. Sometimes eye abnormalities occur in one-third of inherited systemic diseases, such as Tay-Sachs or Marfan syndrome.

Genetic testing for rare eye diseases? “Genetic testing allows us to get a definitive and more precise diagnosis,” DeBenedictis says. “Most cancers and heart disease are not caused by a single gene. The same applies to ophthalmology.”

Identifying the specific gene alerts doctors if your children (and future generations) are at risk for kidney, hearing or other ailments. “Sometimes both parents have to be carriers. Other times men are affected while women are carriers.”

That gene may gain you entry into clinical trials of the latest treatments yet to be offered widely, DeBenedictis says. 

Just one FDA-approved symptom-delaying treatment exists, for Leber’s heredity optic atrophy, Leber’s congenital amaurosis, retinitis pigmentosa and other illnesses due to the mutant gene RPE65.

Should you seek genetic screening, go to a counselor experienced in eye disorders, she says. “There’s no such thing as one perfect test. If the screening doesn’t look at the specific genes that cause the condition, it’s not the right test.”

WHEN WAS YOUR LAST EYE EXAM? Find an eye doctor near you and have your vision checked for signs of eye conditions for which you have a family history.

Page published on Thursday, January 2, 2020