Farsightedness: Causes and corrective treatments
It happens when the eyeball or the lens is too short, or the cornea is too flat.
Also known as long-sightedness or hyperopia, it affects between 5 and 10 percent of the United States (U.S.) population.
It can either develop as the muscles weaken from approximately 40 years of age onwards, also known as presbyopia, or be present from birth.
Signs and symptoms
Farsightedness creates difficulty with clearly viewing close-up objects.
The most common signs and symptoms of farsightedness:
- objects nearby appear blurry
- the person needs to squint or strain their eyes to see clearly
- a headache or discomfort occurs after prolonged reading or writing
- eyestrain develops, which burns or aches in or around the eyes
- the person cannot perceive depth effectively
Left untreated, other eye conditions can develop, such as a lazy eye, or amblyopia, and crossed eyes, or strabismus.
Two parts of the human eye make it possible to focus.
The cornea: The clear, front part of the eye that receives and focuses light into the eye.
The lens: A transparent structure inside the eye that focuses light rays onto the retina.
The retina is a layer of nerves at the back of the eye that senses light and sends impulses through the optic nerve to the brain.
The optic nerve connects the eye to the brain and carries these focused light signals formed by the retina to the brain. The brain then interprets them as images.
The optimal shape for an eye is with a perfectly smooth curvature of the cornea and lens. The cornea and the lens refract, or bend, the incoming light rays. When this happens, an image is focused sharply on the retina. The smoother the curve is, the clearer the incoming image will be.
Farsightedness occurs when light is not refracted properly through an uneven, less smooth cornea or lens. It is a type of refractive error. Refractive errors can also cause myopia, or shortsightedness, and astigmatism.
The light rays focus at a point behind the retina, and not onto it, because of the imperfect shape. They travel to the back of the retina before they have been bent properly by the lens and cornea, resulting in blurred vision when objects are closer.
People who are born with hyperopia may be able to focus on distant objects during childhood. However, eventually it may become more difficult to focus and even distant objects may not be clear.
In rare cases, farsightedness may result from:
- fovea hypoplasia (macular hypoplasia), a rare medical condition involving the underdevelopment of the macula, a small area on the retina.
Macular hypoplasia is often linked with albinism.
Experts believe farsightedness may be hereditary, so it can be passed down from parents to children.
An optometrist can carry out a standard eye exam to diagnose farsightedness.
Optometrists can assess vision, prescribe corrective lenses and diagnose common eye issues. Alternatively, an ophthalmologist, or eye specialist, may carry out the exam if a more complex issue is suspected.
In farsightedness, or hyperopia, light is refracted to a point behind the retina due to excessive curvature of the cornea.
A person should have an eye exam if they are experiencing any of the above symptoms, or if they reach 40 years of age without symptoms of farsightedness.
Younger children should also have vision testing at the following stages:
- at birth
- during their first year of life
- around 3 and a half years old
- around 5 years old
A person who already wears corrective lenses will need more frequent exams to ensure the prescription of their lenses remains appropriate.
Most eye conditions can be corrected successfully, but there is a risk of further complications if left untreated.
A complete eye test should check the following:
- ability to focus on near objects
- general eye health, to determine whether there are any eye conditions or physical abnormalities
- visual acuity, or sharpness, using a Snellen chart of letters that decrease in size dilation, or widening, of pupils
- side vision
- ocular motility, or eye movement
- the front of the eye
- retina and optic nerve
If a patient wears prescription eyeglasses or contact lenses, they may need to wear them during the exam.
The eye specialist also looks for signs of eye conditions by shining a light into the patient's eyes and observing their reaction. They will look for disorders such as glaucoma or diabetic retinopathy.
Hyperopia treatment aims to help light focus correctly on the retina. Corrective lenses or refractive surgery may achieve this.
Most younger people with hyperopia do not need corrective lenses because they can compensate by focusing on nearer objects.
A pair of spectacle lenses, when correctly prescribed, can greatly assist the correction of farsightedness.
However, by the age of 40 years, when the lenses are less flexible, most people with long-sightedness need corrective lenses.
There are two primary types of corrective lens:
- Eyeglasses: These may include bifocals, trifocals, and standard reading glasses.
- Contact lenses: Various types of contact lens are available, with differing levels of softness and intended duration of wear.
Refractive surgery is normally used for nearsightedness, or myopia, but it can also treat hyperopia.
- Laser-assisted in situ keratomileusis (LASIK): A laser is used to reshape the center of the cornea into a steeper dome.
- Laser epithelial keratomileusis (LASEK): A laser is used to reshape the outer edges of the cornea into a steeper curvature.
- Photorefractive keratectomy (PRK): The surgeon removes the outer layer of the cornea and a similar procedure to the LASEK is carried out. The outer layer then grows back over about 10 days.
- Conductive keratoplasty (CK): The cornea is reshaped using a radiofrequency-emitting probe placed at its edge which causes slight shrinkage to the peripheral collage.
Laser surgery may not be suitable for those who:
- have diabetes
- are pregnant or breastfeeding
- have a weakened immune system
- have other eye problems, such as glaucoma or cataracts
Risks of laser surgery
All surgical procedures have some risks.
Rarely, laser surgery may result in the following complications:
- Worse post-operative vision: The vision may be worse than before if the surgeon misjudges how much tissue to remove from the cornea.
The diagnosis of hyperopia can be tested for by an optometrist.
- Epithelia in-growth: The surface of the cornea starts growing into the cornea itself, leading to further vision problems. This may require additional surgery.
- Ectasia: The cornea becomes too thin, vision worsens, and there is a risk of total vision loss. - Microbial keratitis: This is an infection of the cornea
A 2005 study found the risk of complication following LASIK surgery to be as follows:
- 0.6% chance of a correction error
- 1.3% chance of epithelial in-growth
- 0.2% chance of ectasia
- 0.16% chance of microbial keratitis
The risk factors are thought to be similar in LASEK and PRK surgery.
Possible complications of hyperopia
Complications in adults are rare. The condition worsens with age, but stronger glasses usually enable the person to see normally.
Complications only tend to occur when hyperopia goes untreated in children.
Strabismus, or squint: The eyes are not properly aligned and they focus on different things. This may affect depth perception and make it difficult to determine how far away objects are. The other eye may become weakened, leading to amblyopia.
Amblyopia: One eye becomes dominant, usually due to strabismus. If a child mainly uses one eye to focus, the other eye may gradually become weaker. Left untreated, the patient may lose vision in that eye.
Both complications are treatable.
Wearing a patch over the stronger eye can encourage the brain to take more notice of the weaker eye. This strengthens the eye muscles.
Prescription eyeglasses may help align the eyes.
In severe cases, surgery may be needed to realign the eyes and strengthen the eye muscles.
Adults who develop hyperopia and do not get corrective lenses may find that their quality of life is undermined.