Eye Care

Astigmatism means that a corneal or lens surface is oval like a rugby ball instead of spherical like a basketball. Most astigmatic surfaces have two curves - a steeper curve and a flatter curve. This causes light to focus on more than one point in the eye, resulting in blurred vision at distance or near. Astigmatism often occurs along with nearsightedness or farsightedness.

Signs and Symptoms

Blurred vision (near and distance)

Detection and Diagnosis

Astigmatism can be detected and measured with corneal topography, keratometry, vision testing and refraction.

Treatment

Astigmatism can be corrected with glasses, contact lenses, or surgically. The most common surgeries used to correct corneal astigmatism are astigmatic keratotomy (procedures that involve placing a microscopic incision on the cornea) and LASIK. The objective of these procedures is to reshape the cornea so it becomes more spherical or uniformly curved.

A guide to the many parts of the human eye and how they function.

The ability to see is dependent on the actions of several structures in and around the eyeball. The graphic below lists many of the essential components of the eye's optical system.

When you look at an object, light rays are reflected from the object to the cornea, which is where the miracle begins. The light rays are bent, refracted and focused by the cornea, lens, and vitreous. The job of the lens is to make sure the rays come to a sharp focus on the retina. The resulting image on the retina is upside-down. Here at the retina, the light rays are converted to electrical impulses which are then transmitted through the optic nerve, to the brain, where the image is translated and perceived in an upright position!

Think of the eye as a camera. A camera needs a lens and a film to produce an image. In the same way, the eyeball needs a lens (cornea, crystalline lens, vitreous) to refract, or focus the light and a film (retina) on which to focus the rays. If any one or more of these components is not functioning correctly, the result is a poor picture. The retina represents the film in our camera. It captures the image and sends it to the brain to be developed. The macula is the highly sensitive area of the retina. The macula is responsible for our critical focusing vision. It is the part of the retina most used. We use our macula to read or to stare intently at an object.

Illustrations by Mark Erickson
With acknowledgement to St. Lukes Eye Hospital.

(Farsightedness)

Farsightedness or hyperopia, occurs when light entering the eye focuses behind the retina, instead of directly on it. This is caused by a cornea that is flatter, or an eye that is shorter, than a normal eye. Farsighted people usually have trouble seeing up close, but may also have difficulty seeing far away as well.

Young people with mild to moderate hyperopia are often able to see clearly because their natural lens can adjust, or accommodate to increase the eye's focusing ability. However, as the eye gradually loses the ability to accommodate (beginning at about 40 years of age), blurred vision from hyperopia often becomes more apparent.

Signs and Symptoms

• Difficulty seeing up close
• Blurred distance vision (occurs with higher amounts of hyperopia)
• Eye fatigue when reading
• Eye strain (headaches, pulling sensation, burning)
• Crossed eyes in children

Detection and Diagnosis

Hyperopia is detected with a vision test called a refraction. Very young patients may require cycloplegic eyedrops prior to this test so that they are unable to mask their farsightedness with accommodation.

Treatment

The treatment for hyperopia depends on several factors such as the patient's age, activities, and occupation. Young patients may or may not require glasses or contact lenses, depending on their ability to compensate for their farsightedness with accommodation. Glasses or contact lenses are required for older patients.

Refractive surgery is an option for adults who wish to see clearly without glasses. LASIK, clear lens replacement, LTK and intraocular contact lenses are all procedures that can be performed to correct hyperopia.

Illustrations by Mark Erickson
With acknowledgement to St. Lukes Eye Hospital.

(Nearsightedness)

Nearsightedness or myopia, occurs when light entering the eye focuses in front of the retina instead of directly on it. This is caused by a cornea that is steeper, or an eye that is longer, than a normal eye. Nearsighted people typically see well up close, but have difficulty seeing far away.

This problem is often discovered in school-age children who report having trouble seeing the chalkboard. Nearsightedness usually becomes progressively worse through adolescence and stabilizes in early adulthood.

Signs and Symptoms

• Blurry distance vision
• Vision seems clearer when squinting

Detection and Diagnosis

Nearsightedness is detected with a vision test and refraction.

Treatment

The treatment for nearsightedness depends on several factors such as the patient's age, activities, and occupation. Vision can be corrected with glasses, contact lenses or surgery. Refractive procedures such as LASIK can be considered for adults when the prescription has remained stable for at least one year.

Presbyopia is a term used to describe an eye in which the natural lens can no longer accommodate. Accommodation is the eye's way of changing its focusing distance: the lens thickens, increasing its ability to focus close-up. At about the age of 40, the lens becomes less flexible and accommodation is gradually lost. It's a normal process that everyone eventually experiences.

Most people first notice difficulty reading very fine print such as the phone book, a medicine bottle, or the stock market page. Print seems to have less contrast and the eyes become easily fatigued when reading a book or computer screen. Early on, holding reading material further away helps for many patients. But eventually, reading correction in the form of reading glasses, bifocals, or contact lenses is needed for close work. However, nearsighted people can simply take their glasses off because they see best close-up.

Signs and Symptoms

• Difficulty seeing clearly for close work
• Print seems to have less contrast
• Brighter, more direct light required for reading
• Reading material must be held further away to see (for some)
• Fatigue and eyestrain when reading

Detection and Diagnosis

Presbyopia is detected with vision testing and a refraction.

Treatment

The treatment for presbyopia is very simple, but is entirely dependent on the individual's age, lifestyle, occupation, and hobbies. If the patient has good distance vision and only has difficulty seeing up close, reading glasses are usually the easiest solution. For others, bifocals, trifocals and varifocals (glasses with reading and distance correction) or separate pairs of reading and distance glasses are necessary. Another option is monovision: adjusting one eye for distance vision, and the fellow eye for reading vision. This can be done with contact lenses or permanently with refractive surgery.

Illustrations by Mark Erickson
With acknowledgement to St. Lukes Eye Hospital.

(Crossed or turned eye)

Strabismus is a problem caused by one or more improperly functioning eye muscles, resulting in a misalignment of the eyes. Normally, each eye focuses on the same spot but sends a slightly different message to the brain. The brain superimposes the two images, giving vision depth and dimension. Here's an easy way to see how the eyes work together: hold your finger at arm's length. While looking at your finger, close one eye, then the other. Notice how your finger changes position. Even though the images are slightly different, the brain interprets them as one.

Each eye has six muscles that work in unison to control movements. The brain controls the eye muscles, which keep the eyes properly aligned. It is critical that the muscles function together for the brain to interpret the image from each eye as a single one.

Strabismus must be detected early in children because they are so adaptable. If a child sees double, his or her brain quickly learns to suppress or block out one of the images to maintain single vision. In a very short time, the brain permanently suppresses vision from the turned eye, causing a weak or amblyopic eye. Children may also develop a head tilt or turn to compensate for the problem and eliminate the double image. Unlike children, adults with a newly acquired strabismus problem typically see double.

There are many causes of strabismus. It can be inherited, or it may be caused by trauma, certain diseases, refractive errors and sometimes eye surgery.

Signs and Symptoms

Adults are much more likely to be bothered by symptoms from strabismus than young children. It is unusual for a child to complain of double vision. Children should undergo vision screening examinations to detect problems early. The younger the child is when strabismus is detected and treated, the better the chance of normal vision. The following are common signs and symptoms:

• Turned or crossed eye
• Head tilt or turn
• Squinting
• Double vision (in some cases)

Detection and Diagnosis

Strabismus is detected with a comprehensive eye examination and special tests used to evaluate the alignment of the eyes.

Treatment

The appropriate treatment for strabismus is dependent on several factors including the patient's age, the cause of the problem, and the type and degree of the eye turn. Treatment may include patching, corrective glasses and prisms, together with vision therapy or, as a last resort, surgery.

Vision therapy, together with possible refractive error correction, attempts to teach the brain to utilise both eyes together as a team. For this treatment to be effective, it must be done at a young age before the child can develop amblyopia.

Surgery is sometimes performed for both adults and children to straighten a crossed eye. The procedure may be done with local or general anaesthesia. There are several different surgical techniques used to correct strabismus. The appropriate one is dependent on the muscle involved and the degree of the eye turn.

Illustrations by Mark Erickson
With acknowledgement to St. Lukes Eye Hospital.