Lesson 7 - Refractive Errors

Question 1

Simple myopic astigmatism

Answer 1

The eye is normal in one meridian, and 90 degrees away the eye is nearsighted.

Question 2

Simple hyperopic astigmatism

Answer 2

The eye is normal in one meridian and 90 degrees away it is farsighted

Question 3

Compound myopic astigmatism

Answer 3

The eye is nearsighted in both meridians, but more nearsighted in one meridian than the other.

Question 4

Compound hyperopic astigmatism

Answer 4

The eye is farsighted in both meridians, but more farsighted in one meridian than the other.

Question 5

Mixed astigmatism

Answer 5

One meridian is nearsighted, and the other is farsighted.

Question 6

Presbyopia

Answer 6

The lens becomes less elastic and can no longer focus near objects on the retina.

Question 7

Hyperopia (farsightedness)

Answer 7

The eyeball is too short and light focuses behind the retina

Question 8

Astigmatism

Answer 8

The corneal surface is not round. It is more curved in one direction than in the direction perpendicular to it

Question 9

Myopia (nearsightedness)

Answer 9

The eyeball is too long; the light entering the eye ends up focusing before it gets to the retina.

Question 10

Esotropia

Answer 10

The eye turns inward

Question 11

Strabismus

Answer 11

Strabismus occurs when the 6 muscles of the eye can’t work together in the right way to focus both eyes on a target.

Question 12

Exotropia

Answer 12

Strabismus where the eye turns outward

Question 13

Hypertropia

Answer 13

Strabismus where the eye turns up

Question 14

Hypotropia

Answer 14

Strabismus where the eye turns down

Question 15

Emmetropa

Answer 15

A person without any refractive error

Question 16

Anisometropia

Answer 16

The eyes have very different refractive powers

Question 17

Amblyopia

Answer 17

The eyes can’t work together, and a lazy eye occurs. This might occur for two reasons: 1. The eyes don’t line up, or 2. There is a large difference in refractive power between the two eyes.

Question 18

What is the most common vision problem in the United States?

Answer 18

Myopia is the most common vision problem in the United States, affecting 30% of the population.

Question 19

List and describe the two anatomical types of myopia

Answer 19

In axial myopia, the eyeball is elongated rather than spherical. Therefore, light rays entering the eye focus in front of the retina instead of right on it. In refractive myopia, the refractive power of the cornea or lens is too strong, causing the same effect.

Question 20

Accommodation

Answer 20

Muscle fibers attached to the lens contract to change the shape of the lens, allowing near objects to come into focus.

Question 21

Doctors can correct myopia how?

Answer 21

Doctors can correct myopia with minus power lenses or contact lenses. Minus lenses redirect light rays so they focus farther back in the eye on the retina. In many cases, doctors can use refractive surgery—which reshapes the cornea—to accomplish the same goal.

Question 22

Doctors can correct hyperopia how?

Answer 22

Plus-powered glasses lenses or contact lenses can correct hyperopia by causing the light to bend sooner and strike the retina correctly. Refractive surgery can also correct this problem.

Question 23

About 16 percent of the population has this focusing problem.

Answer 23

Astigmatism

Question 24

What percent of the general public is affected by hyperopia?

Answer 24

25%

Question 25

Astigmatism is different from nearsightedness and farsightedness because it makes vision ___.

Answer 25

Astigmatism is different from nearsightedness and farsightedness because it makes vision blurry at all distances. They may even see “ghost images” around objects

Question 26

Doctors can correct astigmatism how?

Answer 26

Doctors can correct this condition with glasses, contact lenses, or refractive surgery

Question 27

List and describe the 5 types of astigmatism

Answer 27

1. Simple myopic astigmatism - This is when there is no power in one axis or meridian, and 90 degrees away from that axis or meridian, the eye is nearsighted. Prescription example: plano –4.00 x 090.
2. Simple hyperopic astigmatism - In this type, the power is plano in one axis. In the other axis, 90 degrees away, it’s farsighted. Prescription example: +4.00 -4.00 x 090.
3. Compound myopic astigmatism - Here, the eye is nearsighted in both axes. However, it’s more nearsighted in one axis than the other. Prescription example: -2.00 -2.00 x 180.
4. Compound hyperopic astigmatism - In this type of astigmatism, the eye is farsighted in both meridians, but it’s more farsighted in one meridian than the other. Prescription example: +2.00 +2.00 x 090.
5. Mixed astigmatism - In this case, one meridian is nearsighted, and the other is farsighted. Prescription example: +2.00 -4.00 x 090.

Question 28

Doctors correct presbyopia how?

Answer 28

Doctors can correct presbyopia with reading glasses or contact lenses.

Question 29

While aging is the cause of most presbyopia, it can also develop at an earlier age in people with…

Answer 29

While aging is the cause of most presbyopia, it can also develop at an earlier age in people with diabetes, multiple sclerosis, or some cardiovascular diseases. In addition, some drugs—particularly antidepressants, diuretics, and antihistamines—can contribute to this condition.

Question 30

People can develop strabismus if…

Answer 30

People can develop strabismus if they suffer head trauma, have a stroke, have epilepsy or multiple sclerosis, or develop brain tumors. Thyroid conditions and nerve or muscle disorders can also cause this problem. Sometimes, kids who are farsighted (hyperopes) develop what we call accommodative strabismus or accommodative esotropia because they’re overconverging while trying to focus up close.

Question 31

Strabismus can affect…

Answer 31

Strabismus can affect either one eye or both eyes.

Question 32

As many as 5 percent of children have this problem, and it’s often present at birth.

Answer 32

Strabismus

Question 33

While it’s especially common in “preemies” and children with developmental problems like Down syndrome or cerebral palsy, most kids with __ have no other health problems.

Answer 33

While it’s especially common in “preemies” and children with developmental problems like Down syndrome or cerebral palsy, most kids with strabismus have no other health problems.

Question 34

Strabismus can be either___ or ___.

Answer 34

Strabismus can be either intermittent or constant. People with intermittent strabismus are more likely to exhibit the problem when they’re tired, sick, or stressed.

Question 35

Depth perception (also called stereopsis)

Answer 35

Depth perception or stereopsis—the fusing of images from the two eyes into a clear picture. Stereopsis is what allows us to see in three dimensions.

Question 36

The most common tools doctors use to treat strabismus are?

Answer 36

The most common tools doctors use to treat strabismus are eye muscle surgery and vision therapy.

Question 37

Orthoptics

Answer 37

Orthoptics (which means straight eyes) is the science of using instruments to help realign the eyes.

Question 38

Vision Therapy

Answer 38

When a person who’s had misaligned eyes for some time has surgery to align the eyes, the straightened eye has to start using a different part of the retina. Vision therapy exercises help train that new part of the retinal nerve fiber layers to receive signals and transport them to the brain. Vision therapy involves orthoptics, but it also includes eye exercises that can improve visual and perceptual efficiency even if the eyes are straight. The approaches doctors use in vision therapy include computer programs, lenses, prisms, eye patches, and eye-hand coordination exercises. Vision therapy typically is most successful for young children

Question 39

Monocular vision

Answer 39

vision in only one eye

Question 40

When treating patients with monocular vision, all eye care professionals should recommend…

Answer 40

When treating patients with monocular vision, all eye care professionals should recommend that they wear sunglasses consistently when they’re outdoors and advise them to use protective eyewear whenever they play sports or do hobbies such as woodworking or gardening. Always tell them to use safety glasses if there is any risk of danger at the workplace.

In addition, always stress the importance of having impact-resistant lenses in their regular glasses and wearing impact-resistant lenses—even if they don’t need prescription lenses. Counsel contact lens wearers not to overuse their lenses (if they insist on wearing contact lenses) or take any unnecessary risks that would endanger their good eye.

And here’s another good tip for patients with monocular vision: Recommend that they wear sunglasses with a slight wrap to them to help prevent the risk of things flying into the good eye from the periphery.

Question 41

Prism lenses

Answer 41

Likely to be used in vision therapy. These are lenses that have a thick base and a thin apex.
Lenses bend light. The thicker base of a prism slows down the light passing through it, while the thinner apex lets the light through more quickly. As a result, the light passing through the prism bends toward the base and bends toward the apex as it leaves the prism. Prisms displace an image, making it appear in a different direction. This moves the patient’s eye in the desired direction. As a result, prism can be prescribed to cause an eye to appear cosmetically straighter or can be prescribed to aid the focus of a slightly turned eye.

The prisms in lenses can have bases pointing up, down, left, or right. Doctors can use prisms to train the eye to move in a different direction if the eyes are turned too far in, out, up, or down while reading or looking in the distance.

Question 42

Lens designs for myopia

Answer 42

Myopia is usually corrected by single-vision glasses worn for distance only. Remember that myopia is a problem with blurred vision usually in the distance, so the prescription is usually prescribed for distance only. Sometimes the person is so nearsighted that they still need a prescription for near, but it will be less strong. In this case, they can have two pairs: one for distance and one for near. This is commonly the case for computer monitor users who don’t need their strong distance prescription for close work but still need a weak prescription.

Bifocals and progressive lenses are sometimes prescribed for myopia as well if the patient is presbyopic also. In addition, a young myopic person may be prescribed bifocals or progressives lenses to enable them to have a lesser or no prescription to look through when they look down to read.

Question 43

Lens designs for hyperopia

Answer 43

Hyperopes, usually need their glasses to read, but sometimes also need glasses for both distance and near, so like myopes, they can be prescribed single-vision glasses for near only, one for distance only or progressives or bifocals.

Question 44

Lenses for astigmatism

Answer 44

Astigmatism affects vision for all distances, so people with astigmatism are usually prescribed glasses to be used all the time, but if they also have myopia or hyperopia, then the previously discussed options will need to be considered as well. There are contact lenses available for astigmatism as well.

Most people need at least two or more pairs of prescription glasses, one clear and one sunglass.

Question 45

Lenses for presbyopia

Answer 45

Recall from the previous lesson all the lens choices for presbyopia (multifocal lenses). The doctor will usually have the specific lens design specified on the prescription since there are so many options. If not, you will need to ask your patient if they have had progressive lenses before or not. Usually, people who have had progressives before will continue with them; however, if you have a patient who did not like their progressive lenses for whatever reason, you can offer them a separate single-vision pair for distance and one for near, a bifocal, a trifocal, or contact lenses.

Question 46

What is the difference between “against-the-rule” astigmatism and “with-the-rule” astigmatism?

Answer 46

Remember, astigmatism is when your eye’s cornea or lens is irregularly shaped. Normally, the cornea and lens are curved equally in all directions.

If we view the eye as a sphere, “against-the-rule” is astigmatism where the steepest curve lies near the 180-degree meridian (imaginary line connecting east and west points of the cornea), and “with-the-rule” astigmatism (line connecting north and south points) is near the 90-degree meridian. With-the-rule is by far the most common type of astigmatism.