Refractive Errors of the Eye - Types, Causes, Symptoms, Diagnosis and Management

Introduction

People undergo a lot of eye-related problems as they grow older. Common vision problems experienced are grouped into a term known as ‘refractive errors of the eye’.

Refraction means changing the path of waves passing from one object to another. Refractive errors of the eye are caused due to changes in the shape and size of the cornea layer and the lens since the focusing ability of the eye decreases. In a changed size and shape of the cornea and lens, the light entering the eye for vision will not be directed appropriately, and thus a refraction error occurs.

Common refractive errors of the eye are,

• Myopia - Also known as nearsightedness, the patient can see only the objects placed nearby.

• Hyperopia - Also known as farsightedness, the patient can see only objects placed farther away.

• Presbyopia - A gradual loss of the eye’s ability to focus on nearby objects.

• Astigmatism - A gradual loss of the eye’s ability to focus on objects at all distances.

This article will explain all these conditions in detail. Its causes, symptoms, diagnosis and management will be explained.

What Are the Causes and Symptoms of Myopia?

Myopia, also known as nearsightedness, is a condition which tends to run in genes. It is a condition in which only the objects placed nearby can be seen clearly, and farther away objects blur out. This condition can be corrected with proper eyeglasses. It commonly affects children and adults.

Most common signs and symptoms of myopia are,

• Only nearby objects will be visible and distant objects will form a blurry image.

• Due to the straining of the eyes, headaches can occur.

• Night vision will be drastically affected. Driving at night becomes difficult.

• Frequent squinting of eyes to see the objects.

A child will most likely be affected by myopia, especially during the early school years. The affected will show signs like the persistent rubbing of the eyes, quinting all the time, need to be near the objects to view it precisely, and no knowledge about the distantly placed objects.

Causes of Myopia

A healthy cornea will have a precise dome-shape, and the lens is a clear layer. These layers have a proper curvature for refracting the light entering the eyes. In the case of myopia, the corneal layer will have a deep curvature, resulting in the light being focused in front of the retina and not exactly on the retina, causing blurry images. In short, the eyeball will be a little longer than the normal length. Family history is considered one of the biggest risk factors for myopia.

What Are the Causes and Symptoms of Hyperopia?

Hyperopiaalso known as farsightedness, the patient will be able to see distant objects clearly, and the nearby objects will appear blurry. It tends to run in families and is seen in children and adults.

• Objects placed farther away are seen, and the nearer ones appear blurry.

• Episodes of headaches will occur due to straining the eyes too much.

• The affected ones can feel strained eyes after doing tasks like reading, writing, etc.

Causes of Hyperopia

In case of hyperopia, the corneal layer will have less curvature, or the eyeball will be shorter than normal. Here, the light will be focused at the back of the retina and not on the retinal layer.

What Are the Causes and Symptoms of Presbyopia?

In this condition, the eyes will fail to focus on nearby objects and is most commonly seen in people aged above 40 and up to approximately 65. The affected people will discover the presence of this condition, only when they find it difficult to read papers, etc.

• People will get the tendency to hold the reading material at a farther distance, to read clearly.

• Headaches due to eye strain can be noticed.

• Focusing near objects appears blurry.

Causes of Presbyopia

The lens of the eyes is a flexible layer. It is bound by a muscle which helps it to focus on objects. While focusing on nearby objects, the muscle tends to constrict. When trying to focus on distant objects, the muscle relaxes. As a person ages, the lens will harden and lose its flexibility. Thus, the focussing of nearby objects becomes tough, resulting in presbyopia. Age, medical conditions like diabetes, multiple sclerosis and taking drugs such as antidepressants and antihistamines are found to be risk factors for presbyopia.

What Are the Causes and Symptoms of Astigmatism?

Astigmatism is the condition in which the eyes fail to focus both the nearby and farther placed objects clearly. It is usually present at birth.

• A general blurred vision will be noticed.

• Headaches due to eyestrain can occur.

• Frequent squinting of the eyes can be noticed.

• Night vision will be affected.

Causes of Astigmatism

This condition is caused when either the cornea or the lens attains an egg-shape. In this case, the corneal layer or the lens will have two mismatched curves and thus two images will be formed, which eventually overlap and cause blurred vision.

How to Diagnose the Refractive Errors of the Eye?

The most used test to diagnose the refractive errors of the eye such as myopia, presbyopia, hyperopia and astigmatism is the refraction assessment. This test is done by asking the patient to focus on a chart placed 20 feet away through different lenses (of different strength). Then the ophthalmologist will enquire about which lens provided clear vision and which did not. Thus, arriving at the diagnosis. A general eye exam using dilation eye drops will be done to study the layers of the eye clearly.

How to Manage the Refractive Errors of the Eye?

1. Myopia

The treatment should enable the light to focus on the retinal layer precisely and not front or back. Myopia can be corrected with eyeglasses, contact lenses, and surgeries.

• Eyeglasses - The lenses are an important part of treating myopia. Concave lenses (minus power lenses) are used to focus light directly onto the retina.

• Contact Lenses - Multiple focal contact lenses are used to correct myopia and slow its progression.

• Surgery - Some people may opt for surgery to get rid of the condition once and for all. But in some cases, patients will have to wear eyeglasses even after the surgery. The most preferred surgical procedures are as follows.

All these surgeries are done with the aim of bringing back the shape of the corneal layer

to normal.

1. Laser-assisted in situ keratomileusis (LASIK).

2. Laser-assisted in situ keratectomy (LASEK).

3. Photorefractive keratectomy.

• Recent studies have shown that a low-dose of atropine can slow down the progression of myopia greatly.

2.Hyperopia

Convex lenses, in which the middle part is thick like a magnifying glass, are used to correct hyperopia. Eyeglasses, contact lenses and surgeries are used to correct the condition.

• Eyeglasses and Contact Lenses - Eyeglasses with convex lenses are used to correct the condition of hyperopia. People who have difficulty wearing eyeglasses can get contact lenses.

• Surgery - Surgical procedures will be done to flatten the corneal layer for proper focussing. Different surgical procedures performed are

1. Laser-assisted in situ keratomileusis (LASIK).

2. Laser-assisted in situ keratectomy (LASEK).

3. Photorefractive keratectomy.

3.Presbyopia

Presbyopia can only be improved and not cured. Eyeglasses, contact lenses and surgeries can be performed to improve the condition.

• Eyeglasses and Contact Lenses - Bifocals are the preferred ones. It will have two lenses. One for distant vision and one for focussing the nearby objects clearly. Multifocal and monovision contact lenses are advised to be used. Progressive eyeglasses, in which both the lenses are blended together, are also in use.

• Surgery - Resurfacing the corneal layer is the ultimate aim of the surgery. Different surgical methods available are,

1. Laser-assisted in situ keratomileusis (LASIK).

2. Laser-assisted in situ keratectomy (LASEK).

3. Photorefractive keratectomy.

4. Conductive keratoplasty.

4.Astigmatism

• Eyeglasses and Contact Lenses - Eyeglasses for astigmatism will include a cylindrical lens in order to improve the light’s ability to pass through the cornea. Special toric contact lenses are also used. It is a hard gas-permeable lens used to reshape the cornea.

• Surgery - Astigmatism can be cured by doing a surgical procedure and different procedures available are,

1. Small incision lenticule extraction (SMILE).

2. Epi - (LASIK).

3. Laser-assisted in situ keratomileusis (LASIK).

4. Laser-assisted in situ keratectomy (LASEK).

5. Photorefractive keratectomy.

Conclusion

These refractive errors can be prevented completely from happening, but proper management will prevent the condition from affecting life. All four refractive errors commonly occur. So getting the eyes checked frequently will prevent the condition from becoming worse.