What is Hyperopia or Hypermetropia?
Hypermetropia or long (far) sightedness is a common eye defect where a person faces difficulty in seeing objects that are kept nearby clearly but has no trouble seeing the distant objects. Hypermetropia is common in new-born babies as they have small eyeballs. Gradually, it gets corrected with time as the eyeball grows to its normal size. The most common symptoms of Hypermetropia or Hyperopia are blurry vision while focusing on close objects, eye strain, tiredness of the eye, and frontotemporal headaches. Young children with severe far-sightedness may suffer from double vision as a result of over-focusing.
A person with hypermetropia may develop rare complications such as strabismus and amblyopia. There is a high risk for hypermetropic patients with a short axial length of developing primary angle-closure glaucoma. Therefore, a routine check-up of eyes should be regularly done for all hypermetropic patients.
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What Causes Hyperopia?
The causes of hypermetropia or hyperopia are listed below.
Hypermetropia occurs when there is a shortening of the eyeball along the axis. As a result, the light rays that enter the eyes fall behind the retina instead of falling on the retina which creates blurry vision.
An increase in the focal length of the eye lens also causes hypermetropia.
Hypermetropia occurs when the cornea of the eye is not curved enough, i.e., the lens or cornea is flatter than normal.
The stiffening of ciliary muscles is another cause of hypermetropia.
Types of Hypermetropia
The types of hypermetropia are listed below.
Simple Hypermetropia - Simple hypermetropia includes axial hypermetropia (i.e. hypermetropia caused when the axial length of the eyeball is too short) and curvature hypermetropia (i.e. hypermetropia caused when the curvature of cornea or lens is flatter than normal). It is the most common type of hypermetropia.
Pathological Hypermetropia - Pathological Hypermetropia is caused either due to congenital or due to acquired conditions. There are four types of pathological hypermetropia. They are senile or acquired hypermetropia, positional hypermetropia, aphakic hypermetropia, and consecutive hypermetropia.
Functional Hypermetropia - It is commonly seen in patients suffering from third intracranial nerve palsy and internal ophthalmoplegia where paralysis of the eye’s ability to accommodate occurs.
Severity of Hypermetropia
Hypermetropia is classified into three types based on severity:
Low: Power up to +2 D.
Moderate: Power ranging from +2.2 - 5 D.
High: Power more than 5 D. Rare cases include power exceeding 6 - 7 D.
How to Correct Hypermetropia?
Hypermetropia can be simply corrected by using corrective glasses or contact lenses. A convex lens is used in correcting hypermetropia.
Hypermetropia can be treated surgically. The various surgical treatments are as follows.
Photorefractive Keratectomy (PRK): Photorefractive Keratectomy is a refractive technique in which a minimal amount of corneal surface is removed. It may have complications like astigmatism and regression effect due to epithelial healing, and corneal haze.
Laser Epithelial Keratomileusis: It is similar to PRK. In this method, alcohol is used to loosen the corneal surface.
Laser-Assisted in Situ Keratomileusis (LASIK): Reshaping of the cornea is done in LASIK so that usage of contact lenses or eyeglasses is no longer needed.
Did You Know?
Vision defects are diagnosed by using an eye chart known as the Snellen Chart. It is an eye chart that is used to measure the clarity of vision and visual acuity. It was developed by Dutch ophthalmologist Herman Snellen in 1862 and hence, the chart is named after him. Nowadays, the Log MAR chart is used by many ophthalmologists and vision scientists.
FAQs on Eye Defects Hypermetropia or Hyperopia
1. What exactly is hypermetropia, also known as farsightedness?
Hypermetropia, or farsightedness, is a common vision defect where a person can see distant objects clearly, but nearby objects appear blurry. This happens because the light rays from objects are focused behind the retina instead of directly on it, leading to an out-of-focus image for close-up vision.
2. What are the main physical causes of hypermetropia in an eye?
Hypermetropia is primarily caused by one of two physical conditions related to the eye's structure:
- The eyeball is too short from front to back, which causes the light to focus past the retina.
- The focal length of the eye lens is too long. This means the lens is not curved enough, or its converging power is too weak, to bend light rays sufficiently to focus on the retina.
3. How is hypermetropia corrected using a specific type of lens?
Hypermetropia is corrected by wearing spectacles or contact lenses with a convex lens of appropriate power. A convex lens is a converging lens. It helps by pre-converging the light rays before they enter the eye, which reduces the work the eye's natural lens has to do. This additional focusing power ensures the final image is formed correctly on the retina.
4. What is the main difference between hypermetropia and myopia?
The main difference lies in what part of a person's vision is affected and why. In hypermetropia (farsightedness), nearby objects are blurry because light focuses behind the retina. In contrast, in myopia (nearsightedness), distant objects are blurry because light focuses in front of the retina. Consequently, their corrections are opposite: hypermetropia needs a convex lens, while myopia needs a concave lens.
5. Why can someone with hypermetropia see distant objects clearly but struggles with nearby objects?
This happens because light rays from distant objects are almost parallel and require less bending (converging) to focus on the retina. A hypermetropic eye can usually manage this. However, light rays from nearby objects are diverging (spreading out) and require much stronger bending. The eye's lens in a hypermetropic person lacks the sufficient converging power to focus these diverging rays onto the retina, causing them to form a blurry image behind it.
6. How is hypermetropia different from presbyopia, if both affect near vision?
While both conditions make it difficult to see nearby objects, their causes are different. Hypermetropia is a refractive error usually caused by the eyeball being too short or the lens having a long focal length. It can be present from a young age. Presbyopia, on the other hand, is an age-related condition that typically starts around the age of 40. It occurs because the ciliary muscles weaken and the eye lens loses its flexibility, reducing its ability to accommodate or change focus for near vision.
7. Is there a difference between the terms 'hypermetropia' and 'hyperopia'?
No, there is no functional difference. Hypermetropia and hyperopia are simply two medical terms for the exact same vision defect. Both refer to the condition commonly known as farsightedness or long-sightedness. 'Hypermetropia' is a more traditional term often used in educational and clinical texts.
8. Can you explain what happens to light rays from a nearby object in a hypermetropic eye?
In a hypermetropic eye, when light rays from a nearby object enter, the eye's lens is unable to bend them sharply enough to focus them on the retina. Due to this insufficient converging power, the light rays travel towards a theoretical focal point that is located behind the physical retina. As a result, the image that actually forms on the surface of the retina is blurry and out of focus.
