UNDERSTANDING REFRACTIVE ERRORS

For a person to see clearly, light rays entering the eyes must be bent or refracted by the cornea and the lens so that they can come into focus on the retina. The retina is the light-sensing layer of the back of our eye that receives the picture formed by these light rays and sends this image to the visual centre of our brain by way of the optic nerve.

If you have a refractive error, this means that the shape of your eye is preventing your eye from refracting or bending the light properly. This results in your seeing an image that is blurred. Focusing problems of the eye, which require correction by glasses or contact lenses, are called refractive errors. Although we refer to refractive error as an eye condition or disorder, these are not diseases. 

Different types of refractive error include:

1. Myopia, also called short-sightedness or near-sightedness
2. Hypermetropia (Hyperopia) also called or long-sightedness or farsightedness
3. Astigmatism – those using cylindrical correction in their glasses
4. Presbyopia – (Aging Eyes)

1.Myopia: 

Near-sightedness, or myopia, is the most common refractive error of the eye, and it has become more prevalent in recent years.

Myopia occurs when the eyeball is too long, relative to the focusing power of the cornea and lens of the eye. This causes light rays to focus at a point in front of the retina, rather than directly on its surface.

Near-sightedness also can be caused by the cornea and/or lens being too curved for the length of the eyeball. In some cases, myopia is due to a combination of these factors.

Myopia typically begins in childhood and you may have a higher risk if your parents are near-sighted. In most cases, near-sightedness stabilizes in early adulthood but sometimes it continues to progress with age.

Myopia Symptoms and Signs

If you are near-sighted, you typically will have difficulty reading road signs and seeing distant objects clearly, but will be able to see well for close-up tasks such as reading and computer use. Other signs and symptoms of myopia include squinting, eye strain and headaches. Feeling fatigued when driving or playing sports also can be a symptom of uncorrected near-sightedness. 

If you experience these signs or symptoms while wearing your glasses or contact lenses, schedule a comprehensive eye examination with your optometrist or ophthalmologist to see if you need a stronger prescription.

Myopia Treatment

Near-sightedness can be corrected with glasses, contact lenses or refractive surgery. Depending on the degree of your myopia, you may need to wear your glasses or contact lenses all the time or only when you need very clear distance vision, like when driving, seeing a chalkboard or watching a movie.

If you’re near-sighted, the first number (“sphere”) on your eyeglasses prescription or contact lens prescription will be preceded by a minus sign (–). The higher the number, the more near-sighted you are.

Refractive surgery can reduce or eliminate your need for glasses or contacts. The most common procedures are performed with an excimer laser.

2.Hyperopia:

Also known as farsightedness, is a common vision problem, affecting about a fourth of the population. People with hyperopia can see distant objects very well, but have difficulty focusing on objects that are up close.

Hyperopia Symptoms and Signs

Farsighted people sometimes have headaches or eye strain and may squint or feel fatigued when performing work at close range. If you get these symptoms while wearing your eye glasses or contact lenses, you may need an eye exam and a new prescription.

This vision problem occurs when light rays entering the eye focus behind the retina, rather than directly on it. The eyeball of a farsighted person is shorter than normal.

Many children are born with hyperopia, and some of them “outgrow” it as the eyeball lengthens with normal growth.

Sometimes people confuse hyperopia with presbyopia, which also causes near vision problems but for different reasons.

Hyperopia Treatment

Farsightedness can be corrected with glasses or contact lenses to change the way light rays bend into the eyes. If your glasses or contact lens prescription begins with plus numbers, like +2.50, you are farsighted.

You may need to wear your glasses or contacts all the time or only when reading, working on a computer or doing other close-up work.

Refractive surgery, such as LASIK is another option for correcting hyperopia. Surgery may reduce or eliminate your need to wear glasses or contact lenses. 

3. Astigmatism:

Astigmatism might be the most misunderstood vision problem. Even the name is challenging to many people, who incorrectly call it “stigmatism.”

Like near-sightedness and farsightedness, astigmatism is a refractive error, meaning it is not an eye health problem; it simply is a problem with how the eye focuses light.

In an eye with astigmatism, light fails to come to a single focus on the retina to produce clear vision. Instead, multiple focus points occur, either in front of or behind the retina (or both).

Astigmatism Symptoms

Astigmatism usually causes vision to be blurred or distorted to some degree at all distances.

Symptoms of uncorrected astigmatism are eye strain and headaches, especially after reading or other prolonged visual tasks.

Squinting also is a very common symptom of uncorrected astigmatism.

Causes of Astigmatism

Astigmatism usually is caused by an irregularly shaped cornea. Instead of the cornea having a symmetrically round shape (like a baseball), it is shaped more like a football, with one meridian being significantly more curved than the meridian perpendicular to it.

(To understand what meridians are, think of the front of the eye like the face of a clock. A line connecting the 12 and 6 is one meridian; a line connecting the 3 and 9 is another.)

The steepest and flattest meridians of an eye with astigmatism are called the principal meridians.

In some cases, astigmatism is caused by the shape of the lens inside the eye. This type of astigmatism is called lenticular astigmatism, to differentiate it from the more common corneal astigmatism.

Types of Astigmatism

There are several types of astigmatism:

• Myopic astigmatism. One or both principal meridians of the eye are near-sighted. (If both meridians are near-sighted, they are myopic in differing degree.)
• Hyperopic astigmatism. One or both principal meridians are farsighted. (If both are farsighted, they are hyperopic in differing degree.)
• Mixed astigmatism. One principal meridian is near-sighted, and the other is farsighted.

Astigmatism also is classified as regular or irregular. In regular astigmatism, the principal meridians are 90 degrees apart (perpendicular to each other). In irregular astigmatism, the principal meridians are not perpendicular. Most astigmatism is regular corneal astigmatism, which gives the eye a football shape.

Irregular astigmatism can result from an eye injury that has caused scarring on the cornea, from certain types of eye surgery or from keratoconus, a disease that causes a gradual thinning of the cornea.

Astigmatism Test

Astigmatism is detected during a routine eye exam with the same instruments and techniques used for the detection of near-sightedness and farsightedness. Your eye doctor can estimate your amount of astigmatism by shining a light into your eye while manually introducing a series of lenses between the light and your eye. This astigmatism test is called retinoscopy.

Though many eye doctors continue to perform retinoscopy, this manual procedure has been replaced or supplemented in many eye care practices with automated instruments that provide a faster preliminary test for astigmatism and other refractive errors.

Whether retinoscopy or an automated refraction is performed as a preliminary astigmatism test, your optometrist or ophthalmologist will refine the preliminary finding with a manual refraction prior to issuing your eyeglasses prescription.

Astigmatism Correction

Astigmatism, like near-sightedness and farsightedness, usually can be corrected with eyeglasses, contact lenses or refractive surgery.

In addition to the spherical lens power used to correct near-sightedness or farsightedness, astigmatism requires an additional “cylinder” lens power to correct the difference between the powers of the two principal meridians of the eye.

So, an eyeglasses prescription for the correction of myopic astigmatism, for example, could look like this: -2.50 -1.00 x 90.

• The first number (-2.50) is the sphere power (in dioptres) for the correction of myopia in the flatter (less near-sighted) principal meridian of the eye.
• The second number (-1.00) is the cylinder power for the additional myopia correction in the more curved principal meridian. (-2.50 + -1.00 = -3.50 D)
• The third number (90) is called the axis of astigmatism. This is the location (in degrees) of the flatter principal meridian, on a 180-degree rotary scale (in which 90 degrees designates the vertical meridian of the eye, and 180 degrees designates the horizontal meridian).

If you wear soft toric contact lenses for astigmatism correction, your contact lens prescription will likewise include a sphere power, cylinder power and axis designation.

Gas permeable contact lenses also correct astigmatism. Because these lenses are rigid and optically replace the cornea as the refracting surface of the eye, a cylinder power and axis may or may not be needed, depending on the type and severity of astigmatism correction required.

Refractive surgery such as LASIK also can correct most types of astigmatism.

CORRECTION OF REFRACTIVE ERRORS

There is not adequate scientific evidence that eye exercises, vitamins or pills can prevent or cure refractive errors. Correction of refractive errors can be achieved by any means which can change the focusing power of the eye. This can be achieved by prescription glasses, contact lenses or by refractive surgery. Eyeglasses and contact lenses are common methods for correcting refractive errors. However, the aid of prescription glasses and/or contact lenses means a life-time of dependence on these means to see clearly. These temporary aids besides needing a constant maintenance and expenditure also limit the patient’s life – style in several ways. These drawbacks of the temporary visual aids led to the search and development of the refractive surgery which is a permanent remedy to refractive errors. Refractive surgery which was started back in 1940s during the second world war has indeed come a long way and is currently one of the most technologically advanced, successful and safe surgery done on the eyes. Refractive surgery takes you from wearing glasses or contact lenses to clear natural vision in a matter of minutes.

For those who find glasses or contacts a major inconvenience in their active lifestyle, they may consider refractive surgery as an option to correct or improve vision. Refractive surgical procedures are used to adjust your eye’s focusing ability by either reshaping the cornea or changing the eye’s refractive ability through the use of a lens that is placed inside the eye.

4.TREATMENT OPTIONS IN REFRACTIVE SURGERIES:

Refractive surgery is about freedom – the freedom to allow you to make lifestyle choices that were not available to you before. This was because you were totally dependent on glasses or contact lenses. Though refractive surgery is mostly understood to refer to LASIK, there are many more procedures than just LASIK which are used to remove glasses or contact lenses. 

There is no best method for correction of refractive error. The most appropriate method depends on your eyes and your lifestyle. Contact Angel Eyes today to learn more about which option for correction your refractive error may be most effective for you, or to schedule a personalized consultation with one of our physicians.

Angel Eyes offers all of the latest refractive surgery procedures available including:

Laser option for Vision Correction: 

Laser vision correction, or laser refractive eye surgery use excimer lasers to reshape the curvature of the cornea. Two methods are currently employed for doing the laser vision correction:

LASIK

– Custom Aspheric Lasik

– Lepto Lasik

– Corneal Wavefront Guided Lasik

– Ocular Wavefront Guided Lasik

PRK

– Trans-PRK 

Non – Laser Option for Vision Correction:

 In all those patients where the laser option is not suitable, they can go in for the non-laser option. Also, the non-laser option of vision correction may also be chosen as a first choice for its own benefits.

• Implantable Collamer Lenses (ICL / Phakic IOLs)
• Clear (Refractive) Lens Exchange