Singapore Lasik

MYOPIA | LASIK

Myopia
Myopia was a term developed by the Greek physician Galen around AD 175 which when literally translated means “to close eye”. It was used to describe the act of squinting or partially closing the eyes to see far or distant objects more clearly.

Myopia, or in its layman’s term shortsightedness, is often thought of as a condition where a person can only see near and not far – and this is not entirely correct. Myopia can be correctly defined as a refractive condition of the eye in which parallel rays of light entering the eye come to a focus in front of the retina when the accommodative system or focusing mechanism of the eye is relaxed. The amount of myopia a person has is defined by the power of the lens that will correct the refractive error and cause the parallel rays of light to come to focus on the retina (see Fig 1-1 Myopia).

To help us better understand what myopia is, it is important to know how the eye functions and how it develops (see Fig 1-2 Anatomy of the Eye).

The eyeball is round and it has a protective tough white outer coat called the sclera. The sclera is covered by a relatively transparent, thin membrane called the conjunctiva. The conjunctiva lines the inside of the eyelids and the outer surface of the eye.

The cornea is the transparent clear structure in the front part of the eye that allows light to enter the eye.

The anterior chamber is the space between the cornea and the iris / lens behind. It is filled with a transparent liquid called the aqueous humor.
The iris, which is the colored structure behind the cornea and in front of the lens, controls the amount of light entering the eye.

Fig. 1-1 Myopia

Fig. 1-2 Anatomy of the Eye

Fig. 1-4 Visual Acuity Chart with Ocludar

Fig. 1-5 Automated Refraction

Fig. 1-6 Subjective Refraction

	The pupil is the opening in the center of the iris and the size of the pupil is controlled by the contraction or relaxation of the muscles in the iris. The lens of the eye is like the lens of a camera – it focuses light onto the retina at the back of the eye. The retina of the eye is like the film of a camera – it is the light sensitive layer at the back of the eye that is responsible for vision. The optic nerve is the structure of the eye where all the nerve fibers of the retina collect together to carry images to the brain. The optic disc is the place where all the nerve fibers of the retina gather before leaving the eye. Many studies have found that myopia tends to run in families. The risk is higher if both parents are myopic. Myopia has also been found to be correlated to the amount of near work performed – for example reading, computer work, detailed work such as jewelry repair, etc. Other risk factors of myopia include racial or ethnic group - myopia is much more common in Orientals and Japanese than Caucasians - and genetic syndromes. There are many different types of myopia, and it has often been classified based on the refractive error present into the following: Low myopia -> from -0.25D (-25 degrees) to -3.0D (-300 degrees), Moderate myopia -> from -3.0D (-300 degrees) to -6.0D (-600 degrees), and High myopia -> from -6.0D (-600 degrees) and upwards It is important to emphasize that the low myopic eye is structurally and anatomically very much like a normal non myopic eye. However, the highly myopic eye may be very different and may have sight threatening complications such as retinal detachments, glaucoma, myopic macula chorioretinal degeneration, macula holes and bleeding behind the retina due to abnormal blood vessels (choroidal neovascular membrane). Fig. 1-3 Further Illustration on Myopia

	The primary symptoms of myopia are blurry vision and difficulty in seeing distant objects. It is often detected with a vision test and refraction. The vision test is one of the simplest yet most important components of an eye examination. Each line of the vision acuity chart (see Fig 1-4) is assigned a notation in the form of a fraction to represent your visual acuity. The numerator is the distance in meters the patient is from the chart. The denominator represents the distance an eye with “normal” vision can read in the same one line. Interpreting the numbers is simple. For example, if you can read only until the 6/9 line, it means you’re able to see at six meters what someone with normal vision is able to see at a distance of nine meters. Refraction is a test done to determine a person’s best visual acuity by correcting their refractive errors. It is usually done by using an automated refractor machine (see Fig 1-5) first, followed by a subjective refraction (see Fig 1-6) A subjective refraction is done by placing lenses in a trial frame and using a visual acuitychart, the patient will then decide the lenses that give them the best vision and visual comfort. With these tests, the best refractive correction is determined.

	Lasik Surgery LASIK, or in its medical term Laser in Situ Keratomileusis, is now the most favored and popular refractive surgery technique to correct myopia in adults. LASIK surgery addresses refractive errors, specifically myopia and astigmatism. It aims to reduce, if not eliminate, a person’s dependence on glasses or contact lenses through the improvement of visual acuity. Here are several methods of LASIK surgery that are more commonly used: Conventional LASIK Conventional LASIK is a traditional software program used to correct low myopia (less than 400 degrees) with low astigmatism (less than 200 degrees). It involves using the cool beams of light from the laser to gently reshape the cornea to match your prescription. Tissue-Saving Mode LASIK Tissue-Saving Mode LASIK is the latest technology and a better option to WaveFront LASIK. Unlike WaveFront LASIK, it efficiently minimizes the amount of corneal tissue to be removed in order to produce the desired prescription change. It is suitable for patients with high myopia and thin corneas. Zyoptix Aspheric LASIK This is the latest breakthrough in LASIK technology, which promises to reduce the side effects commonly experienced after LASIK surgery, such as glare, haloes and night vision problems. It maintains the natural Aspheric shape of the cornea, therefore minimizing the possibility of aberration and ultimately providing better quality of vision – even in dim light conditions. It is best suited for those with very high myopia, thin corneas and large pupils in dim light conditions. Presbyopia LASIK Presbyopia LASIK gives the best results when performed for those with hyperopia and presbyopia. Epi-LASIK Epi-LASIK is a technology that works only on the surface of the eye. It is safer, and is less likely to cause dry eyes and infection. Different levels of refractive error and corneal thickness will require different LASIK surgery treatment. Alternatives to LASIK Surgery

	Spectacles are the most popular and safest method of vision correction for nearsightedness, farsightedness and astigmatism. They should first be considered before making a decision for LASIK. However, they have disadvantages of being a hindrance in daily or most outdoor activities. High power glasses also often look unsightly, feel cumbersome and are prone to cause spectacles intolerance. Contact lens wear is the other popular non-surgical method of vision correction, as contact lens users do not suffer from many of the disadvantages of spectacles. However, much time and money is spent fitting and maintaining them. More importantly, contact lens wear can give rise to potentially serious medical eye conditions such as cornea ulcers, Giant Papillary Conjunctivitis and corneal scarring.