Saturday, 23 July 2011

Timely Diagnosis of Astigmatism

Published in "Panorama"

Timely diagnosis of Astigmatism

Recent research point out that up to 40% of children today are short sighted and many of them have astigmatism too. This is partly attributed to the conditions in which these children live! The incidence of astigmatism in the Gulf region is pretty high because children here tend to be more confined to closed areas and also tend to use the computer for long periods of time at a stretch, says Dr.Arif Ponnambath, Specialist Ophthalmologist, Zulekha Hospital, Dubai.

Astigmatism is one of a group of eye conditions known as refractive errors which is characterised by a variation in the shape of the cornea. It is a condition in which the cornea of the eye is asymmetrically curved, more oval than spherical, causing blurred or out-of-focus vision. Normally the cornea is smooth and equally curved in all directions and light entering the cornea is focused equally in all directions. In astigmatism, the front surface of the cornea is curved more in one direction than in the other. This abnormality may result in blurred vision. The distortion results because of an inability of the eye to focus light rays to a point. Dr.Ponnambath explains that most astigmatic corneas have two curves – a steeper curve and a flatter curve which cause light to focus on more than one point in the eye. “When there is an alteration in the corneal shape in a particular axis, it leads to a blurring of the image along that axis. This is because the light falling on that particular axis on the cornea is focused at a different point, either in front of, or behind the retina. This results in blurred vision at close range or at a distance that is, Astigmatism may be associated with myopia (short sightedness) or with hyperopia or long sight.”

Are there some children who are prone to astigmatism? Dr.Ponnambath responds, “The cause of astigmatism is not really known. Often it is found to be present from birth. The condition is genetic to some extent but not totally. In fact one of my patients, a young boy, had compound mixed astigmatism while neither of his parents had any problem with their eye sight. Incidentally, this is the most complicated form of astigmatism where one image is formed in front and another formed behind the retina and therefore, it is a trifle difficult to treat.”

Astigmatism can be acquired through an injury that causes the lens or the cornea to become distorted. This can happen from trauma, scarring or even from previous surgical procedures involving the eye. Also, a condition called keratoconus where the cornea becomes thin and cone-shaped, may be a risk factor for astigmatism. Diabetes is another risk factor for astigmatism because the high blood sugar levels can cause changes in the lens shape.

Depending on whether the astigmatism is mild, moderate or severe, it may present symptoms of blurred or distorted vision, eye strain, headache and eye fatigue. Astigmatism is usually diagnosed and measured with corneal topography, keratometry, vision testing and refraction.

A common complication of undetected and untreated astigmatism is ‘lazy eye’ or Amblyopia, reveals Dr.Ponnambath. “Small children, around the age of five or six years, do not usually respond to the blurring of image because they don’t know to express that they actually cannot see the blackboard properly. In such children there is an imbalance between the powers of the two eyes and one eye alone may be astigmatic. In such children, the potential of developing Amblyopia is common and unfortunately, we see plenty of cases of Amblyopia in this region. What is ironical is that, even educated parents are not aware of this condition which results in more number of children going undetected! Ideally, this condition should be treated before a child turns nine years of age; else it will worsen and treatment may not yield good results.”

Some people with very high degrees of astigmatism may have cornea problems such as keratoconus.

The heartening news is that, there are sophisticated diagnostic tools which would enable specialist ophthalmologists to detect astigmatism even in three year olds who cannot respond to questions, assures Dr.Ponnambath.

Emphasizing the need for timely diagnosis and intervention, Dr.Ponnambath explains, “The focusing power of children is extremely high. There is a small muscle in the eye which is akin to the focusing drum in an SLR camera. In a child, this muscle is extremely active. So when there is a problem of vision, the child, unaware to itself, tries to overcome the condition by using this muscle excessively. Therefore we have to neutralize this muscle to get the correct number or power of the eye. Astigmatism is not a preventable condition. Also, it may increase slowly. Hence regular eye care can help to ensure that proper vision is maintained.”

Dr.Ponnambath cautions parents against visiting optometrists or computer eye testing clinics to find out the correct eye power. “We will have to dilate the neutral diagonal muscle that will give the total power of the eye as per individual situation, depending on whether the child has a squint. The squint itself may have come about due to excessive accommodation of the muscle. So taking the totality of the conditions, we may have to under-correct, over-correct or correct fully, the existing condition.”

If the extent of astigmatism is slight and is not associated with any other problems of refraction such as myopia or hyperopia, no corrective measure may be required. In every other instance, correction may be done with glasses, contact lenses or surgery. The aim of surgical treatment is to reshape the cornea to make it more spherical or uniformly curved. The most common surgeries to correct the condition are LASIK and astigmatic keratotomy, a procedure that involves making a microscopic incision on the eye.

Dr.Ponnambath emphasizes, “With respect to children, I would not advice contact lens early, up to a certain age. One reason for this is contacts require careful handling which small children will not be able to manage. Secondly and more importantly, children grow very fast and with their growth, correspondingly the eyeball also changes in size and power; the refractive error needs to be continually reassessed every six months for changes. Thirdly, children are more easily exposed to dust and this could lead to conditions of allergy, especially in hot and humid climatic conditions like we have here in the UAE. So sediments of dust on the contact lens can give you a vicious cycle of problems of allergy. If good hygiene is not maintained, there is every chance of microbes forming into the contacts, resulting in infection of the cornea which may then be a very tricky situation to deal with.”

On the issue of using LASIK surgery in children, Dr.Ponnambath is equally emphatic, “Using LASIK for children is out of question. At least not until they are eighteen years of age when the eye matures and has attained its full size and it is possible to make a proper calculation of its power for appropriate correction to be done.”


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