Unattended or uncorrected short-sightedness is one of the most common causes of vision loss, says Dr Aman Mallik
Understanding the eye
Are you having difficulty in seeing distant objectsIJ Is your vision blurryIJ Sometimes it may be easy to read what is written on your laptop or books, but you have trouble watching the television or movies. This may be indications of myopia, commonly known as short sightedness. It is usually the effect of a bulged cornea or an elongated eyeball. When the cornea bulges more than its usual curvature, the lens tend to refract more and the image is formed in front of the retina and when the light-detecting nerve cells on the retinal surface are unable to detect, as the image is not focused on it, a blurry image is sensed by the brain. Refraction by the eye lens has to be minimal in order to focus on the distant objects.
The physics of the eye
The eye’s ability to adjust itself allows it to view a clear image of both short and long-distant objects. When the eye wants to focus on the nearby objects, it enlarges its lens curvature, hence reducing the focal length. This ability of the eye to focus on near as well as far objects by adjusting its focal length to form a clear image on the retina is known as the power of accommodation. As the power of accommodation is limited, focal length of the eye lens cannot be reduced beyond a certain limit. Due to this wide variance in focal length, eyes are prone to more vision defects. More often, the defect may be in only one side of the spectrum, either the inability to assume a short focal length and focus on nearby objects or a long focal length to focus on distant objects.
Is Myopia hereditaryIJ
In nearsightedness, as the name suggests, people have no trouble in focusing on nearby objects, but the eye is unable to focus on distant objects. This vision defect is also known as myopia, which is a very common refractive error. Most of the parents who are nearsighted and had to wear glasses throughout childhood are concerned whether their child will have it too.
If you are one of them, don’t worry as myopia is not strictly hereditary. But why all children don’t become shortsighted is still a mystery; though hereditary may be one of the factors. The risk that the child is nearsighted doubles if both parents are nearsighted. But this may not be the exact way to determine who will be shortsighted by simply looking at the family tree. As there may be cases wherein all family members have perfect vision but one kid suffers from myopia. The cause is believed to be a combination of both genetic and environmental factors. The risk factors include working with focus on close objects or spending a lot of time indoors along with family history of the condition.
Are bookworms at riskIJ
Reading a lot of books is good for acquiring knowledge, but is it good for your eyesIJ Will it hamper your visionIJ It may be possible that focusing fatigue due to excessive reading or holding the books too close to your eyes for a long time can prove to be a reason in increasing the risk of myopia in kids. Then is it more likely that bookworms are nearsighted than othersIJ The evidence is not so clear cut. Urban population faces this more than the rural or primitive society. It could be that the excessive use of gadgets these days has made the graph exponential. Recent researches state an interesting fact: The conventional and contact lenses prescribed since years for correcting myopia may actually aggravate the risk.
Control methods
Myopia is the most widely spread vision defect and is estimated to be prevalent among one-fifth of the world population. Rates are equally shared among adult men and women from 15 to 45 per cent. Unattended or uncorrected short-sightedness is one of the most common causes for losing vision, developing cataracts, macular degeneration, retinal detachment, glaucoma or Vitamin A deficiency. Timely correction of the defect by use of eyeglasses, contact lens or surgery can be useful.
Easiest and the safest of all is the use of eyeglasses, whereas contact lenses may provide a wider field of vision. Refractive surgeries tend to carry a risk that the shape of cornea could be changed permanently.
· Eyeglasses: Concave lenses are used for correction as they carry negative power (reciprocal of focal length, expressed in diopters). The more negative the power, the more is the severity of myopia.
· Refractive surgery: Alteration of corneal curvature or additional lens inside the eye.
· PRK/lASEK: Ablation of corneal tissue from the corneal surface. Relatively safer for myopia of up to six diopters, but can be painful post-operation.
· Phakic intra-ocular lens: Additional lens is added instead of modifying the corneal surface. Relatively better control of the refractive change, but this method has potential of serious long-term complications like cataract, glaucoma etc.
Preventive measures
The best thing that a parent can do is to allow their child to go outside and play. Yes, you heard that right; get your kids to spend more time playing outside but without their glasses, preferably in areas where it is easy for them to focus on distant objects like in playgrounds, backyards etc. This may be related to natural light exposure and is applicable for adults too.
The writer is Ophthalmologist at Sharp Sight Group of Hospitals, New Delhi