What are refractive errors?

In a normal eye ,the light rays focus on retina and image formed is sent through the optic nerve to the brain. Refractive errors occur when the shape of the eye prevents light from focusing directly on the retina. The image is formed either behind or in front of retina and spectacles lens shift the image to focus exactly on retina for us to see clearly .The length of the eyeball (longer or shorter), changes in the shape of the cornea, or changes in lens can cause refractive errors.

What are the different types of refractive errors?

The types of refractive errors are myopia, hyperopia, astigmatism and presbyopia. These are related to optics of eye.

Myopia (near-sightedness) is a condition where near objects appear clear, while objects far away appear blurry. With myopia, light comes to focus in front of the retina instead of on the retina. This happens due to increase length of eye ball or steep cornea or lenticular changes.

Hyperopia (farsightedness) is a condition where distant objects may be seen more clearly than objects that are near. However, people experience hyperopia differently. For people with significant hyperopia, vision can be blurry for objects at any distance and near. Hyperopia occurs due to shorter eye ball length or flat cornea or lenticular changes.

Astigmatism is a condition in which the eye does not focus light evenly onto the retina.This can cause images to appear blurry and stretched out. Astignatism occurs due to changes in corneal curvature and can present with myopia or hyperopia also. Presbyopia is an age-related condition in which the ability to focus near objects becomes more difficult. Presbyopia affects most adults over age 38.

What are the signs and symptoms of myopia?

Blurred vision is the most common symptom of refractive errors. Other symptoms may include:

• Objects far away appear blurry
• Need to rub eyes often
• Excessive blinking
• Glare or halos around bright lights
• Squeezing eyelids to focus or Squinting
• Headaches or Eye strain

How is myopia diagnosed?

An eye care professional can diagnose refractive errors during a comprehensive eye examination. People with a refractive error often visit optometrists with complaints of visual discomfort or blurred vision. However, some people don’t get to know that they aren’t seeing as clearly as they could. It is mandatory for every child to undergo routine eye examination yearly so that refractive errors can be picked up early. When a child comes in opd for first time, there is a vision test and accordingly further evaluation of refractive error is done . Cycloplegic eye drops or ointment is used to determine the refractive error objectively without the accommodating effort of a child coming into play.

What should be the follow-up schedule?

Children with simple myopia should be examined 6 monthly. Once myopia stabilizes follow up can be annually. Follow-up examination should be more frequent when warranted by any other co-existing conditions. Contact lens wearers generally require more frequent follow-up for evaluation of lens fit and corneal physiology. Usually the myopia gets stabilised anytime between 14 to 17 years of age. In some children, the myopia keeps on increasing for few more years due to increase in length of eyeball which is due to the childs genes mapping.

WHAT IS THE TREATMENT OF MYOPIA?

Prescribed eye glasses - This is a simple, safe way to sharpen vision caused by nearsightedness. The variety of eyeglass lenses is wide and includes single vision, bifocals, trifocals and progressive multifocals and can be given to any age group.

Contact lenses - These lenses are worn right on your eyes. They are available in a variety of materials and designs, including soft and rigid, gas permeable in combination with spherical, toric and multifocal designs. Advised for people old enough to manage putting them on daily, able to maintain hygiene and take sufficient care. So not suitable for children.

Refractive surgery - Refractive surgery reduces the need for eyeglasses and contact lenses. A laser beam is used to reshape the cornea, which results in a decreased nearsighted prescription or even lenses are put inside the eye. These procedures include LASIK, LASEK, PRK and ICL.

What are the risks of myopia?

Myopia increases the risk of retinal detachment .Though rare but timely detection of a hole or break and then sealing it by laser prevents retinal detachment. Hence a 2 yearly retina periphery examination in OPD is recommended .

What Is Myopia Control?

If your child has myopia (nearsightedness), you're probably wondering if there is a cure — or at least something that can be done to slow its progression so your child doesn't need stronger glasses year after year. Myopia typically develops during the early school years and tends to progress more rapidly in pre-teens than in older teenagers. This is why myopia control studies usually involve relatively young children. Although an outright cure for nearsightedness has not been discovered, a number of recent studies suggest it may indeed be possible to at least control myopia by slowing its progression during childhood and among teenagers.

These treatments can induce changes in the structure and focusing of the eye to reduce stress and fatigue associated with the development and progression of nearsightedness. Treatments that are currently available for slowing the progression of myopia include spectacle lenses, contact lenses, and pharmaceutical agents.

WHAT ARE THE TREATMENT OPTIONS FOR MYOPIA CONTROL?

Bifocals and Progressive Addition Lenses (PALs) - The largest of the treatment trials with multifocal lens was the Correction of Myopia Evaluation Trial (COMET), which showed that there is a role for retinal defocus in myopia progression and suggest that myopic children with large accommodative lags and near esophoria may benefit from wearing PALs.

Contact Lenses – Some studies show that contact lenses with a special dual-focus multifocal design with full corrective power in the center of the lens and less power in the periphery, had less progression of myopia.

Orthokeratology - Orthokeratology is the use of specially designed gas permeable hard contact lenses that are worn during sleep at night to temporarily correct nearsightedness and other vision problems so glasses and contact lenses aren't needed during day time. Few studies have shown that overnight orthokeratology suppressed elongation of the eyes of children, hence reducing the progression of myopia. Some even advice several hours a day until the curvature of your eye evens out. But these are not commonly used due to its complexity and cost.

Pharmaceutical Agents – like Atropine and Pirenzepineeye drops

Which drug is effective in controlling myopia ?

Atropine eye drops — are used to dilate the pupil and temporarily paralyze accommodation and completely relax the eyes' focusing mechanism. Because research has suggested nearsightedness in children maybe linked to focusing fatigue, investigators have looked into using atropine to disable the eye's focusing mechanism to control myopia. Recent well-designed studies using topical diluted atropine, have demonstrated statistically and clinically significant reductions in the progression of myopia. Low dose atropine has emerged as an effective option, as highlighted by the Atropine in the Treatment of Myopia studies ( ATOM 1 and ATOM 2 ). It has been shown to slow the progression but not fully arrest it. It is being widely used because it has minimal effects on pupil size, accommodation and near vision. It has been recommended for children between 5 – 15 years of age especially whose myopia is rapidly increasing. The treatment requires putting one drop of 0.01% Atropine daily for at least 2 years initially after whichthe child should be monitored to keep the low myopia status until the end of adolescence.The risks associated with these diluted atropine treatment, when taken under medical supervision, are relatively low and the benefits may last long. If there is a rebound growth after stopping, then the drops can be restarted. 5 year results of various studies have shown a 50% reduction in myopia progression. Therefore getting a diagnosis as early as possible and using atropine consistently through the eye’s growth years are the key.

Pirenzepine — Pirenzepine, is similar to atropine, but is less likely to produce mydriasis and cycloplegia. Not many studies are completed on this and hence not available commercially.