REFRACTIVE ERRORS - PATIENT INFORMATION

Q: My husband and I have glasses. What are the chances that my child will get glasses?

A: At birth practically all eyes are hypermetropic (farsighted) to the extent of 2.5 to 3.0 diopters and as the growth of the body proceeds the axial length increases until when adolescence is passed. The eye should normally be emmetropic (without any number). As a matter of fact it is found that in over 50% of the population emmetropia is not reached, some degree of hypermetropia persists. On the other hand, the eye may become myopic (short sighted). It is generally genetic (i.e. hereditary). If both the parents are wearing glasses then there are high chances of child getting glasses. To rule out whether a child needs glasses or not, regular eye check up at definite intervals is advisable.

Q: What are the various therapies available to treat refractive errors ?

A: As we have seen that the basic problem for a person with a refractive error (i.e. eye number) is that the focused image of the seen object is not formed at the plane of the retina. So the basic principle of treatment is to shift the focused image on the retina to see the object perfectly clear. To do this there are different methods used by the ophthalmologist.

Note: only the following methods of treating the refractive errors are effective. No sort of exercise or medicine can cure the refractive error.

1. Optical treatment: This is the simplest & most commonly used method. Refractive errors are corrected by the use of glasses or contact lenses.

• Glasses—

For Hypermetropia, Convex or Plus(+) number glasses are used. For Myopia, Concave or Minus(-) number glasses are used.

For Astigmatism, Cylindrical glasses are used.

• Contact lenses –

This is the next most widely used method.

Contact lenses are of various types:-

1. Hard lenses.
2. Semi soft lenses-

• Regular semi soft lenses.

• Extended wear semi soft lenses.

1. Soft lenses-

• Regular soft.

• Daily disposables.

• Cosmetic soft lenses.

1. Surgical treatment: It is recommended after the age of 18 years. The eye number has to be stable for at least 6 months. The various surgeries that can be performed are:

1. Radial keratotomy (RK): It decreases myopia by flattening the cornea by making multiple radial incisions of varying depth. The following complications may occur:

• Accidental corneal perforation
• Vision threatening complications like infection
• Rupture of eye globe by trauma due to weakened scar
• Overcorrection
• Undercorrection
• Unstable vision.

1. Astigmatic keratotomy: It is similar to RK and is used in treatment of cases of astigmatism. Here only one meridian/axis is cut to make a more curved axis flatter.
2. PRK: PRK with Excimer laser involves the reshaping of the outer surface of the cornea. The range of correction is from -1.0 to - 6.0 D and +1.0 to +4.0 D.

The disadvantage is that it has a longer visual recovery period.

3. LASIK: This is the latest and the safest procedure.

Principle: A thin layer of cornea is cut like a flap with a precise cutting instrument. This clear flap is lifted up and folded upon to the top eye. Excimer laser is applied over the internal part of the cornea to reshape it and the flap is placed back in its original position where it heals into place with no stitches.

Range of correction :- -1.0 to -18.0 D and +1.0 to +8.0D. It corrects astigmatism upto +/- 4.0 D. Its advantage is that visual recovery is very rapid. Within one or two days most patients see clearly.

Last updated on 12-07-2001

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