Types of refractive errors

Refractive Errors Dr Himanshu web

WHAT IS REFRACTIVE ERROR?

Refractive error is a condition in which the parallel rays of light coming from infinity do not come to a focus in the light sensitive layer of the retina.

WHAT ARE THE types of refractive error?

  1. Simple myopia or nearsightedness is a condition in which near objects are seen clearly, but distant objects are not clear. This occurs due to light rays focus in front of the retina due to either longer eye ball or increased corneal curvature. Commonly it starts in school-age children. This is the commonest refractive error seen in the society.
  2. Hypermetropia or farsightedness is a condition in which distant objects are usually seen clearly, but close ones are not clear. Farsightedness occurs if your eyeball is shorter than the normal or the cornea is less curved than normal, so light entering your eye is focused behind the retina.
  3. Astigmatism: Astigmatism is a condition where the front surface of your eye, the cornea, is irregular in shape pre-venting the light to focus at one point on the back of your eye, the retina. As a result, the vision would be blurred at all distances.
  4. Presbyopia (Eyesight of old age): Presbyopia is a condition in which the crystalline lens of the eye loses its flexibility thus making it difficult to focus on near objects. Presbyopia usually becomes noticeable in the early to mid-40s. Presbyopia is a natural part of the aging process and is not a disease, hence it cannot be prevented.
  5. High myopia usually describes myopia of -6.00 or more. High myopia could be progressive even after 20 years of age and may increase very severely, which is called pathological myopia. People with high myopia are more likely to have retinal detachments, macular problem (central part of the retina) and glaucoma. They are also more likely to experience floaters (shadow-like or insect like shapes which appear in the field of vision). Roughly 30% of myopes have high myopia.

All the cases of high myopia need at least annual retinal examination to avoid any serious complications.

WHAT PROBLEMS DOES A PERSON WITH REFRACTIVE ERROR FACE?

A sign of nearsightedness is difficulty in seeing distant objects like TV screen and the child may want to watch it from very near or difficulty in seeing blackboard in the school, for which the child may want to copy from the student sitting next instead of looking at the blackboard. These children may have poor class work or class notes in-spite of being regular and good at home work.

Common signs of farsightedness include difficulty in clearly seeing near objects, headaches, eye strain, and/or fatigue after close work. Although the hyperopia is not as common as myopia, the common vision screenings often done in schools are generally ineffective in detecting this condition. A comprehensive ophthalmological examination is required in all those with above mention complaints.

The signs of presbyopia include inability to read small prints at normal reading distance, the tendency to hold reading materials away from the eyes, inability to thread the needle, eye fatigue and headache after doing close work.

HOW TO TREAT THESE REFRACTIVE ERRORS?

Refractive errors can be corrected by prescribing concave or minus power lens (in case of myopia), convex lens or plus power lens (in case of hypermetropia) and cylindrical lens (for astigmatism) in the form of glasses/contact lenses.

IS THERE ANY WAY TO GET RID OF THESE GLASSES/CONTACT LENSES?

Yes, with advancement in the technology now there are quite a few options for removal of glass power. Laser refractive surgeries and phakic intraocular lens (permanent lens placed inside the eye) are some of them.

Please remember not every eye is suitable for these operations. We do many tests to check the suitability of the individual procedures.

CAN YOU TELL US LITTLE MORE ABOUT THESE OPERATIONS?

Sure. In general we can divide these operations into cornea based and the lens based surgeries. Currently in vogue are cornea based procedures such as LASIK, ReLEx SMILE and PRK (or surface ablation). Sometimes, when the cornea is not suitable we can consider placing a permanent lens inside the eye in front of natural lens such as ICL or EyePCL.
In case of very high refractive error or presence of cataract we can also consider performing an early cataract surgery with multi-focal intraocular lens (10L) implantation. However, these things can only be decided after a thorough eye checkup only.

WHAT IS LASIK?

There are two steps in the LASIK procedure. First, the surgeon creates a micro-thin corneal flap, which is lifted to expose the inner cornea. Second, corneal tissue is ablated by an excimer laser and thus removing the refractive error. The first step of making flap can be done either with ultra-thin automatic blade called Microkeratome (Blade LASIK) or using another laser called femtosecond laser (Blade free LASIK or Femtosecond laser LASIK).

UNDERSTANDING THE LASIK PROCEDURE:

With its excellent safety profile, patient comfort and superior visual outcomes, Blade free LASIK is among the fastest-growing refractive surgical techniques in the country today.

WHAT IS RELEx SMILE?

ReLEx SMILE, is the latest advancement in the field of laser refractive surgery. Using the femtosecond laser andwithout making a flap, a part of the cornea (lenticule) is removed based on the amount of refractive error. Thus improving patient’s comfort level and preserving the strength of the cornea.

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