Refractive errors

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Refractive errors

Previously only people over the age of needed spectacles. Today, college-aged people wear contact lenses. So much so that refractive errors affect everyone irrespective of age. Due to the changing diet and lifestyle of today’s generation, refractive error is increasing.

Vision:

§  The act or power of seeing.

§  The light from the object we see comes to the eye as light rays.

§  It enters through the circular membrane ‘cornea’, passes through the lens of the eye, and falls as an image on the retina.

§  The optic nerve there, coverts the images into electrical impulses and carries them to the brain.

§  The brain processes them and makes sense of what we see. Any deficiency in this phenomenon affects vision.

Myopia:

§  People with short sightedness have more curvature of the cornea.

§  As a result, light passing through the cornea is bent in front of the retina and focused into an image.

§  Thus, they see distant objects dimly and near objects clearly.

Hypermetropia:

§  People with this defect have a flat cornea. Not sufficiently curved.

§  Thus, the image of light transmitted through the lens falls beyond the retina.

§  Therefore, nearby objects are dim and distant objects are clearly visible to them.

 

Astigmatism:

§  Astigmatism is a common and generally treatable imperfection in the curvature of the eye that causes blurred distance and near vision.

§  With astigmatism, the lens of the eye, which is the front surface of the eye, has an irregular curve.

§  If the light transmitted through the lens is not focused on the retina at the same angle, but at different angles, the vision will be reduced. This is called Astigmatism.

§  That is, on the retina of a normal eye, light falls uniformly at all angles of the clockwise circle.

§  But for those who have astigmatism, the light falls on six and twelve angles of the clock circle. It does not fall in the angles of three and nine. Then the vision will decrease.

§  People with astigmatism see the letters in italics while reading.

Primary symptoms of Astigmatism:

§  Blurry, distorted, or fuzzy vision at all distances.

§  Eyestrain.

§  Difficulty seeing at night.

§  Eye irritation.

§  Squinting.

§  Headaches.

Keratoconus:

§  The cornea of the eye is cone-shaped in people with keratoconus.

§  A cone-shaped cornea causes blurred vision and may cause sensitivity to light and glare.

§  Reading, driving, watching television etc. will be difficult.

Healthy cornea versus Cornea with keratoconus

Treatment:

Old treatment method:

§  People with myopia advised to wear glasses with concave lens.

§  Myopia sufferers are advised to wear spectacles with concave lens.

§  Hyperopia sufferers are advised to wear spectacles with convex lens.

§  Similarly, the old treatment methods are to tell people with astigmatism to wear glasses fitted with both types of lenses (concave & convex lenses) as needed, and for those who don’t want to wear glasses, to wear contact lenses.

New treatment method:

A modern method of treatment for refractive errors has arrived which is performed without knife and without blood.

1.     Lasik: (Laser-assisted in situ keratomileusis)

It changes the structure of the cornea, allowing the light beam transmitted through it to fall properly on the retina, enabling the eye to see clearly without glasses and contact lens.

1.     Hinge flap. 2. Excimer laser beam. 3. Repositioned flap.

        Excimer laser:

§  An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or chips, eye surgery, and micromachining.

§  The excimer laser alters the refractive state of the eye by removing tissue from the anterior cornea through a process known as photoablative decomposition.

§  LASIK is a refractive procedure in which the femtosecond laser is used to create a thin flap from the surface of the cornea. The corneal flap is 100-140 microns thick. The corneal flap is then lifted, and the excimer laser is used to re-shape the remaining cornea to produce the desired correction. The flap is then re-positioned on the corneal surface over the treated area.

§  In people with myopia, the lens membrane is too stretch, so it is straightened with this laser. Thus, the incoming light falls on the retina properly and corrects the vision.

§  People with farsightedness don’t have enough curvature of the lens membrane. So, they sharpen it with this laser. As a result, the incoming light is curved sufficiently and falls on the retina properly. This makes the vision clear.

§  A small incision is made on the cornea for people with astigmatism. Microkeratome or Femtosecond laser is used for this. Once the membrane is opened, the laser is directed to the area of the cornea that needs to be repaired. Once the cornea is repaired, the membrane that was originally opened is put back in its original position and closed. Then it will stick automatically. Due to this, the vision is now clear. The treatment is over within a few minutes. Hence, the patient does not need to stay in the hospital.

Who need this treatment:

§  The abovementioned treatment can be done for people between 18 to 50 years. Moreover, their cornea should be healthy.

§  Visual impairment must be in the early stage.

§  People with keratoconus, retinal defect, uncontrolled diabetes, dry eye, severe eye infection, pregnancy, etc. cannot undergo this treatment.

Treatment for keratoconus:

§  There is a special contact lens for keratoconus. It’s called Rigid gas permeable contact lens. A disadvantage of this is that it needs to be changed at regular intervals.

§  Now a plastic material called ‘C3 R Intact’ will be implanted on the cornea. This treatment is receiving good response.

§  Like placing a pencil between the pages of a book, the cornea is slightly separated and two plastic objects inserted between them. It normalizes the structure of the cornea, corrected vision.

§  No hospital stay is required for this treatment which can be completed in ten minutes. No surgery required.

§  It provides many times better vision than other treatments. Importantly, vision is very clear at night.