contact lens use Indications & Contraindications

Indications of contact lens use

1. Optical indications include anisometropia, unilateral aphakia, high myopia, keratoconus and irregular astigmatism. Optically they can be used by
every patient having refractive error for cosmetic purposes.

Advantages of contact lenses over spectacles:
(i) Irregular corneal astigmatism which is not possible to correct with glasses can be corrected with contact lenses.

(ii) Contact lenses provide normal field of vision.

(iii) Aberrations associated with spectacles (such as peripheral aberrations and prismatic distortions) are eliminated.

(iv) Binocular vision can be retained in high anisometropia (e.g., unilateral aphakia) owing to less magnification of the retinal image.
 

 (v) Rain and fog do not condense upon contact lenses as

SPECTACLES

The lenses fitted in a frame constitute the spectacles. It is a common, cheap and easy method of prescribing corrective lenses in patients with refractive errors and presbyopia. Some important aspects of the spectacles
are as follows:

Lens materials
1. Crown glass of refractive index 1.5223 is very commonly used for spectacles. It is ground to the appropriate curvature and then polished to await the final cutting that will enable it to

Treatment OF APHAKIA

Treatment
Optical principle is to correct the error by convex lenses of appropriate power so that the image is formed on the retina (Fig. 1).

Modalities for correcting aphakia include:
 (1) spectacles, (2) contact lens, (3) intraocular lens, and (4) refractive corneal surgery.

1. Spectacles prescription has been the most commonly employed method of correcting aphakia, especially in developing countries. Presently, use of aphakic spectacles is decreasing. Roughly, about +10 D with cylindrical lenses for surgically induced astigmatism are required to correct aphakia in previously emmetropic patients. However, exact number of glasses will differ in individual case and should be estimated by refraction. An addition of +3
to +4 D is required for near vision to compensate for loss of accommodation.

Advantages of spectacles. It is

What is APHAKIA

APHAKIA

Aphakia literally means absence of crystalline lens from the eye. However, from the optical point of view, it may be considered a condition in which the lens is absent from the pupillary area. Aphakia produces a high degree of hypermetropia.

Causes
1. Congenital absence of lens. It is a rare condition.
2. Surgical aphakia occurring after removal of lens is the commonest presentation.
3. Aphakia due to absorption of lens matter is noticed rarely after trauma in children.
4. Traumatic extrusion of lens from the