Types Of Contact Lenses

 

 

Contact lenses are excellent devices in vision correction.

They eliminate the inherent optical distortion from spectacles. The wearer also enjoy a realistic object distance and size, unrestricted visual field, and absence of physical burden from spectacles. 

They are medical devices which must be professionally fitted and the wearer adequately instructed on their use. Serious eye complications can develop if any of these is neglected.
 

Conventional Soft daily wear contact lenses are made of flexible hydrophilic (water loving) material which contain 35% to 70% water. The diameter varies from 13 mm to 15 mm. They are available in almost any optical correction with either colorless, transparent tint or opaque iris patterns to change the eye colour or to cover corneal or iris defects. 

Soft lenses are usually instantly comfortable therefore are well suited for occasional wear and not susceptible to irritation from foreign bodies when in dusty or windy environment. They are also more secure for vigorous and contact sports. 

Due to hydrophilic nature of the material, they are more readily to have protein deposit and have shorter life span. Most authorities recommend these lenses should be replaced yearly or earlier if they are used daily for long hours or wearers with poor quality of tear. 

Rigid gas permeable contact lenses are made of dense and solid material, generally provide a sharper vision than soft lenses. They contain very little water and do not require much tear to maintain their structure integrity. RGP are easier to maintain and last much longer than soft lenses. They may be somewhat uncomfortable initially but after adaptation they are equally as comfortable as soft lenses. 

As soft lenses, they are available in almost any optical correction. 

Compare to soft lenses, RGP lenses also superior in oxygen transmissibility, more tolerance to poor hygiene, and much less contact lens related problems, such as allergies, dry eyes, microbial infection. 

Disposable soft contact lenses are made specially to be thrown away periodically - daily, once weekly or two, or monthly. They are very useful for people with allergies or frequent lens deposit build-up problems as the lenses are replaced before problem develops. They have fewer lens related eye complications than conventional daily wear modalities 

The greatest advantages of using daily disposable contact lens are the elimination of the hassles of lens cleaning, irritation from deposits built-up on the lens, and the use of a sterile lens every day increases safety significantly by reducing the risks of contamination by pathogenic organisms which have been shown to be linked with contaminated lens storage case/solution or poor wearer compliance in their use. 

Cosmetic soft contact lenses are made using molecular imprinting and are colored using various methods such as dye dispersion, vat-dye tinting, chemical-bond tinting, and dye printing to create various opaque iris patterns. Some are produced by allowing pigments enclosed between two layers of lens material to prevent direct contact with your eyes.

They are used for either just to change eye colour on normal healthy eyes or to mask unsightly disfigured cornea or iris malformatiom to reduce glare and improve quality of vision. 

Multifocal contact lenses are contact lenses with multiple prescriptions all in one lens. Typically a prescription for normal objects viewed at a distance, a prescription for intermediate distances and one for normal reading. This setup helps people with presbyopia correct age-related vision problems where the eye can no longer focus on objects up close.

Advantages to multifocals

  • Better visual acuity for the range of distances from near to far
  • A less abrupt switch between prescriptions
  • The ability to see in most conditions without extra eyewear

Drawbacks to multifocals

  • More difficult to adjust to due to a different viewing experience
  • Accompanied by mild hazy or shadowy vision during the adjustment period
  • More expensive because of the increased complexity in design

 

Myopic Control Contact Lenses

 

Orthokeratology (Ortho-k)

Ortho-k is a non-surgical treatment option for vision correction involve the use of computer-guided specially designed contact lenses. These lenses are worn overnight to temporary reshape the superficial cornea resulting in clear vision during the day without the need for glasses or regular contact lenses.

 

Ortho-k lenses are suitable for all ages requiring vision correction and they are particularly beneficial for children. 

Extensive studies have shown Ortho-k lenses significantly reduces the speed of myopic progression in children. Ocular axial length elongation is also markedly retarded when compared with children vision corrected with normal glasses and regular contact lenses.

Ortho-k are also excellent for adults and children requiring good vision all day and are not suitable to wear glasses or contact lenses in active sports, swimming and other water related activities.