Contact Lenses

By Eyecare NG

Types   |   Uses   |  Before Use   |   Contraindications

Contact lenses are lenses that are worn directly on the surface of the eye. They are thin medical devices, mainly prescribed for the correction of refractive errors and presbyopia as well as conditions like keratoconus.

Contact lenses provide great options for most people that need prescription eyewear but do not like wearing eyeglasses. They are also used for cosmetic purposes such as enhancing or changing eye colour, creating special eye effects and covering eye defects like corneal scars.

Types

Contact lenses can be classified using various criteria such as lens design, lens pliability, wearing schedule and replacement schedule.

Based on lens design

  • Single vision contact lens: These are lenses that have the same power all-round. They are also called spherical contact lenses and are used to corrected myopia or hyperopia.
  • Toric lenses: These are contact lenses used to correct astigmatism.
  • Multifocals: These are contact lenses designed to improve vision at different distances. They are used to correct presbyopia together with refractive errors such as myopia, hyperopia, and astigmatism
  • Cosmetic contact lenses: These are contact lenses worn for cosmetic purposes like changing the colour of the eyes, creating special effects and masking eye defects (like corneal scars).
  • Scleral lenses: These are contact lenses that extend beyond the cornea on to the sclera (the white part of the eyes). They are larger in diameter and are mostly used for the management of corneal irregularities like keratoconus.

Based on lens pliability

  • Soft contact lens: These are thin, malleable contact lenses that easily conform to the shape of the surface of the eye.  They are made from plastics or silicon and come in daily wear and extended wear types. They are more popular than hard contact lenses because they are more comfortable to wear and people easily adapt to them.
  • Hard contact lens:  These are rigid contact lenses that maintain their shape on the surface of the eye. The first type of hard contact lens produced was large and very uncomfortable to wear. The hard contact lenses available today are smaller, more flexible and less discomforting than the conventional hard lenses. However, compared to soft contact lenses, it takes more time to adapt to them.

Based on wearing schedule

There are 2 major types of contact lenses based on wearing schedule. They include:

  • Daily wear lenses: These are contact lenses that are designed to be worn only during the waking hours and must be removed at the end of the day before sleeping.
  • Extended wear lenses: These contact lenses can be worn both during the day and at night. The contact lens wearer can sleep with the lens on for up to seven days at a stretch before removing them.

Both types of lenses can either be single-use lenses (lenses that are used once and discarded) or reusable lenses (lenses that can be removed, cleaned, stored and used again).

Based on the replacement schedule

There 4 major types of contact lenses based on lens replacement schedule. They include:

  • Daily Disposable Contact Lenses (DDCL): These are single-use contact lenses designed to be replaced daily.
  • Disposable Contact Lenses:  These lenses are designed to be disposed after being used for 2 weeks or less.
  • Frequent Replacement Lenses: These are lenses designed to be disposed monthly, or quarterly depending on their specified replacement schedule.
  • Conventional Lenses: These are lenses that can be used for 6 months to one year before they are replaced. Due to the growing preference for disposable lenses, the use of conventional lenses has decreased significantly.

These lenses can either be daily-wear lenses (worn during the day and removed at night before sleeping) or extended-wear lenses (worn both day and night for up to 7 days before they are removed)

Uses 

Contact lenses can be used for the following:

  • To correct refractive errors and presbyopia
  • To treat corneal irregularities such as keratoconus
  • To perform orthokeratology (a procedure in which the cornea is temporarily reshaped with special contact lenses in order to control myopia)
  • As a bandage for some uninfected corneal abrasion.
  • For enhancing or changing the colour of the eyes.
  • To mask eye deformities like corneal scars. 
  • To deliver some eye medications that need to be released slowly into the eyes.

Before use

Before using contact lenses, it is important you consult your eye doctor and get your eyes evaluated to ensure they are suitable for you and to also evaluate your needs and determine the best type and fit for you.

Contact lens evaluation generally involves:

  • Detailed history taking by your eye doctor
  • Visual acuity measurement
  • Refraction (to determine the accurate lens prescription)
  • Keratometry to determine the diameter and curvature of your cornea. These measurements are important for determining the base curve and diameter of your contact lenses.
  • Measurement of the distance between the upper eyelid and the lower eyelid called the interpalpebral distance.
  • Tests to evaluate the quantity and quality of your tear film and the general health of your eyes.
  • Other tests that the eye care practitioner may deem necessary.

Based on the outcome of the evaluation, your eye care practitioner may proceed to do fit some trial contact lenses. The trial contact lenses while on the surface of your eyes will be assessed for fit and comfort. If they are the right fit for you, the original lens can then be ordered for you.

Contraindications of Contact Lens Use

The use of contact lenses are contraindicated under the following conditions:

  • Presence of an active eye disease, inflammation or injury such as corneal abrasion.
  • Use of medications (including eye drops) that are contraindicated with contact lenses or care solutions.
  • Allergy to contact lens materials or care solutions.
  • Inability to adhere to lens care instructions either due to age, illness, disability or other conditions.
  • Inability to insert and remove contact lenses without help.
  • History of non-compliance with wearing and replacement schedules as well as lens care instructions.

Some contact lens types are also contraindicated for people who experience dry eyes.