Soft Contact Lenses

Introduction

Refractive errors [such as myopia (short sightedness) and hyperopia (long sightedness)] can be corrected with eyeglasses or contact lenses.

For most people, the choice is a matter of appearance, convenience, cost, risk and comfort.

Types of Soft Contact Lenses

Soft contact lenses are made of various plastic polymers that absorb water (hydrophilic).

These materials differ in terms of oxygen permeability (expressed in Dk units, where D stands for diffusion and k for solubility), water content (varying between 20 and 70 percent water by weight), surface quality (wettability), ultraviolet absorption and structural consistency (stiffness or modulus).

Lenses with higher oxygen permeability are generally considered a healthier option.
Dk/t is a measure specific to the individual lens, rather than its material, and refers to the oxygen permeability (Dk) of the material normalized for the thickness of the lens (t). The higher the Dk/t value, the more breathable the lens.
Other material characteristics include water content, surface quality (wettability), ultraviolet absorption, and modulus (stiffness).

Because soft lenses can absorb chemicals, and deposits can bind to the surface, all soft lenses require a replacement schedule based on the individual patient and the type of lens prescribed.

Quarterly
Monthly
1 to 2 weeks
Daily - Because they are disposed after each day's use, no disinfection is required.

Safe Use

General care

Do not expose to your contacts to any water (which includes lake, pond and ocean water).
Do not wear contact lenses overnight unless your eye care provider has prescribed them to be worn that way.
Always wash your hands before handling contact lenses to reduce the chance of getting an infection.
Remove the lenses immediately and consult your eye care professional if your eyes become red, irritated, or your vision changes.
Lens should be removed before using eye drops and wait 15 minutes after administration before reinserting. This is especially important with drops containing benzalkonium chloride (BAK).

Contact lens solution

Clean and disinfect your lenses properly.
Never use nonsterile water (distilled water, tap water, or any homemade saline solution). Exposure of contact lenses to water has been associated with Acanthamoeba keratitis, a corneal infection that is resistant to treatment and cure.
Do not put your lenses in your mouth to wet them. Saliva is not a sterile solution.
Never reuse any lens solution. Clean, rinse, and air-dry your lens case each time lenses are removed.
Do not use contact lens solutions that have gone beyond the expiration or discard date.
Replace your contact lens storage case every 3-6 months.

Application and Removal

Application of all types of lenses involves, with clean hands, placing the prepared lens directly on the center of the cornea while holding the lids and lashes to create an opening large enough to clear the diameter of the lens.

Soft lenses are removed by pinching the edges of the lens at the four and eight o'clock positions with the thumb and index finger while holding the upper lid out of the way.

Instilling a drop of wetting solution or artificial tears makes removal easier.

If the lens is not readily removed, it is possible the lens is in the eye but not on center.

The most likely place to find the dislocated lens is under the upper lid (usually folded). To check for this, have the patient look straight down while holding the upper lid up as high as possible. If found, the lens can be pinched out from there. It may be necessary to evert the lid to find a lens that has adhered to the inner surface of the upper lid.

Soft Lens Solutions

Soft lens materials provide a good medium for microbial growth, so lens cleaning and disinfection are required with approved systems.

Multipurpose solutions are intended to be "all-in-one" solutions that are used to rinse, clean, disinfect, and store lenses during their overnight soaking.
Peroxide systems use hydrogen peroxide to disinfect and passively oxidize surface deposits. These systems require that the peroxide solution be "neutralized" prior to lens use, and different techniques (one- or two-step) are used for accomplishing this.

NOTE: Due to specific lens requirements or patient sensitivity, preservative-free saline may be recommended for lens application or for lens rinsing.

Potential Complications

Serious conditions associated with contact lenses include corneal ulcers, corneal abrasions, and infectious keratitis. Evaluation by an eye care provider should be arranged promptly if patients experience blurred vision, pain, or photophobia.

Contact lens wear and/or lens care solutions can provoke many eye reactions, such as

Redness
Itching
Contact lens-induced dry eye (CLIDE)
Allergic reactions
Conjunctivitis (microbial, mechanical, allergic or inflammatory)
Contact lens-induced acute red eye (CLARE)

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