Care and fitting of contact lenses

 
Contact lens help
Lens fitting and care
Lens insertion and removal
Contact lens disinfection
Contact lens protein removal
Lens solution incompatibility
Contact lens history
Contact lens future
Contact lens glossary
 
Types of contact lens
Soft contact lenses
Hard contact lenses
Disposable contact lenses
Extended wear contact lenses
Bifocal contact lenses
Contact lenses for astigmatism
Therapeutic contact lenses
 
Contact lens problems
Contact lens dry eyes
Damage to lenses
Contact lens infections
Eyelid inflammation
Corneal complications
Contact lens conjunctivitis
Giant papillary conjunctivitis
Peripheral corneal infiltrates
 
Fitting of Contact Lens and Follow Up Care

There are two usual methods for contact lens fitting. The first is the procedure in which taking measurements is involved in order to determine the parameters. The curve of the cornea is measured using keratometry or videometry. The diameter of the iris is measured horizontally, the palpebral aperture is measured vertically and the diameter of the pupil is also determined. All these findings are taken together to determine the contact lens parameters to be ordered.

The second type of fitting is the diagnostic lens procedure where, after the aforementioned measurements are taken, corresponding and appropriate lenses are chosen from the eye specialists’ contact lens trial set and tested on the patient’s eye. The set is kept on the eyes for 15-20 minutes so that the lacrimation decreases and, in the case of soft lenses, this test period is very important. The temperature on the eye is greater than the surrounding temperature thereby forcing fluid out of the lenses, so a point of equilibrium must be reached. The relationship between the back surface of the contact lens and the front surface of the eye must be perfected to result in a good lens fit.

Positioning of Contact Lenses

Corneal lens fitting is necessary for superior positional or intrapalpebral aperture positioning of the lenses. For either, the lens should be situated at the centre of the eye in a horizontal manner. The lower edge of the lens should be 1-2mm above the lower eyelid. In case of superior positioning, the upper edge of the contact lens must be under the upper eyelid and not above the superior limbus. In case of intrapalpebral positioning, the upper edge of the lens should be immediately beneath the upper eyelid. After positioning, while blinking the lens should ideally shift 1-2mm and then come back to its original position and remain there.

In case of rigid lenses to check how well the lens adjusts to the cornea, sodium flourescin is used which mixes with the film between the lens and the cornea and, if illuminated with a black light, it shows various patterns. The more perfect the correspondence between the curves of the cornea and lens, the fluorescence is bluish black while less than perfect adjustment will give off a brighter yellowish green fluorescence.

Determining Flat and Steep Lenses

The ideal is to use lenses that are not too flat and not too steeply curved so they fit the curvature of the eye and don’t irritate the eye. The sides of the lenses give information about the sag of the lens. If the lens sides turn away from the eyes after blinking, it is a case of a flat lens whereas if the lens sides press heavily on the cornea or buliar conjunctiva, this points to a steep lens. A lens, which moves excessively away from the centre after blinking, is found to be too flat whereas a steep curved lens will never move.

In case the position movement or back surface fitting relationship does not match the required standards, trial lenses with several parameters are tried. After the appropriate fit is obtained, the lens power is calculated by computation or directly by a method of refraction over the trial lenses. The quality of the vertex distance also needs to be considered following the calculation of the spherical power of the contact lenses.

When rigid lenses that have a spherical base curve are fitted, the lachrymal tear film occupies the space between the cornea and back surface of the lens so the toricity of the cornea filled by the lacrimal layer neutralizes the corneal cylinder. Thus, the flattest corneal meridian or flat K becomes the point of reference for all calculations. However, in soft contact lenses with a spherical base curve there is no lacrimal film as the anterior of the lens drapes the cornea allowing little neutralization of corneal cylinder to occur.

Follow up Care

Since the contact lens is an external device made of plastic situated over the cornea, appropriate care of the lenses and subsequent follow up checks become imperative to maintaining lenses as well as health of the eyes. Though after the compulsory initial frequent check ups when someone first starts to use contact lenses, one visit a year after that is still necessary as problems can occur any time over the years. The shape of the eye can change and the prescription may need to be changed as well. Check ups include examination of history, eyesight, lens fit, tissue integrity, patient compliance and physical structure of lenses.

A contact lens acts as an optical patch or bandage. While acting as the former it reduces the passage of oxygen and carbon dioxide to and from the cornea. The patch creates hypoxia and disrupts the corneas natural aerobic metabolic cycle. To check these follow up care becomes a must.

As a bandage, contact lenses create stress on the tissues underneath and this reduces the moistness of the eye surface. It can also become infected with organic and inorganic deposits and can also be scratched, clipped or torn. To counter all these dangers taking advice from the eye doctor is necessary.