fitting and care of contact lenses


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Fitting Contact Lenses and Follow Up Care

METHOD FOR CONTACT LENS FITTING

  • MEASUREMENTS. In this procedure the curve of the cornea is measured using keratometry or videometry. The diameter of the Iris and pupil are measured and the palpebral aperture is measured. The Iris is measured horizontally and the palpebral aperture is measured vertically. All measurements are used together to determine the proper lens to be ordered.
  • DIAGNOSTIC LENS PROCEDURE. After measurements are taken, a close match from the eye doctors samples are used for a 15-20 minute trial. This time period is very important particularly for soft contact lenses. The time allows for the lacrimation to decrease. Additionally because of temperature differences between the eye and the air, fluid leaves the soft contact lens. The 20-minute trial period allows for equilibrium to be reached. Lastly the trial period ensures that the back surface of the contact lens and the front surface of the eye form a good fit.

CONTACT LENS POSITION

  • Proper corneal fit is important for intrapalpebral aperture or superior positioning of the lenses. The contact lens should be at the center of the eye horizontally for either type of positioning and the lower edge of the contact lens should be 1-2 mm above the lower eyelid. The upper edge of the contact lens must be under the upper eyelid and not above the superior limbus for superior positioning. The upper edge of the lens should be just beneath the upper eyelid, for intrapalpebral positioning,
  • In the case of soft lenses, once positioned the lens should shift 1-2mm during blinking and then return to its’ original resting place. This is indicative of a good fit. In the case of hard lenses fit is determined by use of sodium flourescin. When illuminated with a black light, a bluish black fluorescence indicates a good fit, while a yellowish green indicates a less than perfect adjustment.

OTHER FIT REQUIREMENTS

  • Lenses that allow for the best fit and least irritation are neither excessively flat nor steeply curved. In a case that the lens is too flat, the sides of the lens will turn away from the eye after blinking or move away from the center. Alternately, if a lens presses against the bulbar conjunctiva or the cornea or never moves, the lens is too steep. If proper fit is difficult to achieve, several trial lenses may be required.
  • After fit is obtained proper lens power and vortex distance must be calculated.
  • With regards to rigid lenses that have a spherical base curve, the corneal cylinder is neutralized because the lachrymal tear film occupies the space between the cornea and back surface of the lens and the toricity of the cornea becomes filled by the lachrymal layer. Therefore, the flat K, or flattest corneal meridian is the point of reference for all calculations. However, in soft contact lenses there is corneal cylinder neutralization because the spherical base curve causes no lachrymal film as the anterior of the lens drapes the cornea.

FOLLOW UP CARE

  • Follow up care is vital to maintain the health of the eye. Initially frequent visits may be required. After long term wear visits may be reduced to annual check ups. Check ups include examination of recent medical history, changes in eyesight/prescription requirements, lens fit issues resulting from changes in the eye’s shape, tissue integrity problems that may have resulted from irritation, patient compliance and the physical structure of lenses. A check up also includes a check of the cornea to insure proper function and that there is no infection.
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