fitting and care of contact lenses
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
pupil are measured and the palpebral aperture is measured.
The Iris is measured horizontally and the palpebral aperture
measured vertically. All measurements are used together to determine
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
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
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
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
OTHER FIT REQUIREMENTS
- Lenses that allow for the best fit and least irritation are
neither excessively flat nor steeply curved. In a case that
is too flat, the sides of the lens will turn away from the eye
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.
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
is the point of reference for all calculations. However, in
soft contact lenses there is corneal cylinder neutralization
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
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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