Page 69 - The Book Pi in eye

9 PI AFTER PREVIOUS LASIK AND RK

Prelex is a good option, even if you have had previous eye surgery.
Special exams are required to calculate the exact shape of the cornea
after Lasik, RK, or CK. These surgeries change the relative distance
between the front and back part of the cornea. Let us first refresh our
knowledge about these procedures.

What is RK?

Vertical deep incisions are made into the cornea in a spoke like
fashion. Each incision causes the cornea to bulge around the incision
and at the same time flattening the center of the cornea. Therefore the
power of the cornea decreases and myopia or nearsightedness can be
treated.
There are some unique problems associated with Radial
Keratotomy. The incisions decrease the tensile strength of the
cornea. It’s shape and therefore the power become more responsive
to the pressure within the eye. There is diurnal fluctuation of the
pressure of the eye in normal people. It is usually highest in early
morning and decreases during the rest of the day and night. As a
consequence the cornea which has been weakened by RK is more
curved in the morning and less so in the evening. The power is more
in the early hours of waking and decreases over the next few hours.
Therefore the vision for reading may be better in the morning but the
distance vision improves during the day. The cornea bellows like the
sail of a boat.

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