Page 72 - The Book Pi in eye

Rajesh Khanna, MD

What is corneal cross linking?

A method to strengthen the cornea; using riboflavin irradiated by
UV radiation. The free radicals generated from covalent bonds
between collagen fibers of cornea, increasing its rigidity and strength.

How these surgeries affect Cataract or Prelex procedure?

After any of these surgeries determining the state of the cornea
and the effective optical zone is very important. These factors would
be of paramount importance in determining the choice of the lens.
Measurements listed before like color corneal topography and
refractions are to be diligently performed.
The lens calculations can be especially challenging in these
previously operated eyes. The corneal power gets altered and also the
relation between the front part and back part of the cornea. The
instruments like corneal keratometer are unable to account for these
alterations. It is imperative to find the true power of the central part
of the cornea to generate the correct power of the pi to be implanted.
There are some mathematical formulae which when used with past
experience can give great results.
A new device OR range may be used during the surgery to help
come up with the exact power. After the cataract is removed but
before the lens is inserted this device is fitted on to the microscope.
It works like an autorefractor yielding the power and astigmatism of
the aphakic eye. Based on this information it can calculate the lens to
be inserted.
A small optical zone may hinder with effective functioning of
multifocal, and an accommodative implant, which is Crystalens,
would be the preference. Crystalens would also be the choice if there
is irregular astigmatism or RK with more than 4 incisions or severe
dry eyes. Restor and Tecnis may be implanted if astigmatism, dryness
can be treated or optical zone can be enlarged.
The preexisting corneal flap from Lasik, cuts from RK, scars from
CK or other corneal surgeries may affect the sizes and locations of
the openings. Water entering the potential spaces can hinder
visualization. Wounds may leak and may need a stich. The healing
may be slower. The outcomes make the patient very happy.

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