Page 30 - The Book Pi in eye

Rajesh Khanna, MD

vision or mono vision has been employed to overcome this dilemma.
In this technique, one eye is set for distance and while the other is set
for middle or near. It sounds good in theory, but in reality,
binocularity or depth perception is sacrificed. Also intermediate vision
may suffer. Only 20 % of people may even like monovision. Others
may experience dizziness, jump in images and confusion. This is the
advantage of Prelex: all vision in all three zones is attained while
retaining depth perception.
To perform Lasik, a flap needs to be fashioned either by a
femtosecond laser or microkeratome. The flap fashioned in Lasik has
some drawbacks. It weakens the cornea and interferes with the
corneal nerves. Lasik cannot be performed on very thin corneas, or
abnormally shaped corneas, for fear of causing the cornea to bulge
forward.
Damage to the central corneal nerves may induce dry eyes and
make preexisting dryness worse. Prelex can still be performed on such
thin or dry corneas. Another advantage of Prelex over Lasik is that the
center of the cornea is not violated.

Pi in eye LASIK

Distance and near vision Distance or near vision

Permanently glasses free Need for glasses by age 45
Binocular vision at all distances Not above age 45

Thin, thick or keratoconus Contraindicated
cornea
Avoids dry eyes Causes dry eyes
Can be performed in extreme No
nearsighted eyes
Can be performed in high No
hyperopes or farsighted eyes
Can be performed over Avoided
previous Lasik, RK, PRK
Prevents future cataracts No

Figure 4.1 Comparing Pi in eye and Lasik

24