Refractive Lens Surgery

7
Correction of Keratometric Astigmatism:
Staar Toric IOL Refractive Lens Surgery
Stephen Bylsma
Financial interest: Dr. Bylsma is a consultant to Staar Surgical Company.
CORE MESSAGES
2 Clinically significant corneal astigmatism is encountered frequently
by the refractive lens surgeon.
7.1 Introduction
2 Off-axis rotation of a toric IOL will decrease the desired astigmatic
correction in proportion to the magnitude of deviation.
2 The Staar toric IOL has been widely studied, with the reports showing
a consistent, predictable effect of reduction of preoperative
refractive cylinder for the group of eyes studied.
Successful refractive surgery must correct
clinically significant preoperative astigmatism
to reach the goal of emmetropia [1]. Refractive
lens surgery, using either clear lens
extraction or cataract surgery, is a unique
form of refractive surgery in that one of the
two refractive components of the eye that
produce astigmatism is completely replaced.
In the straightforward case when pre-existing
astigmatism is purely lenticular, a spherical
intraocular lens (IOL) will restore emmetropia
from the aphakic state. However, refractive
lens surgeons more commonly encounter
patients in whom significant corneal
asymmetry is the primary cause for astigmatism.
In these cases, a spherical IOL alone will
not suffice; alternative or adjunctive treatments
are required to reach emmetropia in
the presence of significant corneal astigmatism.
Clinically significant corneal astigmatism
is encountered frequently by the refractive
lens surgeon. Astigmatism has been reported
to occur in 14–37% of adults [2–5]. One large
study of refractive errors measured a mean
refractive cylinder of ≥0.75 D in 37% and
≥1.5 D in 13% of 3,654 individuals between
49 and 97 years old, with an age-dependent
increase in the mean refractive cylinder from
–0.6 D in those less than 60 years old to –1.2
D for those above 79 years old [5]. The modest
difference between the incidences of refractive
errors found in other populationbased
studies is likely due to a difference in
the mean age of each study [6].
Corneal astigmatism may be surgically
reduced by two differing approaches: optical
correction versus tissue (structural) treatment.
Optical correction employs an inert,
manufactured optic (toric IOL) to correct
simultaneously both the spherical and astigmatic
refractive error components of the