That same year, Ruhswurm used only the +2.0-D toric power STIOL in 37 eyes with a mean preoperative refractive cylinder of 2.7 D and found 48% to achieve UCVA of 20/40 or better, with a
Trang 1length), underwent full FDA clinical trial,
lead-ing to its approval in 1998 Data from the
over-all FDA study showed 76% of cases within 10
degrees, 88% within 20 degrees, and 95%
within 30 degrees of the intended cylindrical
axis The uncorrected visual acuity (UCVA) of
eyes with the STIOL was significantly
im-proved compared to those that received the
spherical IOL of similar design Two years
lat-er, the FDA went on to designate the STIOL as
a “new-technology” IOL due to its
demon-strated improvement of UCVA in astigmatic
patients when compared to a spherical IOL
Thereafter, the longer TL model was
intro-duced in the lower diopter powers (£24 D) as
a prophylactic against off-axis rotations in
these larger myopic eyes To date, both STIOL
models have been widely evaluated [34–41]
These reports are quite consistent in
demon-strating a predictable improvement in UCVA
with the STIOL, yet they do differ widely in the
occurrence of early off-axis rotation
In 2000, Sun and colleagues [35, 36]
retro-spectively compared 130 eyes that received
the Staar AA-4203-TF to 51 eyes that received
a spherical IOL with LRI The STIOL was
found to be superior to LRIs in producing
UCVA of≥20/40 (84% vs 76%) as well as in
reducing refractive cylinder to £0.75 D (55%
vs 22%) and to £1.25 D (85% vs 49%).
Twelve eyes (9%) underwent STIOL
reposi-tioning for off-axis rotation That same year,
Ruhswurm used only the +2.0-D toric power
STIOL in 37 eyes with a mean preoperative
refractive cylinder of 2.7 D and found 48% to
achieve UCVA of 20/40 or better, with a
re-duction of refractive cylinder to 0.84 D
post-operatively [37] No cases of STIOL rotation
greater than 30 degrees were observed,
al-though 19% rotated up to 25 degrees
One year later, Leyland’s group used vector
analysis software to calculate the magnitude
of expected correction produced by the
STI-OL in 22 eyes [38] The group achieved 73%
of the planned reduction of astigmatism,
in-cluding the 18% of cases that experienced
off-axis rotation by more than 30 degrees In
a smaller study of four eyes, a digital overlaytechnique was used to measure precisely theSTIOL axis postoperatively; 75% of eyes weredetermined to be within 5 degrees and clini-cal slit-lamp estimates of axis were found to
be quite precise in all cases [39] All these ports exclusively studied the shorter TF mod-
re-el, as it was the only design available to theinvestigators at the time of their studies.More recent studies include data on thelonger TL model Till reported on 100 eyes andfound a magnitude of reduction of 1.62 D forthe +2.0-D toric power and 2.86 D for the +3.5-
D power in the 89% of eyes that were observed
to be within 15 degrees of the intended axis[40] No difference in rotation rate betweenSTIOL models was observed In contrast,Chang compared the 50 cases receiving thelonger TL model against the 11 receiving theshorter TF model and found a significant dif-ference in rotation rates specifically for the TFgroup in the lower diopter range [41] No case
of rotation of more than 10 degrees was served in any of the 50 eyes with the TL or inthe five eyes with the higher-power TF Howev-
ob-er, three of six eyes with the lower-power TFmodel required repositioning This stronglysuggests that lengthening the original (short)
TF model in the lower power range (£24 D)
may prove to be very beneficial in ing early off-axis rotations of the STIOL
discourag-In summary, the STIOL has been widelystudied, with the reports showing a consis-tent, predictable effect of reduction of preop-erative refractive cylinder for the group ofeyes studied The variability in the magnitude
of correction of the STIOL in these numerousstudies is not surprising, as the amount ofrefractive (spectacle) astigmatism correction
of a given IOL varies with the overall tive error of each patient [42]; myopes willachieve greater spectacle correction of astig-matism than hyperopes due to vertex-dis-tance issues Regardless, the STIOL has beenclearly shown to be highly predictable in thecorrection of astigmatism at the time of re-fractive lens surgery
Trang 2Another consistent finding of these
clini-cal studies is that, although each group of
eyes studied shows good efficacy of mean
cylinder reduction by the STIOL, a small
per-centage of individuals were found to
experi-ence an early significant off-axis rotation The
variability in these findings is likely
multifac-torial First, earlier studies used the shorter
STIOL exclusively (TF model), which is now
thought to be of inadequate length for larger
eyes [34–39] Some later reports that included
the TL model did not provide
diopter-specif-ic data on whdiopter-specif-ich TF cases underwent rotation
[40] Change provided the one study that
detailed the diopter-specific results of each
STIOL model, and the longer TL model in the
lower diopter range showed no rotations [41],
suggesting that recent design modifications
of the STIOL may indeed improve future
outcomes Second, surgical technique varies
among surgeons, including the completeness
of viscoelastic removal between the STIOL
and the posterior capsule Third, the axis of
implantation was marked on the eye
preoper-atively in the upright position by some
inves-tigators, while others used a Mendez gauge at
the time of implantation; torsional rotation of
the eye that occurs in the recumbent position
may have produced mild misalignments in
some cases Next, a few cases of implantation
on the improper axis were suspected in some
reports, yet these eyes were included in the
calculation of overall rate of STIOL
malposi-tion Finally, and most obviously, there is
clearly a tendency for the STIOL to rotate
spontaneously within the capsule between
the time of implantation and the first
post-operative day examination
Regardless of the reasons for variability
among rates of off-axis rotation, it is clear
that occasional cases of off-axis alignments
will be encountered It is not known why
some individuals experience spontaneous
ro-tational malposition of the STIOL in the
ear-ly postoperative period Presumabear-ly there is a
disparity in size between the capsule and the
STIOL in some eyes Larger capsules may be
found in myopic eyes as well as in cases ofenlarged, hard, and more advanced 4+ nuclei[43, 44] Other factors, including eye rubbing
or digital compression, may play a role insome cases Fortunately, these same clinicalstudies that document early malpositionsalso clearly demonstrate that repositioning ofthe off-axis STIOL after 1 or 2 weeks uniform-
ly restores the desired effect, and late tions are very rare
rota-Other clinical studies have used the STIOL
to correct excessive astigmatism with novelprocedures To correct excessive amounts ofastigmatism, Gills combined LRIs with theSTIOL or used multiple STIOLs in “piggy-back” fashion [45–47] Other suggestions thathave not been well studied include placing amultifocal IOL in the sulcus as a piggybackover a bag-fixated toric IOL, or using toricIOLs to create pseudo-accommodation byleaving a residual refractive cylinder to aid inreading
In summary, these numerous clinical ies have clearly demonstrated the clinical re-sults that can be expected when using theSTIOL to produce improved UCVA in astig-matic eyes undergoing lens refractive sur-gery We now turn our attention to the specif-
stud-ic recommendations with whstud-ich refractivelens surgeons must be familiar to achieve thebest clinical outcomes for their patients
7.4 Using the STIOL 7.4.1 Preoperative Issues
One of the advantages of using the STIOL forthe correction of astigmatism is that refrac-tive lens surgeons must learn few new tech-niques or procedures No significant changes
to spherical IOL calculations are required, but
a few specific steps must be taken to insure asuccessful outcome when using the STIOL
The first step is for surgeons to review cent cases and determine the keratometricchanges that occur postoperatively in their
re-Chapter 7 Correction of Keratometric Astigmatism 63
Trang 3hands While most refractive lens surgeons
today use clear cornea incisions of 3.0 mm or
less and do not induce significant astigmatism,few,
if any,create truly “astigmatically neutral”incisions
Thus,it is important to review the way in which the
cornea changes,as it is the goal of STIOL
implanta-tion to treat the postoperative,not preoperative
ker-atometry
The next step is to calculate the STIOL
power The STIOL is available in SE powers
from 9.5 to 28.5 D, and each SE power is
avail-able in two distinct toric powers (+2.0 and
+3.5 D) The surgeon’s preferred IOL
calcula-tion formula is used in an identical fashion as
with spherical IOLs to determine the STIOL
SE power If the SE power is between 21.5 and
23.5 D, a choice of IOL models must be made
Due to the increased rotational stability
demonstrated by Chang [41], the longer TL
model should be chosen The unique step
re-quired when using the STIOL is to choose
either the +2.0-D toric power or the +3.5-D
toric power as determined by keratometry
Due to vertex distance issues, a perfectly
aligned +2.0-D STIOL is expected to correct
1.4 D of keratometric cylinder, and the
+3.5-D STIOL corrects 2.3 D of regular
corneal astigmatism Thus, the manufacturer
recommends that the +2.0-D toric power
STIOL be used for preoperative keratometric
astigmatism between 1.4 and 2.2 D; the
+3.5-D toric power is used when the
ker-atometry shows greater than 2.2 D of
astig-matism (Fig 7.2) Therefore, the only
differ-ence in choosing the power of the STIOL
compared to a spherical IOL is that the toric
power must be specified Adjustments to the
calculations are not needed otherwise
Once the specific STIOL is selected, the tended axis of implantation is then deter-mined and recorded The STIOL is a plus-cylinder lens, and should be aligned as wouldany plus-cylinder lens to neutralize the ker-atometric astigmatism
in-Topography is strongly encouraged to ify that the astigmatism is regular and to as-sist with determination of the steep cornealaxis Irregular corneal astigmatism will not
ver-be appropriately corrected by the STIOL Thechosen axis for STIOL alignment must bedocumented for later use in the operatingroom unless qualitative keratometry is to beused intraoperatively to align the STIOL.Finally, on the day of surgery, the eyeshould be marked with the patient in the up-right position to avoid misalignments due totorsional changes that may occur in the re-cumbent position Some surgeons allow thepreoperative team to do this, while others willnot delegate this duty A marking pen may beused at either the vertical or horizontalmeridian for later orientation with a Mendezgauge to insure proper alignment of the STI-
OL at the time of implantation Alternatively,qualitative keratometry may be used intraop-eratively, in which case this step may be omit-ted
7.4.2 Implanting the STIOL
Implanting the STIOL is similar to
implanti-ng other plate-haptic IOLs from the samemanufacturer As with all plate-haptic IOLs,the STIOL should not be implanted without
an intact capsule and complete continuouscurvilinear capsulorrhexis Current cartridgedesign allows delivery through a 3.0-mmclear cornea incision The cartridge tip doesnot need to enter entirely into the anteriorchamber, but does need to enter fully thecorneal incision Retracting the plunger sev-eral times as the STIOL is pushed down thecartridge is required to insure no overriding
of plunger that could tear the trailing haptic
Fig 7.2. Standard nomogram for choosing STIOL
toric power based on the amount of preoperative
keratometric astigmatism
K-Astigmatism
<1.4 1.4 –2.3
≥2.4
Toric Power 0 +2.0 +3.5
Trang 4The leading haptic is placed into the capsule
filled with viscoelastic, and the trailing haptic
is placed with a second instrument as with
other plate-haptic IOLs
Once the STIOL is placed fully within the
capsule, the STIOL is oriented into the
de-sired axis Careful removal of viscoelastic
from between the posterior capsule and the
STIOL is important to help stabilize the
im-plant from early rotation, and this is done
pri-or to final pri-orientation along the desired axis
The axis is determined using the previously
placed limbal orientation marks or using
qualitative keratometry with projected light
After final irrigation/aspiration of
viscoelas-tic and verification of a water-tight incision,
the STIOL orientation is again checked Some
surgeons prefer to leave the eye slightly soft to
encourage early contact between the capsule
and the STIOL
7.4.3 Postoperative Management
Management of eyes with the STIOL
implant-ed is similar to spherical IOL cases If an
off-axis rotation of the STIOL is encountered, it is
best managed on an individual basis As
clin-ical studies have shown, off-axis rotations of
the STIOL may occur in the very early
post-operative period, with later rotations rarely
observed In most cases of mild rotation, the
UCVA remains excellent and no intervention
is needed For larger rotations, the patient’s
tolerance of the malposition should be
con-sidered In refractive lens surgery, where
pa-tients have an intense desire for excellent
UCVA, even moderate rotations may require
repositioning to the desired axis The best
time for repositioning is 2–3 weeks after
im-plantation If repositioned earlier, capsule
fi-brosis may not be sufficient to prevent the
lens from returning to its original
malposi-tion After 3 weeks, the fibrosis of the capsule
intensifies, making repositioning more
diffi-cult After 2–3 months, the capsule assumes
the orientation of the long axis of the
plate-haptic with significant fibrosis, and tioning to a new axis is difficult if not im-possible Although some eyes may requireNd:YAG capsulotomy for posterior capsuleopacification, there have been no reports ofSTIOL malposition occurring after lasertreatment
reposi-7.5 Improving Outcomes
with the STIOL:
Author’s Observations and Recommendations
Experience with the STIOL over the past
6 years has provided several important sights that have improved the author’s clinicaloutcomes when using the STIOL for refrac-tive lens surgery Discouraged by the occa-sional off-axis rotations in the first year afterFDA approval, the author considered discon-tinuing use of the STIOL at the same time thatdata were becoming available that suggested
in-a novel method to promote stin-abilizin-ation ofthe STIOL against rotation As reported pre-viously [48], implanting the STIOL in a “re-versed” position, with the toric surface facingthe posterior capsule rather than the anteriorcapsule, appeared to improve but not cure thefrequency of off-axis rotations The rationalefor initially implanting the STIOL in thismanner, and the findings that resulted, will bebriefly reviewed here, with additional in-sights to follow
Why was the STIOL ever intentionally planted in the reversed position? After FDAapproval and initial enthusiasm for resultsobtained with the STIOL, occasional patientswere encountered with “borderline” astigma-tism For example, a patient may present with1.2 D of corneal astigmatism, which is belowthe manufactured suggested limit of 1.4 D.The STIOL could “flip” the astigmatic axis insuch a patient However, theoretical opticscalculate that the toric power of the STIOLwould be decreased by 8% if the optic wasreversed, as the toric (anterior) surface of the
im-Chapter 7 Correction of Keratometric Astigmatism 65
Trang 5STIOL in the reversed position would then be
closer to the nodal point of the eye and less
effective toric power would result without
changing the SE For these borderline
pa-tients, the STIOL was intentionally reversed,
and the results were startling
The first observation occurred when the
implant was placed into the capsule in the
re-versed position Compared with the normal
position, the reversed position seemed to
re-sist manipulation when rotating the STIOL
into the desired axis Although this
observa-tion was interesting, the significance of it was
not immediately realized, and implanting the
STIOL in the reversed position was reserved
for only those occasional eyes with
border-line astigmatism Later, the first years’ data
were analyzed and suggested that eyes with
the optic reversed showed outstanding
out-comes While the reason for these results may
have been multifactorial, the decision was
made to implant all STIOLs in the reversed
position, and the resulting data further
sug-gested that this technique was useful in
re-ducing the rate of malpositions
A retrospective analysis was performed on
171 eyes Postoperative UCVA and residual
refractive cylinder were compared between
eyes implanted with the STIOL in the
stan-dard vs reversed position Surprisingly, a
sta-tistically significant increase in the
percent-age of eyes achieving 20/40 or better UCVA
was found for the STIOL in the reversed vs
standard position (83% vs 58%
respective-ly) Also, there was a significantly improved
UCVA for the STIOL in the reversed vs
stan-dard position (0.60 ± 0.18 vs 0.49 ± 0.21).
Finally, the reverse-STIOL position group
showed a significant increase in the
percent-age of eyes achieving a residual refractive
cylinder £0.5 D (56% vs 34%).
Thus, the STIOL in the reversed position
was observed to promote improved UCVA
and reduction of refractive cylinder despite
an expected 8% reduction of toric power in
this position It is proposed that the STIOL
was more stable in this reversed position, and
fewer off-axis rotations occurred The moreprecise rotational alignment was more im-portant than the very mild reduction of toricpower
These data are not to be interpreted thatthe “reversed” STIOL provides more toricpower On the contrary, a perfectly alignedSTIOL with the toric surface facing the ante-rior capsule will correct more corneal astig-matism than the same lens in the reversedposition The importance of the reversed po-sition is that it stabilizes the STIOL againstrotation Therefore, for a large group of eyes,more reversed STIOLs will be on-axis, andthe mean UCVA will be improved
Therefore, based on these findings, it isrecommended that all eyes be implanted withthe optic of the STIOL intentionally reversed,and the toric power is chosen based on themodified “reversed” nomogram (Fig 7.3) Forkeratometric asymmetry of 1.2–2.1 D, use the+2.0-D toric power in the reversed position,and for corneal astigmatism above 2.2 D, usethe +3.5-D STIOL in the reversed position.Using this nomogram will insure the axis isnot overcorrected and, together with otherrecommendations here, will help to minimizethe frequency of off-axis rotations
In addition to using the reversed gram and implanting the STIOL in thereversed position to discourage early malpo-sitions, other observations and recommen-dations are shared here as the chapter closes.With regards to preoperative recommen-dations, aside from using the “reversed”nomogram to choose the toric power of theSTIOL, the main problem to avoid is eyes withirregular astigmatism Obviously, topograph-ical data are required to detect such cases Aprudent protocol is to have all patients withmore than 1.25 D of keratometric asymmetrywho are scheduling for surgery to undergotopography Another suggestion specificallyfor clear lens extraction patients who are ex-pecting excellent UCVA is to inform the pa-tient about the potential need for reposition-ing While most patients do not need such
Trang 6intervention, those that do are very accepting
of such intervention when they are prepared
in advance If repositioning is performed in
the operating room, which is suggested,
fi-nancial arrangements for such a procedure
should likewise be understood in advance A
reasonable approach is to estimate the
fre-quency of returning to the operating room
for 100 patients, then calculate the costs for
those visits, and incorporate that cost into the
overall charge to all patients If cash-pay
pa-tients who require repositioning are charged
for the procedure, they feel a
“double-wham-my” of requiring a second surgery and having
to pay for it
Intraoperative suggestions start with the
recommendation of implanting all STIOLs in
the reversed position to promote rotational
stability Simply open the package, grasp the
STIOL, turn the upward (anterior) surface
to-ward the floor, and load it into the cartridge,
thus reversing the optic The second
sugges-tion is to use endocapsular
phacoemulsifica-tion techniques rather than flipping
tech-niques The frequency of STIOL off-axis
rotations was found to increase dramatically
for cases in which the nucleus was
“tire-ironed” into a vertical position and
under-went phaco-flip (data not shown) While the
reasons for this observation are unknown, it is
suspected that increased manipulation of the
capsule while prolapsing and emulsifying the
nucleus with the flip technique caused some
stretching or enlargement of the capsule
At the time of implantation, it is
recom-mended to avoid a rapid expulsion of the
lens; if it “shoots” into the capsular bag, there
is a tendency for the STIOL to rotate towardsthe axis that it was forced into the bag A gen-tle “push-pull” retraction of the plunger isuseful in delivering the leading haptic slowlyinto the capsule Next, the choice of viscoelas-tics may be important, as pointed out byChang [41], who recommends avoiding dis-persive viscoelastics that coat the IOL such asViscoat He achieved good results with sodi-
um hyaluronate 1.0%, while the author erally uses methylcellulose 1% (Occucoat)with good results As mentioned previously, it
gen-is critical to remove the vgen-iscoelastic from hind the IOL to prevent early rotations Next,when moving the STIOL into its final posi-tion, it is recommended to rotate both sides ofthe optic to promote equal forces on all sides
be-of the implant Finally, it is critical to recheckthe STIOL axis at conclusion of the surgery,including after speculum and drape removal.Postoperative management recommenda-tion includes the use of a shield at bedtimeover the operative eye Patients may place thisthemselves There is a suspicion that someoff-axis rotations may occur overnight due toexternal pressure in those eyes without ashield If repositioning is needed, a sterilefield in the operating room is strongly recom-mended for safety, but some surgeons may in-tervene at the slit-lamp Repositioning in theoperating room may be performed through aparacentesis with a cystatome on a BSS free-flow line Gentle rocking on both sides of theoptic will free early capsule adhesions, andthe STIOL is rotated to the desired axis with-out the need of a keratome incision or vis-coelastic
In conclusion, this chapter has reviewedthe clinical aspects important to understand-ing the development and use of the STIOL.This lens is quite effective in treating cornealastigmatism at the time of lens refractive sur-gery, yet occasional patients may requirerepositioning of the STIOL in the early post-operative period, with resulting excellentUCVA As improvements in STIOL designcontinue and as our understanding increases
Chapter 7 Correction of Keratometric Astigmatism 67
Fig 7.3. “Reversed” nomogram for choosing
STIOL toric power based on planned reversal of
STIOL optic to aid in stabilization against off-axis
Trang 7about the dynamics at work in the eye during
the perioperative period, there are high
ex-pectations that our refractive lens patients
with significant astigmatism will consistently
reach emmetropia
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42 Novis C (2000) Astigmatism and toric ular lenses (review) Curr Opin Ophthalmol 11:47–50
intraoc-43 Vasavada A, Singh R (1998) Relationship tween lens and capsular bag size J Cataract Re- fract Surg 24:547–551
be-44 Vass C, Menapace R, Schmetterer K et al (1999) Prediction of pseudophakic capsular bag diameter based on biometric variables.
J Cataract Refract Surg 25:1376–1381
45 Gills J, van der Karr M, Cherchio M (2002) Combined toric intraocular lens implantation and relaxing incisions to reduce high preexist- ing astigmatism J Cataract Refract Surg 28: 1585–1588
46 Gills JP (2003) Sutured piggyback toric traocular lenses to correct high astigmatism.
in-J Cataract Refract Surg 29:402–404
47 Gills JP, van der Karr MA (2002) Correcting high astigmatism with piggy back toric in- traocular lens implantation J Cataract Refract Surg 28:547–549
48 Bylsma S (2004) Toric intraocular lenses.In: Roy
FH, Arzabe CW (eds) Master techniques in cataract and refractive surgery Slack, Thorofare
Chapter 7 Correction of Keratometric Astigmatism 69
Trang 9Astigmatism is caused by refractive
aberra-tions in the cornea or lens that focus light
un-evenly onto the retina, consequently
distort-ing images In recent years there has been
increasing interest in correcting astigmatism
at the time of cataract surgery or clear lens
ex-change to achieve emmetropia Cataract
sur-geons and their patients today hope to achieve
20/20 or better visual acuity and not have to
rely on spectacles or contact lenses for the
cor-rection of distance vision Approximately
15–29% of cataract patients have astigmatism
measuring more than 1.50 D of corneal or
re-fractive astigmatism [1, 2] Pre-existing
astig-matism is due to lens or corneal aberrations,
while post-surgically-induced astigmatism
results from incision wounds made in the
course of surgery that affect the cornea
Historically, alternatives for the correction
of astigmatism subsequent to cataract
sur-gery included the utilization of: contact
lens-es, glasslens-es, or refractive surgery post-cataractsurgery This spectacle dependency followingcataract surgery continued until the toric in-traocular lens (IOL) was introduced in 1998[3] Prior to the development of the toric IOL,two surgical procedures were considered forcorrecting pre-existing astigmatism: astig-matic keratotomy (incisional limbal or cornealrelaxation) and varying the length and loca-tion of the cataract incision [4] More recent-
ly, the excimer laser has become anotheralternative to implantation of a toric IOL forthe correction of astigmatism
The results of astigmatic keratotomy havebeen relatively unpredictable and may induceundercorrection or overcorrection of astig-matism [5, 6] In addition, there is a limit tohow much cylinder can be corrected by usingcorneal incisions and/or varying the incisionsite A study performed by Gills et al deter-mined that patients with very high astigma-
Correction of Keratometric Astigmatism:
AcrySof Toric IOL
Stephen S Lane
CORE MESSAGES
2 AcrySof toric IOL clinical results demonstrated improved
uncorrect-ed visual acuity, best spectacle-correctuncorrect-ed visual acuity, and runcorrect-educuncorrect-edastigmatic refractive cylinder when compared to AcrySof IOL,monofocal lens
2 AcrySof toric IOL’s biomaterial and truncated edged optic designreduce posterior capsule opacification accumulation
2 Implantation utilizing a toric IOL offers greater predictability andreversibility than astigmatic keratotomy
8
Trang 10tism (>5.00 D) may benefit from the
combi-nation of corneal or limbal incisions with
toric IOL implants when the amount of
cylin-der present exceeds the powers available with
a toric IOL alone [7] The high cost of excimer
laser correction makes this a less desirable
alternative for cylinder correction for many
people
An effective toric IOL must have the
capa-bility of improving visual acuity and
main-taining rotational stability so as not to
dimin-ish the effects of the correction provided by
the toric lens
8.1 AcrySof Toric IOL
Alcon Laboratories Inc has recently
devel-oped an exceptionally stable toric IOL to aid
in the correction of astigmatism (Fig 8.1)
The AcrySof toric IOL, model SA60TT, is
de-signed to focus the light, otherwise scattered
by corneal and/or lenticular astigmatism, in
order to limit image distortion The AcrySof
toric IOL corrects for aphakia as well as
pre-existing or post-surgically-induced corneal
astigmatism The structure of the AcrySof
toric IOL is based on the presently marketed
AcrySof single-piece IOL, SA60AT monofocal
lens The toric lens design is comprised of a
foldable, single-piece, acrylic polymer, with
UV absorber The AcrySof toric IOL is
intend-ed for long-term use and is implantintend-ed into the
capsular bag following phacoemulsification
Its overall length is 13.0 mm with a 6.0 mm
diameter asymmetrical biconvex optic This
IOL easily folds in half and may be inserted
through an incision measuring between
3.0 and 3.5 mm using the Monarch II
Injec-tor Larger incision lengths may result in
an increase in surgically induced corneal
astigmatism The AcrySof toric IOL
exam-ined in a clinical investigation was provided
in three cylinder powers at the IOL plane:
1.50 D, 2.25 D, and 3.00 D Additional power
options are intended to be available to the
market The SA60TT covers a spherical range
between 16.0 D and 25.0 D in 0.5-D ments
incre-The AcrySof toric IOL’s material and sign offer a number of advantages Posteriorcapsule opacification (PCO), also known as asecondary cataract that forms over the visualaxis, often impairs visual acuity This compli-cation was reported more frequently withearlier IOL designs Two major features of theAcrySof toric IOL limit PCO The first is theAcrySof biomaterial, which adheres to thecapsular bag via a single layer of lens epithe-lial cells The resulting lack of space throughwhich essential life-sustaining nutrients canpass to and from these cells ultimately leads
de-to their death and subsequently de-to the directadherence of the AcrySof material to the cap-sular bag via common extracellular proteinssuch as fibronectin and collagen IV Thisoverall process is sometimes referred to asthe “no space, no cells” concept, which creates
Fig 8.1. The AcrySof toric IOL: the lens is marked with three alignment dots on each side to delineate the axis of the cylinder to be aligned on the steep meridian (Courtesy of Alcon Laboratories Inc.)
Trang 11an unfavorable environment for cell
prolifer-ation [8] In addition to this biomaterial
ad-hesive property being effective at aiding in
the reduction of PCO, it may also account for
the exceptional rotational stability necessary
for a successful toric IOL
The second feature of the AcrySof toric IOL
that increases its ability to maintain a clear
posterior capsule and ultimately reduces the
need for a Nd:YAG capsulotomy is the design
of the posterior optic edge [8, 9] Nishi et al
demonstrated in an animal study that the
sharp-edged optic design of the AcrySof IOL
incorporates a PCO-reducing effect [10]
Proven in a separate study, the AcrySof IOL’s
square truncated optic edge created a barrier
to migration of lens epithelial cells, leaving the
visual axis clear of PCO [8]
The stable-force haptics are another
bene-ficial design attribute of the AcrySof toric
IOL These haptics are designed for
maxi-mum conformance to the capsular bag,
offer-ing the greatest possible surface area for
ad-herence between the IOL and the capsular
tissue This in turn leads to greater stability of
the IOL, and to a pronounced “shrink-wrap”
effect (Fig 8.2), which takes place during the
early postoperative time course It is this
property that is likely responsible for ing” the lens in place
“lock-In essence, the AcrySof single-piece IOLplatform provides the ideal material and de-sign features for a toric IOL The soft acrylicmaterial allows for small-incision surgery, thenatural PCO reduction characteristics allowfor fewer postoperative complications, andthe adhesion and capsular bag conformanceproperties allow for highly stable and pre-dictable positioning of the IOL
sur-9 o’clock limbus while the patient is in an right position Once the patient is positionedfor surgery, a Dell astigmatism marker is used
up-to mark the axis of the steep corneal
meridi-an using the previously placed 3 meridi-and 9 o’clock
Chapter 8 Correction of Keratometric Astigmatism 73
Fig 8.2. AcrySof toric
IOL implanted into
the eye (Courtesy
of Stephen Lane, MD)
Trang 12marks as reference points for the 180-degree
meridian Following phacoemulsification, the
IOL is inserted into the capsular bag utilizing
a Monarch II injector Following insertion,
the lens begins to unfold naturally within the
capsule The surgeon then carefully aligns
axis indication marks on the IOL with the
steep meridian of the cornea Care must be
taken to remove the ophthalmic viscosurgical
device (OVD) from behind the IOL without
disrupting the IOL position A final
position-ing step followposition-ing OVD removal may be
nec-essary to reposition the lens on axis
One key for a successful surgical outcome
is choice of astigmatic power of the IOL and
the proper identification of the axis of the
steep meridian of the cornea Both are
calcu-lated using software provided by Alcon
Labo-ratories Inc., called the toric IOL calculator
The A-constant and keratometric analysis are
entered into the software, and the toric IOL
calculator uses this information, along with
an assumption of the astigmatic effects of the
cataract incision, in order to calculate the
appropriate astigmatic power correction and
position of the steep axis
8.3 US Clinical Trial Results
Best spectacle-corrected visual acuity
(BSCVA), uncorrected visual acuity (UCVA),
residual astigmatism, and lens rotation were
assessed during a comparative, multi-center,
prospective, clinical trial between the AcrySof
toric IOL, model SA60TT (SA60T3, SA60T4,
SA60T5) and a control IOL, AcrySof single
piece, model SA60AT.Approximately 250
sub-jects were implanted with SA60TT and 250
subjects were implanted with SA60AT All
subjects were followed for 1 year following
first eye implantation
8.3.1 Visual Acuity Outcomes
At the 80–100 day visit, 100% (n = 77) of toric subjects and 97.1% (n = 68) of control sub-
jects achieved BSCVA 20/40 or better In
com-paring UCVA, 94.6% (n = 74) of toric subjects while only 73.1% (n = 67) of control subjects
achieved 20/40 or better (Table 8.1)
Table 8.1. Visual acuity (BSCVA and UCVA), all jects AcrySof toric IOL (SA60TT) compared to AcrySof IOL monofocal (SA60AT)
sub-80–100 day data SA60TT SA60AT
BSCVA n = 77 n = 68
20/20 or better 76.6% 67.6%
subjects subjects 20/25 or better 89.6% 91.2% 20/30 or better 97.4% 95.6% 20/40 or better 100 % 97.1% Worse than 20/40 0% 3%
UCVA n = 74 n = 67
20/20 or better 31.1% 11.9%
subjects subjects 20/25 or better 63.5% 26.7% 20/30 or better 83.8% 46.3% 20/40 or better 94.6% 73.1% Worse than 20/40 5.4 % 26.9%