Three-hundred-sixty degree barrier effect of a square

J CATARACT REFRACT SURG - VOL 33, JANUARY 2007
Three-hundred-sixty degree barrier effect
of a square-edged and an enhanced-edge
intraocular lens on centripetal lens
epithelial cell migration
Two-year results
Ashokkumar V. Vyas, FRCS (Ophth), Rajesh Narendran, MRCOphth, Peter J. Bacon, FRCOphth,
David J. Apple, MD
PURPOSE: To study the 360-degree barrier effect of an intraocular lens (IOL) with a square edge at the
optic and an enhanced square edge at the optic–haptic junctions (Rayner 570C C-flex) on centripetal
migration of lens epithelial cells (LECs) over a 2-year period.
SETTING: Department of Ophthalmology, Scarborough Hospital, Scarborough, United Kingdom.
METHODS: In a prospective study of 40 consecutive eyes, a C-flex IOL was implanted in the bag after
phacoemulsification surgery. Eyes with intraoperative complications, requiring additional procedures,
without 360-degree overlap of the optic, or with capsule block syndrome were excluded. Follow-up
was at 6, 10, 18, and 24 months. At each visit, high-magnification retroillumination digital photographs
were taken using a slitlamp-attached digital camera. The barrier effect to LEC migration across the
optic edge and the enhanced square edge at the optic–haptic junction was graded as complete
(no epithelial pearls or sheet), partial (few epithelial pearls without sheet), and minimal/none
(epithelial sheet behind the IOL optic).
RESULTS: Twenty-four patients came to the final follow-up at 24 months. Fifteen of these eyes (63%)
had a complete barrier effect throughout the 360 degrees of the IOL. Three eyes (13%) had a partial
barrier effect throughout the 360 degrees of the IOL. Three eyes had a complete optic barrier effect but
a partial optic–haptic junction barrier effect. Three eyes had a partial optic barrier effect but a complete
optic–haptic junction barrier effect. No eye had epithelial sheets extending behind the optic at any
location.
CONCLUSIONS: This study showed the barrier effect of the edge design of the C-flex IOL and the efficacy of the enhanced edge in preventing LEC migration at the optic–haptic junction. The enhanced
edge was as effective as a sharp square edge in restricting the LEC migration.
J Cataract Refract Surg 2007; 33:81–87 Q 2007 ASCRS and ESCRS
The centripetal migration of lens epithelial cells (LECs)
leading to development of posterior capsule opacification
(PCO) after phacoemulsification surgery for cataract can
be reduced in several ways.1 Apple et al.2 report 6 factors
related to surgical technique and intraocular lens (IOL)
choice that can reduce the overall PCO rate. Of these, an
IOL optic with a square edge has proved to be one of the
most effective ways of reducing LEC migration.3–9 Animal
studies show that the absence of a square edge at the optic–
Q 2007 ASCRS and ESCRS
Published by Elsevier Inc.
haptic junctions is the ‘‘Achilles heel’’ in IOL design as it allows free centripetal migration of LECs irrespective of IOL
material.10 The 570C C-flex (Rayner Intraocular Lenses
Ltd.) is the first IOL designed to address this issue. In addition to the square edge at the optic, it has an enhanced edge
that runs as an elevated ridge at the optic–haptic junction on both sides of the IOL. This idea originated from
a study of negative-power Centerflex IOLs that consistently
showed reduced LEC migration from the presence of a
0886-3350/07/$-see front matter
doi:10.1016/j.jcrs.2006.08.048
81
BARRIER EFFECT OF THE ENHANCED IOL EDGE ON LEC MIGRATION
360-degree sharp edge of the biconcave optic.11 In a separate observation, Amon found a higher incidence of LEC
migration at the optic–haptic junction than at the optic
edge of Centerflex IOLs without an enhanced edge
(M. Amon, MD, personal communication, September,
2001). Indeed, experimental studies of the C-flex IOL in
rabbit eyes found a significant barrier effect of the enhanced
edge.12
The present study examined the barrier effect to LEC
migration at the optic edge and optic–haptic junction in
human eyes over a period of 2 years.
PATIENTS AND METHODS
In a prospective study from September 2003 to February
2004, 40 consecutive patients (40 eyes) were recruited. Preoperative exclusion criteria were diabetes, glaucoma, and uveitis. Intraoperative exclusion criteria were posterior capsule rupture,
vitrectomy, pupil stretch, capsule tension ring insertion, use of trypan blue, and absence of 360-degree overlap of anterior capsule
over the optic. Eyes developing capsule block syndrome were
also excluded.
All cases were operated on under topical anesthesia by the
same surgeon (A.V.V.). The power of the IOLs implanted ranged
from 16.00 to 26.00 diopters. The surgical steps included a clear
corneal temporal incision of 3.0 mm or smaller and a wellcentered continuous curvilinear capsulorhexis (CCC) aimed at
5.25 mm diameter but no smaller than 4.5 mm diameter. Hydrodissection and hydrodelamination were followed by phacoemulsification using the divide-and-conquer technique. A C-flex IOL
was implanted in the capsular bag using the supplied single-piece
single-use injector. The ophthalmic viscosurgical device was
removed by the rock-and-roll method. The anterior capsule
was not polished. Good IOL centration was ensured. All patients
received prednisolone 1% drops 4 times a day for 4 weeks and
chloramphenicol 0.5% drops 4 times a day for 2 weeks.
Design of 570C C-flex Intraocular Lens
The 570C C-flex is a hydrophilic acrylic IOL with an overall
size of 12.0 mm and optic size of 5.75 mm (Figure 1). The haptics
have antivaulting haptic technology to resist capsule contraction
forces. The IOL has a square edge at the optic and outer and inner
edges of the haptics. The optic–haptic junctions have an enhanced
square edge to complete the 360-degree protection from LEC
migration.
Figure 1. A: The Rayner 570C C-flex IOL, which has a 360-degree barrier of
square edge at the optic and an enhanced square edge at the optic–haptic junction. B: The enhanced square edge at the optic–haptic junction.
Postoperative Visits
At each visit, the pupil was dilated with tropicamide 1% and
phenylephrine 2.5% drops, each instilled twice at an interval of
10 minutes. Retroillumination photographs were taken with a Nikon Coolpix 4500 digital camera attached to 1 of the empty eyepiece slots of a slitlamp with a Haag-Streit DA 01 ocular adapter.
The photographs were then transferred to Adobe Photoshop software. Image brightness and contrast were altered when necessary.
Photographs taken at the 2-year follow-up were examined by
2 investigators (A.V.V., R.N.). Figure 2, A to D, shows the drawings
that were used to grade the barrier effect in each photograph. The barrier effect at the optic edge (optic edge group) and the optic–haptic
junction (optic–haptic junction group) were analyzed separately.
The barrier effect to the centripetal migration of LECs was
described as follows:
1. Complete. No epithelium was seen extending on the posterior capsule behind the IOL optic (Figure 2, A).
Accepted for publication August 24, 2006.
2. Partial. Some epithelium was seen extending on the pos-
From the Moran Eye Center, Department of Ophthalmology and
Visual Sciences (Apple), Salt Lake City, Utah, USA, and Scarborough Hospital (Vyas, Narendran, Bacon), Scarborough, North
Yorkshire, United Kingdom.
terior capsule behind the optic, but only in the form of
scattered epithelial pearls and not in the form of a sheet
of epithelium (Figure 2, B).
3. Minimal or none. Both epithelial pearls and sheets were
seen extending on the posterior capsule behind the optic
(Figure 2, C).
4. Unrelated. Nonmigratory, isolated, and scattered epithelial
pearls or areas of fibrosis of the posterior capsule were
seen away from the edge (Figure 2, D). These were excluded from the study.
No author has financial or proprietary interest in any material or
method mentioned.
Corresponding author: Ashok V. Vyas, Department of Ophthalmology, Scarborough Hospital, Scarborough, North Yorkshire
YO12 6QL, United Kingdom. E-mail: [email protected].
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BARRIER EFFECT OF THE ENHANCED IOL EDGE ON LEC MIGRATION
Figure 2. A: Complete barrier effect; the LECs are outside the optic edge,
with none behind the optic. The arrow on either side of the edge indicates
the extent of the centripetal migration of LECs and barrier function of the
edge. B: Partial barrier effect; the LECs are outside the optic edge, with
a few behind the optic close to the optic edge. C: Minimal/no barrier effect; the LECs are outside the optic edge, and many more are progressing
behind the optic from the optic edge centripetally. D: Unrelated to the
barrier effect; the LECs are outside the optic edge; with a few scattered,
nonmigratory LECs behind the optic; complete barrier effect (serial high
magnification digital photographs of the IOL edge show LEC proliferation
of varying degree outside the edge but no progressive epithelial pearls
migration inside the edge behind the optic).
Eyes with growth of epithelium in the central 3.0 mm diameter area of the posterior capsule were further examined using
EPCO 2000 software.
RESULTS
Of the 40 consecutive eyes operated on, 2 with a history
of diabetes and 1 with pupil stretch during surgery were
excluded from the study. Also, 3 eyes with extension of
the CCC outside the optic edge and 1 with capsule block
syndrome were excluded. The remaining 33 eyes, which
had 360-degree overlap of the optic with anterior capsule,
were examined at 10, 18, and 24 months. Twenty-four patients came to the final follow-up at 24 months.
There was no discrepancy between the 2 investigators
in the barrier effect grades for any photograph taken at the
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BARRIER EFFECT OF THE ENHANCED IOL EDGE ON LEC MIGRATION
2-year follow-up. Results of the barrier effect to centripetal
migration of LECs in the 24 eyes that completed the 2-year
follow-up are shown in Table 1. Fifteen eyes (63%) had
a complete barrier effect throughout the 360 degrees of
the IOL. Three eyes (13%) had a partial barrier effect
throughout the 360 degrees of the IOL. Three eyes had
a complete optic edge barrier effect but a partial optic–haptic junction barrier effect. Three eyes had a moderate optic
edge barrier effect but an excellent optic–haptic junction
barrier effect. No eyes had epithelial sheets extending
from the optic edge or the optic–haptic junction.
Scattered epithelial pearls were present outside the
central 3.0 mm area of the optic in 7 of the 24 eyes.
Two eyes had a few nonmigratory LECs just within the
central 3.0 mm area and were placed in the unrelated
category.
The capsule followed the contour of both the enhanced
edge and square edge (Figures 3 and 4), suggesting an encasing effect of the capsule on the IOL at the optic edge and
at the optic–haptic junction.
DISCUSSION
To our knowledge, this is one of the few studies in
which the function of the optic edge in human eyes was
closely scrutinized over a period of 2 years. A more recent
study based on similar digital photographs found a ‘‘damming’’ effect to migrating LECs at the square posterior
edge at 1 month.13 Our study was an objective assessment
of LEC migration in relation to the square edge and enhanced edge of the optic. We put forward criteria by which
these changes can be graded by digital photography.
Table 1. Degree of efficacy of barrier effect to centripetal migration of LECs at the square optic edge (optic edge group) and at the enhanced square edge
(optic–haptic junction group) at 24 months in 24 eyes.
Optic Edge Group
Optic–Haptic Junction Group
Case
6 Mo
10 Mo
18 Mo
24 Mo
6 Mo
10 Mo
18 Mo
24 Mo
Comments at 24 Mo
1
2
3
4
C
C
C
C
NA
NA
NA
NA
NA
C
NA
C
P
C
C
C
C
C
C
C
NA
NA
NA
NA
NA
C
NA
C
P
P
C
P
5
6
C
C
NA
NA
C
NA
C
P
C
C
NA
NA
C
NA
C
C
7
8
9
10
11
C
C
C
C
C
NA
C
C
NA
C
NA
P
C
C
C
C
P
C
C
C
C
C
C
C
C
NA
C
C
NA
C
NA
C
C
C
C
C
C
C
C
C
12
C
C
NA
P
C
C
NA
C
13
C
C
C
C
C
C
C
C
14
15
16
17
18
C
C
C
C
C
NA
NA
C
NA
NA
C
NA
C
C
C
C
C
P
C
P
C
C
C
C
C
NA
NA
C
NA
NA
C
NA
C
C
C
C
C
C
C
P
19
20
21
22
C
C
C
C
NA
C
C
C
C
NA
C
C
C
C
C
C
C
C
C
C
NA
C
C
C
C
NA
C
P
C
C
C
P
23
24
C
C
C
C
NA
NA
C
C
C
C
C
C
NA
NA
C
C
Few epithelial pearls only
Few epithelial pearls only
d
Few epithelial pearls all over
posterior capsule
Early fibrosis
Few epithelial pearls where optic
edge meets haptic
d
Few scattered epithelial pearls
d
d
Non progressive epithelial pearls
from 6 months
Epithelial pearls between 4.00 mm
and 5.75 mm diameter
Early fibrosis outside central
4.0 mm diameter
d
d
Few scattered epithelial pearls
d
Epithelial pearls in periphery
of one quadrant
d
d
d
Few epithelial pearls at 1 optic–haptic
junction outside central 4.0 mm
d
d
C Z complete; NA Z not available; P Z partial
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BARRIER EFFECT OF THE ENHANCED IOL EDGE ON LEC MIGRATION
Figure 3. A: Example of a complete barrier effect in the optic edge group
(case 24). B: A sketch of the complete barrier effect at the optic edge.
Figure 4. Case 22. The enhanced edge at the optic–haptic junction provides a barrier effect. Note the LECs behind the haptic (left arrow), collection of LECs in the empty slot (middle arrow), and LECs peripheral to the
optic edge (right arrow).
Lens Epithelial Cells and the C-flex Intraocular Lens
Lens epithelial cells show continuous changes in distribution and morphology starting from the early days after
cataract surgery.14 Most of the epithelial cells reside in
the equatorial area of the capsule bag, with a few remaining
on the surface of the posterior capsule after surgery. The
LECs from the equatorial region multiply and migrate in
a centripetal direction. Modern IOL designs aim at restricting these activities peripheral to the IOL optic area. A
square edge to the optic has proved to be an effective design
Figure 5. A: Example of a complete barrier effect in the optic–haptic junction group (case 14). B: A sketch of the complete barrier effect at the
optic–haptic junction.
in this context.2–9 In traditional IOL design with J-shaped
or C-shaped haptics, the optic–haptic junction is a small
part of the optic circumference. Increasing this arc of unprotected optic–haptic junction, even by a small degree,
can allow a significant increase in the centripetal migration
of LECs.15 Similar observations with the Centerflex IOL
without an enhanced edge have been made (unpublished
data). The optic–haptic junction without a square edge
design is potentially the Achilles heel of such an IOL.
Indeed, our study showed the presence of LECs behind
the flat haptic, signifying the need for an additional barrier
(Figures 4 and 5). The enhanced edge of the 570C C-flex
IOL is specifically designed to add this further barrier to
the centripetal migration of LECs around the full circumference, including the optic–haptic junction.
Another important factor in reducing LEC migration is
360-degree overlap of the IOL surface with the anterior
capsule.16–17 Therefore, eyes without 360-degree overlap
of anterior capsule were excluded from our study.
Overall Barrier Function of the C-flex Intraocular Lens
As many as 63% of the eyes showed complete barrier
function at both the optic edge and the optic–haptic
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BARRIER EFFECT OF THE ENHANCED IOL EDGE ON LEC MIGRATION
junction over the first 2 years of follow-up. A further 13%
had a partial barrier effect (Figure 6) around the 360 degrees of the optic.
While assessing the barrier effect, it is important to
judge the most likely origin of LECs. Photographs repeated
over a period of many months show a definite pattern of
progress of these cells. A spreading sheet of epithelium
from the optic edge would undoubtedly indicate a failure
of the barrier function of the optic edge.
Case 11 (Figure 7) highlights the possibility of category 4 (unrelated to barrier effect of the edge). At 6 months,
there were 2 areas of epithelium, both near the optic–haptic
junctions. These did not increase in size throughout the
2-year period, indicating a complete barrier function. It is
possible that for their proliferation, LECs on the posterior
capsule left behind from the surgery are dependent on mitogenic and nutritional factors brought by migrating LECs
from the equatorial region. A complete barrier effect of the
enhanced edge would isolate these LECs and would remain
unchanged (Figure 7). Contact inhibition of LEC proliferation by a hydrophilic IOL surface is less likely to play a
major role.
In all cases, the central 3.0 mm diameter of the posterior capsule remained relatively free of epithelium. An
EPCO 2000 analysis of the central 3.0 mm diameter was
not significant in any eye, indicating the edge’s excellent
barrier function.
Barrier Function of the Optic Edge
Our study showed a 75% complete barrier effect and
25% partial barrier effect at the optic edge. Here, the barrier
effect is from the effect of the sharp, square edge. Case 24
(Figure 3) had exuberant growth of LECs outside the optic
at 6, 10, 18, and 24 months but none behind the optic. The
Figure 6. Example of a partial barrier effect in the optic edge group at 24
months (case 6).
epithelial pearls clung to the optic edge but were not
allowed to progress beyond this (Figure 4, right arrow).
Barrier Function of the Enhanced Edge
Identical to results in the optic edge group, there
was a 75% complete barrier effect and 25% partial barrier
effect at the optic–haptic junction. Here, the barrier effect
is from the enhanced edge. The enhanced edge was as effective as a sharp square edge in restricting the centripetal migration of LECs. A complete barrier effect at the
optic edge does not necessarily mean an excellent barrier
effect at the optic–haptic junction. Although there was
a close correlation, 6 eyes (16%) had a complete or partial barrier effect at the optic edge or optic–haptic junction. Furthermore, the effect at 1 optic–haptic junction
may not be exactly replicated at the fellow optic–haptic
junction.
Figure 7. Case 11 showing no progression
of the epithelium behind the optic and
a complete barrier effect at the optic–haptic junction over 2 years. The preexisting
epithelium at 6 months did not progress,
even at 2 years.
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BARRIER EFFECT OF THE ENHANCED IOL EDGE ON LEC MIGRATION
Future of Photographic Assessment of the Barrier
Function
Although neodymium:YAG capsulotomy rates and
EPCO scores give an assessment of the PCO rate for a given
IOL, they do not evaluate and compare the barrier function
of the individual features of IOL design. This study used
a method by which the function of the optic edge and
optic–haptic junction can be assessed objectively. We put
forward a simple classification that may assist in the evaluation of future IOL designs.
CONCLUSION
Our study showed the barrier effect of the edge design
of the C-flex IOL. It further demonstrated the specific efficacy of the enhanced edge in preventing LEC migration at
the optic–haptic junction, even when the square edge design failed. The barrier function of the enhanced edge at
the optic–haptic junction was as effective as that of a sharp
square optic edge.
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