Astigmatism Following 2 IOL Injection Techniques: Wound Assisted Versus Wound Directed

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Astigmatism Following 2 IOL Injection Techniques
Wound Assisted Versus Wound Directed

• Jay J. Meyer, MD
• Hart B. Moss, MD
• Kenneth L. Cohen, MD
• University of North Carolina, Dept. of
  Ophthalmology
• The authors have no financial interest in the
  subject matter of this E-Poster.

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Background

• There has been a trend toward reducing cataract
  incision size with subsequent reduction in
  surgically induced astigmatism (SIA). Bimanual
  sleeveless phacoemulsification allows further
  reduction in the clear corneal incision (CCI)
  size. Many IOLs available in the US are directly
  injected through 2.4 mm CCIs. However,
  wound-assisted injection of IOLs through 2.2 mm
  CCIs, in which the cartridge tip does not project
  completely into the anterior chamber, is an
  alternate method.1
• Some studies suggest that surgical trauma may be
  different between these two methods of IOL
  injection. Intraocular pressure has been found to
  rise as high as 306 mm Hg using wound-assisted
  injection through 2.2 mm CCIs compared to 85 mm
  Hg using a wound-directed technique.2 Studies of
  wound sizes before and after wound-assisted IOL
  injection have documented enlargement of the
  original CCI, indicating trauma to the CCI during
  injection.3,4
• No studies have compared SIA or endothelial cell
  loss, important indices of surgical trauma,
  following IOL injection by these two techniques.

1. Tsuneoka H, et al. Ultrasmall-incision
bimanual phacoemulsification and AcrySof SA30AL
implantation through a 2.2 mm incision. J
Cataract Refract Surg 2003 291070-1076. 2.
Kamae, KK, et al. Intraocular pressure changes
during injection of microincision and
conventional intraocular lenses through incisions
smaller than 3.0 mm. J Cataract Refract Surg
2009 351430-1436. 3. Osher, RH. Microcoaxial
phacoemulsification, Part 2 Clinical study. J
Cataract Refract Surg 2007 33408-412. 4. Thomas
Kohnen, et al. Incision sizes before and after
implantation of SN60WF intraocular lenses using
the Monarch injector system with C and D
cartridges. J Catarct Refract Surg 2008
341748-1753.
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Objective

• To compare surgically induced astigmatism (SIA)
  following 2 techniques of IOL injection
• Secondary outcomes endothelial cell loss, wound
  enlargement, BSCVA, complications

Wound Assisted (2.2mm) (Cartridge tip in wound)
Wound Directed (2.4mm) (Cartridge tip over pupil)
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Methods

• Prospective randomized trial of patients with
  cataracts and no other eye disease or prior
  surgery
• Pre-operative and one month post-operative
  refraction, specular microscopy, and corneal
  topography were recorded for each eye.
• Surgical Technique
• Two temporal limbal paracentesis incisions were
  made at 8 and 10 or 2 and 4 oclock, using a 1.2
  x 1.4 mm trapezoid blade, followed by bimanual
  microincision phacoemulsification by the same
  surgeon (KLC) and enlargement of the right hand
  incision to 2.2 or 2.4mm.
• Patients randomized to receive IOL (Tecnis
  1-piece IOL model ZCB00, AMO) insertion using a
  wound-assisted (cartridge tip within the wound)
  technique through a 2.2 mm CCI or a
  wound-directed (cartridge tip over pupil)
  technique with a 2.4 mm CCI.
• The Alcon D-cartridge and Monarch III injector
  were used.
• Wound size measured using incision gauges
  (Duckworth and Kent).
• All wounds were sutureless.
• Analysis
• Topographic and Refractive SIA (diopters) were
  compared between the groups and
• a nonsurgical control group composed of 23
  fellow eyes.
• SIA was calculated using the Alpins method of
  vector analysis.1

1. Alpins NA, Goggin M. Practical astigmatism
   analysis for refractive outcomes in cataract and
   refractive surgery. Survey of Ophthalmology.
   2004, 49(1) 109-122.

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Results

• 40 patients completed the study Wound-Assisted
  (WA, n20), Wound-Directed (WD, n20).
• No significant differences in mean refractive SIA
  or topographic (p0.39) SIA between groups
  including the non-surgical control (n23).
• Mean wound enlargement was 10.2 in the WA and
  9.1 in the WD group (p0.68).
• In the WA group, 90 had BCVA of 20/20 compared
  to 85 in the WD group at the 1 month follow up
  (p0.63).
• Mean endothelial cell loss was 8.1 in the WA and
  9.3 in the WD group (p0.20).

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Mean Topographic SIA (D)
Mean Refractive SIA (D)
Wound Assisted Wound Directed P Value
0.60 /- 0.41 0.92 /- 0.65 0.09
Wound Assisted Wound Directed Non-Surgical Control P Value
0.38 /- 0.22 0.46 /- 0.28 0.34 /- 0.27 0.27
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Mean Refractive Astigmatism (D)
Wound Assisted Wound Directed P Value
Preop 0.81 /- 0.39 0.93 /- 0.55 0.39
Postop 0.69 /- 0.40 0.82 /- 0.47 0.39
P Value 0.47 0.46
Mean Topographic Astigmatism (D)
Wound Assisted Wound Directed P Value
Preop 0.71 /- 0.58 1.16 /- 0.83 0.08
Postop 0.57 / 0.59 0.58 /- 0.66 0.97
P Value 0.53 0.02
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Mean endothelial cell count (cells/mm2)
Wound Assisted Wound Directed P Value
Preop 2273 /- 328 2254 /- 452 0.88
Postop 2089 /- 416 2044 /- 425 0.76
Difference -184 -210 0.82
Mean Incision Size (mm)
Wound Assisted Wound Directed P Value
Preop 2.21 /- 0.04 2.35 /- 0.05 lt0.01
Postop 2.44 /- 0.06 2.57 /- 0.06 lt0.01
P Value lt0.01 lt0.01
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Conclusions

• Wound-assisted and Wound-directed lens injection
  at the studied incision sizes are comparable
  techniques with no significant differences in
  SIA, wound enlargement, endothelial cell loss,
  BSCVA, or complications.
• Amount of SIA was not statistically different
  from a non-surgical control group, indicating
  minimal SIA following either technique

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Discussion

• Wound enlargement was not significantly different
  between the two groups in this study although
  final wound size was larger in the wound-directed
  group.
• Even though final wound size was significantly
  larger in the WD group (2.57mm) compared to the
  WA group (2.44mm), absolute wound enlargement was
  not different. There was a trend toward less SIA
  in the WA group which did not reach statistical
  significance. This is consistent with a previous
  study that showed no differences in SIA between
  2.2mm and 2.6mm incisions, although final wound
  size was not measured.6

6. Wang J, et al. The effect of micro-incision
and small incision co-axial phaco-emulsification
on corneal astigmatism. Clin and Exper
Ophthalmology. 2009 37664-69
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Discussion (contd)

• Mean topographic SIA of the WA and WD groups did
  not differ significantly from a non-surgical
  study group, suggesting possible astigmatic
  neutrality following both methods of lens
  insertion. The exact minimum wound size for
  astigmatic neutrality has yet to be determined,
  but is at least less than 2.8 mm based on one
  study.7,8
• As technological advances allow further
  reductions in wound sizes, additional studies are
  needed to define any benefits of the reduced
  incision size.

1. Masket S, Wang L, Belani S. Induced astigmatism
   with 2.2- and 3.0-mm coaxial phacoemulsification
   incisions. J Refract Surg. 20092521-24.
2. Kaufmann C, et al. Astigmatic change in biaxial
   microincisional cataract surgery with enlargement
   of one incision a prospective controlled study.
   Clin and Exper Ophthalmology 2009 37 254-61