Astigmatism Following 2 IOL Injection Techniques: Wound Assisted Versus

Wound Directed

Jay J. Meyer, MDHart 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.

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; 29:1070-1076.

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; 35:1430-1436.

3. Osher, RH. Microcoaxial phacoemulsification, Part 2: Clinical study. J Cataract Refract Surg 2007; 33:408-412.4. 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; 34:1748-1753.

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)

MethodsProspective 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 o’clock, 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.

Results•40 patients completed the study: Wound-Assisted (WA, n=20), Wound-Directed (WD, n=20). •No significant differences in mean refractive SIA or topographic (p=0.39) SIA between groups including the non-surgical control (n=23).•Mean wound enlargement was 10.2% in the WA and 9.1% in the WD group (p=0.68).•In the WA group, 90% had BCVA of 20/20 compared to 85% in the WD group at the 1 month follow up (p=0.63). •Mean endothelial cell loss was 8.1% in the WA and 9.3% in the WD group (p=0.20).

Mean Topographic SIA (D)Wound Assisted

Wound Directed

Non-Surgical Control P Value

0.38 +/- 0.22 0.46 +/- 0.28 0.34 +/- 0.27 0.27

Mean Refractive SIA (D)Wound Assisted Wound Directed P Value

0.60 +/- 0.41 0.92 +/- 0.65 0.09

Mean Refractive 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

Mean Topographic 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

Wound Assisted

Wound Directed

P Value

Preop 2.21 +/- 0.04 2.35 +/- 0.05 <0.01

Postop 2.44 +/- 0.06 2.57 +/- 0.06 <0.01

P Value <0.01 <0.01

Mean Incision Size (mm)

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

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

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; 37:664-69

Discussion (cont’d)•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.7. Masket S, Wang L, Belani S. Induced astigmatism with 2.2- and 3.0-mm coaxial phacoemulsification incisions. J Refract Surg. 2009;25:21-24.8. 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