A Superior Capsulotomy
Friedman NJ, Palanker DV, Schuele G, et al.
J Cataract Refract Surg. 2011;37:1189-1198
In contemporary cataract surgery, the shape, diameter, and position of the anterior capsulotomy are important factors in postoperative refractive outcomes. The anterior capsulotomy is presently created manually and therefore is inconsistent in position and dimension. If the capsulotomy is too small, the intraocular lens (IOL) can be pushed posteriorly by the anterior capsule, causing hyperopia. If it is too large (outside the optic of the IOL), the unrestrained IOL optic can position itself more anteriorly than expected, resulting in an unintended myopic postoperative outcome. If the capsulotomy is decentered, the IOL optic could be tilted or decentered, resulting in astigmatism or a compromised retinal image.
In this study of patients undergoing cataract surgery, Friedman and associates studied whether the dimensions of the anterior capsulotomy can be created more precisely and dependably with an optical coherence tomography-guided femtosecond laser. The article included an in vitro porcine eye study of the strength of the edge of the anterior capsulotomy created with the femtosecond laser compared with manually created capsulotomies.
The human study compared 39 patients who received femtosecond laser anterior capsulotomies in one eye, 24 of whom received traditional manual capsulotomies in the fellow eye. The size, circularity, and position of the capsulotomies in the laser-treated eyes were far more predictable than in the eyes with the manual capsulotomies. The resected anterior capsule disk deviated 29 μm (standard deviation [SD]: ± 26 μm) from the intended diameter in the laser eyes, whereas the manually created disks deviated 337 μm (SD: ± 258 μm) Mean deviations from circularity were 6% and 20%, respectively. The center of the laser capsulotomies averaged 77 μm from the intended position. No nicks or tears occurred, and all capsulotomies were complete. The strength of laser-created capsulotomies in the porcine capsule study was approximately twice that of the manually created group.
In modern cataract surgery, surgeons have the opportunity not only to eliminate the cataract but also to provide the patient with excellent vision without glasses, something that they may have not experienced since childhood. However, emmetropia is not routinely achieved. Only 45% of eyes come to within ± 0.50 diopters of neutrality. This error is largely because the actual anterior-posterior position of the IOL, otherwise known as the effective lens position, is not predictable because of the size, shape, and position of the traditional manually created anterior capsulotomy. Although other factors such as postoperative capsular bag and capsulotomy opening contracture are likewise unpredictable, it is reasonable that if the capsulotomy can be created uniformly, eliminating the most influential variable in lens position, better postoperative refractive results can be expected. In doing so, the patient's own expectations for spectacle independence can be more reliably realized.
The ability to make a precisely shaped and sized anterior capsulotomy also opens the door for new IOLs that are physically engaged in the anterior capsulotomy opening. In this way, the IOL optic could be precisely centered on a desired lateral position, such as the visual axis, the line of sight, or the physiologic pupil center. In addition, an IOL may be designed to integrate with the capsulotomy to facilitate pseudoaccommodation of the IOL by enabling either anterior-posterior movement of the IOL or movement of the 2 optics in a dual optic "accommodating" IOL.
A further potential advantage of having a precise anterior capsule opening is that the 360-degree overlap of the anterior capsule on the optic of the IOL would be expected to reduce posterior capsule opacification by "shrink wrapping" the rim of the capsulotomy tightly against the optic of the IOL. This tight adhesion could inhibit the migration of lens epithelial cells onto the posterior capsule behind the IOL, minimizing the necessity of yttrium aluminum garnet posterior capsulotomy.
The porcine lens anterior capsular strength study demonstrates that the laser capsulotomy rim is at least as strong as a manually created one and is perhaps stronger. Making the capsulotomy ab externo to the eye with the femtosecond laser also has the potential to prevent the capsular tears and peripheral extensions that occasionally occur with manual capsulotomies.
Using the femtosecond laser for capsulotomy prior to cataract surgery could therefore improve refractive outcomes and reduce capsulotomy-related complications. Further clinical study, however, is necessary to verify these potential advantages.
Abstract
Femtosecond Laser Capsulotomy
Friedman NJ, Palanker DV, Schuele G, et al.
J Cataract Refract Surg. 2011;37:1189-1198
Study Summary
In contemporary cataract surgery, the shape, diameter, and position of the anterior capsulotomy are important factors in postoperative refractive outcomes. The anterior capsulotomy is presently created manually and therefore is inconsistent in position and dimension. If the capsulotomy is too small, the intraocular lens (IOL) can be pushed posteriorly by the anterior capsule, causing hyperopia. If it is too large (outside the optic of the IOL), the unrestrained IOL optic can position itself more anteriorly than expected, resulting in an unintended myopic postoperative outcome. If the capsulotomy is decentered, the IOL optic could be tilted or decentered, resulting in astigmatism or a compromised retinal image.
In this study of patients undergoing cataract surgery, Friedman and associates studied whether the dimensions of the anterior capsulotomy can be created more precisely and dependably with an optical coherence tomography-guided femtosecond laser. The article included an in vitro porcine eye study of the strength of the edge of the anterior capsulotomy created with the femtosecond laser compared with manually created capsulotomies.
The human study compared 39 patients who received femtosecond laser anterior capsulotomies in one eye, 24 of whom received traditional manual capsulotomies in the fellow eye. The size, circularity, and position of the capsulotomies in the laser-treated eyes were far more predictable than in the eyes with the manual capsulotomies. The resected anterior capsule disk deviated 29 μm (standard deviation [SD]: ± 26 μm) from the intended diameter in the laser eyes, whereas the manually created disks deviated 337 μm (SD: ± 258 μm) Mean deviations from circularity were 6% and 20%, respectively. The center of the laser capsulotomies averaged 77 μm from the intended position. No nicks or tears occurred, and all capsulotomies were complete. The strength of laser-created capsulotomies in the porcine capsule study was approximately twice that of the manually created group.
Viewpoint
In modern cataract surgery, surgeons have the opportunity not only to eliminate the cataract but also to provide the patient with excellent vision without glasses, something that they may have not experienced since childhood. However, emmetropia is not routinely achieved. Only 45% of eyes come to within ± 0.50 diopters of neutrality. This error is largely because the actual anterior-posterior position of the IOL, otherwise known as the effective lens position, is not predictable because of the size, shape, and position of the traditional manually created anterior capsulotomy. Although other factors such as postoperative capsular bag and capsulotomy opening contracture are likewise unpredictable, it is reasonable that if the capsulotomy can be created uniformly, eliminating the most influential variable in lens position, better postoperative refractive results can be expected. In doing so, the patient's own expectations for spectacle independence can be more reliably realized.
The ability to make a precisely shaped and sized anterior capsulotomy also opens the door for new IOLs that are physically engaged in the anterior capsulotomy opening. In this way, the IOL optic could be precisely centered on a desired lateral position, such as the visual axis, the line of sight, or the physiologic pupil center. In addition, an IOL may be designed to integrate with the capsulotomy to facilitate pseudoaccommodation of the IOL by enabling either anterior-posterior movement of the IOL or movement of the 2 optics in a dual optic "accommodating" IOL.
A further potential advantage of having a precise anterior capsule opening is that the 360-degree overlap of the anterior capsule on the optic of the IOL would be expected to reduce posterior capsule opacification by "shrink wrapping" the rim of the capsulotomy tightly against the optic of the IOL. This tight adhesion could inhibit the migration of lens epithelial cells onto the posterior capsule behind the IOL, minimizing the necessity of yttrium aluminum garnet posterior capsulotomy.
The porcine lens anterior capsular strength study demonstrates that the laser capsulotomy rim is at least as strong as a manually created one and is perhaps stronger. Making the capsulotomy ab externo to the eye with the femtosecond laser also has the potential to prevent the capsular tears and peripheral extensions that occasionally occur with manual capsulotomies.
Using the femtosecond laser for capsulotomy prior to cataract surgery could therefore improve refractive outcomes and reduce capsulotomy-related complications. Further clinical study, however, is necessary to verify these potential advantages.
Abstract