Surgical correction of astigmatism during cataract surgery

Abstract

High levels of corneal astigmatism are prevalent in a significant proportion of the population. During cataract surgery pre-existing astigmatism can be corrected using single or paired incisions on the steep axis of the cornea, using relaxing incisions or with the use of a toric intraocular lens. This review provides an overview of the conventional methods of astigmatic correction during cataract surgery and in particular, discusses the various types of toric lenses presently available and the techniques used in determining the correct axis for the placement of such lenses. Furthermore, the potential causes of rotation in toric lenses are identified, along with techniques for assessing and quantifying the amount of rotation and subsequent management options for addressing postoperative rotation. Correcting corneal astigmatism during cataract surgery can increase spectacle independence. For the patient, this has economic benefits 4 as well as desirable cosmetic and practical advantages. Spectacle correction of astigmatism creates meridional magnification, which when coupled with the associated back vertex distance produces retinal images that are asymmetrically magnified and distorted. Such images have been reported to reduce spatial perception 5 and adaptation to them is particularly challenging for elderly individuals, 6 in whom cataracts are more prevalent. Contrary to this, if corneal astigmatism is corrected at the corneal or intraocular lens (IOL) plane, then no significant meridional magnification is induced due to a negligible vertex distance. 7The effect of clear corneal incisions (CCIs) on surgically-induced astigmatism has been extensively examined. If placed along the steep corneal axis, the clear corneal incisions flatten the cornea, reducing the residual astigmatism. The larger the clear corneal incision, the greater the flattening effect. 8 Studies have shown that the average surgically induced astigmatism using a 3.0 to 3.2 mm clear corneal incision is~0.50 D.9,10 The temporal cornea allows easy access for incisions and is the preferred site of most surgeons, 11 however, incisions performed on the steepest axis result in superior postoperative uncorrected vision.12 Opposite clear corneal incisions require a second clear corneal incision to be placed along the steep axis of the cornea on the opposing side of the pupil. This has a larger effect than a single clear corneal incision and can correct more than one dioptre of corneal astigmatism.13,14 Limbal relaxing incisions, otherwise known as peripheral corneal relaxing incisions, can also be used to correct astigmatism C L I N I C A L A N D E X P E R I M E N T A LOPTOMETRY

Evaluation of Rotation and Visual Outcomes After Implantation of Monofocal and Multifocal Toric Intraocular Lenses

“…1,2,[11][12][13] Both misalignment (differences between preoperatively calculated IOL position and real IOL position just after surgery) and rotation (differences between real IOL position just after surgery and IOL position at postoperative follow-up visits) are critical to a successful surgery in terms of visual quality. If the IOL rotates 15° off axis after surgery, there will only be half correction of the power and the resultant cylinder will be shifted to a new axis.…”

“…There are several studies on toric IOL rotation, 1,2,[11][12][13] but to the best of our knowledge this is the first study to compare rotational stability between monofocal and multifocal toric IOLs and between different designs. Moreover, in this study, monofocal toric IOLs were compared with the surgery protocol performed by the same surgeon.…”

Relationship between age, corneal astigmatism, and ocular dimensions with reference to astigmatism in eyes undergoing routine cataract surgery

“…Correcting astigmatism improves quality of life, provides spectacle independence, and improvement in visual outcomes. 7 In recent years, toric IOLs are increasingly used as firstline measures for correcting corneal astigmatism of 41.5 D at the time of phacoemulsification. 6,8 In this study, 44.2% of eyes had corneal astigmatism 41 D, which is higher than Chen et al 9 (41.3%), Ferrer-Blasco et al 10 (34.8%), Hoffman et al 11 (36.0%), and Khan et al 12 (40.41%).…”

Toric Intraocular Lenses for the Correction of Astigmatism

“…For the patient, this has economic benefits as well as desirable cosmetic and practical advantages. Spectacle correction of astigmatism creates meridional magnification, which when coupled with the associated back vertex distance produces retinal images that are asymmetrically magnified and distorted (1). …”

“…Two-step methods require marking the cornea at the zero and 180 degree positions pre-operatively and then aligning a degree gauge with these markings intra-operatively to establish the correct position (1). The iris architecture is intricate and full marking is done manually or by using the instrument in a sitting position (1,5). Another difference lies in the fact that the shaft of toric IOL to coincide with the axis of the cylinder, marked preoperatively.…”