Factors affecting surgically induced astigmatism in manual small-incision cataract surgery

Abstract

Cataract is the most common cause of avoidable blindness in the world. While cataract surgery is continually evolving, manual small-incision cataract surgery (MSICS) still remains highly relevant, especially with the threat of the coronavirus disease 2019 (COVID-19) still looming large over the world. MSICS today has a renewed significance, since it does not involve the use of any advanced machinery and relies mainly on easily sterilizable instruments, thereby making it a safe and inexpensive option. A self-sealing valvular tunnel entry forms the basis of MSICS, and proper positioning and construction of the tunnel is imperative to the success of the surgery. With more and more people demanding spectacle independence after surgery, it becomes important to have a thorough understanding of the factors that may influence surgically induced astigmatism in MSICS. These include the incision location, size and shape, configuration of the sclero-corneal tunnel, pre-existing ocular pathology, role of sutures, amongst others. With proper knowledge, many of these factors can be modulated to achieve best results.

Topographic and surgical risk factors for high postoperative residual astigmatism after small incision lenticule extraction in patients with different degrees of myopia: a retrospective cohort study

“…In addition, posterior corneal irregularity after refractive surgery could be associated with the occurrence of postoperative astigmatism and corneal curvature changes [ 28 ]. Moreover, the location and length of the corneal incision during cataract surgery influence the degree of postoperative astigmatism [ 29 , 30 ]. Since SMILE surgery is also a corneal surgery that involves a change in corneal curvature and the creation of corneal incision [ 8 ], related parameters may influence the degree of postoperative astigmatism after SMILE surgery, similar to LASIK and cataract surgery.…”

“…In addition, the manifest cylinder included ocular residual astigmatism, which is not correlated with corneal regularity [ 35 , 36 ]; thus, the association between preoperative manifest cylinder power and high postoperative residual astigmatism may not be as strong as that between the topographic cylinder and high postoperative residual astigmatism. The length of the corneal incision is related to the degree of surgically induced astigmatism in cataract surgery patients [ 29 , 30 ], and we speculate that a longer corneal incision leads to corneal instability in the early postoperative period, mainly in the high myopia population; thus, incision-related astigmatism was more prevalent in that group. However, further research is needed to prove this hypothesis.…”