Use of Cannula in Small Incision Cataract Surgery—A Hidden Gemstone

Mastering manual small-incision cataract surgery (MSICS) can be particularly challenging for beginner surgeons. One of the most common hurdles during early training lies in creating an appropriately sized scleral tunnel and achieving a smooth keratome entry. Premature entry and iris prolapse are frequent complications during this stage of the surgery.[1–3] Additionally, the size of the tunnel is crucial for achieving a self-sealing sclero-corneal wound as well as smooth delivery of dense brown or hard cataracts.[4] Similarly, a small capsulorrhexis can make nucleus prolapse difficult, potentially leading to more severe complications such as zonular dialysis, posterior capsular rupture, or even nucleus drop.[5,6] To address these challenges, we recommend the use of an ophthalmic viscoelastic device cannula and a hydro-dissection cannula, both with 7 mm angled tips, in 23G or 27G sizes [Figure 1a] which are used frequently in the anterior chamber during surgery. First, measure from the tip to the bent portion of the canula with a Castroviejo calliper which measures 7 mm (approximately 6.5 to 7 mm). This is followed by staining the cannula with gentian violet. The stained cannula is placed 2 mm from the limbus. This marked area guides the surgeon in placing a straight incision on the sclera followed by sclero-corneal tunnelling [Figure 1b-d]. The same cannula is used to assess mydriasis [Figure 2a and b] intra-operatively and take appropriate steps in tackling mid-dilated or poorly dilating pupils, such as stretch pupilloplasty, multiple sphincterotomy, iris hook, or pupil expansion device, which can vary from case to case. The same cannula is used to measure the diameter of the capsulorrhexis for safe nucleus prolapse, which is critical in dense cataracts.Figure 1: (a) OVD cannula and hydro-dissection cannula 6.5–7 mm tip to bend. (b–d) marking of sclero-corneal tunnel incision with cannulaFigure 2: Measurement of pupil dilatation with cannula. (a) small pupil. (b) well-dilated pupilThis step can be performed prior to attempting nucleus removal to recheck the incision size, ensuring it is adequate for a secure and self-sealing wound. Furthermore, this technique allows the surgeon to verify key parameters during the procedure, such as the capsulorrhexis size and pupil diameter. The advantage of using these cannulas lies in their simplicity—no extra steps or additional instruments are required, and the measurements are not influenced by corneal magnification. This approach, therefore, benefits not only beginner surgeons but also experienced cataract surgeons. By facilitating precise measurement of critical factors such as incision size, capsulorrhexis diameter, and pupil size, this technique offers a straightforward yet effective way to improve surgical outcomes. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.