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OCT used as a tool for pupilloplasty evaluation
Spectral-domain OCT offers high-resolution visualization of the architecture of these knots.
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OCT is based on the principle of Michelson interferometry. It uses a near infrared wavelength source for visualization of ocular structures. There are two different types of OCT systems based on type of processing: time domain and spectral domain. SD-OCT provides faster acquisition and higher resolution as compared with TD-OCT. It takes 26,000 A-scans per second with a rate of 256 to 1,024 frames per second. The depth resolution in tissue is 5 µm, and the transverse resolution is 15 µm. There have been various indications for SD-OCT in ophthalmology. The pupil can be assessed by SD-OCT, but there have not been any reports on this. We utilized SD-OCT to visualize the pupil after single-pass four-throw pupilloplasty, as seen in Figure 1.
Surgical technique of SFT pupilloplasty
Under peribulbar anesthesia and sterile precautions, using the side-port keratome, two stab incisions were made on either side of the limbus along the defect of the iris. The proximal iris defect was grasped with end-opening forceps (Figure 2), and the needle of the polypropylene single-arm suture was passed. The distal end of the iris defect was grasped with end-opening forceps, and the 26-gauge needle was passed through it and railroaded through the needle. The Prolene needle end was anchored onto the barrel of the needle on the opposite end and brought outside the eye. A Sinskey hook was introduced inside the anterior chamber. A loop was formed by hooking the Sinskey hook along the suture, and the hook was pulled through the opposite paracentesis. The suture end was passed four times into the loop, and the two ends were pulled to approximate the knot, which slid on the iris in the anterior chamber. The suture ends were cut within the anterior chamber and the wounds hydrated.
Source: Dhivya Ashok Kumar, MD, FRCS, FICO, and Amar Agarwal, MS, FRCS, FRCOphth
SFT pupilloplasty morphology
A Prolene suture knot with the embedded iris formed the knot complex in single-pass four-throw pupilloplasty. That knot complex configuration was assessed by SD-OCT. We noted a prominent iris bump in the knot region, and it was the major pattern of knot seen (63.8% of cases) (Figure 3). The other patterns were double bumps, loops, flat and mulberry. Single hump was one elevation of the knot complex, double humps were two elevations separated by a small flattening of the iris in between, and mulberry was defined as an irregular corrugated surface (Figure 4). Peripheral anterior synechiae and tethering of the iris were also noted.
In a small study of knot analysis by SD-OCT, the mean length and height of the knot were observed as 784.1 ± 433.7 µm and 317.7 ± 110.4 µm, respectively. There was no significant difference in the length and height of the knot with respect to the duration after pupilloplasty. The incised Prolene suture end was detected as a hyperreflective line arising from the knot complex region, and the length was measured in micrometers (Figure 5). It was documented as either vertically oriented (when the suture end was noted to be straight into the anterior chamber perpendicular to the iris surface) or flat (when the end was staying partly or wholly on the iris surface). The positioning of the Prolene suture end in the chamber by the end of the procedure was noted to be vertical in the majority of eyes (80.6%). The average length of the cut end of the Prolene suture protruding in the anterior chamber (Figure 6) was 465.8 ± 321.1 µm. Such vertical orientation to the iris plane of the Prolene suture in the anterior chamber can hinder graft unrolling during an endothelial keratoplasty and may cause mechanical endothelial damage. Therefore, positioning of Prolene in the anterior chamber becomes vital for surgical outcomes after endothelial keratoplasty. Thus, we recommend surgical correction of pre-existing iris and pupil deformities before embarking on endothelial keratoplasty. However, in our analysis, no significant difference in endothelial cell density was noted with relation to the suture cut end-corneal vault. The distance between the knot complex and the IOL ranged from 72 µm to 672 µm.
Summary
Although there are numerous iris suturing techniques and pupil reconstruction procedures, there are not many studies on the OCT assessment of the architecture of these pupilloplasty knots. Positioning of the knots and their suture ends is necessary to reduce the postoperative endothelial loss. Moreover, follow-up evaluation using SD-OCT gives high-resolution visualization and also aids in proper documentation.
References:
Kumar DA, et al. Indian J Ophthalmol. 2019;doi:10.4103/ijo.IJO_885_18.
Kumar DA, et al. J Cataract Refract Surg. 2017;doi:10.1016/j.jcrs.2017.07.027.
For more information:
Amar Agarwal, MS, FRCS, FRCOphth is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Incorporated, publisher of Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: dragarwal@vsnl.com; website: www.dragarwal.com.
Disclosures: The authors report no relevant financial disclosures.