Minimally invasive micro sclerostomy may be alternative to trabeculectomy
The gold standard surgery for decreasing IOP in patients with glaucoma is trabeculectomy. However, it has possible disadvantages, such as failure secondary to subconjunctival fibrosis and postoperative bleb-related ocular inflammation. This has led surgeons around the globe to introduce various trabeculectomy modifications for ideal IOP control with fewer complications.
Along this line, minimally invasive micro sclerostomy (MIMS, Sanoculis) is a recent innovative technique that combines the mechanism of conventional trabeculectomy and simple needling. Conjunctival dissection and manipulation have been curtailed to a minimum.
The surgical tool is composed of stainless steel 420 (Figure 1) and consists of a penetration tip to allow the insertion of the tool into the eye tissue; a mechanism for removal of the thin tissue layer; and a shank to enable the coupling of the instrument to the rotating system.
A multiuse component is designed to activate the surgical tool in order to remove the corneoscleral tissue by rotary motion. The activation component comprises a controller that manages the activation pulse duration and RPM; a motor; a handpiece that is an interface between the activation component and the surgical tool, which transmits the rotary motion from the motor to the surgical tool; and a footswitch to assist the user to activate the machine. One activation cycle time is 0.1 second, and surgical tool speed is 8,000 RPM.
MIMS surgical technique
Under sterile conditions, the index eye is anesthetized by peribulbar anesthesia in the operating room. Subconjunctival mitomycin C 0.02% is injected in the region of the preferred sclerostomy site and flushed immediately with balanced salt solution. Approximately 60 minutes after the injection of MMC, the eye is prepared according to routine surgical preparation for glaucoma filtering surgery. A lid speculum is placed, and while the patient is looking down, the conjunctiva is grasped with 0.12 forceps 5 mm to 7 mm from the limbus. The MIMS surgical tool is introduced via a small conjunctival opening 10 mm to 15 mm from the corneoscleral limbus and advanced gently (Figure 2a). When the MIMS tip is positioned at the penetration site, it is pushed into the anterior chamber via the limbus area.
Correct positioning of the tool is assessed using a surgical microscope, and the tip is visualized through the transparent cornea. Once the tip is inserted into the anterior chamber and proper positioning is ascertained, the MIMS foot pedal is pressed to create the drainage channel (Figure 2b). The MIMS system is then withdrawn from the eye, and an intraoperative bleb (Figure 3) can be seen with the microscope. The speculum is removed, and topical antibiotic and steroid are administered.
Principle and advantages
The device is inserted under the conjunctiva, without creating a surgical incision in the conjunctiva, through the corneoscleral junction and into the anterior chamber. The surgical tool is then rotated to create a 50 µm to 100 µm diameter corneoscleral channel in order to allow for drainage of the aqueous humor from the anterior chamber into the subconjunctival space. To create the corneoscleral channel, a piece of tissue is removed with the surgical tool. The ideal filtration surgery should include minimal to no conjunctival dissection so as to prevent subconjunctival fibrosis, as expected in the MIMS procedure. It should also maximize the amount of untouched conjunctiva so as to allow space for a repeat trabeculectomy or other glaucoma surgery in the future if required. In addition, because the surgical procedure is aimed to be for outpatients in the future, a faster and easier technique is always expected.
Pilot study and results
Preliminary trials of the MIMS procedure have been promising in primary open-angle glaucoma. Four patients were evaluated with a final 8,000 RPM, and a desired sclerostomy size of 50 µm to 100 µm was obtained. An IOP reduction was seen after MIMS in study patients. Mild subconjunctival hemorrhage (Figure 4), conjunctival button hole and postoperative mild anterior chamber reaction were some of the complications noted. OCT pictures revealed no major safety issues. All high-resolution OCT images of the channels demonstrated channel walls transparent to the OCT light with no signs of thermal or mechanical damage. Channels were recognized by OCT only by missing corneal tissue in their lumen (ostium) (Figure 4). The channel wall has maintained its clarity on OCT throughout the 6-month follow-up period.
The primary performance endpoint of obtaining surgical success, defined as the ability to surgically create a drainage channel, was 95.5% achieved. However, control of IOP over the long term and morphological variations induced by conjunctival or sclera fibrotic changes have to be evaluated in future studies in a large population. Nevertheless, interim reports on the MIMS technique show that the method may be promising in the near future to help make glaucoma surgery simpler.
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- 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: firstname.lastname@example.org; website: www.dragarwal.com.
Disclosure: Agarwal reports he is a consultant for Sanoculis. Kumar reports no relevant financial disclosures.