Reviewed by Mahmoud F. Rateb, MD
A slit beam mounted on a surgical microscope can enhance visualization during cataract surgery, particularly in patients with corneal opacification, according to Mahmoud F. Rateb, MD.
Dr. Mahmoud uses the slit beam diaphragm of the surgical microscope (Haag Streit HS-Hi-R NEO 900) to identify important structures, such as the anterior capsule, nucleus, cortical matter, and posterior capsule.
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“I found that when I examined patients with corneal opacities and cataracts with the slit beam I could see details inside the eye better, such as the anterior capsule, the nucleus, and sometimes other minute details,” said Dr. Mahmoud, lecturer and consultant of ophthalmology, Assiut University Hospital, Egypt.
“But when I tried to use a surgical microscope in the operating room during procedures, I literally saw nothing. It was very difficult to see anything inside the eye,” he said, explaining why he developed the new technique, adapting a common examination tool for complex surgeries.
The barrier he wanted to overcome stems from the difference between the diffused coaxial light in the microscope and the lighting in the slit beam. When Dr. Rateb began performing cataract surgery under the slit beam, he found that this eliminated the glare from scatter produced by the irregular corneal lamellae characteristic of corneal opacities.
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As Dr. Rateb fine-tuned the technique, he learned from surgical technicians that he could adjust the direction and angle of the light, which also improved visualization.
Dr. Rateb noted that about 20% of his patients have severe corneal opacities associated with the high prevalence of trachoma in Egypt. These patients may be simultaneously placed on waiting lists for both cataract surgery and keratoplasty but may not be scheduled for the corneal transplant for years. In the interim, many will need cataract surgery to improve their visual acuity.
“The slit beam technique is a very good option for doctors dealing with a large number of patients with such corneal opacities,” he said.
“I’ve told my colleagues that performing cataract surgery with corneal opacities is not an impossible thing,” Dr. Rateb said. “You can still do it and give your patients hope until they can get a corneal graft. Some of those patients really see well after surgery even with no graft. At least you can remove their dense cataracts without complications.”
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At Assiut University Hospital, where Dr. Rateb practices, cases involving corneal opacities are among the most common procedures in which endophthalmitis develops, due to residual cortex material from the complex cataract surgery. With enhanced visualization, the risk of inflammation may be lower.
Dr. Rateb conducted a literature search while honing the slit beam illumination technique for cataract surgery and found only one other report in which a surgeon had tried something similar. This was a video in which a surgeon used the slit beam during a procedure but did not indicate that he used this form of lightning throughout the procedure or for every case. In contrast, Dr. Rateb uses it throughout the surgery.
Although it appears to be uncommon to use slit illumination during cataract surgery, the concept is not entirely novel, Dr. Rateb said.
“It’s not a new technique,” he said. “The slit beam has been used by corneal surgeons during DMEK and DSEK to enhance visualization and see the graft, especially to determine if it’s in the correct position.”
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Another technique that has been developed specifically for cataract surgery in patients with corneal opacities is chandelier illumination, in which fiber optics are inserted through a pars plana incision to provide virtual illumination behind the lens. However, this is more invasive than using the slit beam, Dr. Rateb said.
Fiber optics can also be inserted in the anterior chamber.
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“This technique can enhance the detail somewhat but it does not enhance the depth perception,” Dr. Rateb said. “That’s a point where the slit beam technique has an advantage. It can enhance visualization and also enhances depth perception through optical sectioning of the light going through the cornea and the lens tissue.”
Mahmoud F. Rateb, MD
E: [email protected]
This article was adapted from Dr. Rateb’s presentation at the 2016 meeting of the American Society of Cataract and Refractive Surgery. Dr. Rateb did not indicate any financial interest in the subject matter.