24 EyeWorld Asia Pacific | June 2024 REFRACTIVE SURGERY by Liz Hillman, Editorial Co-Director Clearing Up The Confusion: Get The Right Anterior Chamber Depth For ICL Among the important indications for use of the EVO ICL (STAAR Surgical) — age, amount of myopia, astigmatism correction, etc. — there is one parameter that some surgeons say could be causing confusion. “Yes, I do think there can be some confusion,” Audrey Rostov, MD, said. “Yes, absolutely. It’s confusing,” William Trattler, MD, added. “100% agree (...) there is significant confusion,” Scott D. Barnes, MD, finally concurred. The FDA’s indication specifies that the EVO ICL should be used in patients “with an anterior chamber depth of 3.0 mm or greater.” It further defines this as “when measured from the corneal endothelium to the anterior surface of the crystalline lens.” “There is confusion because nobody agrees on what the term ‘anterior chamber depth’ really means. Does it include the epithelium or is it measured just from the endothelium? Depending on which textbook and which literature report you look at, it may say anterior chamber depth is measured from the endothelium,” Dr. Barnes said, adding later that some instruments report ACD from epithelium to anterior capsule and others have the ability to subtract the cornea and report the measurement from the endothelium or both. “Yes, absolutely there is confusion on it, and some instruments cannot separate that out and they just record ACD. Some instruments separate it out and report ACD endo vs. ACD epi (as with Orbscan); others report ACD internal vs. external, as with Pentacam where “ext” includes the corneal thickness and “int” is from the endothelium. Some others will also display AQD or AD, meaning ‘aqueous depth,’ which means the ACD without the corneal thickness. You have to know your machines and what they’re reporting.” Dr. Rostov expressed similar views. In terms of sizing for the ICL, she said, “it’s important to know that you should be measuring from the endothelium, not the epithelium. You want to make sure about this because otherwise you could choose the wrong size lens or you may not even have enough anterior chamber depth to permit use of the ICL.” Dr. Rostov said she uses Pentacam (Oculus) to measure anterior chamber depth from the endothelium as well as white to white. If a surgeon is using biometry for these measurements, like the IOLMaster (Carl Zeiss Meditec), improper sizing could occur. Dr. Rostov has found that white to white measurements with biometers are generally larger. With Pentacam, Dr. Rostov said she can set it to measure from endothelium (internal). If you were to use a device that measures from the epithelium (external cornea), you need to subtract out the pachymetry of the cornea, she said. “The reason this is important is you want to make sure you get the right sizing of ICL,” Dr. Rostov said. “If you put in ICL and you don’t have enough anterior chamber depth, you could get narrowing of the anterior chamber. The vault of the ICL could be too high. In a shallow anterior chamber, you have the potential for angle closure glaucoma. Make sure you have enough AC depth. Strict on-label use of the ICL is a 3-mm anterior chamber depth as measured from the endothelium.”
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