EyeWorld Asia-Pacific December 2015 Issue

24 December 2015 EWAP FEATURE issue is that they’re crowded, said Uday Devgan, MD , Devgan Eye Surgery, Los Angeles. “You’re in very close proximity to the corneal endothelium because the anterior chamber is so shallow,” he said. There’s less room for the surgeon to work, and the phaco energy is closer to the cornea and can potentially damage it more. Other risks with a short eye are increased risk of capsule rupture and risk of choroidal hemorrhage. In long eyes, you basically have the opposite, Dr. Devgan said. There is a lot more room to work, but sometimes there can be too deep of an anterior chamber, and that’s usually seen when you get reverse pupillary block, he said. “The tissues are more thinned out and they can get this over deepening,” he said. Additionally, access to the cataract is more challenging. The main complication is retinal detachment. Special preoperative testing Dr. Allen thinks a careful preoperative retinal examination is important to rule out occult retinal pathology in the extreme axial myope. “Any suspicious retinal findings should be referred out for possible prophylactic treatment and counseling with a retinal specialist,” he said. Preoperatively, for high axial hyperopes, Dr. Tipperman said it may be helpful to administer IV mannitol, and intraoperatively, liberal use of OVD can help deepen the chamber and assist with lysis of adhesions. “In extremely short eyes with very shallow chambers it may be helpful to perform a limited pars plana vitrectomy,” he said. The shallow chamber and potential for positive pressure puts patients with a short eye at risk for significant iris prolapse. “It is helpful to create a longer than normal corneal incision to help avoid iris prolapse,” Dr. Tipperman said. IOL calculation considerations Both the Wang-Koch adjustment and Holladay 1 formula have helped Dr. Allen for long axial length eyes. “IOL calculations in short eyes are more challenging due to the relative proximity of the IOL to the retina and the large impact a small change in effective lens position may have on refractive accuracy,” he said. “Manufacturing tolerances in high IOL powers (>30 D) allow for greater variability, which may impact refractive accuracy as well.” Dr. Tipperman explained why those with axial myopia are a challenge to measure. “If the biometrist just measures the longest axial length of the eye, they will overestimate the true ‘refractive length’ to the actual fovea,” he said. “This is one of the advantages of optical biometry where the measurement is obtained by having the patient look at a fixation target and measuring the exact distance to the fovea regardless of its location.” Although optical biometry is very accurate for measuring high axial myopes, Li Wang, MD, and Doug Koch, MD, demonstrated that the measured axial length biometry should be adjusted for patients with a measured axial length of greater than 25.2 mm when using the Holladay 1 and 2, SRK-T, Haigis, and Hoffer Q formulas, 1 he said. This adjustment does not need to be made with the Barrett formula. At times the IOL power calculations for high myopes will yield a zero or 1 D power lens. “In these cases it is still preferable to place an IOL within the capsular bag since (1) this decreases the potential for PCO—and because high axial myopes are at risk for RD this is especially beneficial, and (2) in the event the patient does require a YAG capsulotomy, the IOL will act as a physical barrier and prevent vitreous from coming forward into the anterior segment,” Dr. Tipperman said. Intraoperative surgical considerations Although the majority of cataract surgery is performed under topical anesthesia, it should be noted that if possible it is preferential to avoid retrobulbar or peribulbar anesthesia in patients with high axial myopia because the presence of staphyloma in these patients increases the potential for inadvertent globe perforation, Dr. Tipperman said. Intraoperatively, those with short eyes are at risk for developing positive pressure and choroidal effusions and hemorrhages. “These can also be seen in the early postoperative period along with aqueous misdirection syndrome,” Dr. Tipperman said. “A myopic shift in the early postoperative period may be the first sign that aqueous misdirection is developing.” Dr. Devgan offered tips for both short and long eyes. In a tiny eye, using plenty of viscoelastic to deepen the space is important, he said. “When you break up the cataract, do it within the capsular bag,” he added. “Don’t try to prolapse the nucleus out of the capsular bag because there’s not enough room.” For long, myopic eyes you should avoid flattening of the anterior chamber so you don’t put pressure or traction on the vitreous base, he said. IOL choices Dr. Allen said that in long eyes, the main consideration is the potential for possible retinal surgical intervention in the future and the remote possibility of requiring silicone oil. “Therefore, an acrylic lens is favored,” he said. The standard range of most acrylic lenses will accommodate all but the most extreme long eyes, he added. “For the extreme axial myope, a low power lens or even a minus lens may be required.” The Sensar AR40 (Abbott Medical Optics) is available in low and minus powers and is an excellent choice, Dr. Allen said. In short eyes, an acrylic lens with a thin profile, such as the SA/SN60WF (Alcon, Fort Worth, Texas), is Dr. Allen’s typical lens of choice. “But its power range is only up to +30 D,” he said. The older, non-aspheric SA/SN60AT lens is available in powers up to +40 D, which will accommodate the majority of short axial length eyes, he said. “If a piggyback lens is required, a silicone sulcus IOL may be implanted without concern for interlenticular lens opacification.” The key, especially in a myopic patient, Dr. Devgan said, is to err on the side of residual myopia when you do lens calculation. For hyperopic patients, they are usually just happy not to be hyperopic, he said. Changing the IOL power by a little makes a big difference. EWAP Reference 1. Wang L, et al. Optimizing intraocular lens power calculations in eyes with axial lengths above 25.0 mm. J Cataract Refract Surg . 2011;37:2018–2027. Editors’ note: Dr. Allen has financial interests with Bausch + Lomb (Bridgewater, NJ) and Alcon. Drs. Devgan and Tipperman have no financial interests related to this article. Contact information Allen: q_allen@yahoo.com Devgan: devgan@gmail.com Tipperman: rtipperman@mindspring.com Considerations - from page 22