Eyeworld Daily News

10 | EYEWORLD DAILY NEWS | MAY 17, 2020 DAILY NEWS ASCRS VIRTUAL ANNUAL MEETING continued from page 8 Dr. Ayres discussed deter- mining clinically significant lens changes, saying that he thinks this is one of the easier things to troubleshoot in pa- tients with keratoconus. There is a large overlap in complaints with keratoconus, corneal ecta- sia, and cataracts. These complaints include reduced vision (corrected and uncorrected), glare, and difficulty reading. These can be due to the cornea or the lens. So how do you know which is which? If the symptoms are getting worse and the cornea is not, you can be fairly sure that the cornea is not to blame, Dr. Ayres said, so you want to make sure that the patient has an established topography and that it is stable. If it is not sta- ble, this is where crosslinking would come into play, and you should make sure that patient is crosslinked and stabilized before moving on to cataract surgery. Make sure the patient is out of contact lenses before you establish stability so that biometry is as accurate as possible. Change in manifest refraction over time, without change in the corneal param- eters, is a clear sign that the cataract is to blame. Dr. Ayres said to also look closely at the cornea. Using a gas permeable lens can help separate the corneal component from the lenticular opacity. He added that signif- icant scarring or hydrops may be etiology for reduced vision, and in some cases, the cornea and the lens may be limiting vision. "Calculation of lens power is notoriously difficult in the keratoconus patient," Dr. Ayres said. There are multiple chal- lenges, including measurement of axial length. Patients with more severe keratoconus tend to have a hard time fixating, so you may have keratometric irregularity as well as axial length discrepancies. The more severe the keratoconus, the more variability you will see in keratometric values. Dr. Ayres noted that there may be a slight advantage in Scheimpflug systems with more advanced keratoconus, though there is some irregular- ity using this system as well, and he added that Placido topographers show an increase in variability with keratoconus patients. So far, we haven't been able to accurately map the more severe keratoconus patient, he said, but in mild keratoconus, the issue isn't as bad. Moving on to address biometry in keratoconus pa- tients, Dr. Ayres said there's no real consensus as to which IOL formula may be preferred, which he said "makes no sense." Confounding variables include steep apical cornea, change in the anterior/pos- terior cornea curvature, and deep anterior chamber. There have been several studies, usually with a small number of patients, looking at differ- ent formulas but there is "so much noise in the system, so many confounding variables," he said. For example, Dr. Ayres said that one small series found that the SRK II was the preferred method for mild keratoconus, and in another series with newer formulas, the SRK/T was most accurate. Many of the formulas will leave the patient hyperopic due to overestimation of the corneal power, Dr. Ayres said, and in some cases K values will have to be estimated with the assumption that a PKP may be performed in the future. Dr. Ayres then shifted gears to talk about astigma- tism management. "Treating astigmatism in the keratoconus patient can be quite challeng- ing because you're never sure what they're going to need," he said. Multiple factors have to be known, including stability of the cornea and refraction; if the patient wears glasses, a soft contact lens, or a rigid contact lens; and if the magnitude and axis are measurable and within treatment parameters. Dr. Ayres also discussed surgical considerations once you've decided to move ahead with cataract surgery in a ker- atoconus patient. The clinical exam is of the utmost impor- tance, he stressed. You want to see where the thinning is, if there's corneal scarring, and what the anterior chamber depth is. Then, you'll want to modify your technique depend- ing on the clinical exam. He offered several surgical pearls: • Move the main incision to an area of minimal thinning (superio-temporal wound or superior approach). • You may need to consider a near-clear or scleral tunnel approach. • Have a very low threshold to place a suture in the wound. • Irregular shape of the cornea may make red reflex difficult to see, so OVD on the ocular surface may help with visual- ization. • Have a low threshold for use of capsular stain. • Use of an RGP may aid in visualization. When do you treat the cor- nea? Dr. Ayres said this should happen when there is clinically significant corneal scarring, non-healing hydrops, high levels of irregular astigmatism and inability to wear an RGP, and if there is an inadequate view into the anterior cham- ber for safe cataract removal. If there is significant corneal pathology, Dr. Ayres concluded that is when it's time to do a corneal transplant followed by or at the same time as cataract surgery. He suggested staging PKP first then cataract removal, if lens changes are mild. Editors' note: Dr. Beckman has financial interests with a number of ophthalmic companies. Dr. Ayres has no financial interests related to his presentation. ASCRS is your trusted source for innovative education and philanthropy, for every stage of your career. Join today: ASCRS.org

• Cover