Eyeworld

EW CATARACT 66 February 2018 Asia-Pacific Association of Cataract & Refractive Surgeons (APACRS) website. Question: Is the traditional teaching of flipping the axis still considered undesirable? Dr. Hill: No. The objective is to either target the lowest anticipated amount of refractive astigmatism or leave about 0.25 D of WTR astigma- tism, regardless of the original orien- tation of the steep meridian. Question: How do you validate the axis and power meridian with asym- metrical bowtie? Dr. Hill: If the astigmatic lobes are greater on one side of the corneal vertex than the other, the corneal astigmatism is termed asymmetric. If the center of each of the astigmat- ic lobes is aligned with a different meridian, the astigmatism is termed irregular. The toric IOL is best suited to regular, symmetrical astigmatism. How much asymmetry and irregu- larity is an individual decision on the part of the surgeon. The full webinar is available on the ASCRS Center for Learning at www.ascrs.org/center-for-learning/ video/optimizing-iol-power-calcula- tions-and-outcomes. EW Editors' note: Dr. Hill has financial in- terests with Alcon (Fort Worth, Texas), Carl Zeiss Meditec, and Haag-Streit. Dr. Wang has financial interests with Carl Zeiss Meditec and i-Optics (The Hague, the Netherlands). Contact information Hill: hill@doctor-hill.com Wang: liw@bcm.edu astigmatic lobes and the corneal vertex. Where the line intersects the axis scale is the orientation of the steep meridian. Sim-Ks are not used for this process. The topographic axial power map also validates the presence of regular, symmetrical astigmatism. The steep meridian is used to validate the autokeratome- try by showing the same orientation of the steep meridian. Question: When a patient has had an enhancement after an initial treatment, what's the best way to calculate the power? Dr. Wang: If the historical methods are used in eyes with an enhance- ment, the stable refraction after the enhancement should be used. If methods using no prior data are used, they can be treated as eyes without enhancement, since only the measurements obtained before the cataract surgery will be used. Question: Can one use the Wang- Koch adjustment on Holladay 2 calculations? Dr. Hill: It's set up for Holladay 1. I think originally it was set up for Holladay 2, and Jack Holladay, MD, now has his own axial length adjustment in the Holladay IOL consultant software specifically for the Holladay 2 formula. Dr. Wang: Yes, the Wang-Koch adjustment can be used on Holladay 2 calculations. Question: Can you discuss what you consider extreme axial myopia and extreme axial hyperopia? The numbers of axial lengths? Dr. Hill: There isn't any hard defini- tion for extreme axial myopia, but I think anything above 27–28 mm would come under that category, and certainly 30 mm. In the catego- ry of extreme axial myopia, a couple of things start to happen. One is the incidence of staphyloma goes up significantly, and if we're using an optical biometer for an eye with a staphyloma, typically you get what's called the refractive axial length, which is the distance from the optical vertex to the foveal center. If you try and do a regular immersion ultrasound measurement, you're going to get the anatomic length— the distance from the corneal vertex to the greatest distance posterior, which is the bottom of the staphy- loma—so keep in mind that as the axial length increases at 28 mm, the incidence of staphyloma increases. Question: Which K values from the Pentacam (Oculus, Wetzlar, Germa- ny) should be input into the Barrett Toric Calculator? Dr. Hill: Autokeratometry (IOLMas- ter or LENSTAR Ks) is what works best with the Barrett Toric Calcula- tor. If the integrated K feature of the Barrett Toric Calculator is used, the front surface Ks would be used. Question: Does the post-myopic LASIK ASCRS calculator require any change in axial length for long eyes, or should we keep axial length as is? Dr. Hill: The axial length is not ad- justed for any of the post-keratore- fractive calculation methods. Question: Could the new genera- tion formulas be put on the ASCRS website? Dr. Hill: Hill-RBF can be accessed from the Tools area on the main page of the ASCRS website. The Bar- rett Universal II formula is on the Experts continued from page 65 Dr. Hill: At the present time, the only biometer with the Hill-RBF method is the LENSTAR. Question: How can I get a copy of the IOLMaster and LENSTAR valida- tion guidelines? Dr. Hill: These can be found at www.doctor-hill.com/biometry_vali- dation.html. Question: Do you have an adjust- ment like the Wang-Koch for the AL-Scan (Nidek, Gamagori, Japan) to adjust for high axial length? Dr. Hill: The question is, does the AL-Scan require something differ- ent? I think the Wang-Koch axial length adjustment would be the same for all optical biometers. Dr. Wang: I agree with Dr. Hill that the Wang-Koch axial length ad- justment would be the same for all optical biometers. Question: Does the IOLMaster 700 measure the posterior cornea? Dr. Wang: Yes, it is for research use currently and is not approved in United States yet. Question: Would you expect the same axial length adjustment for optical biometry with OCT as well? Dr. Wang: Yes. The newer optical biometry with OCT has comparable axial length readings, and the same axial length adjustment can be used. Question: Which K readings are most accurate for toric IOL calcula- tion? Which axis measurement do you trust most? Dr. Hill: The steep meridian is validated using a topographic axial power map and drawing a line through the center of the two

• Blank Page
• Blank Page (1)