Eyeworld

56 | EYEWORLD | FALL 2025 C ORNEA BEYOND THE ROUTINE by Ellen Stodola Editorial Co-Director About the physicians Amar Agarwal, MD Chairman Dr. Agarwal's Group of Eye Hospitals Chennai, India Jack Holladay, MD, MSEE, FACS Clinical Professor Department of Ophthalmology Baylor College of Medicine Houston, Texas Jack Parker, MD, PhD Parker Cornea Vestavia Hills, Alabama a topographic map, the more the irregularity; you'll see patches of yellow, green, and blue, which are measures of irregularity that you can see on a topography, he said. He also noted that physicians will want to pay attention to the RMS higher order aber- ration (HOA) values. In the cornea, we use the higher order aberrations, which are those irregularities on the surface, so they're the high points and the low points, he said. Irregular astigmatism is an older term for higher order aberrations, Dr. Holladay said. When wavefront came around, people stopped using irregular astigmatism because they could quantitate it and describe it with what are called Zernike coefficients. Now, that doesn't make that much difference because what counts is how much the total irregularity is, and that's where the RMS HOA value comes in. Dr. Holladay spoke about the "Holladay Report," an interpretation guideline he put together for the Pentacam (Oculus). In it, he noted, "RMS HOA WE (6 mm), the RMS higher order aberration wavefront error over the 6 mm zone of the cornea, is a measure of corneal irregularity. A normal cornea has 0.37 μm. As the value increases above 0.66 μm, the image degradation from the cornea will become more noticeable, and above 1.00 μm, the patient will probably already have complaints about visual quality. The use of multifocal IOLs should be carefully considered with increasing amounts of corneal irregularity because it further reduces the contrast of the retinal image and glare and halos." Dr. Holladay described a study he did with Dr. Agarwal, showing that outcomes are related to the RMS HOA value because there are pa- tients who have 2.0, 3.0, or 4.0 μm (10 times the normal value, which should be about 0.37), and those people are going to have bad vision. The effect of HOAs is directly proportional to the size of the pupil. A pinhole can help isolate these values to a small area and significantly reduce the effect of the HOAs. The RMS HOA value is present on all topog- raphers and tomographers, Dr. Holladay said. "Every single one has the RMS HOA 6 mm zone value because that's a standard value that you need." However, he noted that this value can A stigmatism, whether regular or irregular, is something that many ophthalmologists are familiar with. Amar Agarwal, MD, Jack Holladay, MD, MSEE, FACS, and Jack Parker, MD, PhD, discussed the issue and how to deal with it, particularly highlighting Dr. Agarwal's pinhole pupilloplasty technique. Astigmatism is the warpage of the front surface of the eye, Dr. Parker said. "The front surface of the eye should be round like a sphere, and if it's not, if it's warped, we call that astig- matism," he said, noting that the astigmatism will either be regular or irregular. Regular astigmatism is fully correctable with glasses or a soft contact lens, and this type is common. Occasionally, there will be irregular astigmatism, which is an abnormal shape of the cornea in which it is twisted or warped in a complex way; glasses and soft contact lenses won't fix it. There are certain diseases you can be born with or develop, like keratoconus, that may cause irregular astigmatism, Dr. Parker said. Additionally, things like trauma or prior surgery can cause a distortion of the surface of the eye. These are aberrated corneas, Dr. Agarwal said, noting the term that he coined, "aberro- pia." 1 Aberropia is found in patients who have higher order aberrations, and there's a problem with the clarity of their vision (resolution). Dr. Parker said that topography or tomog- raphy are the most objective indicators of the shape of the cornea. But often, you don't even need technology to diagnose irregular astigma- tism. "You look at the eye, the best corrected vision is poor with glasses or contacts, and on exam, you see they have a big scar or the shape of the eye is twisted. These are usually grossly obvious things, which you can confirm with various imaging tools." You can also see these distortions with the direct ophthalmoscope or retinoscope, which show scissoring of the light reflex indicating irregular astigmatism. Meanwhile, Dr. Holladay described the value of topography and tomography, technol- ogies that most surgeons have, in determining irregular astigmatism. He noted the axial and tangential maps, which show the front surface of the cornea. The more colors that you see in Dealing with a non-routine cornea: irregular astigmatism and a potential solution

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