Topographer - Aberrometer
Question: My boss asked me to reach out to you to find out if you have had any experience with an topographer/aberrometer like an OPD III or iTrace in the past. I know you have been retired from private practice, but you have written and/or collaborated in several articles that talk about aberrometry. We are mainly wanting to know if preop aberrometry will help us make a better decision on potential premium IOL patients, with data like corneal coma, angle kappa/alpha and to possibly separate internal aberrations from corneal aberrations.
Answer: Yes … the OPD III is a combination Topographer and Aberrometer that is very useful in PREOPERATIVE CATARACTION SURGERY for determining whether a person is a good candidate optically for a Multifocal or EDOF IOL. The best measure is the Higher Order Aberrations RMS Wavefront Error over the 6 mm zone of the cornea. This LINK fully explains it on page 2. Here the two relevant paragraphs. It is much better than just looking at coma.
The optical quality of the cornea is also a factor. A study by McCormick in 2005 in Ophthalmology showed the average HO RMS wavefront error for a normal virgin cornea was 0.38 ± 0.14 µm over a 6-mm zone. (Tomography example in Figure 4 is 0.30 µm.) The average magnitude of an asymptomatic successful postoperative conventional LASIK cornea was 0.58 ± 0.21 µm, and the average of symptomatic patients was 1.31 ± 0.58 µm. The average age was 44 years (range: 24 to 64 years). The contribution of the crystalline lens in this age group would be negligible and similar to a monofocal IOL.
The additional loss in optical performance from the multifocal IOL suggests that patients with HO RMS corneal wavefront errors over a 6-mm zone above 0.50 µm are not a good candidates for a diffractive multifocal IOL regardless of the cause of their poor corneal optical quality (post-refractive surgery, penetrating keratoplasty, keratoconus, irregular astigmatism, etc.). The only exception is dry eye, which if successfully treated will show an improvement of the HO RMS corneal wavefront error to below 0.50 µm.