To the Editor:
We appreciate the interest of Manuel Rodriguez-Vallejo in our paper,1 and the comments made to it. There seem to be 2 main points regarding the article.
The first concerns the use of an optical visual quality analysis system (HD Analyzer, Visiometrics, Terrassa, Spain). It is based on the double-pass design, through which the ocular media and retinal reflections provide complete information and accurate estimates of optical quality.2 It assesses and quantifies all higher-order aberrations and intraocular forward and backward scattering to reliably predict retinal image quality after intraocular lens (IOL) implantation.3 This system has been successfully applied to measure the optical quality of different types of multifocal IOLs.4,5 However, because of the nature of the diffractive IOL, in which light is partially lost, there are certain limitations on accurately assessing optical quality. Furthermore, HD Analyzer measures a 4.0 mm area and recognizes the diffusion that occurs in the diffractive rings at the center of the IOL. Hence, higher objective scatter index values can be measured in a Symfony IOL with diffractive rings. Nevertheless, I consider HD Analyzer more credible than a quality of vision questionnaire or other questionnaire data (CatQuest-9SF, spectacle independence, vision satisfaction, and dysphotopsia). In my experience, postsurgical surveys are not very reliable. Typically, in studies evaluating the results of multifocal IOLs, 1 group is made up of about 20 people. However, some patients were very dissatisfied after surgery, for other reasons exemplified by meibomian gland dysfunction, which gave the lowest score for all items of the questionnaire. Consequently, the reliability of the overall survey is reduced.
I performed the HD Analyzer on hundreds of patients with various multifocal IOL implants. The overall results are believed to exhibit a certain trend. Realistically, thus far, the optical quality of the diffractive IOL cannot be accurately measured using any current equipment. Namely, a uniform value of each IOL can be obtained using an HD Analyzer as a reference for evaluating the optical quality of a diffractive IOL.
The paper author quoted assessed the optical quality of a device other than the HD Analyzer.6 There are subtle differences amongst the devices.
The latter is related to defocus curves. The best-corrected visual acuity was examined by an optometrist, and the defocus curves were measured by an ophthalmologist. The optometrist carried out a manifest refraction and then the ophthalmologist made the test glasses for the patient. Visual acuity measured with the test glasses was set at 0 D location. Although this outcome is expected to be consistent with the best-corrected visual acuity, it is not necessary. There was a slight difference in LogMAR 0.05 for 174 persons over the age of 60 years. An ophthalmologist who conducted a clinical study did not question the reliability of the study for this reason. In fact, in a study of many elderly patients, some patients had slightly lower visual acuity than that observed during manifest refraction.
Kyungmin Koh, MD, PhD
1. Jeon YJ, Yoon Y, Kim T, Koh K. Comparison between an intraocular lens with extended depth of focus (Tecnis Symfony ZXR00) and a new monofocal intraocular lens with enhanced intermediate vision (Tecnis Eyhance ICB00). Asia Pac J Ophthalmol. 2021;10:542–547.
2. Kang KH, Song MY, Kim KY, et al. Visual performance and optical quality after implantation of a new generation monofocal intraocular lens. Korean J Ophthalmol. 2021;35:112–119.
3. Labuz G, Reus NJ, van den Berg TJ. Comparison of ocular straylight after implantation of multifocal intraocular lenses. J Cataract Refract Surg. 2016;42:618–625.
4. Chen T, Yu F, Lin H, et al. Objective and subjective visual quality after implantation of all optic zone diffractive multifocal intraocular lenses: a prospective, case-control observational study. Br J Ophthalmol. 2016;100:1530–1535.
5. Liao X, Lin J, Tian J, et al. Evaluation of optical quality: ocular scattering and aberrations in eyes implanted with diffractive multifocal or monofocal intraocular lenses. Curr Eye Res. 2018;43:696–701.
6. Alio JL, D'Oria F, Toto F, et al. Retinal image quality with multifocal, EDoF, and accommodative intraocular lenses as studied by pyramidal aberrometry. Eye Vis (Lond). 2021;8:37.