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U.S. Food and Drug Administration

Confocal Laser Methods for Quantitative Evaluation of Dioptric Power Characteristics of New-Technology Intraocular Lens Implants

Catalog of Regulatory Science Tools to Help Assess New Medical Devices 

This regulatory science tool (RST) is a confocal laser method to evaluate the dioptric power of commercially available and new-technology intraocular lens (NTIOL) implants.

Technical Description

This regulatory science tool (RST) is a set of laboratory confocal laser methods (CLM) developed for preclinical evaluation of dioptric power characteristics of commercially available and new-technology intraocular lens (NTIOL) implants. The CLM sensing technology for intraocular lens (IOL) evaluation is based on an apertureless fiber-optic confocal laser approach [1-3]. Employing the CLM principle, the dioptric power of IOL implants is determined by precise spatial location of the IOL focal point and measurement of the IOL focal length. The CLM designs include additional specialized setups that can be applied as test tools for IOL dioptric power evaluation of both positive and negative monofocal IOLs as well as toric, multifocal, accommodative, and extended depth of focus (EDF) IOLs [1-8]. In quantitative evaluation of IOL dioptric power, the CLM test tools provide the following features:

  • Sub-micron accuracy (≤ 1 µm) in spatially locating IOL focal points and measuring focal lengths.
  • High repeatability (< 0.01 D) in dioptric power measurement.
  • A broad dioptric power range (0 D to >±30 D) for testing both positive and negative IOL.
  • Applicability of CLM methods for testing monofocal, multifocal, toric, accommodative, and EDF IOLs. 

Intended Purpose 

The CLM tools are intended for uniformity testing, accuracy assessment, power range characterization, and dioptric power evaluation of commercially available and NTIOLs. 

Testing

To evaluate the key properties of CLM tools including the measurement accuracy, repeatability, and applicability to various NTIOLs, multiple tests were performed, as documented in the peer-reviewed studies cited below. These tests include the following studies:

  • Positive and negative monofocal IOLs: Tested IOLs of positive (+5 D to + 30 D) and negative (-5 D to -20 D) power with a repeatability of 0.004-0.06/0.003-0.013 D for positive/negative IOLs [1,3,5].
  • Exact-power-labeled IOLs: Tested exact-power-labeled IOLs of 16 D to 27 D for predicting power accuracy and postoperative refractions. The dioptric power accuracy achieved under the test conditions in this study is 0.001 D [5].
  • Toric IOLs: Tested toric IOLs with spherical equivalent (SE) powers of 5 D, 20 D and 34 D, and cylinder (C) powers of 1.5 D to 4.0 D. The SE and C power repeatability is 0.002 D to 0.05 D [2,4].
  • CLM tools for dioptric power evaluation of representative IOL samples of positive and negative monofocal IOLs, accommodative IOLs, exact-power-labeled IOLs, toric IOLs, multifocal IOLs, extended depth of focus IOLs, and laser-assisted power-adjusted IOLs. 
  • Quantitative CLM tool assessment of key limiting test conditions: Performed quantitative studies for assessing key limiting test conditions on the IOL power evaluation: (1) environmental temperature [6]; (2) multiwavelength dispersion effect [7]; and (3) laser beam width effect [8]. 

Limitations

The developed CLM tools impose specific requirements and limitations on key CLM components. Two main requirements for the CLM laser sources are: 1) the laser wavelength is within the IOL standard wavelength range of 546 nm ± 10 nm, consistent with consensus standard ISO 11979-2:2024 [9]; and 2) laser power stability of ≤ 0.1% was used in the reported studies [3]. Equivalent or better stability is expected for comparable measurement accuracy. To achieve the highest accuracy in dioptric power measurements, the linearly scanning accuracy in locating the IOL focal point is ≤ 1 µm, which is facilitated by the use of a longer focal-length configuration, particularly for IOL samples with dioptric power ≤5 D. Additionally, the environmental temperature for in-situ IOL testing was maintained at a temperature of 35°C ± 2°C [6], consistent with ISO 11979-2 [9].

Supporting Documentation

Patents

  1. I. Ilev, “Confocal fiber-optic laser device and method for intraocular lens power measurements”, U.S. Patent No. 7,719,668. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/7719668
  2. I. Ilev, B. Walker, R. James, and D. Calogero, “Confocal laser method and device for power measurement of toric intraocular lens”, U.S. Patent No. 10,302,528. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/10302528

Peer-Reviewed Publications

  1. I. Ilev, “A simple confocal fiber-optic laser method for intraocular lens power measurement”, EYE, v. 21, pp. 818-823, 2007(Nature Journal). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10759314/pdf/nihms-1953204.pdf
  2. B. Walker, R. James, D. Calogero, and I. Ilev, “Confocal laser method for quantitative evaluation of critical optical properties of toric intraocular lenses”, Journal of Cataract and Refractive Surgery, v. 42, pp. 455-461, 2016. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10773575/pdf/nihms-1954064.pdf
  3. I. Ilev, R. Faaland, D. Kim, R. James, and D. Calogero, “Innovative confocal laser method for exact dioptric power measurement of intraocular lens implants”, Chinese Optics Letters, v. 6, pp. 876-878, 2008. https://www.researching.cn/ArticlePdf/m00005/2008/6/12/COL06120876.pdf
  4. B. Walker, R. James, D. Calogero, and I. Ilev, “Impact of environmental temperature on optical power properties of intraocular lenses”, Applied Optics, v. 54, pp. 453-457. 2014. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10793105/pdf/nihms-1956281.pdf
  5. B. Walker, R. James, D. Calogero, and I. Ilev, “Quantifying the multiwavelength dispersion effect on dioptric power measurement of intraocular lenses”, IEEE Photonics Journal, v. 7, pp. 6802607, 2015. https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7206777
  6. B. Walker, R. James, A. Chakravarty, D. Calogero, and I. Ilev, “Assessing the effect of laser beam width on quantitative evaluation of optical properties of intraocular lens implants”, Journal of Biomedical Optics, v. 19, pp. 055004, 2014. https://pubmed.ncbi.nlm.nih.gov/24817618/ 
  7. International Organization for Standardization. Ophthalmic implants – Intraocular lenses – Part 2: Optical Properties and Test Methods. Geneva, Switzerland, ISO, 2024 (ISO 11979-2:2024). 

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