An Intraocular Lens Power Calculation Formula Based on Optical Coherence Tomography: A Pilot Study

Center for Ophthalmic Optics and Lasers, Doheny Eye Institute, Los Angeles, Calif., USA.
Journal of refractive surgery (Thorofare, N.J.: 1995) (Impact Factor: 3.47). 06/2010; 26(6):430-7. DOI: 10.3928/1081597X-20090710-02
Source: PubMed


To develop an intraocular lens (IOL) power calculation formula based on optical coherence tomography (OCT) that would not be biased by previous laser vision correction.
Twenty-seven eyes of 27 cataract patients without prior laser vision correction who underwent phacoemulsification were included in the study. An optical coherence biometer (IOLMaster, Carl Zeiss Meditec) measured anterior corneal curvature and axial eye length. A high-speed (2000 Hz) anterior segment OCT prototype mapped corneal thickness and measured anterior chamber depth and crystalline lens thickness. Posterior corneal curvature was computed by combining IOLMaster keratometry with OCT corneal thickness mapping. A new IOL formula was developed based on these parameters. One month after phacoemulsification, the manifest refraction spherical equivalent (MRSE) was measured. The prediction error in postoperative MRSE of the OCT-based IOL formula was compared with that of three theoretic formulae: SRK/T, Hoffer Q, and Holladay II.
The mean prediction error in postoperative MRSE of the OCT-based formula was 0.04+/-0.44 diopters (D). The SRK/T was the best of the theoretic formulae, and its prediction error was -0.35+/-0.42 D. Twenty-one (78%) eyes were within 0.50 D using the OCT formula compared to 18 (67%) eyes using the SRK/T. No statistically significant differences were noted among the formulae.
For cataract patients without prior laser vision correction, the OCT-based IOL formula was as accurate as the current theoretic formulae. This new formula is based on direct OCT assessment of the posterior curvature and avoids the calculation errors inherent in conventional IOL formulae.

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Available from: David Huang, Aug 17, 2015
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    • "Corneal power is typically measured using keratometry, Placido-based videokeratography, slit-lamp scanning or Scheimpflug imaging [11]. However, the traditional lack of measurements of the posterior corneal surface has led to approximations (i.e., keratometric index) [5], which do not hold in abnormal corneas [12]. In addition, non-paraxial ray tracing approaches would require complete corneal shape information beyond corneal power. "
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    ABSTRACT: In vivo three-dimensional (3-D) anterior segment biometry before and after cataract surgery was analyzed by using custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT). The system was provided with custom algorithms for denoising, segmentation, full distortion correction (fan and optical) and merging of the anterior segment volumes (cornea, iris, and crystalline lens or IOL), to provide fully quantitative data of the anterior segment of the eye. The method was tested on an in vitro artificial eye with known surfaces geometry at different orientations and demonstrated on an aging cataract patient in vivo. Biometric parameters CCT, ACD/ILP, CLT/ILT Tilt and decentration are retrieved with a very high degree of accuracy. IOL was placed 400 μm behind the natural crystalline lens, The IOL was aligned with a similar orientation of the natural lens (2.47 deg superiorly), but slightly lower amounts (0.77 deg superiorly). The IOL was decentered superiorly (0.39 mm) and nasally (0.26 mm).
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    • "OCT of the anterior segment is valuable for diagnosis of corneal disorders such as keratoconus, and for pre- and post-operative assessment during surgical procedures such as keratomileusis (LASIK), phototherapeutic keratectomy (PTK), astigmatic keratotomy and lamellar keratoplasty [7]. Contact lens fitting and intraocular lens (IOL) power calculation can be performed using volumetric OCT data [8,9]. In addition, OCT is used in anterior chamber angle evaluation for glaucoma diagnosis and management [10]. "
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