Presentations optical Biometery for medical students

optical Biometery Presentations

1. Optical Biometry By Bareq Mared Thamer SuperVisor Ibraheem Jafarzada por

2. Intraocular lens (IOL) power calculation is the single most important determinant of functionally improved result of a technically precise cataract surgery. We have discussed recent advances in the field of optical biometry and IOL power calculation formulae as a means to achieve better postoperative visual outcome. The use of automated optical biometry device, the current ‘gold standard’ of IOL power calculation, dates back to 1999. We have highlighted the evolution of newer optical biometry devices and the technology they are based on, and their advantages and limitations. We have done technical comparison of contemporary biometers and have included contextual current review of literature. We have described newer generation IOL power formulae, IOL power calculation in high to extreme myopia, toric calculators and intraoperative aberrometry , and concluded our discussion with a note on future prospects of IOL power calculation Abstract

3. Introduction Cataract surgery is the most common surgical procedure performed worldwide. The goal of cataract surgery is not just the removal of cataract, but to provide the patien sharp, clear vision without glasses. Despite the growing popularity of laser‑assisted in situ keratomileusis (LASIK) and the growing interest in phakic intraocular lenses (IOLs) and other refractive procedures, cataract surgery provides a wider range of refractive error correction than any other surgical procedure, hence emerged the concept of “refractive cataract surgery.” For performing refractive catarac surgery, a cataract surgeon now has, in his armamentarium a host of technological innovations such as femtosecond laser‑assisted cataract surgery and the Zepto capsulotomy device to name a few. To match patient’s expectations of crisp and spectacle‑free vision, premium IOLs, namely multifocal IOLs, accommodating IOLs and toric IOLs are available. These technological advancements can help achieve better outcomes after cataract surgery. However, the improved outcomes are dependent on precise and accurate biometry. Newer biometry instruments that perform ocular measurements with micron precision and newer IOL calculation formulae to provide precise IOL power required

4. OPTICAL BIOMETRY To provide the best possible refractive outcome is the goal of the surgeon, whether the eye of the patient is normal or short or long or postrefractive surgery. Accurate measurement of all ocular parameters to obtain information about the complete geometry of the eye is required to arrive at the correct IOL prediction for each patient. Optical biometry is a highly accurate noninvasive automated method for measuring the anatomical details of the eye. Accurate anatomical measurements are critical for precise IOL power calculation. For many years, the gold standard of axial length (AL) measurement was ultrasound (US) biometry. The introduction of optical biometry in the late 1990s revolutionized the precision of IOL power calculation.

5. IOLMASTER 500 The IOL Master 500 ( Carl Zeiss Meditec AG, Jena, Germany) [Figure 1] is an all-in-one biometer which measures AL, K, and other ocular parameters as well as performs IOL power calculations. It is based on the concept of PCI and operates as a modified Michelson Interferometer.[15,18,19] PCI biometry was first developed by Austrian physicist Fercher and Roth[20] who performed the first in vivo AL measurement in 1986. The principle involves a dual beam of infrared (IR) light (780 nm) emitted by a semiconductor laser diode. A signal is produced as a result of interference between the light reflected from the tear film and that reflected by the retinal pigment epithelium. The photodetector receives the interference signal to calculate the optical distance (OD) between the corneal surface and retina.This OD is used to derive the other geometrical intraocular distances.

6. The employment of optical AL instead of anatomic AL has significantly improved the refractive results of cataract surgery. The IOLMaster 500 has been shown to consistently measure AL accurately to within ±0.02 mm.This translates into a 5–10-fold precision in AL measurement. With >100 million power calculations performed worldwide, the IOLMaster 500 is the current gold standard biometer

7. IOLMASTER 700 IOLMASTER 700 [Figure 2] was the first optical biometer to incorporate SS-OCT technology.[16,17,28-31] Its advantages over the earlier devices are as follows: 1. It provides full-length OCT image of the eye. The device performs 2000 scans/s. It can identify unusual ocular geometry (e.g., crystalline lens tilt/ decentration ) 2. It is more accurate. Measurements can be verified visually resulting in fewer “refractive surprises” 3. The OCT image provides a fixation check. The biometer’s fixation check feature alerts the user to a suboptimal scan if the image captured does not show the foveal pit. The fixation check also helps identify macular pathologies such as macular holes and age-related macular degeneration, though the findings need to be verified with a dedicated retina OCT 4. Unique telecentric K and distance-independent K: The unique software of IOLMaster 700 allows highly accurate distance-independent corneal surface measurements, independent of PS and even in restless patients 5. Better cataract penetration rates: the IOLMaster 700 can perform biometry even through dense cataracts 6. Software includes “ Haigis Suite” (which includes Haigis , Haigis ‑T for torics , and Haigis‑Lfor postrefractive surgery eyes) and other IOL power calculation formulae (SRK/T formula: Sanders- Retzlaff - Kraff formula; T for theoretical, Hoffer Q, Holladay 1 and 2, and Barrett Universal II) This device is especially suited for Toric IOLs. IOLMaster 700 contains inbuilt toric calculator (Barrett Toric calculator and Haigis ‑T for toric IOLs), and there is no need to use a separate online toric calculator

8. LENSTAR LS 900 LENSTAR LS 900 [Figure 3] uses the principle of OLCR. Apart from the parameters measured by IOLMaster , the Lenstar also measures LT. Use of LT, in conjunction with the latest state-of-the-art IOL calculation formulas (Barrett, Olsen, Holladay 2), translates into more accurate biometry. The latest version of Lenstar LS900 is equipped with the Hill‑radial basis activation function (Hill‑RBF), Barrett Universal II, Barrett True-K, and Barrett Toric calculator. Some of its other features are 1.Automated positioning system allows for dynamic eye tracking of patient. 2.Dual‑zone K (at 1.65 and 2.3 mm) and T‑cone topography (allows true Placido topography of the central cornea) 3.Contains EyeSuite IOL which is a comprehensive set of premium IOL calculation formulae for cataract surgery patients and patients postkeratorefractive surgery. Table 2 compares the technical specifications of IOLMaster 500 and Lenstar LS 900.

9. EYESTAR 900 The new device based on SS-OCT was launched in October 2017. The device contains EyeSuite software and provides elevation-based topography maps of both front and back of cornea and provides biometry data of the entire eye from cornea to retina. In addition, it provides two‑dimensional (2D) and three‑dimensional (3D) images of anterior segment as well as crystalline lens. Data acquisition process is smooth and fast, ensuring patient comfort. The device contains the latest IOL power calculation formulae such as Hill-RBF and Barrett Universal 2. Various authors have reported excellent agreement between AL measurements by IOLMaster and the Lenstar .[16,33-36] Epitropoulos compared AL acquisition and other parameters by IOLMaster 500 (version 7.1 software) with those from Lenstar LS 900 in 105 cataractous eyes of 63 patients.[37] AL was acquired by the composite mean value of five measurements (composite‑5 IM) and 20 measurements (composite‑20 IM) of IOL Master 500 version 7.1 software and the standard mean of the first five measurements on standard‑5 LS Lenstar LS900. He observed

10. ARGOS ADVANCED OPTICAL BIOMETER (MOVU) The Argos [Figure 5] uses a 1060-nm and 20-nm bandwidth SS-OCT technology to collect 2D OCT data of the eye. The fast image reconstruction algorithm of the instrument is used to provide real-time 2D imaging of the eye. The 1050 nm light cause less scatter than shorter wavelengths leading to more photons being available to make measurements and hence better penetration through dense cataract. Equipped with Video K with IR light-emitting diode ring illumination, Argos measures AL, CCT, ACD, LT, PS, aqueous depth, WTW, K, and astigmatism. The biggest advantage of Argos is its ability to image through very dense cataracts through an “Enhanced Retinal Visualization” mode [Figure 6] that increases imaging sensitivity of the retinal area by 100 times (without increasing laser power). The Argos uses a propriety swept laser source specifically designed for deep imaging (>50 mm) at fast 3000 lines/s A‑line rate. The Argos also features an “Analysis mode” which allows the surgeons to verify the results obtained. Shammas et al. reported good repeatability and reproducibility and comparability of measurements obtained by Argos biometer , IOLMaster 500, and Lenstar LS900.[31] The study was performed on 107 eyes. AL was correctly measured in 96% of cases with the Argos compared with 79% for Lenstar and 77% for IOL Master 500.

11. ALADDIN Aladdin [Figure] combines OLCR biometry with anterior topography, Zernike corneal wavefront analysis, and pupillometry in one instrument. Following are its important advantages: 1.It provides information about corneal asphericity [Figure 8] by mapping 24 Placido rings (on cornea) and analyzing 1024 data points using its real corneal radii technology. It provides extensive information on status of anterior surface of cornea including presence of corneal irregularities, common signs of keratoconus, and information about higher-order aberrations 2. Dynamic pupillometry allows better assessment of lens centration, constriction, and dilation of pupil in photopic and mesopic conditions to assist in premium IOL selection. 3. Zernike wavefront analysis allows evaluation for higher-order aberrations and corneal surface anomalies like keratoconus It contains inbuilt toric calculators – Barrett IOL Suite and Abulafia –Koch regression formula The 850-nm superluminescent diode allows the Aladdin to penetrate even high-density cataracts

12. AL‑SCAN (NIDEK) This easy to use PCI-based biometer [Figure 9] uses an 830 nm IR laser diode for AL measurement. It has following features: 1.It contains “3D autotracking ” to track patient’s eye movements along the X, Y, and Z planes. The “ autoshot ” feature allows device to capture the scan as soon as it senses correct alignment 2.Topography and K with double mire rings help evaluate for aberrations. It measures K at 36 points 3.It employs Scheimpflug imaging to measure CCT and ACD (a Scheimpflug system images the anterior segment with a camera perpendicular to a slit beam, thus creating an optical section of cornea and lens). It also provides data about pupil position

13. GALILEI G6 LENS PROFESSIONAL The Galilei G6 [Figure 10] combines OLCR optical biometry, dual‑ Scheimpflug imaging, and Placido ‑disc topography. Some of its features are as follows: 1.It provides high‑definition pachymetry and 3D anterior chamber analysis 2.It measures total corneal wavefront , curvature, and K data of anterior as well as posterior cornea, that is, provides complete data to plan cataract or refractive surgery 3.Ray-traced posterior corneal surface data to detect bulging or asymmetry in late stages 4.The combination of Scheimpflug imaging with optical biometry makes Galilei G6, especially suitable for IOL selection in postkeratorefractive surgery eyes and also (including keratoconus screening) of refractive surgery candidates. It is also helpful in devising corneal implants and in planning and follow-up of keratoplasty patients 5.It includes newer IOL power formulas including Shammas No-History, Barrett Universal, and Barrett True-K Toric calculator. The comparability of biometric measurements and IOL power calculation between IOLMaster 500 and Galilei G6 was studied by Ventura et al. They found similar results

14. Figure 9: A Nidek AL Scan (AL‑Scan, Nidek Co., Aichi, Japan) biometry and phakic intraocular lens power printout. AL = axial length, ACD = anterior chamber depth, R1 = flattest radius of corneal curvature; R2 = steep radius; 90° apart from r1 Figure 10: The Galilei G6optical biometer (Galilei G6, Ziemer . Port, Switzerland)

15. HOLLADAY 2