A comparative analysis of methods for calculating IOL power [Elektronische Ressource] : combination of three corneal power and two axial length measuring techniques / vorgelegt von Ainura Stanbekova

Ainura Stanbekova

Description

Aus dem Department für Augenheilkunde Universitäts-Augenklinik Tübingen Sektion Experimentelle Ophthalmochirurgie Leiter: Professor Dr. B. Jean A Comparative Analysis of Methods for Calculating IOL Power: Combination of Three Corneal Power and Two Axial Length Measuring Techniques Inaugural-Dissertation zur Erlangung des Doktorgrades der Medizin der Medizinischen Fakultät der Eberhard-Karls-Universität zu Tübingen vorgelegt von Ainura Stanbekova aus Bishkek, Kirgisische Republik 2008 Dekan: Professor Dr. I. B. Autenrieth 1. Berichterstatter: Prof. Dr. B. Jean 2. Berichterstatter: Prof. emer Dr. H. J. Thiel Dedicated to my mother Kenzhe Abdyldaeva Table of contents: 1. Introduction ................................................................................................. 5 History of IOL power calculation ..................................................................... 5 Purpose ........................................................................................................ 11 2. Patients and methods................................................................................ 12 2.1. Patients.................................................................................................. 12 2.2. Methods.................................................................................................

Sujets

• Gesundheit

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2008
• Nombre de lectures: 11
• Langue: English

Extrait

Aus dem Department für Augenheilkunde Universitäts-Augenklinik Tübingen Sektion Experimentelle Ophthalmochirurgie Leiter: Professor Dr. B. Jean         A Comparative Analysis of Methods for Calculating IOL Power: Combination of Three Corneal  Power and Two Axial Length Measuring Techniques     Inaugural-Dissertation  zur Erlangung des Doktorgrades der Medizin     der Medizinischen Fakultät der Eberhard-Karls-Universität zu Tübingen         vorgelegt von Ainura Stanbekova aus Bishkek, Kirgisische Republik     2008

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dekan:

 

 

1. Berichterstatter:

2. Berichterstatter:

Professor Dr. I. B. Autenrieth

Prof. Dr. B. Jean

Prof. emer Dr. H. J. Thiel 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dedicated to my mother Kenzhe Abdyldaeva

 

Table of contents:   1.   Introduction ................................................................................................. 5   History of IOL power calculation ..................................................................... 5   Purpose ........................................................................................................ 11   2.   Patients and methods................................................................................ 12   2.1. Patients.................................................................................................. 12   2.2. Methods ................................................................................................. 12   2.3. Statistics ................................................................................................ 22   3.   Results ...................................................................................................... 23   3.1. Visual acuity........................................................................................... 23   3.2. Refraction .............................................................................................. 25   3.3. Corneal power ....................................................................................... 25   3.4. Axial length ............................................................................................ 30   3.5. Anterior chamber depth ......................................................................... 32   3.6. IOL A-constant ....................................................................................... 33   4.    37Discussion .................................................................................................   4.1. Keratometric readings............................................................................ 37   4.2. Axial length and anterior chamber depth ............................................... 43   4.3 Refractive error prediction....................................................................... 49   5.   Conclusion ................................................................................................ 57   6.   References ................................................................................................ 58    

 

1. Introduction   History of IOL power calculation    The history of cataract surgery goes back to 5th century B.C. From Sanskrit manuscripts the earliest type of cataract surgery was known as couching. This techniques permitted dislocation of the mature cataract into the vitreous cavity and enabled the patient to see better. The first idea of substituting an optical device for the opaque crystalline lens belonged to Tadini in 1766 (Fechner, Fechner et al., 1979). The evolution of cataract surgery took a giant step in 1949 when Harold Ridley, developed and implanted the first intraocular lens (Ridley, 1952) and provided evidence for tolerance of a foreign body in the eye and the prospect of restoring functional vision. At present time, cataract surgery is one of the most frequently performed and successful operations in the world. The techniques and results of cataract surgery have changed dramatically during the past three decades. The technique has moved from intracapsular cataract extraction (ICCE) to extracapsular cataract extraction (ECCE). Phacoemulsification, small incisions alone with advances in intraocular lens materials and designs, viscoelastic agents, topical anesthesia have increased safety and efficiency of cataract surgery and become the standards. These advances in technique and equipment have led to a dramatic increase in the popularity of phacoemulsification.   As cataract surgery technology and intraocular lens (IOL) technology have improved remarkable and become safe, the patients have been expecting better postoperative refractive results, which are determined by the precise intraocular lens power calculation (Hillman, 1982). The calculation is normally based on corneal power, axial length (AL) measurements and IOL calculation formulae. These three factors are considered to be the most critical factor for accurate IOL power calculation. Axial length is usually measured by applanation A-scan ultrasound, which is widely used technique (Binkhorst, 1981; Olsen and Nielsen, 1989; Leaming, 2001). In A-scan biometry, the sound travels at a frequency of

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approximately 10 million Hz (10 MHz). This extremely high frequency allows for restricted penetration of the sound into tissues. The biometer measures axial lengths, the distance between the anterior corneal vertex and internal limiting membrane of the retina, along the optical axis with a resolution of 200m and precision of 150m (Olsen, 1989).   The method requires the use of topical local anesthesia and contact of the cornea with a probe of A-scan, as ultrasound energy is emitted from the probe tip by pulsing electricity. Studies based on ultrasound biometry demonstrated 54% of all IOL power miscalculations result from wrong AL measurements (Olsen, 1992). The measurement error in axial length of 100m results in postoperative refractive error of 0.25D (Binkhorst, 1981) to 0.28D (Boerrigter, Thijssen et al., 1985; Olsen, 1987(a); Drexler, Findl et al., 1998). The IOLMaster is a noncontact partial coherence interferometry (PCI) method for AL measurement, which has recently become commercially available (Fercher, Hitzenberger et al., 1993; Drexler, Findl et al., 1998; Haigis, Lege et al., 2000).   It uses infrared diode laser (λ nm) of high special 780 coherence and short coherence length (160m). The optical scan uses an external Michelson interferometer to split the infrared beam into coaxial dual beams allowing the technique to be intensive to longitudinal eye movement. Both components of the beam illuminate the eye and are reflected at each interface where the change in refractive index occurs. If the optical path length is within the coherence length interference signal is detected by a photodetector (Hitzenberger, 1991). The IOLMaster measures the ocular axial length between the corneal vertex and retinal pigment epithelium along the visual axis using red fixation beam, with a resolution of 12m and precision of 5m (Hitzenberger, Drexler et al., 1993; Drexler, Findl et al., 1998; Drexler, Hitzenberger et al., 1998; Findl, Drexler et al., 1998; Haigis, Lege et al., 2000; Findl, Drexler et al., 2001; Lam, Chan et al., 2001; Vogel, Dick et al., 2001; Kiss, Findl et al., 2002; Santodomingo-Rubido, Mallen et al., 2002; Nemeth, Fekete et al., 2003), (Haigis, 1999). Advantages of this technique is that there is no need for local anesthesia and pupil dilation   (Drexler, Findl et al., 1998; Findl, Drexler et al., 2001), therefore method reduces the potential risk of corneal erosions or

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infection (Hitzenberger, Drexler et al., 1993; Rose and Moshegov, 2003). The technique is observer-independent method for AL measurement (Drexler, Findl et al., 1998; Lam, Chan et al., 2001; Vogel, Dick et al., 2001; Santodomingo- Rubido, Mallen et al., 2002; Findl, Kriechbaum et al., 2003; Tehrani, Krummenauer et al., 2003(b)). The measurement obtained by IOLMaster has been reported more accurate and reproducible than that by US in a normal eye (Eleftheriadis, 2003; Goyal, North et al., 2003)   and in a pseudophakic eye (Haigis, 2001; Goyal, North et al., 2003). Since introducing the ultra-high precision PCI, this method has proven its accuracy in IOL power calculation   using different lens formulas too (Drexler, Findl et al., 1998; Findl, Drexler et al., 1998; Vogel, Dick et al., 2001; Connors, Boseman et al., 2002; Nemeth, Fekete et al., 2003; Ueda, Taketani et al., 2007).   The incredible technique of phacoemulsification and IOL material and design provided rapid improvements in ophthalmology in recent decades and has made modern cataract surgery safe and effective. Axial eye length with an error of approximately 0.2 D is no longer the dominating error if the measurements are performed by interferometry; the same is true for corneal radii in normal eyes (Preussner, 2007). But if the total error threshold is below the error of refraction, the accuracy of the IOL power calculation formula must be improved. This important part of IOL power calculation has been growing in recent years especially in eyes that have had refractive surgery. In the early 1970s, first commercially available ultrasound instrumentation was adopted to clinical practice. This period gave birth to the first theoretical and empirical intraocular lens power calculation formulae. The first formula for the determination of intraocular lens power was published by Fyodorov, Kolinko and Kolinko (Fyodorov SN, 1967). All   original formulae by Fyodorov (Fyodorov SN, 1967), Binkhorst (Binkhorst, 1972), Colenbrander (Colenbrander, 1973), Fyodorov (Fyodorov, Galin et al., 1975), Thijssen (Thijssen, 1975), van der Heijde (van der Heijde, 1975) and Hoffer   (Hoffer, 1982) are first generation theoretical formulae. They required axial length of the eye, the corneal power in diopters, corneal radius and position of the intraocular lens

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