Clinical evaluation of the Oculus Keratograph.docx
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1、Contact Lens & Anterior Eye 35 (2012) 171174 Contents lists available at SciVerse ScienceDirect Contact Lens & Anterior Eye jou rn al h om epa ge: Clinical evaluation of the Oculus Keratograph N. Best a,b , L. Drury a , J.S. Wolffsohn b, a Specsavers, 41 High Row, Darlington, Co Durham DL3 7QW, UK
2、b Life and Health Science, Aston University, Ophthalmic Research Group, Birmingham, UK a r t i c l e i n f o a b s t r a c t Keywords: Non-invasive tear break-up time Tear lm stability Keratometry Objective Corneal topography Aim: To determine the validity and reliability of the measurement of corne
3、al curvature and non-invasive tear break-up time (NITBUT) measures using the Oculus Keratograph. Method: One hundred eyes of 100 patients had their corneal curvature assessed with the Keratograph and the Nidek ARKT TonorefII. NITBUT was then measured objectively with the Keratograph with Tear Film S
4、can software and subjectively with the Keeler Tearscope. The Keratograph measurements of corneal curvature and NITBUT were repeated to test reliability. The ocular sensitivity disease index questionnaire was completed to quantify ocular comfort. Results: The Keratograph consistently measured signica
5、ntly atter corneal curvatures than the ARKT (MSE difference: +1.83 0.44D), but was repeatable (p 0.05). Keratograph NITBUT measurements were signicantly lower than observation using the Tearscope (by 12.35 7.45 s; p 0.001) and decreased on subsequent measurement (by 1.64 6.03 s; p 0.01). The Keratog
6、raph measures the rst time the tears break up anywhere on the cornea with 63% of subjects having NITBUTs 5 s and a further 22% having readings between 5 and 10 s. The Tearscope results were found to correlate better with the patients symptoms (r = 0.32) compared to the Keratograph (r = 0.19). Conclu
7、sions: The Keratograph requires a calibration off-set to be comparable to other keratometry devices. Its current software detects very early tear lm changes, recording signicantly lower NITBUT values than conventional subjective assessment. Adjustments to instrumentation software have the potential
8、to enhance the value of Keratograph objective measures in clinical practice. 2012 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved. 1. Introduction In optometric practice corneal curvature is routinely measured with a keratometer prior to rigid lens tting. A keratomet
9、er is an instrument used to examine the central 3.03.5 mm of the cornea providing information on the radii of curvature, the directions of the principle meridians, the degree of corneal astigmatism and the presence of any corneal distortion. Keratometers only assesses the central corneal curvature,
10、but most corneas atten towards the periphery as prolate ellipses 1. Videokeratoscopes, generally known as topographers, typically assess corneal curvature over a wider (up to 10 mm diameter) region of the cornea by reecting an illuminated placido disc of known proportions off the tear lm and compari
11、ng this to the imaged reection. Image processing software detects the location of the rings objectively in multiple meridians and displays the data in the form of contour maps along with simulated keratometry readings in the principal axes. As well as providing generally more Corresponding author at
12、: Life and Health Science, Aston University, Aston Tri- angle, Birmingham B4 7ET, UK. Tel.: +44 0121 2044140; fax: +44 0121 2044048. E-mail address: j.s.w.wolffsohnaston.ac.uk (J.S. Wolffsohn). reliable information on corneal topography over a wider corneal area the reection quality of the placido m
13、ires indicates the quality of the tear lm over time. Whilst this has been utilised in a research setting 2, until now no commercial devices have been available to objectively assess non-invasive tear break-up time. Objectively analysing the placido reections from the tear lm over time after a blink
14、has been shown to have higher sensitivity, but similar speci- city in predicting symptomatic dry eye than uorescein break-up time. Tear stability is routinely assessed in clinical practice to aid in the diagnosis of dry eye disease and to help predict the likelihood of contact lens induced dry eye i
15、n neophyte contact lens wearers. This is most commonly done by assessing the tear lm break up time (BUT), a measurement of the time which elapses between a patient blinking and their tear lm beginning to break up or a subsequent uncontrollable blink. It is often assessed following the instillation o
16、f sodium uorescein dye into the tears and observation with a slit lamp microscope using blue light and a yellow enhancement lter 3. There is concern that the presence of uorescein in the tear lm will destabilise the tears and for this reason it is preferable to measure tear lm non-invasively without
17、 rst instilling uorescein 46 This type of tear lm measurement is referred to as non- invasive tear break-up time (NITBUT) although it should be noted 1367-0484/$ see front matter 2012 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved. http:/dx.doi.org/10.1016/j.clae.20
18、12.04.002 172 N. Best et al. / Contact Lens & Anterior Eye 35 (2012) 171174 that changes in meniscus curvature have been observed even with this minimally invasive technique suggesting it is easy to induce minor degrees of reex tearing 6. The repeatability of measurements with one of the main subjec
19、- tive devices for assessing NIBUT, the Tearscope (Keeler, Windsor, UK) appear to be more reliable that other techniques such as obser- vations through a slit lamp or of video keratoscope mires, although Tearscope measures are still quite variable 7 and there is consid- erable interexaminer variabil
20、ity 8. The Diagnostic Methodology Subcommittee of the International Dry Eye Workshop stated it was important to develop objective analysis methods of NIBUT to help standardise tear lm examination methods and improve compara- bility of measurements 6. The Keratograph (OculusOptikgerate GmbH, Wetzlar,
21、 German) is the rst commercially available device with software (“Tear Film Scan”) which permits an automated, examiner independent tech- nique for measuring NITBUT. The aim of this study was to determine the validity and reliability of the measurement of corneal curvature and NITBUT measures using
22、the Keratograph. 2. Methods One hundred consecutive patients with no known anterior eye disease (average age 37 13 years, range 1967 years; 65 female) were recruited from the staff and patients of a community opto- metric practice in the North East of England. Consent was obtained after explanation
23、of the study and possible consequences of taking part. The study was approved by the ethical committee of Aston University and conformed to the Declaration of Helsinki. Due to the similar nature of the two eyes, data from only right eyes were analysed to avoid statistical bias. A single keratometry
24、reading was captured with a validated Tonoref II (Software version 1.05; Nidek, Nagoya, Japan) 9 following alignment of the instrument head with the centre of the pupil and after the patient had been asked to blink. Two further topography images of the patients right eye were sub- sequently captured
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