Clinical evaluation of the Oculus Keratograph
Introduction
In optometric practice corneal curvature is routinely measured with a keratometer prior to rigid lens fitting. A keratometer is an instrument used to examine the central 3.0–3.5 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, but most corneas flatten 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 reflecting an illuminated placido disc of known proportions off the tear film and comparing this to the imaged reflection. 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 reliable information on corneal topography over a wider corneal area the reflection quality of the placido mires indicates the quality of the tear film 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 reflections from the tear film over time after a blink has been shown to have higher sensitivity, but similar specificity in predicting symptomatic dry eye than fluorescein 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 in neophyte contact lens wearers. This is most commonly done by assessing the tear film break up time (BUT), a measurement of the time which elapses between a patient blinking and their tear film beginning to break up or a subsequent uncontrollable blink. It is often assessed following the instillation of sodium fluorescein dye into the tears and observation with a slit lamp microscope using blue light and a yellow enhancement filter [3]. There is concern that the presence of fluorescein in the tear film will destabilise the tears and for this reason it is preferable to measure tear film non-invasively without first instilling fluorescein [4], [5], [6] This type of tear film measurement is referred to as non-invasive tear break-up time (NITBUT) although it should be noted that changes in meniscus curvature have been observed even with this minimally invasive technique suggesting it is easy to induce minor degrees of reflex tearing [6].
The repeatability of measurements with one of the main subjective devices for assessing NIBUT, the Tearscope (Keeler, Windsor, UK) appear to be more reliable that other techniques such as observations through a slit lamp or of video keratoscope mires, although Tearscope measures are still quite variable [7] and there is considerable interexaminer variability [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 film examination methods and improve comparability of measurements [6].
The Keratograph (OculusOptikgerate GmbH, Wetzlar, German) is the first commercially available device with software (“Tear Film Scan”) which permits an automated, examiner independent technique 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 the Keratograph.
Section snippets
Methods
One hundred consecutive patients with no known anterior eye disease (average age 37 ± 13 years, range 19–67 years; 65 female) were recruited from the staff and patients of a community optometric practice in the North East of England. Consent was obtained after explanation 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
Topography
The average corneal curvature was 7.74 ± 0.29 mm with an average difference between the orthogonal meridians of 0.14 ± 0.15 mm (ARKT measures). On average the MSE as measured by the Keratograph was found to be more positive than the ARKT (MSE difference: +1.83 ± 0.44D, p < 0.001; Fig. 1). However, there was no significant difference in the astigmatic components (differences, J0 = +0.01 ± 0.27D, p = 0.61; J45 = −0.03 ± 0.18D, p = 0.13; Fig. 2). The Keratograph topography repeated measures were similar for MSE
Discussion
Approximately half of current contact lens wearers suffer from dryness and discomfort, particularly towards the end of the day [14]. This inevitably leads to dissatisfaction and possible discontinuation of lens wear. Prior to fitting their patients with contact lenses there are a number of tests available to the practitioner to assess the quality and quantity of tears, to allow advice to be given on an individual's suitability for contact lenses and to recommend the most appropriate modality
Acknowledgement
The Keratograph was kindly loaned to the authors by the Birmingham Optical Group, UK.
References (15)
- et al.
Analysis of the repeatability of tear break-up time measurement techniques on asymptomatic subjects before, during and after contact lens wear
Contact Lens and Anterior Eye
(1998) - et al.
Comparison between Lenstar LS 900 non-contact biometry and OcuScan RXP contact biometry for task delegation
Journal Francais d Ophtalmologie
(2011) - et al.
Demographics of UK contact lens prescribing
Contact Lens and Anterior Eye
(2008) - et al.
Corneal topography: a clinical model
Ophthalmic and Physiological Optics
(1986) - et al.
Tear film stability analysis system: introducing a new application for videokeratography
Cornea
(2004) - et al.
Optimization of anterior eye fluorescein viewing
American Journal of Ophthalmology
(2006) - et al.
A non-invasive instrument for clinical assessment of the pre-corneal tear film stability
Current Eye Research
(1985)
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