Clinical evaluation of the Oculus Keratograph

doi:10.1016/j.clae.2012.04.002

Contact Lens and Anterior Eye

Volume 35, Issue 4, August 2012, Pages 171-174

https://doi.org/10.1016/j.clae.2012.04.002 Get rights and content

Abstract

Aim

To determine the validity and reliability of the measurement of corneal 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 Scan 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 significantly flatter corneal curvatures than the ARKT (MSE difference: +1.83 ± 0.44D), but was repeatable (p > 0.05). Keratograph NITBUT measurements were significantly 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 Keratograph measures the first 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).

Conclusions

The Keratograph requires a calibration off-set to be comparable to other keratometry devices. Its current software detects very early tear film changes, recording significantly lower NITBUT values than conventional subjective assessment. Adjustments to instrumentation software have the potential to enhance the value of Keratograph objective measures in clinical practice.

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.

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To examine the changes caused by fluorescein in the tear film by analyzing the qualitative parameters such as breakup location and also detailed quantitative parameters. Methods: After determining the break-up time (BUT) value and breakup locations by the Non-invasive break-up time (NI-BUT) method, we re-evaluated the changes in the tear film stained with fluorescein using the topographical method. We called the topographic evaluation of the tear film stained with fluorescein as the Hybrid-BUT test. The results for the parameters obtained for each participant by the NI-BUT and Hybrid-BUT tests were compared.
Our study was conducted with 82 participants aged between 18 and 58 years (mean age 34.1 ± 11.1). The mean first break-up time value (BUT₁) was 4.1 ± 2.7 s on the NI-BUT test versus 5.1 ± 3.2 s on the Hybrid-BUT test (p = 0.029). The mean average of all break-up time values (BUT_Avg) for each participant was 7.2 ± 3.2 s on the NI-BUT test versus 8.4 ± 3.1 s on the Hybrid-BUT test (p = 0.004). After dividing the corneal surface into quadrants of 90°, there was no significant difference in the comparison of the locations of the first breakup (QUAD_{(First breakup)}), the second breakup (QUAD_{(2nd breakup)}) and the third breakup (QUAD_{(3rd breakup)}) between the two tests (p>0.05).
Fluorescein affects quantitative values rather than qualitative parameters in tear film. We observed that the change caused by fluorescein in tear film break-up time could be detected objectively and in a documented manner using Hybrid-BUT test.
Diagnostic Instruments
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This chapter reviews the equipment needed by contact lens practitioners to appropriately undertake the initial assessment, fitting and follow-up care of the contact lens patient. It includes equipment to examine the quality and quantity of the tear film, meibomian glands, cornea, conjunctiva and lids. Multifunctional instruments that are able to undertake several functions, digital imaging of the anterior segment, ocular thermography, corneal sensitivity, pachymetry and equipment to assist with myopia control are also covered.
Changes caused by fluorescein in tear film by hybrid break-up time test- part one; on quantitative values
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To examine the effect of fluorescein on the tear film by measuring tear break-up time (BUT).
In this prospective study, after determining the natural BUT value of the tear with the non-invasive break-up time (NI-BUT) method, we re-evaluated the changes in the tear film stained with fluorescein using the topographical method. The topographic evaluation of tears stained with fluorescein was called as Hybrid-BUT (H-BUT) test. The first BUT (BUT₁), the second BUT (BUT₂), the third BUT (BUT₃), the fourth BUT (BUT₄), and the fifth BUT (BUT₅) values of each participant's NI-BUT and H-BUT tests were compared.
The present study was conducted with 82 participants. Although the mean BUT₁ value was 4.1 ± 2.7 s in the NI-BUT test, it was 5.1 ± 3.2 s in the H-BUT test (p = 0.029). The mean BUT₂ value was 5.0 ± 3.0 s in the NI-BUT test, and 6.2 ± 3.3 s in the H-BUT test (p = 0.029). The mean BUT₃ value in the NI-BUT test was 5.8 ± 3.4 s, and 7.2 ± 3.7 s in the H-BUT test (p = 0.021). The mean BUT₄ value in the NI-BUT test was 6.2 ± 3.4 s and 7.9 ± 3.9 s in the H-BUT test (p = 0.009).
Fluorescein causes changes in the break-up time test, and depending on this, in the tear film pattern. These changes can be compared and detected quantitatively and objectively of the fluorescein-stained tear film with the NI-BUT test and the topographic devices by using the H-BUT test.
Tear film interferometry assessment after intense pulsed light in dry eye disease: A randomized, single masked, sham-controlled study
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DR-1 (Kowa, Nagoya, Japan) was performed non-invasive TFLL quality with the Yokoi DE severity grading system; grade 1: somewhat grey colour, uniform distribution; grade 2: somewhat grey colour, non-uniform distribution; grade 3: a few colours, nonuniform distribution; grade 4: many colours, nonuniform distribution; TFLL interferometry [11]. NITBUT: Keratograph 5 M (Oculus, Germany) is a clinical instrument that uses an infrared light source of wavelength 880 nm to assess the ocular surface, tear film and meibomian glands (http://www.oculus.de/)[31]. During each assessment time point, non-invasive first tear film breakup time using the Keratograph 5 M (Oculus, Germany) topographer was measured three times consecutively and the median value was recorded.
Inadequate meibomian glands (MGs) secretion can lead to dry eye signs and symptoms. Tear film lipid layer (TFLL) secreted by MGs protects and prevents rapid evaporation of tear film. The purpose was to assess TFLL alteration and function in patients with evaporative dry eye (EDE) using tear interferometry after optimal pulse light technology (OPT) intense pulsed light (IPL).
This prospective randomized examiner-masked sham- controlled study included 86 participants (142 eyes) with DED. IPL or sham procedure was performed on day 0, 21, and 42. Ocular Surface Disease Index (OSDI), non-invasive breakup time (NITBUT), interferometric fringe pattern determined TFLL quality, fluorescein staining (FS), and meibum gland (MG) were assessed at day 0, 21, 42 and 3-month.
At 3-month, TFLL, NITBUT, MG drop-out, MG quality, MG expressibility, FS and OSDI improved significantly (P < 0.05) in the IPL group, while the sham group had no significant improvements. Except for Meibo-score and FS, all parameters significantly correlated with the improvement in TFLL following IPL treatment. Additionally, artificial tears usage was significantly less in the IPL group from D-42 onwards.
IPL treatment demonstrated the ability to improve TFLL quality and clinically reduced sign and symptoms of DED thereby reducing the frequency of artificial tears use.
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The use of swimming goggles (SG) has demonstrated to alter different ocular parameters, however, the impact of wearing SG on the tear film stability remain unknown. The main objective of this study was to determine the short-term effects of wearing SG on tear film surface quality break-up time (TFSQ-BUT).
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TFSQ-BUT was significantly reduced while SG wear in comparison to the baseline measurement (4.8 ± 4.5 s vs. 8.8 ± 6.9 s; corrected p-value = 0.017, d = 0.57, mean difference = 4.0 [0.6, 7.3]; 45% reduction). Immediately after SG removal, TFSQ-BUT rapidly recovered baseline levels (8.2 ± 5.9 s vs. 8.8 ± 6.9 s; corrected p-value = 0.744). The impact of wearing SG on TFSQ-BUT were independent of the gender of the participants (p = 0.934).
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Clinical evaluation of the Oculus Keratograph

Abstract

Aim

Method

Results

Conclusions

Introduction

Section snippets

Methods

Topography

Discussion

Acknowledgement

Contact Lens and Anterior Eye

Journal Francais d Ophtalmologie

Contact Lens and Anterior Eye

Corneal topography: a clinical model

Ophthalmic and Physiological Optics

Tear film stability analysis system: introducing a new application for videokeratography

Cornea

Optimization of anterior eye fluorescein viewing

American Journal of Ophthalmology

A non-invasive instrument for clinical assessment of the pre-corneal tear film stability

Current Eye Research