Hugo Pena-Verdeal

Correlation between tear osmolarity and tear meniscus.

Purpose To examine the relationship between tear meniscus height (TMH) and subjective meniscus grading (subjective tear meniscus [TM]) with tear osmolarity. Methods Tear osmolarity measurements (using TearLab) and digital images of the TM were obtained in 177 consecutive patients undergoing an eye examination at our optometry clinic (Universidad de Santiago de Compostela, Spain) who fulfilled the study’s inclusion criteria. Participants were also administered the McMonnies and Ocular Surface Disease Index questionnaires for the detection of dry eye disease. The lower TM was videotaped by a digital camera attached to a slit lamp in its central portion without fluorescein instillation. After the study, a masked observer extracted an image from each video and measured the TMH using open source software (NIH ImageJ). Subsequently, the masked observer subjectively graded the appearance of each meniscus. For statistical analysis, subjects were stratified by age and by dry eye symptoms as indicated by their scores in the two questionnaires. Results In the whole study population, a significant relationship was observed between osmolarity and TMH (r = −0.41, p < 0.001) and osmolarity and subjective TM (r = 0.35, p < 0.001). A cluster analysis revealed similar correlations when subjects were stratified by age or dry eye symptoms, these correlations being more pronounced in older and more symptomatic subjects. Objective TMH measurements and subjective meniscus quality were also correlated (r = −0.75, p < 0.001). Conclusions Osmolarity and both objective TMH measurements and subjective interpretation of the meniscus showed high correlation, especially in older symptomatic subjects.

Reliability of the non-contact tono-pachymeter Tonopachy NT-530P in healthy eyes

Non‐contact Tonopachy NT‐530P (Nidek Co., LTD) provides intraocular pressure (IOP) and central corneal thickness (CCT) measurements. This study assesses the reliability and repeatability of its IOP measurements in young healthy adult subjects.Background Non-contact Tonopachy NT-530P (Nidek Co., LTD) provides intraocular pressure (IOP) and central corneal thickness (CCT) measurements. This study assesses the reliability and repeatability of its IOP measurements in young healthy adult subjects. Methods IOP was determined in the right eye of 64 healthy patients using Tonopachy followed by the Canon TX-10 non-contact and Goldmann applanation (GAT) tonometers. Tonopachy IOP measurements were corrected (Tonopachy-C) or not (Tonopachy-NC) by the instrument for central corneal thickness. Central corneal thickness measurements provided by Tonopachy were also used to correlate (Pearsons coefficient) central corneal thickness with the GAT and Canon TX-10 IOPs. Repeatability of Tonopachy and GAT was assessed in the right eye of 31 subjects in two separate sessions one week apart. Differences between pairs of instruments and between sessions were determined using Bland–Altman plots. The coefficient of repeatability was calculated as the 95% limits of agreement (LoA) of differences between the two sessions. Results Tonopachy-NC, Tonopachy-C, Canon TX-10 and the Goldmann tonometers showed a mean IOP of 14.62, 15.64, 15.02 and 14.68 mmHg, respectively. Tonopachy-NC and Canon TX-10 readings did not differ significantly from the Goldmann (p > 0.05), with close agreement with both tonometers (GAT versus Tonopachy-NC: -3.84 to 3.96 mmHg; Goldmann versus Canon TX-10: -4.75 to 4.07 mmHg). Tonopachy-C readings differed significantly from Goldmann (mean difference -0.96 mmHg, p = 0.001, LoA from -5.09 to 3.17). Coefficients of repeatability were ± 3.70, ± 3.14 and ± 3.33 mmHg for GAT, Tonopachy-NC and Tonopachy-C, respectively. Central corneal thickness measured with Tonopachy was 530.42 ± 34.96 μm. There was a significant correlation between central corneal thickness and IOP for all tonometers except Tonopachy-C. Conclusions Reasonable agreement was observed between the Goldmann and Tonopachy. This instrument provides reliable and repeatable IOP measurements not influenced by central corneal thickness. The Tonopachy-NC and Canon TX-10 offer similar reliability compared to the Goldmann applanation tonometer in a young normotensive population.

Defining the Optimal Region of Interest for Hyperemia Grading in the Bulbar Conjunctiva

Conjunctival hyperemia or conjunctival redness is a symptom that can be associated with a broad group of ocular diseases. Its levels of severity are represented by standard photographic charts that are visually compared with the patients eye. This way, the hyperemia diagnosis becomes a nonrepeatable task that depends on the experience of the grader. To solve this problem, we have proposed a computer-aided methodology that comprises three main stages: the segmentation of the conjunctiva, the extraction of features in this region based on colour and the presence of blood vessels, and, finally, the transformation of these features into grading scale values by means of regression techniques. However, the conjunctival segmentation can be slightly inaccurate mainly due to illumination issues. In this work, we analyse the relevance of different features with respect to their location within the conjunctiva in order to delimit a reliable region of interest for the grading. The results show that the automatic procedure behaves like an expert using only a limited region of interest within the conjunctiva.

Diurnal variations in tear film break‐up time determined in healthy subjects by software‐assisted interpretation of tear film video recordings

This study was designed to examine diurnal variations in tear film break‐up time (BUT) and maximum blink interval (MBI) and to assess two different ways of calculating these variables on video recordings of the BUT test interpreted with the help of especially designed software. The repeatability of interpreting BUT video recordings was also addressed.

A Novel Framework for Hyperemia Grading Based on Artificial Neural Networks

A common symptom of several pathologies is hyperemia, that occurs when a certain tissue has an abnormal hue of red. An increase of blood flow causes the engorgement of blood vessels, which produces the coloration. Hyperemia is an important parameter that specialists take into account when diagnosing diseases such as dry eye syndrome or problems derived from contact lenses wearing. In this work, we propose an automatic methodology to measure the hyperemia level of the bulbar conjunctiva. This methodology emphasizes the transformation from the extracted features to grading scales, using artificial neural networks for the process.

Interobserver variability of an open-source software for tear meniscus height measurement

PURPOSE Different values of the lower tear meniscus height (TMH) can be obtained depending on the method and technique of measurement employed. The aim of this study was to analyse the interobserver variability of a method for measuring TMH by using an open source software. MATERIAL AND METHODS On a group of 176 subjects, two videos of the central lower tear meniscus, first under slit-lamp illumination and ten minutes later under Tearscope illumination, were generated by a digital camera attached to a slit-lamp. Images were extracted from each video by a masked observer. Two further observers measured in a masked and randomized order the TMH in each illumination method by using an open source software based on Java (NIH ImageJ). TMH was measured from the lower lid to the upper limit of the tear meniscus for both slit-lamp (TMH-SL) and Tearscope (TMH-Tc) illumination methods. Subsequently, in different order, observers assigned a four-grading and a healthy/abnormal subjective classification to each central meniscus. RESULTS No significant differences were found between the TMH measurements obtained by both investigators in slit-lamp or Tearscope image datasets (t-test; both p≥0.136). When comparing TMH measurements stratified by grade, only interobserver significant differences were observed for grades 3 and 4 with silt-lamp (t-test; both p≤0.009). Significant differences on TMH results between subjective subgroups were observed for both illumination techniques (ANOVA, all p≤0.045). CONCLUSION This study showed a useful tool to objectively measure TMH by photography.

Accuracy of a Freezing Point Depression Technique Osmometer.

Purpose The purpose of this study was to examine the precision and accuracy of the Fiske 110 Osmolarity System under different protocols to determine the possible applications of this device in tear film research and clinical practice. Methods Three separate studies were performed. In the first, Fiske 110 measurements were made on undiluted and diluted (1:1, 1:4, and 1:9 dilutions) standard samples of different osmolarity values: 50, 290, and 850 mOsm/kg and 297 and 338 mOsm/L. In the second study, measurements were made on different types of contact lens care solutions. Finally, in an agreement study, measurements were made in two sets of 60 subjects to compare TearLab versus Fiske 110 (using both 2- and 4-&mgr;L tear sample). Results Although osmolarity measurements for undiluted solutions differed statistically from reference standard values, all biases were in the tolerance range proposed by the manufacturer except for the 850-mOsm/kg solution. No significant differences from reference osmolarity values were observed for the 1:1 and 1:4 diluted 297- and 338-mOsm/L H2O solutions, respectively, although all diluted solutions showed a possible bias out of the range provided. Osmolarities for the soft contact lens solutions fell within the range 293 to 309 mOsm/kg with the exception of Opti-Free Express (225 mOsm/kg). In the agreement study, significant differences were observed between measurements obtained using the TearLab and both Fiske 110 procedures, although the Fiske 110 (4 &mgr;L) procedure was closer to the TearLab than the Fiske (2 &mgr;L) procedure. Conclusions For undiluted solutions, the Fiske 110 shows good performance, making it a useful device for osmolarity measurements in lens care solutions or eye drops. A worse performance was observed for more diluted standard solution samples. When testing diluted samples, performance was acceptable for osmolarity values close to tear values.

Break-Up Analysis of the Tear Film Based on Time, Location, Size and Shape of the Rupture Area

The Break-Up Time test (BUT) evaluates the quality and stability of the tear film. It is used for the diagnosis of the dry eye syndrome, a common disorder of the tear film, affecting a significant percentage of the population. This work describes a fully automatic methodology to compute the time in which the break-up occurs and to analyze the rupture zone. This analysis provides useful quantitative and qualitative information for the clinical practice about the location, size and shape of the break-up areas.

Computational Approach for Measuring the Tear Film Break-Up Time in an Unsupervised Manner

Dry eye syndrome is a common disorder of the tear film, affecting a significant percentage of the population. The Break-Up Time (BUT) is a clinical test used for the diagnosis of this disease. In this research, it is proposed an automatic methodology to evaluate the BUT test. This methodology locates the different measurement areas from a video of the tear film, extracts the Region Of Interest (ROI) and performs the BUT test in each measurement area. Furthermore, it is independent of some specific features of each video such as the eye size, the intensity variation, or the starting point of the measurement frame sequence. This methodology has been tested on a dataset composed of 18 videos that have been annotated by four different experts. The average difference between the automatic measurement and the experts’ measures is on the acceptable range considering the high inter-observer variance.

Interobserver and intraobserver repeatability of lipid layer pattern evaluation by two experienced observers

The lipid layer plays a major role in limiting evaporation of the tear film. Based on interference phenomena, there is a test directed to lipid layer pattern (LLP) evaluation, but is affected by subjective interpretation of the patterns. The aim of this study is to compare the LLP evaluation between two experienced observers on a group of healthy patients. Furthermore, the observers re-evaluated the same images in order to check their individual repeatability. LLP was examined using a Tearscope-plus (Keeler, Windsor, UK) attached to a slit lamp. Tear film was recorded by a Topcon DV-3 digital camera video and LLP images were captured. This yielded 124 LLP images that were categorized (based on Guillon’s schema) by two expert observers in two sessions separated by one month. Interobserver repeatability and intraobserver repeatability between both sessions were studied by using Cohen’s kappa coefficient. Comparing LLP categorization between both observers, Cohens kappa coefficient was 0.615 and 0.633 for first and second session, respectively. When comparing LLP categorization by the same observer between both sessions, Cohens kappa coefficient was 0.770 and 0.812 for Observer 1 and Observer 2. These results indicate substantial correlation in all cases [range of 0.61–0.80]. The most frequent misinterpretations were between open and closed meshwork and Wave and closed meshwork patterns. Although substantial correlation was found between categorizations of experienced observers, misinterpretation of the patters may appear even in the same observer. Some misinterpretations between adjacent patterns could be palliated by including intermediate patterns between those categories.