Carlos García-Resúa

Accuracy of the new ICare rebound tonometer vs. other portable tonometers in healthy eyes.

Purpose. The ICare (Tiolat Oy, Helsinki, Finland) is a new portable tonometer that measures intraocular pressure (IOP) with a new rebound method, in which a very light probe is used to make momentary contact with the cornea in slow motion. The purpose of this study is to assess the accuracy of the ICare IOP measurements by comparing them against other portable tonometers: Perkins applanation tonometer and Tono-Pen XL digital tonometer (Medtronic Solan, Jacksonville, FL). Methods. Sixty-five young subjects were assessed with each of the tonometers. ICare tonometry was performed first, followed by Perkins applanation tonometry and Tono-Pen XL in a random order. Regression analysis was used to evaluate the relationship between the Perkins tonometer and the remaining tonometers used in this study. Tonometers were also compared by plotting the difference between the methods against the mean. The hypothesis of zero bias was examined by a paired t test and the 95% limits of agreement (LoA) were calculated. Results. ICare and Tono-Pen XL significantly overestimate IOP when compared with Perkins applanation tonometry. The mean of the difference between Perkins and ICare and Perkins and Tono-Pen XL was (mean ± standard deviation) −3.35 ± 2.28 mm Hg and −2.78 ± 2.53 mm Hg, respectively. The 95% LoA between Perkins tonometry and ICare tonometry were between −7.81 and +1.12 and between Perkins tonometry and Tono-Pen XL tonometry between −7.74 and +2.18. Conclusions. Compared with Perkins tonometry, the ICare tonometer allows clinicians to estimate IOP with a portable, rapid, and noninvasive method with similar reliability to that offered by Tono-Pen XL. Clinicians should be aware of the systematic overestimation of IOP with the ICare. Further research is needed to evaluate the performance of rebound tonometry in populations with higher IOP and assess the reliability of this technique in the early detection and follow up of glaucomatous patients.

Determination of corneal volume from anterior topography and topographic pachymetry: application to healthy and keratoconic eyes.

Purpose:  To describe a method to measure corneal volume from topography and pachymetry, and test its clinical use on a sample of healthy human subjects and a case of circumscribed posterior keratoconus.

New software application for clarifying tear film lipid layer patterns.

Purpose: The lipid layer of the tear film limits evaporation during the interblink interval and also affects tear stability. This study was designed to validate a new software application designed to characterize the tear film lipid layer through texture and color pattern recognition. Methods: Using the Tearscope-plus (slit-lamp magnification ×200), the lipid layer was examined in 105 healthy young adults, and interference photographs were acquired with a Topcon DV-3 digital camera. The photographs were classified by a clinician experienced in examining lipid layer patterns (LLPs), and these classifications were used as the reference standard (reference examiner). Next, LLPs were graded using the new software and further by 2 observers (observer 1 and observer 2) with experience in examining the ocular surface. Results: Strong correlation was detected between the categories determined by the new application and reference examiner (Cramer V 0.85–0.93, P < 0.001). The classifications made using the new application and by observer 1 and observer 2 were also consistent although correlation was weaker (Cramer V 0.56–0.87, P < 0.001). For thinner LLPs, greatest correspondence with the reference was observed using the new software (96.6%), whereas the 2 observers showed better agreement when grading thicker patterns. Notwithstanding, agreement between the 2 observers and the reference examiner was good with at least 81% matched classifications. Best agreement (96.2%) was noted between the new method and observers 1 and 2 for recognizing meshwork patterns, whereas observers 1 and 2 showed greatest correspondence when classifying color fringe patterns. Conclusions: The new application can objectively categorize LLPs using the Tearscope-plus.

Automatic classification of the interferential tear film lipid layer using colour texture analysis

The tear film lipid layer is heterogeneous among the population. Its classification depends on its thickness and can be done using the interference pattern categories proposed by Guillon. This papers presents an exhaustive study about the characterisation of the interference phenomena as a texture pattern, using different feature extraction methods in different colour spaces. These methods are first analysed individually and then combined to achieve the best results possible. The principal component analysis (PCA) technique has also been tested to reduce the dimensionality of the feature vectors. The proposed methodologies have been tested on a dataset composed of 105 images from healthy subjects, with a classification rate of over 95% in some cases.

Clinical assessment of the lower tear meniscus height.

Purpose:  Different values of the lower tear meniscus height (TMH) can be obtained depending on the method and technique of measurement employed. This study aimed to assess (1) differences between the absolute (TMH‐A), reflex (TMH‐R) and fluorescein (TMH‐F) lower tear meniscus heights, (2) differences between the central (TMH‐R), nasal (TMH‐RN) and temporal (TMH‐RT) reflex lower tear meniscus heights and (3) the amount of fluorescein present in the lower tear meniscus, 5 min after fluorescein instillation (TMH‐FV).

Accuracy and repeatability of a new tono-pachymeter for measuring central corneal thickness.

Objectives: The recently developed noncontact tonopachymeter Tonopachy NT-530 P provides intraocular pressure values corrected for central corneal thickness (CCT). The purpose of this study was to assess the accuracy and repeatability of its CCT measurements. Methods: The CCT measurements were obtained in 64 right eyes of 64 young healthy subjects using the Orbscan corneal topography system followed by the Tonopachy and then by ultrasound pachymetry (UP). Another sample of 31 subjects was used to test the repeatability of the tonopachy measurements in 2 separate sessions 1 week apart. To compare the tonometers and determine intersession repeatability for the tonopachymeter, differences in the readings provided by pairs of the instruments or obtained in the two sessions were plotted against mean differences. The hypothesis of zero bias was examined by a paired t-test. The coefficient of repeatability was calculated as the 95% limits of agreement (LoAs) of differences between the 2 sessions. Results: Measurements made using the three instruments were significantly correlated (P<0.001). Mean CCTs (±SD) measured using the Tonopachy, Orbscan (acoustic factor set at 0.92) and ultrasound pachymeter were 530.42±34.96, 526.73±39.53, and 550.69±37.26 &mgr;m, respectively. The differences between modalities (±95% LoAs) were −3.68±24.36 for Orbscan versus Tonopachy, 20.66±14.69 for UP versus Tonopachy, and 23.95±24.21 for UP versus Orbscan. The coefficient of repeatability for the tonopachymeter was ±15.11 &mgr;m. Conclusions: The Tonopachy offers similar CCT measurements to those provided by conventional pachymeters with good repeatability.

Efecto de la instilación del colicursi® anestésico doble (tetracaína 0,1% y oxibuprocaína 0,4%) sobre el espesor corneal central y paracentral

OBJECTIVE To study the effect of 1 drop of combined topical anaesthesia (tetracaine 0.1% and oxybuprocaine 0.4%) on central corneal thickness (CCT) values and at 2.5 mm from the corneal centre in nasal, temporal, superior and inferior hemi meridians, monitored by Orbscan over a period of 16 minutes. MATERIALS AND METHODS The corneal thickness of 12 right eyes of 12 young healthy men was determined using the Orbscan Topography System. Values were determined at the centre and paracentral regions 2.5 mm from the centre every 2 minutes for 16 minutes before and after the administration of 1 drop of double anaesthetic Colircusi which contains tetracaine 0.1% and oxybuprocaine 0.4%. RESULTS There was no obvious trend of central and paracentral corneal thickness value change before and after administration of Colircusi (paired ANOVA, p>0.05). Although corneal thickness variation was not statistically significant, higher differences were observed at the 6 minute time-point for CCT and at 8 minutes for nasal paracentral corneal thickness. CONCLUSIONS One drop of double anaesthetic Colircusi with tetracaine 0.1% and oxibuprocaine 0.4% does not produce any significant change in central corneal thickness or in paracentral regions 2.5 mm from the centre (nasal, temporal, superior and inferior hemi meridians).

Analysis of parameters for the automatic computation of the tear film break-up time test based on CCLRU standards

Dry eye syndrome is affecting a remarkable percentage of population. The prevalence is 10-15% of normal population, and 18-30% of contact lenses users. The break-up time (BUT) is a clinical test used for the diagnosis of this disease. In this work, we perform an analysis of parameters for a global and a local automatic computation of the BUT measure, based on criteria of specificity and sensitivity. We have tested our methodology on a dataset composed of 18 videos annotated by 4 different experts. The local analysis preserves the results of the global approach providing useful additional information about the break-up tear zone.

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.

White light interferometry to characterize the hydrogel contact lens surface

Purpose:  The aim of this study was to characterize, qualitatively and quantitatively, the surface morphology of four unworn conventional hydrogel contact lenses (Omafilcon, Hioxifilcon‐based, Nefilcon A and Ocufilcon B) by White Light Optical Profiling (WLOP). WLOP is an ideal technique for sampling larger areas as well as for higher measurement speed compared with other topography techniques used in contact lens studies.