Automatic assessment of tear film break-up dynamics.

Dry eye syndrome is a common disorder of the tear film which affects a remarkable percentage of the population. The Break-Up Time (BUT) is a clinical test used for the diagnosis of this disease, which computes the time the first tear film break-up appears. This work describes a fully automatic methodology to compute the BUT measurement and evaluate the break-up dynamics until the final blink. This analysis provides useful additional information for the assessment of tear film stability.

[Effect of double anaesthetic Colicursi (tetracaine 0.1% and oxybuprocaine 0.4%) on central and paracentral corneal thickness]. / 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).

[Corneal asphericity in a young adult population. Clinical implications]. / Asfericidad corneal en una población de adultos jóvenes. Implicaciones clínicas.

PURPOSE: To determine the relevance of the different ocular optical components in the refractive state of young adults, paying special attention to the corneal topography represented by the asphericity value. SUBJECTS AND METHODS: Corneal topographies and ultrasonic biometries were obtained from 109 university students with different refractive errors (spherical equivalent range: +3.25 D to -11.00 D). A regression study was performed in order to establish the relationships between corneal asphericity and refractive error, as well as other ocular optical components related to the emmetropization mechanism of the eye. RESULTS: The mean asphericity values were -0.23 (SD 0.08, range: -0.42 to -0.03). All the values correspond to the mathematical description of the prolate ellipse, most commonly accepted for the normal human cornea. The statistical correlation between asphericity and equivalent refractive error was not significant, but a significant correlation was found for the asphericity with respect to the radius of curvature, vitreous chamber depth and axial length. CONCLUSIONS: 1) The asphericity values support the generalised morphology of the prolate cornea as the standard. The influence of this configuration on the contact lens fit, refractive surgery or the visual performance of the eye are discussed. 2) Results suggest that, although a relationship between axial length and corneal topography actually exists, it is not likely that the latter has implications for the emmetropization mechanisms which determine the refractive state of the adult eye.

[Changes in axial length/corneal radius ratio (AL/CR) according to refractive state of the eye. Relationship with ocular components]. / Variación de la ratio longitud axial/radio corneal (LA/RC) con el estado refractivo ocular. Relación con los componentes oculares.

PURPOSE: Determination of the role of the axial length/corneal radius ratio (AL/CR) in the refractive state and investigation of its relationship with the ocular optical components: AL, CR, anterior chamber depth (ACD), crystalline lens thickness (CT) and vitreous chamber depth (VCD). METHODS: The RE (right eye) of 193 University students 22.27 (SD 3.24) years, with different refractive errors (spherical equivalent range: +3.00 D to -11.00 D), being divided into: emmetropes, hyperopes and myopes (low, moderate and high). The ACE, the CT, the VCD and the AL were measured by ultrasonography (unidimensional echography); and the mean CR by videokeratoscopy. RESULTS: The value of AL/CR obtained was 2.98 (SD 0.69) for emmetropes, 2.89 (SD 0.87) for hyperopes, 3.01 (SD 0.07) in low myopias, 3.10 (SD 0.11) in moderate myopias and 3.23 (SD 0.12) in high myopias. The AL/CR ratio showed a higher correlation with the refractive error. Besides, all the refractive groups were observed to have lower CE values as the AL/CR increased. This tendency is statistically significant in hyperopes, emmetropes and low myopes; and is not in moderate and high myopias. All the study groups could be observed to have a positive and statistically significant correlation between AL/CR and ACD. CONCLUSION: The ratio AL/CR is the most important parameter and the best predictor of the refractive state of the human eye. It provides important information on how best to determine the degree of emmetropization given by the crystalline, decreasing its power and the ACD in concordance with the LA. A value for the ratio AL/CR above 3.00 could be considered as a risk factor for the development of myopia in emmetropic eyes.

Accuracy and precision of EyeSys and Orbscan systems on calibrated spherical test surfaces.

BACKGROUND: It is important to know how well the surface topography can be measured with current devices for corneal topographic analysis. There are several applications that need an accurate and precise method to measure corneal shape and variations, such as the effect of contact lens wear and the different refractive surgery techniques. PURPOSE: The aim of this study is to compare the accuracy and reproducibility of the measurement of the central curvature on calibrated steel balls using the EyeSys videokeratoscope and the Orbscan corneal topography system. METHODS: The videokeratoscope (EyeSys Corneal Analysis System 2000, version 3.1) and the Orbscan corneal topography system (Orbscan II version 3.0) were used by four trained investigators to measure a series of five uniform and calibrated test surfaces with known radius of curvature ranging from 6.13 to 9.00 mm. RESULT: No statistically significant difference was found between the videokeratoscope and Orbscan systems in relation to accuracy or precision. The 95% confidence limits showed a close agreement between both instruments. The mean bias was less than +/-0.05 mm for both devices. The precision of the instruments was found to be similar. CONCLUSION: The EyeSys seems to measure more accurately, but the accuracy of the Orbscan was also acceptable, suggesting that both instruments are accurate and precise enough for research and clinical purposes. However, further studies of accuracy and repeatability of topographical measurements on human eyes generated by different topographers are necessary.

Benefits at 3 yrs of an asthma education programme coupled with regular reinforcement.

The benefits at 3 yrs of an asthma self-management education programme coupled with educational reinforcement were assessed at follow-up visits in 63 adults with chronic asthma. Changes in asthma-related morbidity parameters, lung function and use of different classes of drugs before intervention and after 1, 2 and 3 yrs of the asthma education programme were compared using Friedman one-way analysis of variance. Improvements in the number of days off work or school, general practitioner consultations, admissions to emergency services, hospital admissions and nocturnal awakenings, as well as increases in forced expiratory volume in one second (FEV1), were significant. Comparison of data obtained at 1 yr and 2-3 yrs showed significant differences in the number of asthma-associated sleep disruptions, days off work or school and unscheduled visits to the general practitioner, as well as FEV1, but significant differences between the data obtained at 2 and 3 yrs were not observed. The percentage of patients using oral steroids had decreased significantly at 3 yrs. In adults with chronic asthma, an asthma self-management education programme coupled with educational reinforcement was effective at decreasing asthma morbidity, improving lung function and decreasing consumption of oral steroids.

Rigid gas permeable contact lens and corneal topography.

We investigated the effect of high Dk daily wear rigid gas permeable contact lenses on corneal topography. Eight young myopic subjects wore hard contact lenses for 21 days. Corneal topography was monitored using the EyeSys system. It was measured every day during the next 21 days after the fitting. We recorded the corneal radius of curvature at 16 peripheral points approximately 1, 2, 3 and 4 mm along the four principal meridians (nasal, superior, inferior and temporal). Our study showed that daily wear RGP Forum 210 does not produce significant alterations of the corneal curvature as a function of time.

Further information on the knowledge of topographical corneal thickness.

Central and peripheral corneal thickness has been used increasingly to obtain information about physiologic and clinical conditions of the cornea. In this study, a new method based on ultrasonic pachometry for topographical corneal thickness measurement is described. Results suggest that the technique is reliable for clinical determination of global corneal thickness. Measurements taken by one observer on different sessions (intersession variation) and measurements taken by different observers (interobserver variation) are not significant different (p = 0.586 and 0.273, respectively). This new ultrasound topographical pachometric method can be considered a useful tool for determination of topographical corneal thickness. It has implications for the use of topographical ultrasonic pachometry in contact lenses research, refractive surgery, and management of different pathologic conditions.