Manuel Rubiño

Objective measurement of dental color for age estimation by spectroradiometry

Age-related changes in tooth color have been described previously, however, the use of dental color for age estimation in forensic odontology has been limited due to the difficulty of measuring color objectively. This study presents an objective method for determining dental color to estimate the age of an individual. Dentine color in 250 teeth from patients ranging in age from 10 to 89 years was determined by spectroradiometry. Color measurements were performed as suggested in the CIE 1931 (International Commission on Illumination). Chromaticity coordinates (x, y, z), luminance (Y), whiteness index (WIC, Z%, WIC) and yellowness index (YI) were obtained. Correlations between these colorimetric variables and aging were established by linear regression analyses. All the variables fit the mathematical model with correlation coefficients ranging from 0.53 to 0.75. This method of color measurement produced an expected associated error of calibration averaging 13.7 years about the mean estimated values, at a 70% level of confidence. Two different multiple regression models for dental age estimation were tested, and variables that made the greatest contributions to age calculation were identified. To determine the effect of postmortem interval on tooth color and its influence in age estimation, 37 teeth obtained from human skeletal remains buried during an interval ranging from 21 to 37 years were also studied. In this material, the correlation between age and dental color measured by spectroradiometry was weaker than in fresh extracted teeth. It is concluded that determination of dentine color by spectroradiometry is a potentially useful objective method to estimate age in forensic studies in combination with other methods.

Influence of the Luminance and Opponent Chromatic Channels on Stereopsis with Randomdot Stereograms

The present work examines the relationship between random-dot stereograms (via the disparity range parameter) and color-vision mechanisms (via the luminance channel and red-green and tritan directions at isoluminance). The results clearly indicate that the variations in the stereograms along red-green confusion lines contribute to stereopsis. Stereoscopic perception depends on spatial information for stereograms generated with variations along tritan confusion lines. For observers who perceive stereopsis via tritan directions, the results show a gradation in the disparity range, with the disparity range for stereograms generated by luminance variations being greater than for stereograms generated in red-green directions; the latter range is, in turn, greater than for stereograms generated along tritan directions.

Comparative analysis of techniques for measuring the modulation transfer functions of charge-coupled devices based on the generation of laser speckle

Two methods for measuring the modulation transfer function (MTF) of a charge-coupled device (CCD) that are based on the generation of laser speckle are analyzed and compared. The method based on a single-slit aperture is a quick method, although the measurements are limited to values of less than the Nyquist frequency of the device. The double-slit method permits the measurement of values of as much as some 1.8 times the Nyquist frequency, although it is a slower method because of the necessity to move the CCD. The difference between the MTF values obtained with the two methods is less than 0.1 in magnitude; the root-mean-square error between the two curves is 0.046 (4.6%).

Changes in Stereoscopic Depth Perception Caused by Decentration of Spectacle Lenses

The effect that decentered spectacle (ophthalmic) lenses exert on depth perception has been studied, evaluating stereopsis through the disparity range (maximum horizontal disparity) for random-dot stereograms (RDS). The results show that variations in fusional convergence due to increments of decentration can diminish the stereopsis in observers, reducing the region within which stereoscopic correspondence can take place. Decreases in disparity ranges were found for vertical and horizontal prismatic effects, although the prismatic effect necessary for this was less in the vertical case. A decreased disparity range has also been confirmed with figural-stimuli stereograms and using prisms for generating the prismatic effects.

Prevalence of Myopia in an Adult Population of Two Different Ethnic Groups in the Ecuadorian Amazon

PurposeTo determine the prevalence of myopia in the adult populations of two different ethnic communities in the Ecuadorian Amazon.MethodsRefraction with retinoscopy after cycloplegia was performed for 507 Naporuna (an ethnic group indigenous to the jungles of the Ecuadorian Amazon) and for 776 settlers (white-mestizos from the Andes, now living in the Amazon and working for the petroleum industry). Ages ranged from 18 to 45 years. All subjects had little or no formal education.ResultsThe prevalence of myopia was 4.7% among the Naporuna and 5.5% among the settlers; the prevalence of hyperopia was higher, at 17.8% and 36.0%, respectively.ConclusionsThe prevalence of myopia in the two communities studied agrees with the results of other studies showing a low prevalence of myopia among groups with low levels of formal education or groups living a nonurban lifestyle. Jpn J Ophthalmol 2004;48:163–165

Discomfort glare indices: a comparative study

From the luminance distribution measured with a stereoluminancemeter we have studied the variation in the principal indices of discomfort glare while considering the orientation of the line of vision of the observer and the limiting luminance of the glare source. This method provides the ideal orientation for the observer in a lighted environment, minimizes the detrimental effects of glare, and determines the reliability of the indices calculated for discomfort glare.

Optical characterization of ophthalmic lenses by means of modulation transfer function determination from a laser speckle pattern

A method is presented for measuring the modulation transfer function of ophthalmic lenses by use of the generation of laser speckle with an integrating sphere. The measurements are performed with a rectangular double-slit aperture positioned at the output port of the integrating sphere. The distance between the lens and the detector determines the spatial frequency being tested; therefore high frequencies are tested close to the lens and low frequencies are tested far away from the lens. We can conclude that the double-slit method can be a versatile technique for comparing the optical quality of ophthalmic lenses from different makers.

Comparison of spectacle-lens optical quality by modulation transfer function measurements based on random-dot patterns

We present a method for comparing the optical quality of spectacle lenses based on determining the modulation transfer function (MTF) using random-dot patterns. Furthermore, we determine the precision of the method under repeatability conditions of measurement. The experimental device is composed of a laptop computer in which the LCD monitor presents the random-dot pattern, a liquid-crystal tunable filter, the lens under test, and a charge-coupled device detector connected to its control card installed in another computer. The method proposed has major advantages: the lenses can be characterized at different wavelengths; no additional sources to illuminate the pattern are required, the monitors lighting source itself is used; and the characteristics of the pattern can be quickly and easily modified, as we install the control software in the laptop computer. We analyze three spherical spectacle lenses (+5 D) from different manufacturers and, in terms of MTF, the greatest difference found between them is 13.7%. The uncertainty associated with this method falls within the range of 0.001 and 0.06. Given the low uncertainty values, differences found between the lenses are significant. Therefore, the method proposed is a versatile and quick technique to distinguish the optical quality of spectacle lenses from different manufacturers.

Measurements of scattering anisotropy in dental tissue and zirconia ceramic

Knowledge of the optical properties of biological structures is useful for clinical applications, especially when dealing with incoming biomaterials engineered to improve the benefits for the patient. One ceramic material currently used in restorative dentistry is yttrium cation-doped tetragonal zirconia polycrystal (3Y-TZP) because of its good mechanical properties. However, its optical properties have not been thoroughly studied. Many methods for the determination of optical parameters from biological media make the assumption that scattered light is isotropically distributed over all angles. Nevertheless, real biological materials may have an angular dependence on light scattering, which may affect the optical behaviour of the materials. Therefore, the recovery of the degree of anisotropy in the scattering angular distribution is important. The phase function that represents the scattering angular distribution is usually characterized by the anisotropy coefficient g, which equals the average cosine of the scattering angle. In this work, we measured angularscattering distributions for two zirconia ceramic samples, pre-sintered and sintered, with similar thicknesses (0.48 mm and 0.50 mm, respectively) and also for a human dentine sample (0.41 mm in thickness). The samples were irradiated with a He-Ne laser beam (λ = 632.8 nm) and the angular-scattering distributions were measured using a rotating goniometer. The g values yielded were: -0.7970 ± 0.0016 for pre-sintered zirconia, -0.2074 ± 0.0024 for sintered zirconia and 0.0620 ± 0.0010 for dentine. The results show that zirconia sintering results in optical behaviour more similar to those of dentine tissue, in terms of scattering anisotropy.

Retinal-Image Quality and Night-Vision Performance after Alcohol Consumption

Purpose. To evaluate the influence of alcohol consumption on the retinal-image quality and visual performance under surrounding low-illumination conditions. Methods. A volunteer sample of 67 subjects was analyzed. Optical quality of the eye was evaluated by means of the Strehl ratio, the Objective Scattering Index (OSI), and the tear-film quality. We used the visual disturbance index (VDI) to evaluate visual performance under low-illumination conditions and we measured the pupil size under these conditions. The tear-film volume was also measured. All measurements were made before and after alcohol consumption and patients were classified into two groups depending on their breath alcohol content (BrAC): low-alcohol (BrAC < 0.25 mg/L) and high-alcohol content (BrAC ≥ 0.25 mg/L). Results. The VDI was significantly higher after alcohol consumption: the higher the BrAC, the higher the deterioration of the visual discrimination capacity. The pupil size increased significantly for the high-BrAC group. Parameters evaluating optical quality deteriorated after alcohol consumption. Conclusion. The visual performance under low-illumination conditions and the retinal-image quality were deteriorated after alcohol consumption, especially for the high-alcohol group. Furthermore, some physiological changes were observed under effects for high-alcohol contents, such as an increase in the pupil size and disturbances in the tear film, which deteriorated optical quality.