Biomedical subjects

J M Saiz

Publications and source records attributed to J M Saiz.

6 recordsLinked to original sources

PubMed2006

Plasmon spectroscopy of metallic nanoparticles above flat dielectric substrates.

We numerically analyze the spectral properties of localized plasmon resonances in metal nanoparticles when these are above a dielectric substrate. This analysis is performed as a function of the various parameters involved in the problem (relative optical properties, particle-substrate separation, angle of incidence, etc.). It can be shown that from the spectral behavior of the resonance in the far field, information about particle near-field interactions can be obtained.

Journal Article↗

PubMed2006

Monitoring small defects on surface microstructures through backscattering measurements.

The detection and characterization of small defects on particles or structures of a size comparable with the incident wavelength and located on flat substrates is numerically analyzed. For metallic scattering systems, calculations based on the extinction theorem of physical optics show that geometrical information about a small Gaussian defect can be obtained by partially integrating the backscattering patterns.

Journal Article↗

PubMed2005

Two-particle model to study fluctuations of scattered radiation: multiple-scattering effects.

The intensity fluctuations of light scattered from a simple particle aggregate system consisting of two dipole-like particles separated by a fixed distance and floating freely in space are calculated numerically and analyzed statistically. The behavior of two statistical parameters, the second-order factorial moment of the intensity fluctuations and the probability of obtaining zero cross-polarized intensity, are studied as a function of both the particle polarizability and the interparticle distance. Effects of multiple-scattering processes on these statistical parameters are accounted for in particular.

Journal Article↗

PubMed2003

[Optimization of an individualized LASIK surgery. Geometric ray tracing model].

PURPOSE: To develop an objective calculation method that is able to provide a customized surgical correction that allows the patient to reach the emmetropia and the maximum visual acuity after the surgery. METHODS: The study included 187 eyes with myopia or myopic astigmatism that underwent LASIK. The optical characterization of each eye was developed by a complete theoretical model based in Le Grand eye, in which the measured values of radii and thicknesses of the different surfaces have been substituted. By means of a geometric ray tracing, the surgery has been simulated by changing the anterior corneal radius and the corneal thickness within the optical zone to obtain its influence in the ocular image and the visual acuity. We considered the surgery to be < > when the residual equivalent refraction was between 0 and +0.5 D. RESULTS: An interval for the final corneal radius is proposed for each eye in order to reach the best visual acuity (optimal interval). The position of the post-surgical radius in this interval has been related with the success of the surgical process. CONCLUSIONS: An objective method for LASIK has been proposed: i) it calculates a personalized surgical plan that allows the patient to reach the best visual quality, and ii) it can be used as a reference by the surgeon to design his nomogram and to decrease his learning curve.

Adult↗

PubMedDate not supplied

Unexpected corneal flattening after laser in situ keratomileusis.

PURPOSE: To perform a statistical study of the variation (flattening) from the surgical radius (sculpted in the corneal stroma) to the final radius of the first surface of the cornea after laser in situ keratomileusis (LASIK) for correction of myopia. METHODS: The study included 387 eyes with myopia or myopic astigmatism that underwent LASIK using the Nidek EC-5000 excimer laser. Mean age was 34 years (range, 19 to 75 yr). Mean myopia was -5.19 D (range, 0 to -19.00 D) and mean astigmatism was -1.22 D (range, 0 to -5.00 D). The flattening coefficient was defined as: (f) = (Rpost-Rs)/Rs where Rpost. was the corneal radius after surgery (topography performed 1 month after surgery) and Rs was the surgical radius sculpted in the stroma. Mean values and standard deviations of the flattening coefficient were calculated for the 387 eyes for four myopic ranges (0 to -3.00 D, -3.00 to -6.00 D, -6.00 to -9.00 D, and more than -9.00 D), and for three astigmatic ranges (0, -0.25 to -2.00 D, and more than -2.00 D). The correlations between the flattening coefficient and several preoperative ocular variables were obtained. RESULTS: A linear combination of quasi-independent ocular variables (age, anterior corneal radius, corneal thickness, sphere and cylinder) was found in order to maximize the correlation with the flattening for every range. Values for the correlations between 0.4 to 0.5 were obtained. CONCLUSION: The flattening phenomenon was characterized by a flattening coefficient (f).

Adult↗

PubMedDate not supplied

Geometric ray tracing analysis of visual acuity after laser in situ keratomileusis.

PURPOSE: Using a geometric ray tracing model, we explain the increase in visual acuity observed in myopic patients after laser in situ keratomileusis (LASIK). METHODS: This study included 37 eyes of 23 patients who underwent LASIK. All patients had myopia and a spectacle-corrected visual acuity of 0.95 or worse. Clinical tests included biometry, corneal topography, pachymetry, and refraction (with and without cycloplegia). Calculations were made by tracing rays through all the refractive surfaces of the eye based on a Le Grand-type theoretical model of the whole eye. RESULTS: Comparison of spectacle-corrected visual acuity of the eye before surgery, the size of the blur circle calculated by ray tracing, and the magnification for the ocular system facilitated a numerical criterion to assess visual acuity by geometric calculation. This criterion was applied to myopic eyes that underwent LASIK, and the maximum increase in spectacle-corrected visual acuity was predicted. An actual increase in visual acuity of approximately 40% of the predicted maximum was observed in patients. CONCLUSIONS: With geometric ray tracing, it was possible not only to obtain an estimate of the visual acuity before LASIK but also to assess the value of the maximum and probable increases in visual acuity after LASIK.

Adult↗