Clinical Outcomes of a New Asymmetric Intracorneal Ring Segment for the Treatment of Keratoconus.

PURPOSE: To report visual, refractive, and corneal aberrations after implantation of a new asymmetric intracorneal ring segment (ICRS). METHODS: This was a prospective, multicenter clinical study including 30 eyes of 26 patients with keratoconus. All cases were implanted with an ICRS, named the VISUMRING (VR), which had an arc length of 353 degrees and 2 asymmetric sections that can be customized in base width, length, and thickness. Ophthalmic evaluation included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refraction, topography, and anterior corneal aberrations using the Sirius System (CSO, Firenze, Italy). Mean follow-up period was 14.7 ± 7.9 months. RESULTS: Significant improvement of both UDVA and CDVA was observed after 1 year. UDVA improved from 0.08 ± 0.22 to 0.22 ± 0.16 and CDVA from 0.24 ± 0.29 to 0.43 ± 0.18 (P = 0.01). A significant reduction of more than 7 D in the spherical equivalent from -12.38 ± 3.77 D to -5.00 ± 3.26 D (P < 0.05) was noted 1 year after the procedure. In terms of higher-order aberrations, a slight reduction that was not statistically significant in the higher-order and coma-like aberrations was noted at 1 year from 4.32 and 3.82, to 4.12 and 3.55, respectively. Regarding complications, 5 of the 30 cases needed to have the VR explanted throughout the follow-up period due to severe corneal melting. CONCLUSIONS: VR ICRS improves vision and refraction and induces major corneal flattening in patients with keratoconus. Further design enhancement is needed to increase the reduction of the asymmetric corneal aberrations and reduce the extrusion rate.

Validation of a gonio-hyperspectral imaging system based on light-emitting diodes for the spectral and colorimetric analysis of automotive coatings.

In this study, a novel gonio-hyperspectral imaging system based on light-emitting diodes for the analysis of automotive coatings was validated colorimetrically and spectrally from 368 to 1309 nm. A total of 30 pearlescent, 30 metallic, and 30 solid real automotive coatings were evaluated with this system, the BYK-mac and X-Rite MA98 gonio-spectrophotometers, and also with the SPECTRO 320 spectrometer for further comparison. The results showed very precise correlations, especially in the visible range. In conclusion, this new system provides a deeper assessment of goniochromatic pigments than current approaches due to the expansion of the spectral range to the infrared.

Visual and instrumental correlation of sparkle by the magnitude estimation method.

Most real surfaces and objects show variations in appearance with viewing and illumination directions. Besides angular dependency, they also show spatial variation in color, i.e., they exhibit some sort of texture. Of the surfaces we see, surfaces colored by special-effect pigments produce several complex visual effects, like change in color and lightness with viewing and illumination angles, and effects like sparkle and gloss on other textures. In the last two decades, different commercial devices have appeared to help ensure the proper characterization of materials with special-effect pigments. However, the instrumental characterization of sparkle is currently available only by a commercial device integrated into a multi-angle spectrophotometer. As it is difficult to find complete open original studies about the sparkle effect for designing and calibrating this commercial instrument, the main objective of this work was to check whether a good visual and instrumental correlation exists between the sparkle that the observer perceives and the sparkle value provided by the device using some subsets of goniochromatic samples with different types of special-effect pigments and colors. Visual assessments were made by a conventional magnitude estimation method in a directional lighting booth, which belonged to the same company owner of the sparkle instrument, in different geometries and at distinct illuminance levels. The results revealed that there was a good visual correlation of the sparkle grade value. By separately analyzing the factors used in its instrument algorithm, such as sparkle intensity and sparkle area values, it was clearly shown that the correlation was not good or simply did not exist. Consequently, and perhaps in regards to the choice of new special-effect pigments, such as synthetic mica and other future ones, we generated herein even more questions about current mathematical algorithms, and only recognized calculating this texture effect at the industrial level.

Spectral BRDF-based determination of proper measurement geometries to characterize color shift of special effect coatings.

A reduced set of measurement geometries allows the spectral reflectance of special effect coatings to be predicted for any other geometry. A physical model based on flake-related parameters has been used to determine nonredundant measurement geometries for the complete description of the spectral bidirectional reflectance distribution function (BRDF). The analysis of experimental spectral BRDF was carried out by means of principal component analysis. From this analysis, a set of nine measurement geometries was proposed to characterize special effect coatings. It was shown that, for two different special effect coatings, these geometries provide a good prediction of their complete color shift.

Analysis of the colorimetric properties of goniochromatic colors using the MacAdam limits under different light sources.

Technological innovation in all areas has led to the appearance in recent years of new metallic and pearlescent materials, yet no exhaustive studies have been conducted to assess their colorimetric capabilities. The chromatic variability of these special-effect pigments may largely be due to the three-dimensional effect of their curved shapes and orientations when they are directionally or diffusely illuminated. Our study examines goniochromatic colors using the optimal colors (MacAdam limits) associated with normal colors (photometric scale of relative spectral reflectance from 0 to 1) under certain conventional illuminants and other light sources. From a database of 91 metallic and interference samples and using a multi-gonio-spectrophotometer, we analyzed samples with lightness values of more than 100 and others with lightness values of less than 100, but with higher chromaticities than optimal colors, which places them beyond the MacAdam limits. Our study thus demonstrates the existence of chromatic perceptions beyond the normal solid color associated with these materials and independent of the light source. The challenge for future research, therefore, is to replicate and render these color appearances in current and future color reproduction technologies for computer graphics.

Computation and visualization of the MacAdam limits for any lightness, hue angle, and light source.

We present a systematic algorithm capable of searching for optimal colors for any lightness L* (between 0 and 100), any illuminant (D65, F2, F7, F11, etc.), and any light source reported by CIE. Color solids are graphed in some color spaces (CIELAB, SVF, DIN99d, and CIECAM02) by horizontal (constant lightness) and transversal (constant hue angle) sections. Color solids plotted in DIN99d and CIECAM02 color spaces look more spherical or homogeneous than the ones plotted in CIELAB and SVF color spaces. Depending on the spectrum of the light source or illuminant, the shape of its color solid and its content (variety of distinguishable colors, with or without color correspondence) change drastically, particularly with sources whose spectrum is discontinuous and/or very peaked, with correlated color temperature lower than 5500 K. This could be used to propose an absolute colorimetric quality index for light sources comparing the volumes of their gamuts, in a uniform color space.