Even when corrected with the best spectacles or contact lenses, normal human eyes still suffer from monochromatic aberrations that blur vision when the pupil is large. We have successfully corrected these aberrations using adaptive optics, providing normal eyes with supernormal optical quality. Contrast sensitivity to fine spatial patterns was increased when observers viewed stimuli through adaptive optics. The eye's aberrations also limit the resolution of images of the retina, a limit that has existed since the invention of the ophthalmoscope. We have constructed a fundus camera equipped with adaptive optics that provides unprecedented resolution, allowing the imaging of microscopic structures the size of single cells in the living human retina.

/pdf/supernormal-vision-and-high-resolution-retinal-imaging-54uzhrh9sx.pdf

Supernormal vision and high-resolution retinal imaging through adaptive optics

https://dash.harvard.edu/bitstream/handle/1/29005173/Formulation%20of%20Functionalized%20PLGA-PEG.pdf?sequence=1

Formulation of functionalized PLGA-PEG nanoparticles for in vivo targeted drug delivery

We describe a novel randomized method, the method of color-coding for finding simple paths and cycles of a specified length k, and other small subgraphs, within a given graph G = (V,E). The randomized algorithms obtained using this method can be derandomized using families of perfect hash functions. Using the color-coding method we obtain, in particular, the following new results: • For every fixed k, if a graph G = (V,E) contains a simple cycle of size exactly k, then such a cycle can be found in either O(V ) expected time or O(V ω log V ) worst-case time, where ω < 2.376 is the exponent of matrix multiplication. (Here and in what follows we use V and E instead of |V | and |E| whenever no confusion may arise.) • For every fixed k, if a planar graph G = (V,E) contains a simple cycle of size exactly k, then such a cycle can be found in either O(V ) expected time or O(V log V ) worst-case time. The same algorithm applies, in fact, not only to planar graphs, but to any minor closed family of graphs which is not the family of all graphs. • If a graph G = (V,E) contains a subgraph isomorphic to a bounded tree-width graph H = (VH , EH) where |VH | = O(log V ), then such a copy of H can be found in polynomial time. This was not previously known even if H were just a path of length O(log V ). These results improve upon previous results of many authors. The third result resolves in the affirmative a conjecture of Papadimitriou and Yannakakis that the LOG PATH problem is in P. We can show that it is even in NC.

Color-coding

There is a need for a schematic eye that models vision accurately under various conditions such as refractive surgical procedures, contact lens and spectacle wear, and near vision. Here we propose a new model eye close to anatomical, biometric, and optical realities. This is a finite model with four aspheric refracting surfaces and a gradient-index lens. It has an equivalent power of 60.35 D and an axial length of 23.95 mm. The new model eye provides spherical aberration values within the limits of empirical results and predicts chromatic aberration for wavelengths between 380 and 750 nm. It provides a model for calculating optical transfer functions and predicting optical performance of the eye.

Anatomically accurate, finite model eye for optical modeling

Visual stimuli contain a limited amount of information that could potentially be used to perform a given visual task. At successive stages of visual processing, some of this information is lost and some is transmitted to higher stages. This article describes a new analysis, based on the concept of the ideal observer in signal detection theory, that allows one to trace the flow of discrimination information through the initial physiological stages of visual processing, for arbitrary spatio-chromatic stimuli. This ideal-observer analysis provides a rigorous means of measuring the information content of visual stimuli and of assessing the contribution of specific physiological mechanisms to discrimination performance. Here, the analysis is developed for the physiological mechanisms up to the level of the photoreceptor. It is shown that many psychophysical phenomena previously attributed to neural mechanisms may be explained by variations in the information content of the stimuli and by preneural mechanisms.

Sequential ideal-observer analysis of visual discriminations.

Axial chromatic aberration of the human eye.

Local, hemispherical, effective emissivities and integrated cavity emissivities have been computed for isothermal and nonisothermal diffuse conical and cylindrical cavities having lids with circular apertures. The local emissivities of the walls increase rapidly with decreasing aperture diameter and are moderately insensitive to the value of the lid emissivity. The integrated emissivity increases or decreases with the distance of the detector from the cavity; the direction of the change depends upon the cavity geometry. For a nonisothermal cavity, the effective spectral emissivity changes substantially with both wavelength and cavity temperature; consequently, it is in general significantly different from the effective total emissivity.

Emissivities of diffuse cavities: Isothermal and nonisothermal cones and cylinders

Wavelength discrimination curves have been measured for two normal trichromats for three field sizes and various intensities. In order to obtain high-intensity levels in the blue region, a high-pressure xenon arc was used as a source. Results for the 1° field agree essentially with those of previous workers. The higher blue intensities have led to the establishment of a definite minimum at 420 mμ. Results for the smaller field sizes differ considerably from previous data. The chief reason for this seems to he in the viewing technique used. While previous authors employed strict fixation, this paper reports data obtained with a scanning technique. The effect of different methods of plotting is briefly discussed.

Wavelength discrimination for point sources.

Local, hemispherical, effective emissivities and integrated cavity emissivities are computed for isothermal and nonisothermal diffuse cylindro-cones (a cylindrical section of radius R2 and length L2 joined to a conical base of length L1 and half-angle θ), with and without lids, and are compared with corresponding values for the limiting cases of right circular cones and cylinders. The local emissivities everywhere along the walls are considerably higher in a cylindro-cone with a lid than in a similar one without, and also increase rapidly with decreasing cone angle. They are considerably higher in a cylindro-cone than in a cone of length L1 or in a cylinder of length L2. On the other hand, for cavities of the same total length, the cylinder has the highest local emissivities except at and near the base, where the emissivity of the cone is highest. There is a regular transition between these two extremes through various intermediary cylindro-cones. The normal integrated cavity emissivities are higher than the hemispherical emissivities for cavities for which (L1 + L2)/2R2 ≳ 0.8. The local and integrated spectral emissivities of nonisothermal cylindro-cones change markedly with wavelength and somewhat with cavity reference temperature. Approximate local emissivities for nonisothermal cylindro-cones can be obtained from corresponding isothermal ones in a simple manner, with useful accuracy.

Emissivities of diffuse cavities, II: Isothermal and nonisothermal cylindro-cones

Local hemispherical effective emissivities and integrated cavity emissivities are computed for isothermal and nonisothermal diffuse double cones (a conical section joined to a conical frustum) with and without lids, and are compared with corresponding values for cylindrocones. The local emissivities increase and become more uniform with increasing taper of the frustum. They are also considerably higher when there is a lid. For cavities with the same conical section, length, and aperture, a lidded double cone is blacker than a lidded cylindrocone when the front half of the frustum is invisible, but less black otherwise. For double cones of the same length, diameter, and aperture, the best choice of cone and frustum angles depends upon the particular viewing conditions. The integrated cavity emissivities vary only slightly with the angles of cone and frustum when the frustum is relatively long, and the normal emissivity (for a small on-axis detector a large distance away) is higher than the hemispherical emissivity (for a detector that fills the cavity aperture). When the frustum is relatively short, all of these vary substantially with angle, and the hemispherical emissivity can be higher than the normal emissivity. There is a marked variation of both local and integrated emissivities with wavelength in nonisothermal double cones; e.g., for the particular cases illustrated, the normal spectral emissivities change by from 4% to 6% and the hemispherical spectral emissivities by from 17% to 20% between 0.3 and 1 μm for a 1% temperature variation at 1300 K. The amount of the change in these spectral emissivities also depends upon the geometry of the cavity.

Emissivities of diffuse cavities. III. Isothermal and nonisothermal double cones

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