Maria Vinas

Perceptual Adaptation to the Correction of Natural Astigmatism

Background The visual system adjusts to changes in the environment, as well as to changes within the observer, adapting continuously to maintain a match between visual coding and visual environment. We evaluated whether the perception of oriented blur is biased by the native astigmatism, and studied the time course of the after-effects following spectacle correction of astigmatism in habitually non-corrected astigmats. Methods and Findings We tested potential shifts of the perceptual judgments of blur orientation in 21 subjects. The psychophysical test consisted on a single interval orientation identification task in order to measure the perceived isotropic point (astigmatism level for which the image did not appear oriented to the subject) from images artificially blurred with constant blur strength (B = 1.5 D), while modifying the orientation of the blur according to the axis of natural astigmatism of the subjects. Measurements were performed after neutral (gray field) adaptation on naked eyes under full correction of low and high order aberrations. Longitudinal measurements (up to 6 months) were performed in three groups of subjects: non-astigmats and corrected and uncorrected astigmats. Uncorrected astigmats were provided with proper astigmatic correction immediately after the first session. Non-astigmats did not show significant bias in their perceived neutral point, while in astigmatic subjects the perceived neutral point was significantly biased, typically towards their axis of natural astigmatism. Previously uncorrected astigmats shifted significantly their perceived neutral point towards more isotropic images shortly (2 hours) after astigmatic correction wear, and, once stabilized, remained constant after 6 months. The shift of the perceived neutral point after correction of astigmatism was highly correlated with the amount of natural astigmatism. Conclusions Non-corrected astigmats appear to be naturally adapted to their astigmatism, and astigmatic correction significantly changes their perception of their neutral point, even after a brief period of adaptation.

Astigmatism Impact on Visual Performance: Meridional and Adaptational Effects

Purpose Astigmatic subjects are adapted to their astigmatism and perceptually recalibrate upon its correction. However, the extent to which prior adaptation to astigmatism affects visual performance, whether this effect is axis dependent, and the time scale of potential changes in visual performance after astigmatism correction are not known. Moreover, the effect of possible positive interactions of aberrations (astigmatism and coma) might be altered after recalibration to correction of astigmatism. Methods Visual acuity (VA) was measured in 25 subjects (astigmats and non-astigmats, corrected and uncorrected) under induction of astigmatism and combinations of astigmatism and coma while controlling subject aberrations. Astigmatism (1.00 diopter) was induced at three different orientations, the natural axis, the perpendicular orientation, and 45 degrees for astigmats and at 0, 90, and 45 degrees for non-astigmats. Experiments were also performed, adding coma (0.41 &mgr;m at a relative angle of 45 degrees) to the same mentioned astigmatism. Fourteen different conditions were measured using an 8-Alternative Forced Choice procedure with Tumbling E letters and a QUEST algorithm. Longitudinal measurements were performed up to 6 months. Uncorrected astigmats were provided with proper astigmatic correction after the first session. Results In non-astigmats, inducing astigmatism at 90 degrees, produced a statistically lower reduction in VA than at 0 or 45 degrees, whereas in astigmats, the lower decrease in VA occurred for astigmatism induced at the natural axis. Six months of astigmatic correction did not reduce the insensitivity to astigmatic induction along the natural axis. Differences after orientation of astigmatism were also found when adding coma to astigmatism. Conclusions The impact of astigmatism on VA is greatly dependent on the orientation of the induced astigmatism, even in non-astigmats. Previous experience to astigmatism plays a significant role on VA, with a strong bias toward the natural axis. In contrast to perceived isotropy, the correction of astigmatism does not shift the bias in VA from the natural axis of astigmatism.

Dependence of subjective image focus on the magnitude and pattern of high order aberrations.

The image formed by the eyes optics is inherently blurred by aberrations specific to the individuals eyes. We examined to what extent judgments of perceived focus depend on the total magnitude as opposed to the specific pattern of blur introduced by the eyes high order aberrations (HOA). An Adaptive Optics system was used to simultaneously correct each subjects wave aberrations and display natural images blurred by simulated aberrations. To isolate the effects of blur magnitude, images were blurred by pure symmetric defocus, and subjects judged the level of the defocus that subjectively appeared best focused (i.e., neither too blurred nor too sharp). These settings were strongly correlated with the native blur magnitude. To isolate the effect of the HOA pattern, retinal image blur was instead maintained at a constant blur (Strehl Ratio) equal to each subjects natural blur, and subjects judged the best-focused image from pairs of images blurred by different patterns of HOA, one selected from 100 patterns, the other blurred by a reference pattern which included the subjects natural HOA, rotated HOA, or nine other HOA patterns. The percentage of images judged as best focused was not systematically higher when filtered with the subjects own HOA pattern. However, all subjects preferred their own HOA to the rotated version significantly more often (57% versus 45% on average across subjects). The representation of subjective image focus thus appears to be driven primarily by the overall amount of blur and only weakly by HOA blur orientation.

In vivo subjective and objective longitudinal chromatic aberration after bilateral implantation of the same design of hydrophobic and hydrophilic intraocular lenses.

Purpose To measure the longitudinal chromatic aberration in vivo using psychophysical and wavefront‐sensing methods in patients with bilateral implantation of monofocal intraocular lenses (IOLs) of similar aspheric design but different materials (hydrophobic Podeye and hydrophilic Poday). Setting Instituto de Optica, Consejo Superior de Investigaciones Cientificas, Madrid, Spain. Design Prospective observational study. Methods Measurements were performed with the use of psychophysical (480 to 700 nm) and wavefront‐sensing (480 to 950 nm) methods using a custom‐developed adaptive optics system. Chromatic difference‐of‐focus curves were obtained from best‐focus data at each wavelength, and the longitudinal chromatic aberration was obtained from the slope of linear regressions to those curves. Results The longitudinal chromatic aberration from psychophysical measurements was 1.37 diopters (D) ± 0.08 (SD) (hydrophobic) and 1.21 ± 0.08 D (hydrophilic). From wavefront‐sensing, the longitudinal chromatic aberration was 0.88 ± 0.07 D and 0.73 ± 0.09 D, respectively. At 480 to 950 nm, the longitudinal chromatic aberration was 1.27 ± 0.09 D (hydrophobic) and 1.02 ± 0.13 D (hydrophilic). The longitudinal chromatic aberration was consistently higher in eyes with the hydrophobic IOL than in eyes with the hydrophilic IOL (a difference of 0.16 D and 0.15 D, respectively). Similar to findings in young phakic eyes, the longitudinal chromatic aberration from the psychophysical method was consistently higher than from wavefront‐sensing, by 0.48 D (35.41%) for the hydrophobic IOL and 0.48 D (39.43%) for the hydrophilic IOL. Conclusion Longitudinal chromatic aberrations were smaller with hydrophilic IOLs than with hydrophobic IOLs of the same design. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Hábitos alimentarios de las larvas de Engraulis anchoita (Hubbs & Marini, 1935) en las aguas costeras de la Provincia de Buenos Aires, Argentina

The diet of Engraulis anchoita larvae (Hubbs & Marini, 1935) was analyzed using samples collected once a month at a permanent coastal station off Buenos Aires Province, Argentina (Station EPEA), from March 2000 to April 2001. A total of 869 individuals were examined. Eggs (54.05%), copepod nauplii (10.13%), and copepodites (11.82%) were the dominant prey items. The feeding index varied from 1.69 to 40.48%, without showing a clear seasonal pattern. Correlations between predator size and prey size were determined and the results showed significant relationships (P < 0.01) in all cases. In spring and summer, the larvae were small in size, corresponding to first-feeding larvae (< 6.9 mm length) and preyed mainly on small organisms from < 45 to 134 µm width. In autumn and winter, the size of the larvae increased (7.0-19.9 mm length), and they fed mainly on larger prey, from 135 to 279 µm width.

Individual biovolume of some dominant copepod species in coastal waters off Buenos Aires Province, Argentine Sea

Instituto Tecnologico de Chascomus (INTECH) Copepods are key components in the marine communities because of their important role in the transfer of matter and energy from primary producers to higher trophic levels and in the export of organic matter from the euphotic to deeper layers of the oceans (CALBET et al., 2000). Because of their role as prey for fishes at different stages of development, knowledge of zooplankton abundance and biomass in spatial and temporal scales remains a key element of the marine ecosystem approaches (IRIGOIEN et al., 2009). In fisheries science, accurate estimations of abundance, biomass and production of the different components of the food webs are necessary for the construction and implementation of ecosystem models th(CHRISTENSEN; PAULY, 1992). Paracalanus parvus , Ctenocalanus vanus, Calanoides carinatus and Oithona nana are dominant copepod species (50-100 %) in the coastal waters of the Argentine Sea (RAMIREZ, 1981; VINAS et al., 2002). These copepods play an important role in the pelagic food web as the main prey item for larvae (CIECHOMSKI; WEISS, 1974; VINAS; RAMIREZ, 1996) and juveniles and adults of anchovy (ANGELESCU, 1982; PAJARO, 2002). Thus, an accurate estimation of their biomass and productivity is necessary to quantify the transfer of matter and energy across the planktonic food webs. So far, there is only one regional work in which the individual biomass of copepods has been estimated (FERNANDEZ ARAOZ, 1991) in the Argentine Sea, but early copepodite stages were not included because of the mesh size ( ≥ 220 µm) employed. Our aim was to estimate the individual biomass of all the stages of the above-mentioned copepods by the geometric method and to establish, for each species, significant regression models predicting biovolume from some linear body dimension. Volumetric methods, such as the one employed in the present study, are the only choice if samples are also to be used for taxonomic purposes (POSTEL et al., 2000) and the geometric approach is the only suitable in the case of small-sized zooplankton (OMORI; IKEDA, 1984). The conversion of our results into another biomass proxy from the literature may easily be made. In fact, body wet weight can be derived from measurements of body biovolume by applying a factor of 1 for specific gravity (OMORI and IKEDA, 1984). Dry weight can be obtained by multiplying the wet weight by 0.20 and the carbon content can be considered as 40 % of the dry weight (POSTEL et al., 2000). Samples were obtained on October 18

Testing vision with angular and radial multifocal designs using Adaptive Optics

ABSTRACT Multifocal vision corrections are increasingly used solutions for presbyopia. In the current study we have evaluated, optically and psychophysically, the quality provided by multizone radial and angular segmented phase designs. Optical and relative visual quality were evaluated using 8 subjects, testing 6 phase designs. Optical quality was evaluated by means of Visual Strehl‐based‐metrics (VS). The relative visual quality across designs was obtained through a psychophysical paradigm in which images viewed through 210 pairs of phase patterns were perceptually judged. A custom‐developed Adaptive Optics (AO) system, including a Hartmann‐Shack sensor and an electromagnetic deformable mirror, to measure and correct the eyes aberrations, and a phase‐only reflective Spatial Light Modulator, to simulate the phase designs, was developed for this study. The multizone segmented phase designs had 2–4 zones of progressive power (0 to +3D) in either radial or angular distributions. The response of an “ideal observer” purely responding on optical grounds to the same psychophysical test performed on subjects was calculated from the VS curves, and compared with the relative visual quality results. Optical and psychophysical pattern‐comparison tests showed that while 2‐zone segmented designs (angular & radial) provided better performance for far and near vision, 3‐ and 4‐zone segmented angular designs performed better for intermediate vision. AO‐correction of natural aberrations of the subjects modified the response for the different subjects but general trends remained. The differences in perceived quality across the different multifocal patterns are, in a large extent, explained by optical factors. AO is an excellent tool to simulate multifocal refractions before they are manufactured or delivered to the patient, and to assess the effects of the native optics to their performance.

On the uncertainty beneath the name Oithona similis Claus, 1866 (Copepoda, Cyclopoida).

Abstract The marine cyclopoid Oithona similis sensu lato Claus, 1866, is considered to be one of the most abundant and ubiquitous copepods in the world. However, its minimal original diagnosis and the unclear connection with its (subjective) senior synonym Oithona helgolandica Claus, 1863, may have caused frequent misidentification of the species. Consequently, it seems possible that several closely related but distinct forms are being named Oithona similis or Oithona helgolandica without explicit and accurate discrimination. Here the current situation concerning the correct assignment of the two species is revised, the morphological characters commonly used to identify and distinguish each species are summarized, and the nomenclatural implications of indiscriminately using these names in current taxonomic and ecological practice is considered. It is not intended to upset a long-accepted name in its accustomed meaning but certainly the opposite. “In pursuit of the maximum stability compatible with taxonomic freedom” (International Commission of Zoological Nomenclature), we consider that reassessment of the diagnostic characters of Oithona similis sensu stricto cannot be postponed much longer. While a consensus on taxonomy and nomenclatural matters can be attained, we strongly recommend specifically reporting the authority upon which the identification of either Oithona similis s.l. or Oithona helgolandica s.l. has been accomplished.

Comparison of vision through surface modulated and spatial light modulated multifocal optics

Spatial-light-modulators (SLM) are increasingly used as active elements in adaptive optics (AO) systems to simulate optical corrections, in particular multifocal presbyopic corrections. In this study, we compared vision with lathe-manufactured multi-zone (2-4) multifocal, angularly and radially, segmented surfaces and through the same corrections simulated with a SLM in a custom-developed two-active-element AO visual simulator. We found that perceived visual quality measured through real manufactured surfaces and SLM-simulated phase maps corresponded highly. Optical simulations predicted differences in perceived visual quality across different designs at Far distance, but showed some discrepancies at intermediate and near.

Zooplankton Communities of the Argentine Continental Shelf (SW Atlantic, ca. 34°–55°S), An Overview

A profuse literature related to the ecology of the Argentine continental shelf has been produced in the last four decades, documenting its biological richness and high productivity. Distinctive environmental characteristics define particular systems along and across the shelf, which in all cases are inhabited by mammal, bird, fish and cephalopod species in all life history stages, either as spawning, mating, nursery or juvenile grounds or just for adult feeding. At the productive base of these systems, zooplankton certainly plays a crucial role. This paper reviews the available information on zooplankton diversity and ecology for this huge region in the Southwest Atlantic Ocean, with the focus primarily upon copepods and secondarily on hyperiid amphipods and euphausiids. We describe general aspects of biogeographic zonation and diversity for the entire shelf, with emphasis on key zooplankton species. Then, we consider the structure and dynamics of the communities in relation to water masses, frontal areas and the overall circulation, specifically for (i) the northern shelf (34°–41°S), (ii) the Valdes frontal system over the northern Patagonian shelf (41°–45°S) and (iii) the southern Patagonian shelf (47°–55°S). We finally go over the open questions and prospects for the future work on zooplankton in the region.