Top PDF Visual resolution and contrast sensitivity in two benthic sharks

Visual resolution and contrast sensitivity in two benthic sharks

Visual resolution and contrast sensitivity in two benthic sharks

10 times lower than anatomical estimates, a much larger than expected difference (Stell et al., 1975). There are a number of experimental factors that may have led to an underestimation of the optokinetic responses (both gain and resulting estimates of spatial resolution), such as the amount of the visual field the stimulus covered (Wyatt and Pola, 1987), the presence of non-rotating monitor edges (Wyatt and Pola, 1987), the restraint of the animals during the experiment (Dieringer et al., 1983; Gioanni, 1988), as well as a lack of attention towards the stimulus by the animals (Wyatt and Pola, 1987). However, a more likely explanation of the low threshold estimates is that the optomotor system in these species is not sensitive to high spatial frequencies. The optomotor system is designed to counteract image rotations. Estimating image rotations is easiest when viewing distant objects that are less affected by translational self motion and less affected by object motion (distant objects produce, on average, slower retinal speeds). In the underwater environment, distant objects do not contain high spatial frequencies because of the fast degradation of image contrast and blurring with viewing distance (Lythgoe, 1980, 1988; McFarland, 1990; Land and Nilsson, 2012). Low spatial frequency tuning of the optomotor system would therefore allow the system to preferentially ignore close objects (Land, 1999; Eckert and Zeil, 2001). This argument would explain why our results show such a sharp decline in the contrast sensitivity function at spatial frequencies above 0.18 cpd (Fig. 5).
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Effect of retinal laser photocoagulation on contrast sensitivity and visual acuity in patients of diabetic retinopathy

Effect of retinal laser photocoagulation on contrast sensitivity and visual acuity in patients of diabetic retinopathy

Patients undergoing argon laser panretinal photocoagulation (PRP) for proliferative diabetic retinopathy (PDR) developed temporary losses in high spatial frequency CS during the closely spaced PRP treatments. Since Snellen’s visual acuity remained stable at the pre-laser level, these results indicate the need for more sensitive measures of visual resolution to monitor foveal integrity in patients undergoing PRP. 7 Hellstedt et al. 8 suggested that contrast sensitivity is a sensitive indicator of changes in diabetic retinopathy and macular edema, especially at low- to mid- range spatial frequencies. Isolated losses of CS exist in certain diseases, and in many others, loss of contrast sensitivity is more prominent and disturbing to the patient than the loss of visual acuity .9
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Effects of Exercise on Visual Evoked Potentials

Effects of Exercise on Visual Evoked Potentials

for many specific stimuli such as the position of the ball or other players ; the objects in visual space move very quickly and the players decision making proceeds in short time [6] Many visual skills like visual resolution ability, dynamic visual activity, contrast sensitivity, oculomotor function, visual reaction time and visual coincidence anticipation are significant for volleyball players performance[7] There are some proofs that the participation in dynamic reactive training can improve visual reaction processing[8] and visual abilities [9]
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Tooth mineralization and histology patterns in extinct and extant snaggletooth sharks, Hemipristis (Carcharhiniformes, Hemigaleidae)—Evolutionary significance or ecological adaptation?

Tooth mineralization and histology patterns in extinct and extant snaggletooth sharks, Hemipristis (Carcharhiniformes, Hemigaleidae)—Evolutionary significance or ecological adaptation?

Sharks possess a constantly forming series of teeth in which functional teeth are replaced in succession (polyphydont dentition) [1,2,3]. There are two main different patterns how teeth can be arranged within the jaw. They either are added alternatingly within two adjacent tooth series (double vertical row; alternate dentition) or in single tooth files (single vertical row; independent dentition) [4–6] with teeth being shed individually (e.g. in carcharhiniform sharks) [4,6] or in groups up to entire tooth rows (e.g. squaliform sharks) [4,7]. Teeth are ini- tially formed within the dental lamina on the lingual side of the jaws and move toward the functional position on the jaw margin in a conveyor belt-like fashion [5,6,8]. The teeth on the jaw margin (situated labially) are in an erect position suitable for feeding, while those situated on the lingual face of the jaw cartilage are less developed and are inverted (with the tip of the tooth directed lingually towards the dental lamina) or in a semi-erect position. The number of teeth in an erect position within each tooth file varies between species. These erect teeth are the ones in use and thus are considered functional teeth, teeth in a semi-erect or inverted posi- tion form the developing replacement teeth [4].
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Antarctica eye study: a prospective study of the effects of overwintering on ocular parameters and visual function

Antarctica eye study: a prospective study of the effects of overwintering on ocular parameters and visual function

The OCT-measured retinal thickness can vary in the healthy human eye by up to 10% and is not thought to represent a true underlying change [18]. We found a sta- tistically significant decrease in retinal thickness in all ret- inal sectors in all eyes (other than the macula). Whilst the decrease was well under the normal variation of 10% the same OCT measuring device was used for the pre and post-expedition measurements. Furthrmore the decrease was across every eye in all explorers. However, we found no corresponding change in visual acuity and no visual field defects were identified; therefore it is very unlikely that the retinal thinning had a detrimental effect on visual function. Further studies should investigate whether re- peated visits to the polar regions have a larger effect on retinal thickness and should aim to follow up scientists who spend longer periods of time in the polar regions.
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Clinical outcomes following trifocal diffractive intraocular lens implantation for age-related cataract in China

Clinical outcomes following trifocal diffractive intraocular lens implantation for age-related cataract in China

Results: Thirty IOLs were implanted in 26 patients. Distance VA improved significantly from 0.70±0.45 to 0.08±0.11 logMAR (p,0.0001) 1 week postoperatively, and to 0.07±0.13 logMAR ( p,0.0001) at 1 month and 0.05±0.10 logMAR ( p,0.0001) at 3 months. Uncorrected near and intermediate VA, as well as corrected near, intermediate and distance VA, were stable and maintained during the follow-up period. Preoperative anterior chamber depth demonstrated an association with effective adjustment of postoperative spherical equivalent using a regression formula ( p=0.007). No significant differences were observed for VA at defocus curves of 0 to −3 D. Contrast sensitivity at each spatial frequency improved significantly at 1 week, 1 month and 3 months under photopic and photopic with glare conditions. Under mesopic and mesopic with glare conditions, significant differences were observed postoperatively at low and medium spatial frequencies. Patients reported a high level of satisfaction and an absence of glare or halo 3 months postoperatively.
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Microbial ecology for four coral atolls in the Northern Line Islands

Microbial ecology for four coral atolls in the Northern Line Islands

lagoons, and larger seabird populations. All of these trends could influence microbial communities. For example, on Kingman, the autotrophic and heterotrophic microbial communities in the water column were roughly balanced. In oligotrophic waters, photosyn- thetic cyanobacteria are the major energy producers [64] and compete with the heterotrophic bacterial communities for inorganic nutrients [52]. Prochlorococcus utilizes reduced forms of nitrogen and loses competitive dominance in seawater where the levels of nitrates are high [64,65]. On Tabuaeran, the photosynthetic microbes made up 80% of the community and photosynthetic subsystems comprised over 40% of the sequences identified within the metagenome. The dominance by Synechococcus correlated with the increase in nitrogen and phosphate concentrations in the water and is similar to the large scale distribution patterns of autotrophs in the ocean [64]. The increase in photosynthesis on Palmyra and Tabuaeran may have caused the increased concentration of DOC on these atolls (Figure 7A). Similarly, the metagenomes showed that the number of microbial autotrophs in the 0.45–100 micron fraction increased from Kingman (50%) to Palmyra (84%) to Tabuaeran (89%) (Figs. 3A and C). This trend correlated well with the increasing concentration of fixed nitrogen compounds (nitrate, nitrite, and ammonium) and phosphate in the water column (Figures. 7B and C) and may be due to increased upwelling on the progressively larger atolls. The concentrations of nitrate/nitrite and phosphate continue to increase on Kiritimati, but the microbial community became predominantly heterotrophic in nature (72%), suggesting an available carbon source. This observation is consistent with the hypothesis that nutrients from upwelling, and possibly runoff from the island, combined with a loss of herbivory are stimulating benthic macroalgae and phytoplankton. In turn, the algae produces dissolved organic carbon (DOC) which supports more heterotrophic bacterial growth. This is additionally supported by the observation that both the algal cover and the highest numbers of microbes were also observed on Kiritimati.
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Polarization sensitivity as a visual contrast enhancer in the Emperor dragonfly larva, Anax imperator

Polarization sensitivity as a visual contrast enhancer in the Emperor dragonfly larva, Anax imperator

Polarization sensitivity (PS) is a common feature of invertebrate visual systems. In insects, PS is well known for its use in several different visually guided behaviours, particularly navigation and habitat search. Adult dragonflies use the polarization of light to find water but a role for PS in aquatic dragonfly larvae, a stage that inhabits a very different photic environment to the adults, has not been investigated. The optomotor response of the larvae of the Emperor dragonfly, Anax imperator Leach 1815, was used to determine whether these larvae use PS to enhance visual contrast underwater. Two different light scattering conditions were used to surround the larval animals: a naturalistic horizontally polarized light field and a non-naturalistic weakly polarized light field. In both cases these scattering light fields obscured moving intensity stimuli that provoke an optokinetic response in the larvae. Animals were shown to track the movement of a square-wave grating more closely when it was viewed through the horizontally polarized light field, equivalent to a similar increase in tracking ability observed in response to an 8% increase in the intensity contrast of the stimuli. Our results suggest that larval PS enhances the intensity contrast of a visual scene under partially polarized lighting conditions that occur naturally in freshwater environments.
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Electroreception in juvenile scalloped hammerhead and sandbar sharks

Electroreception in juvenile scalloped hammerhead and sandbar sharks

Although the enhanced electroreception hypothesis predicts that hammerhead sharks will demonstrate greater sensitivity to electric fields than carcharhinid sharks, this prediction was not supported by the data. There are several explanations as to why a difference was not seen. A shark might well be able to detect an electric field but not exhibit an overt reaction until the electric field intensity exceeds a behavioral-response threshold, and that threshold may differ between the two species. Perhaps the scalloped hammerhead sharks are indeed more sensitive than the sandbar sharks but also have a greater behavioral inhibition that prevents them from responding immediately upon detection of a stimulus. Thus, two sharks with different sensitivities could have the same behavioral-response threshold, which would superficially make it appear that there was no difference in sensitivity between the species.
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Comparison of Visual Functions and Optical Coherence Tomography Parameters between Normal and Amblyopic Eyes in Anisometropic Amblyopia and Identification of Predictors of
Success for Occlusion Therapy

Comparison of Visual Functions and Optical Coherence Tomography Parameters between Normal and Amblyopic Eyes in Anisometropic Amblyopia and Identification of Predictors of Success for Occlusion Therapy

Amblyopia (commonly known as “lazy eye syndrome”), one of the most common cause, of preventable visual impairment in children 1 , is defined as a unilateral or bilateral decrease in best corrected visual acuity due to form vision deprivation and/or abnormal binocular interaction, for which there is no identifiable pathology of the eye or visual pathway. This disorder is potentially preventable and reversible if detected and treated at a young age 1 . In the absence of any organic lesions in the ocular system, visual pathway or visual cortex, a difference of two or more lines in Snellen's visual acuity (>1 log unit) is indicative of amblyopia 2 . The prevalence of amblyopia in southern India from screening of school children aged 5-15yrs was found to be 1.1% 3 . No gender predilection has been noted 4 .
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Visual symptoms in Parkinson's disease

Visual symptoms in Parkinson's disease

orientation [48, 49] including difficulty in judging verticals and the position of body parts, and in carrying out a route- walking task. Visuo-spatial working memory appears to be selectively impaired early in PD which probably reflects degeneration of the basal ganglia, the dorsal visual stream, and the frontal-prefrontal cortex [1]. Patients may also have problems with memory tasks involving spatial orientation. PD patients often show an impairment of orientation and motion discrimination [50] suggesting that the visual pathway beyond the retina may be a ff ected since these tasks are most likely to involve the visual cortex. In addition, impairments in the ability to perceive and imagine faces have been reported in PD [51]. Medicated and unmedicated patients exhibit facial recognition problems but these deficits are most frequently present in the untreated group [52]. Normal subjects contract their facial muscles while imaging faces, a process which is often impaired in PD patients. In a problem solving task involving arranging coloured balls in pockets on a computer screen, PD patients made more errors on the task than controls and also did not show any dissociation in the amount of time fixating the two halves of the display [53]. The results suggested difficulties in encoding and/or maintaining current goals during problem solving in PD.
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A study of effect on visual acuity and contrast sensitivity following Nd-YAG laser capsulotomy in patients with posterior capsular opacification

A study of effect on visual acuity and contrast sensitivity following Nd-YAG laser capsulotomy in patients with posterior capsular opacification

acuity on Day1 was found to be statistically significant (p value= .001) indicating an immediate improvement in visual acuity after this procedure. Visual acuity done on D7 of capsulotomy showed that the improvement of visual acuity was also found to be statistically significant (p value=.000). Visual acuity done at 1 month of capsulotomy showed the improvement of visual acuity when compared to pre-laser values was found to be statistically significant (p value=.000). Visual acuity done at 3 months of capsulotomy remained same as at 1 month. This improvement when compared to pre-laser visual acuity was found to be statistically significant (p value=.0.000). Mean value of pre-laser contrast sensitivity was compared with contrast sensitivity at D1, D7, 1month and 3months. Pre-laser mean value of contrast sensitivity was 1.1538 which was compared with mean value during follow up (mean value 1.5235). The improvement in contrast sensitivity was found to be statistically significant (p value=0.000). Conclusion: Nd-YAG capsulotomy definitely improves both visual acuity and contrast sensitivity in patients with significant PCO and maximum improvement occurs within first month following Nd-YAG capsulotomy.
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Visual adaptation and the amplitude spectra of radiological images

Visual adaptation and the amplitude spectra of radiological images

sensitivity for frequencies of ~ 2 – 4 c/deg (Kelly, 1975). In contrast, adaptation to the mammogram images produced marked and selective losses in sensitivity to low and medium spatial frequencies. As a result, the CSF more clearly peaks at ~ 4 c/deg and sensitivity to higher fre- quencies remained largely unaffected by the adaptation. This low frequency suppression suggests a more sharp- ened response to spatial frequency when observers are ex- posed to the mammograms and at first glance is in line with the changes in apparent suprathreshold blur revealed by the previous experiment. However, the changes in the CSF were indistinguishable when observers were instead adapted to the sharpened 1/f mammogram images. This is consistent with previous studies showing that adaptation to different amplitude spectra has a strong selective im- pact on lower spatial frequencies, but is not strongly se- lective for the specific spectral slope (Webster & Miyahara, 1997). This pattern was confirmed in a two-way ANOVA comparing frequency and adapting condition, which showed significant main effects of frequency (F(5,40) = 24.8, p < 0.001) and adapt (F(2,40) = 43.4, p < 0.01) as well as a significant interaction between the adapt condition and spatial frequency (F(10,40) = 2.10, p = 0.048). Pre-adapt thresholds differed from thresholds after adapting to both the original (F(1,29) = 68.9, p < 0.001) or sharpened images (F(1,29) = 73.5, p < 0.001), while the ori- ginal and sharpened adapting conditions did not differ from each other (F(1,29) = 0.145, p = 0.71). Thus, the present results suggest that inspecting mammograms does alter the relevant CSF of the observer, but in ways that are similar to adaptation to images with natural amplitude spectra.
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High Frequency CT Findings within 24 Hours after Cerebral Infarction

High Frequency CT Findings within 24 Hours after Cerebral Infarction

The improved spatial and contrast resolution of current generation scanners appears to have Significantly increased the sensitivity of computed tomography in demonstrating acute cerebral[r]

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Visual function assessment in medical imaging research

Visual function assessment in medical imaging research

All subjects who usually wear corrective lenses were asked to wear them during vision testing to assure that refractive errors were corrected. Refractive error refers to the amount of myopia, hyperopia, or astigmatism that might affect the testing. These conditions require correction with glasses or contact lenses to achieve the best possible corrected visual acuity. 30 Because the observers typically would use both eyes to perform image evaluation, the 3 visual functions were measured with both eyes open.

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An Assessment of the Visual Acuity and Contrast Sensitivity of Commercial Vehicle Drivers in Rivers State, Nigeria

An Assessment of the Visual Acuity and Contrast Sensitivity of Commercial Vehicle Drivers in Rivers State, Nigeria

at this time what level of reduction in contrast sensitivity represents an unacceptable risk for driving. Patients should be made aware of any significant reduction in contrast sensitivity. A person who has poor contrast requires a higher contrast to see objects or patterns from a person who has good contrast sensitivity. Impairment of contrast sensitivity can result from a number of different eye and neurological conditions e.g. cataracts, macular degeneration, diabetic retinopathy, brain injury, stroke, trauma or tumor, diplopia and uncorrected refractive error 10 . However, in an evaluation of contrast sensitivity as a screening test at licensure renewal in California, those who failed the screening test were more likely to incur future crashes as compared to those who passed 11 . The significant association
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Enhanced visual fields in hammerhead sharks

Enhanced visual fields in hammerhead sharks

Several factors that influence the evolution of the unusual head morphology of hammerhead sharks (family Sphyrnidae) are proposed but few are empirically tested. In this study we tested the ‘enhanced binocular field’ hypothesis (that proposes enhanced frontal binocularity) by comparison of the visual fields of three hammerhead species: the bonnethead shark, Sphyrna tiburo , the scalloped hammerhead shark, Sphyrna lewini , and the winghead shark, Eusphyra blochii , with that of two carcharhinid species: the lemon shark, Negaprion brevirostris , and the blacknose shark, Carcharhinus acronotus . Additionally, eye rotation and head yaw were quantified to determine if species compensate for large blind areas anterior to the head. The winghead shark possessed the largest anterior binocular overlap (48  deg.) and was nearly four times larger than that of the lemon (10  deg.) and blacknose (11  deg.) sharks. The binocular overlap in the scalloped hammerhead sharks (34  deg.) was greater than the bonnethead sharks (13  deg.) and carcharhinid species; however, the bonnethead shark did not differ from the carcharhinids. These results indicate that binocular overlap has increased with lateral head expansion in hammerhead sharks. The hammerhead species did not demonstrate greater eye rotation in the anterior or posterior direction. However, both the scalloped hammerhead and bonnethead sharks exhibited greater head yaw during swimming (16.9  deg. and 15.6  deg., respectively) than the lemon (15.1  deg.) and blacknose (15.0  deg.) sharks, indicating a behavioral compensation for the anterior blind area. This study illustrates the larger binocular overlap in hammerhead species relative to their carcharhinid sister taxa and is consistent with the ‘enhanced binocular field’ hypothesis.
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Visual acuity and contrast sensitivity of adult zebrafish

Visual acuity and contrast sensitivity of adult zebrafish

Zebrafish (Danio rerio), which were initially used as an animal model in developmental biology due to high fe- cundity and ease of maintenance, has found its way into visual research due to its excellent visual system with a cone-dominated retina [1]. In the past, measurements of visual functions have been performed in larval zebrafish [2]. Furthermore, visual acuity (VA) of larval zebrafish has previously been determined by assessing the optokinetic reflex (OKR) in a self-constructed set-up [3]. Certain vis- ual functions of adult zebrafish (gain of eye velocity at dif- ferent spatial frequencies and contrast levels) have been published [4–6]. However, no empirical data about VA of adult zebrafish are available up to now. A standardized and reliable method for VA measurements is a prerequis- ite to analyze genetically modified fish lines and to evalu- ate the effect of a therapeutic action (e.g. impact of drugs or genetic interventions on the visual system) in addition to histological and ophthalmological examination of adult
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<p>Subjective Perception Of Trifocal IOL Performance, Including Toric Models</p>

<p>Subjective Perception Of Trifocal IOL Performance, Including Toric Models</p>

The fi rst reports addressed to IOLs treating presbyopia with multifocality, date back to 1987. 1 However, it was rapidly noticed the degraded optical qualities of early prototypes. 2–4 Various generations were introduced to practice, ending with the current trifocal one. 5–9 Extensive concerns were addressed to assess advanced visual and optical functions, naming near and intermediate acuities, contrast sensi- tivity and glare and halos. 10–13 While most of research focus on objective measures, 9 – 14 patients ’ perception of IOLs ’ performance remains the cornerstone of lens choice.
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Mesopic Visual Contrast Sensitivity in Patients with Major Depression

Mesopic Visual Contrast Sensitivity in Patients with Major Depression

The present study investigated whether major depression al- ters visual CS at low levels of luminance. The results showed a reduction of CS in patients with major depression compared with healthy volunteers who were matched for age, sex, and educational level. However, unclear is whether the changes observed were caused by depression itself, medications, or a combination of both. Only three of the 10 participants in the experimental group did not use medications. Finding patients with major depression who use only a single medication is dif- ficult, but new research needs to systematically investigate the effect of medication on visual spatial CS. Overall, the present data suggest that major depression caused changes in the mag- nocellular pathway, a pathway that is important in the process- ing of spatial frequencies under low luminance conditions.
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