The Influence of Pigment Migration on Vision of Higher Crustacea

1957 ◽  
Vol 34 (4) ◽  
pp. 447-463
Author(s):  
G. H. P. DE BRUIN ◽  
D. J. CRISP
Keyword(s):  
Visual Acuity ◽  
Refractive Index ◽  
Light Adaptation ◽  
Surrounding Medium ◽  
Light Sensitivity ◽  
Detectable Change ◽  
Corneal Surface ◽  
Pigment Migration ◽  
Wave Guides ◽  
Superposition Eye

1. Exner believed that the movement of the distal pigment during light-adaptation improved the visual acuity of the superposition eye. This hypothesis was tested by measurement of the visual acuity of Leander serratus, Pandalus montagui and Praunus flexuosus under different conditions. 2. When a dark-adapted animal is placed in the light the proximal pigment migrates into the light-adapted position more rapidly than the distal pigment. The distal pigment, but not the proximal pigment, undergoes diurnal rhythm and tends to migrate into the dark-adapted position at night, even when the animal is illuminated. The visual acuity may therefore be tested when the distal pigment is still in the dark-adapted position and the proximal pigment in the light-adapted position. 3. No difference in visual acuity could be detected as a result of changes in the position of the distal pigment. 4. Visual acuity increases and light sensitivity decreases when the dark proximal pigment migrates over the reflecting (tapetal) layer. 5. Eupagurus bernhardus, which lacks the typical tapetum, shows no detectable change in visual acuity or sensitivity after being kept in the dark. 6. These experiments do not support Exner's view of the function of the distal pigment. They indicate that visual acuity is improved by the presence of the dark proximal pigment at the base of the proximal retinulae, probably because this pigment reduces stray reflexions from the back of the eye (halation). 7. It is suggested that since the crystalline cones and crystalline tracts form optically continuous strands with a higher refractive index than that of the surrounding medium they may act as wave guides. If so they would retain light entering the corneal surface from sources close to the axis of the ommatidium, and so concentrate it on the rhabdomes and adjacent retinulae.

scholarly journals Minimum Detectable Change of Visual Acuity Measurements Using ETDRS Charts (Early Treatment Diabetic Retinopathy Study)

2021 ◽  
Vol 18 (15) ◽  
pp. 7876
Author(s):  
María Carmen Sánchez-González ◽  
Raquel García-Oliver ◽  
José-María Sánchez-González ◽  
María-José Bautista-Llamas ◽  
José-Jesús Jiménez-Rejano ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Diabetic Retinopathy ◽  
Early Treatment ◽  
High Reliability ◽  
Minimal Detectable Change ◽  
High Contrast ◽  
Detectable Change ◽  
Low Contrast ◽  
Minimum Detectable Change ◽  
The Mean

In our work, we determined the value of visual acuity (VA) with ETDRS charts (Early Treatment Diabetic Retinopathy Study). The purpose of the study was to determine the measurement reliabilities, calculating the correlation coefficient interclass (ICC), the value of the error associated with the measure (SEM), and the minimal detectable change (MDC). Forty healthy subjects took part. The mean age was 23.5 ± 3.1 (19 to 26) years. Visual acuities were measured with ETDRS charts (96% ETDRS chart nº 2140) and (10% SLOAN Contrast Eye Test chart nº 2153). The measurements were made (at 4 m) under four conditions: Firstly, photopic conditions with high contrast (HC) and low contrast (LC) and after 15 min of visual rest, mesopic conditions with high and low contrast. Under photopic conditions and high contrast, the ICC = 0.866 and decreased to 0.580 when the luminosity and contrast decreased. The % MDC in the four conditions was always less than 10%. It was minor under photopic conditions and HC (5.83) and maximum in mesopic conditions and LC (9.70). Our results conclude a high reliability of the ETDRS test, which is higher in photopic and high contrast conditions and lower when the luminosity and contrast decreases.

scholarly journals Hybrid Grating in Reduced-Diameter Fiber for Temperature-Calibrated High-Sensitivity Refractive Index Sensing

2019 ◽  
Vol 9 (9) ◽  
pp. 1923
Author(s):  
Biqiang Jiang ◽  
Zhen Hao ◽  
Dingyi Feng ◽  
Kaiming Zhou ◽  
Lin Zhang ◽  
...  
Keyword(s):  
Refractive Index ◽  
Simultaneous Measurement ◽  
Surrounding Medium ◽  
High Sensitivity ◽  
Fiber Grating ◽  
Bragg Resonance ◽  
Core Mode ◽  
Promising Alternative ◽  
Sensing Applications ◽  
Highly Sensitive

We propose and experimentally demonstrate a hybrid grating, in which an excessively tilted fiber grating (Ex-TFG) and a fiber Bragg grating (FBG) were co-inscribed in a reduced-diameter fiber (RDF). The hybrid grating showed strong resonances due to coupling among core mode and a set of polarization-dependent cladding modes. This coupling showed enhanced evanescent fields by the reduced cladding size, thus allowing stronger interaction with the surrounding medium. Moreover, the FBG’s Bragg resonance confined by the thick cladding was exempt from the change of the surrounding medium’s refractive index (RI), and then the FBG can work as a temperature compensator. As a result, the Ex-TFG in RDF promised a highly sensitive RI measurement, with a sensitivity up to ~1224 nm/RIU near the RI of 1.38. Through simultaneous measurement of temperature and RI, the temperature dependence of water’s RI is then determined. Therefore, the proposed hybrid grating with a spectrum of multi-peaks embedded with a sharp Bragg resonance is a promising alternative for the simultaneous measurement of multi-parameters for many RI-based sensing applications.

SIZE-DEPENDENT NONRESONANT THIRD-ORDER NONLINEAR SUSCEPTIBILITIES OF CdS CLUSTERS FROM 7 TO 120 Å

1992 ◽  
Vol 01 (04) ◽  
pp. 683-698 ◽  
Author(s):  
YING WANG ◽  
NORMAN HERRON
Keyword(s):  
Refractive Index ◽  
Quantum Confinement ◽  
Optical Switching ◽  
Quantum Confinement Effect ◽  
Surrounding Medium ◽  
Confinement Effect ◽  
Third Order ◽  
Size Dependent ◽  
Size Regime ◽  
Fundamental Wavelength

We report the third-order nonlinear susceptibilities χ(3) of CdS clusters (quantum dots) from 7 to 120 Å, measured by third-harmonic generation technique at a fundamental wavelength of 1.91 µm. In the size regime studied, the value of χ(3) first increases with cluster size and then levels off for cluster diameter larger than 60 Å. The volume normalized χ(3) of CdS cluster is about a factor of 2 higher than that of the bulk. These data can be explained by the enhancement in electric field inside the clusters due to the dielectric confinement effect. The size and wavelength dependences of this local field effect have been calculated for CdS clusters. Several trends in the nonresonant χ(3) can be identified: (i) In the absence of quantum confinement effect, the magnitude of χ(3) should be constant in the < 200 Å size regime. It then increases with increasing particle size until the structural resonance regime is reached. (ii) The magnitude of χ(3) can be enhanced by either lowering the refractive index of the surrounding medium or raising the refractive index of the semiconductors. (iii) Quantum confinement, which shifts the band gap to the blue and lowers the refractive index of the semiconductor clusters, reduces the nonresonant χ(3). This is in direct contrast to the resonant nonlinearity which is enhanced by the quantum-confinement effect. Finally, we discuss the size-dependent figure-of-merit of CdS composites for all-optical switching.

scholarly journals Effect of Solvent Refractive Index on the Surface Plasmon Resonance Nanoparticle Optical Absorption

2007 ◽  
Vol 7 (12) ◽  
pp. 4333-4338
Author(s):  
Gulay Ertas ◽  
Sefik Suzer
Keyword(s):  
Gold Nanoparticles ◽  
Refractive Index ◽  
Surface Plasmon ◽  
Surrounding Medium ◽  
Point Of View ◽  
Experimental Point ◽  
Absorption Bands ◽  
Plasmon Band ◽  
Silver And Gold Nanoparticles ◽  
Band Position

Optical properties of plasmon coupled silver and gold nanoparticles were studied as a function of the refractive index of the surrounding medium. Our studies confirmed that the effect of changes in the refractive index of the surrounding medium was more difficult to demonstrate from an experimental point of view, because of the very high susceptibility of nanoparticles to aggregate in aqueous and organic solvents. Whereas the position of the absorption bands of triiodide in these solvents shows a clear dependence on medium's refractive index, the surface plasmon band position of silver and gold nanoparticles do not exhibit the same dependence. This is attributed to a non-negligible interaction of these solvents with nanoparticle surfaces.

scholarly journals Enhanced Plasmonic Resonance Characteristics of AgNRs–Gold Film Hybrid System

2021 ◽  
Vol 8 ◽  
Author(s):  
Yanping Yin ◽  
Jin Zhu ◽  
Zaoji Wang ◽  
Guojun Ma ◽  
Huining Yuan ◽  
...  
Keyword(s):  
Refractive Index ◽  
Aspect Ratio ◽  
Gold Film ◽  
Spectral Response ◽  
Surrounding Medium ◽  
Resonance Wavelength ◽  
Spectral Shift ◽  
Refractive Index Sensor ◽  
Gap Size ◽  
Refractive Index Sensitivity

In recent years, the plasma gap resonance maintained by metal-film-coupled nanostructures has attracted extensive attention. This mainly originates from its flexible control of the spectral response and significantly enhanced field strength at the nanoparticle–film junction. In the present study, the tunability of local surface plasmon resonances (LSPRs) of nanorods coupled to a gold film is studied theoretically. To this end, the plasmonic resonances in the nanostructure of individual silver nanorod–gold film (AgNR-film) with different parameters are investigated. Obtained results show that the refractive index sensitivity (S) of nanostructures to the environment increases as the aspect ratio (Ar) of nanostructures increase. It is found that when the aspect ratio (Ar) is set to 3.5, the figure of merit (FOM) is the highest. Moreover, the variation in the gap distances of the nanorod monomer–gold film, electric field distribution of nanorods dimer, and the corresponding impact on the gold film are studied. It is concluded that the gap size of nanostructures has an exponential correlation with the resonance wavelength. Considering the remarkable influence of the gap size and the surrounding medium environment on the spectral shift of AgNR-film nanostructures, potential applications of the structure as a refractive index sensor and biomolecule measurement are proposed.

Modelling of semiconductor rib wave guides by a finite difference method

1991 ◽  
Vol 69 (3-4) ◽  
pp. 512-519 ◽  
Author(s):  
A. Delâge
Keyword(s):  
Refractive Index ◽  
Boundary Conditions ◽  
Abrupt Change ◽  
Multiple Quantum Well ◽  
External Boundary ◽  
Multiple Quantum ◽  
Scalar Wave ◽  
Accurate Evaluation ◽  
Wave Guides ◽  
Mode Characteristics

The method of finite differences is used to solve the scalar wave equation for semiconductor rib wave guides. Boundary conditions derived from continuity relations are applied between regions of different refractive index, allowing more accurate evaluation of the propagation constants for ideal cases of abrupt change in the index. Also appropriate external boundary conditions alleviate the inaccuracy generally introduced by setting the field equal to zero on the external limit of the mesh. Our results agree with various other techniques when applied to typical guiding structures. As an example, we model a multiple-quantum-well structure by using an equivalent layered structure. Mode characteristics and confinement factors obtained by the method are of interest in understanding the behaviour of the lasers and modulators fabricated in our laboratory.

scholarly journals Switchable Photonic Nanojet by Electro-Switching Nematic Liquid Crystals

Nanomaterials ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 72 ◽  
Author(s):  
Bintao Du ◽  
Jun Xia ◽  
Jun Wu ◽  
Jian Zhao ◽  
Hao Zhang
Keyword(s):  
Refractive Index ◽  
Liquid Crystals ◽  
Double Layer ◽  
Nematic Liquid Crystals ◽  
Surrounding Medium ◽  
Refractive Index Change ◽  
Electric Energy ◽  
Incident Wavelength ◽  
Photonic Nanojet ◽  
Energy Focusing

This paper first presents a switchable photonic nanojet (PNJ) generated by a polystyrene (PS) microsphere immersed in nematic liquid crystals (NLCs). The PNJ is switched by applying external voltage, which originates from the refractive index change in the surrounding medium caused by the field-induced realignment of liquid crystal molecules. By tuning the refractive index of NLCs larger or smaller than that of the PS microsphere, the PNJ can be switched off or on. Moreover, we present an optimization study to seek a better electric energy focusing property of the PNJ. Our results reveal that the switchability of PNJ can be optimized by applying a shorter incident wavelength, a double-layer microsphere, and a PS ellipsoid. The full width at half-maximum (FWHM) generated by the PS ellipsoid is narrower than that generated by the microsphere with a shorter incident wavelength. The intensity contrast of the PS ellipsoid is higher than that of the double-layer microsphere. As a whole, the switchability of PNJ can be best optimized by a PS ellipsoid. This should open the way for the development of integrated photonic devices.

Comparative analysis of two different types of intracorneal implants in keratoconus: A corneal tomographic study

2020 ◽  
pp. 112067212096344
Author(s):  
Mohammad-Reza Sedaghat ◽  
Hamed Momeni-Moghaddam ◽  
Michael W Belin ◽  
David P Piñero ◽  
Reyhaneh Akbarzadeh ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Spherical Equivalent ◽  
Q Value ◽  
Corneal Surface ◽  
Corrected Distance Visual Acuity ◽  
Different Types ◽  
Corneal Asphericity ◽  
Tomographic Data ◽  
Corneal Shape ◽  
Mean Differences

Objective: To evaluate changes in visual acuity and corneal tomographic outcomes at 6 months after femtosecond-laser assisted implantation of two different types of intracorneal implants in keratoconus. Methods: A total of 39 keratoconus eyes implanted with two segments KeraRing ( n = 22 eyes) or MyoRing ( n = 17 eyes) were enrolled. Tomographic data (Pentacam system, Oculus) were analyzed and correlated with enhancement in uncorrected (UDVA) and corrected distance visual acuity (CDVA). The tomographic indices were front maximum keratometry (Kmax), corneal asphericity (Q-value) on both surfaces, average pachymetric progression indices (PPI), maximum Ambrosio relational thickness (ARTmax), Belin-Ambrósio enhanced ectasia total deviation index (BAD-D), index of surface variance (ISV), vertical asymmetry (IVA), height asymmetry (IHA) and height decentration (IHD). Results: LogMAR UDVA and CDVA improved 2.1 ( p = 0.003) and 0.7 ( p = 0.074) lines with KeraRing, and 8 and 2.5 lines with MyoRing ( p = 0.001). The highest and lowest mean differences in the tomographic indices between both groups were related to ISV and IHD, respectively. Changes in all indices differed significantly between two groups except for changes in front corneal astigmatism, ARTmax, ISV, IVA, IHD and IHA ( p > 0.05). Correlation of changes in CDVA with changes in other parameters was statistically significant only for IHD in the KeraRing group, while changes in in UDVA were significantly correlated with changes in spherical equivalent, back Q-value, ISV, IVA, and IHA only in the MyoRing group. Conclusion: Both implants promote corneal shape regularization and an enhancement in UDVA in keratoconus. A considerable flattening effect and reduction in prolateness in the front corneal surface were observed with MyoRing.

scholarly journals The impact of irregular corneal shape parameters on visual acuity and contrast sensitivity

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Sanita Liduma ◽  
Artis Luguzis ◽  
Gunta Krumina
Keyword(s):  
Visual Acuity ◽  
Contrast Sensitivity ◽  
Cross Sectional Study ◽  
Shape Parameters ◽  
Corneal Surface ◽  
Cross Sectional ◽  
Corneal Shape ◽  
Different Diameters ◽  
The Impact ◽  
Corneal Apex

Abstract Background To understand which irregular corneal parameters determine the visual quality in keratoconus subjects. Methods The cross-sectional study examined the eyes of 44 subjects, graded from the first to third keratoconus stages by Amsler-Krumeich classification. We obtained measurements in two ways: (a) by projecting two perpendicular axes onto a cornea (first, through the central point of the cornea and keratoconus apex; second, as the perpendicular axis) to read the elevation values at points on these axes as parameters characterising the corneal surface; (b) by projecting circles with different diameters around the central part of the cornea (1, 2, and 3 mm) and reading elevation values at points equally displaced on these circles as parameters characterising an anterior surface slope. Irregular corneal shape parameters’ correlations with visual acuity and contrast sensitivity were determined in order to understand which corneal slope parameter has the strongest correlation with visual acuity and contrast sensitivity. Results Parameters characterising the corneal surface’s correlations with contrast sensitivity were from r = 0.25 (p = 0.03) at 3 cpd to r = 0.47 (p < 0.01) at 9 cpd for the highest elevation and from r = 0.33 (p = 0.09) at 5 cpd to r = 0.40 (p < 0.01) at 11 cpd for the lowest elevation in all subjects together, while for visual acuity the parameters were r = 0.30 (p < 0.01) for the highest elevation and r = 0.21 (p = 0.06) for the lowest elevation in all subjects together. The correlation between contrast sensitivity and the highest and lowest corneal point in all measured cornea was stronger for subjects with a peripheral corneal apex than for those with a central apex. In keratoconus subjects, contrast sensitivity displayed a strong correlation with slope in the central part of the cornea (with a radius of 1 mm) ranging from 0.48 (p < 0.01) at 3 cpd to 0.61 (p < 0.01) at 9 cpd. Conclusion Contrast sensitivity has a higher correlation with corneal shape parameters than with visual acuity. Subjects with a peripheral corneal apex had stronger correlations with visual acuity and contrast sensitivity than did subjects with a central apex. In keratoconus subjects, the strongest correlation was for contrast sensitivity and elevation (slope) in the region within a 1 mm radius of the corneal centre in the opposite direction of the keratoconus apex (direction (ax) CB).

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