Wave refraction phenomena over the continental shelf near the Chesapeake Bay entrance /

"October 1974."

The interpretation of crossed orthogonals in wave refraction phenomena.

Mode of access: Internet.

A ripple tank study of wave refraction /

Mode of access: Internet.

Refraction of the eye, its diagnosis and the correction of its errors.

Mode of access: Internet.

Margetts's Longitude tables for correcting the effects of parallax and refraction, on the observed distance taken between the moon and the sun or a fixed star ... and the corresponding time at Greenwich, found by inspection.

Mode of access: Internet.

Simplified method for estimating refraction and shoaling effects on ocean waves /

"November 1975."

Théorie du système optique composé d'une lunette astronomique et d'un double miroir plan : application à la mesure précise des distances en vue de l'étude de l'aberration et de la refraction /

Mode of access: Internet.

A chapter on Fresnel's theory of double refraction,

Author's presentation copy.

The refraction of the eye. A manual for students.

Mode of access: Internet.

Evaluation of an open-field autorefractor's ability to measure refraction and hence potential to assess objective accommodation in pseudophakes

Background: To evaluate the accuracy of an open-field autorefractor compared with subjective refraction in pseudophakes and hence its ability to assess objective eye focus with intraocular lenses (IOLs). Methods: Objective refraction was measured at 6 m using the Shin-Nippon NVision-K 5001/Grand Seiko WR-5100K open-field autorefractor (five repeats) and by subjective refraction on 141 eyes implanted with a spherical (Softec1 n=53), aspherical (SoftecHD n=37) or accommodating (1CU n=22; Tetraflex n=29) IOL. Autorefraction was repeated 2 months later. Results: The autorefractor prescription was similar (average difference: 0.09±0.53 D; p=0.19) to that found by subjective refraction, with ~71% within ±0.50 D. The horizontal cylindrical components were similar (difference: 0.00±0.39 D; p=0.96), although the oblique (J45) autorefractor cylindrical vector was slightly more negative (by -0.06±0.25 D; p=0.06) than the subjective refraction. The results were similar for each of the IOL designs except for the spherical IOL, where the mean spherical equivalent difference between autorefraction and subjective was more hypermetropic than the Tetraflex accommodating IOL (F=2.77, p=0.04). The intrasession repeatability was

Theoretical evaluation of the cataract extraction-refraction-implantation techniques for intraocular lens power calculation

PURPOSE: To evaluate theoretically three previously published formulae that use intra-operative aphakic refractive error to calculate intraocular lens (IOL) power, not necessitating pre-operative biometry. The formulae are as follows: IOL power (D) = Aphakic refraction x 2.01 [Ianchulev et al., J. Cataract Refract. Surg.31 (2005) 1530]; IOL power (D) = Aphakic refraction x 1.75 [Mackool et al., J. Cataract Refract. Surg.32 (2006) 435]; IOL power (D) = 0.07x(2) + 1.27x + 1.22, where x = aphakic refraction [Leccisotti, Graefes Arch. Clin. Exp. Ophthalmol.246 (2008) 729]. METHODS: Gaussian first order calculations were used to determine the relationship between intra-operative aphakic refractive error and the IOL power required for emmetropia in a series of schematic eyes incorporating varying corneal powers, pre-operative crystalline lens powers, axial lengths and post-operative IOL positions. The three previously published formulae, based on empirical data, were then compared in terms of IOL power errors that arose in the same schematic eye variants. RESULTS: An inverse relationship exists between theoretical ratio and axial length. Corneal power and initial lens power have little effect on calculated ratios, whilst final IOL position has a significant impact. None of the three empirically derived formulae are universally accurate but each is able to predict IOL power precisely in certain theoretical scenarios. The formulae derived by Ianchulev et al. and Leccisotti are most accurate for posterior IOL positions, whereas the Mackool et al. formula is most reliable when the IOL is located more anteriorly. CONCLUSION: Final IOL position was found to be the chief determinant of IOL power errors. Although the A-constants of IOLs are known and may be accurate, a variety of factors can still influence the final IOL position and lead to undesirable refractive errors. Optimum results using these novel formulae would be achieved in myopic eyes.

Controlling soliton refraction in optical lattices

We show in the framework of the 1D nonlinear Schrödinger equation that the value of the refraction angle of a fundamental soliton beam passing through an optical lattice can be controlled by adjusting either the shape of an individual waveguide or the relative positions of the waveguides. In the case of the shallow refractive index modulation, we develop a general approach for the calculation of the refraction angle change. The shape of a single waveguide crucially affects the refraction direction due to the appearance of a structural form factor in the expression for the density of emitted waves. For a lattice of scatterers, wave-soliton interference inside the lattice leads to the appearance of an additional geometric form factor. As a result, the soliton refraction is more pronounced for the disordered lattices than for the periodic ones.

Evaluation of the auto-refraction function of the Nidek OPD-Scan III

Background: The aim was to evaluate the validity and repeatability of the auto-refraction function of the Nidek OPD-Scan III (Nidek Technologies, Gamagori, Japan) compared with non-cycloplegic subjective refraction. The Nidek OPD-Scan III is a new aberrometer/corneal topographer workstation based on the skiascopy principle. It combines a wavefront aberrometer, topographer, autorefractor, auto keratometer and pupillometer/pupillographer. Methods: Objective refraction results obtained using the Nidek OPD-Scan III were compared with non-cycloplegic subjective refraction for 108 eyes of 54 participants (29 female) with a mean age of 23.7±9.5 years. Intra-session and inter-session variability were assessed on 14 subjects (28 eyes). Results: The Nidek OPD-Scan III gave slightly more negative readings than results obtained by subjective refraction (Nidek mean difference -0.19±0.36 DS, p<0.01 for sphere; -0.19±0.35 DS, p<0.01 for mean spherical equivalent; -0.002±0.23 DC, p=0.91 for cylinder; -0.06±0.38 DC, p=0.30 for J0 and -0.36±0.31 DC for J45, p=0.29). Auto-refractor results for 74 per cent of spherical readings and 60 per cent of cylindrical powers were within±0.25 of subjective refraction. There was high intra-session and inter-session repeatability for all parameters; 90 per cent of inter-session repeatability results were within 0.25 D. Conclusion: The Nidek OPD-Scan III gives valid and repeatable measures of objective refraction when compared with non-cycloplegic subjective refraction. © 2013 The Authors. Clinical and Experimental Optometry © 2013 Optometrists Association Australia.

Short-term changes in ocular biometry and refraction after discontinuation of long-term orthokeratology

OBJECTIVE: To assess refractive and biometric changes 1 week after discontinuation of lens wear in subjects who had been wearing orthokeratology (OK) contact lenses for 2 years. METHODS: Twenty-nine subjects aged 6 to 12 years and with myopia of -0.75 to -4.00 diopters (D) and astigmatism of ≤1.00 D participated in the study. Measurements of axial length and anterior chamber depth (Zeiss IOLMaster), corneal power and shape, and cycloplegic refraction were taken 1 week after discontinuation and compared with those at baseline and after 24 months of lens wear. RESULTS: A hyperopic shift was found at 24 months relative to baseline in spherical equivalent refractive error (+1.86±1.01 D), followed by a myopic shift at 1 week relative to 24 months (-1.93±0.92 D) (both P<0.001). Longer axial lengths were found at 24 months and 1 week in comparison to baseline (0.47±0.18 and 0.51±0.18 mm, respectively) (both P<0.001). The increase in axial length at 1 week relative to 24 months was statistically significant (0.04±0.06 mm; P=0.006). Anterior chamber depth did not change significantly over time (P=0.31). Significant differences were found between 24 months and 1 week relative to baseline and between 1-week and 24-month visits in mean corneal power (-1.68±0.80, -0.44±0.32, and 1.23±0.70 D, respectively) (all P≤0.001). Refractive change at 1 week in comparison to 24 months strongly correlated with changes in corneal power (r=-0.88; P<0.001) but not with axial length changes (r=-0.09; P=0.66). Corneal shape changed significantly between the baseline and 1-week visits (0.15±0.10 D; P<0.001). Corneal shape changed from a prolate to a more oblate corneal shape at the 24-month and 1-week visits in comparison to baseline (both P≤0.02) but did not change significantly between 24 months and 1 week (P=0.06). CONCLUSIONS: The effects of long-term OK on ocular biometry and refraction are still present after 1-week discontinuation of lens wear. Refractive change after discontinuation of long-term OK is primarily attributed to the recovery of corneal shape and not to an increase in the axial length.