We present a method to measure spherical power in ophthalmic lenses based on the measurement of moiré patterns, using the technique called infinite fringe moiré deflectometry. We develop a theoretical model using a geometrical analysis that was validated by a computer simulation using the LabVIEW software; also we build an experimental setup in which we get experimental data. As results, we obtain a measurement of the spherical power of a set of ophthalmic test lenses in the range of ± 0.50 to ± 3.00 diopters. This power is obtained by measuring the separation between each fringe of moiré pattern, from the obtained data we analyze the theoretical model and we make the necessary corrections, using polynomial regression by the method of least squares, to comply with standard ISO8598. At the same time, some components of the experimental setup were being improved to facilitate its implementation and obtain better experimental data.
Nowadays refractive errors in the human eye affect approximately 10% of world’s population, decreasing vision acuity and life quality. However a simple common solution is the use of an adequate ophthalmic lens. Due to the importance of ophthalmic lenses, the best measurement equipment is required for testing, these days experimental and commercial apparatus are available but with the possibility of improvement. We present a method to measure spherical and cylindrical power in ophthalmic lenses. The system uses an equation obtained from lateral amplification concept and Gauss formula to make calculations. Also an experimental setup is presented for the measurement of ophthalmic lens from -20 diopters to 20 diopters in the case of spherical lenses, and from -6 diopters to 6 diopters in the case of cylindrical lenses. The setup contains a reference object, the lens to be tested and a digital camera connected to a computer with software designed in LabVIEW for the data processing. Satisfactory preliminary results were obtained according to ISO 8598.
Optical beams of Bessel-type whose transverse intensity profile remains unchanged under free-space propagation
are called nondiffracting beams. Experimentally, Durnin used an annular slit on the focal plane of a convergent lens
to generate a Bessel beam. However, this configuration is only one of many that can be used to generate
nondiffracting beams. The method can be modified in order to generate a required phase distribution in the beam. In
this work, we propose a simple and effective method to generate spiral beams whose intensity remains invariant
during propagation using amplitude masks. Laser beams with spiral phase, i.e., vortex beams have attracted great
interest because of their possible use in different applications for areas ranging from laser technologies, medicine,
and microbiology to the production of light tweezers and optical traps. We present a study of spiral structures
generated by the interference between two incomplete annular beams.
Optical beams of Bessel-type, whose transverse intensity profile remains unchanged under free-space propagation, are called nondiffracting beams. In this paper, we propose a simple and effective method to generate spiral beams whose intensity remains invariant during propagation using amplitude masks. We show how the interaction between two incomplete annular beams leads to the formation of a spiral structure. Experimental observations are presented to show the characteristic features of the spiral structure generated. We can modulate the nondiffracting beam modifying the amplitude mask.
A new, simple method to measure the effective focal length of a thick lens or lens system in the laboratory when a lens nodal bench is not readily available is described. Use is made of the Talbot autoimaging effect by placing the lens in a collimated light beam, with a Ronchi ruling in front of the lens and another in the refracted beam.
In this paper we propose a new method of analysis to obtain the spherical power in ophthalmic lenses based on ray
traces of geometric optics techniques, formation, capture and image processing. We determine the spherical power
in ophthalmic lenses considering the total magnification of the optical system and the Gauss's formula. A simple,
practical and easy to implement experimental setup is presented for the measurement of positives and negative
lenses. The setup consists in a circular object displayed in a LCD monitor, the ophthalmic lens to be measured and a
digital camera in order to send information to a PC containing the software algorithm which calculates and displays
the spherical power.
Several techniques have been used to determine the radius of curvature of the cornea. In this article, we describe the use
of a method obtained trough ray analysis, based in geometrical analysis and lateral magnification equation. A pattern of
an increasing point was displayed in a flat screen monitor; images of this point were captured for a test sphere with a
CCD camera. The obtained data was then processed for the calculation of the sphere curvature. The experimental setup
In this paper, we will describe a method used to obtain the power error distribution map for a spherical well corrected ophthalmic lens. The proposed method uses a computer to perform a null test compensation to probe the real refractive correction state of the lens under test. The Hartman test is used to probe an ophthalmic lens and subtract the ideal power distribution map corresponding to the same lens design. In this way we obtain the power error distribution map of the lens. The proposed method may be useful in mass production of spherical ophthalmic lenses.
This paper describes a simple Hartmann test data interpretation that can be used to evaluate the performance in spherical ophthalmic lenses. Considering each spot of the Hartmann pattern like a single ray, using traditional ray tracing analysis it is possible to calculate the value of the spherical power in the point corresponding with each spot. The values of spherical power for each spot obtained by this procedure are used to obtain a spherical power distribution map of the entire lens.