Jaroslaw W. Jaronski

Spatially resolved polarization properties for in vitro corneas

Spatially resolved polarization properties of in vitro mammalian corneas have been studied by using a Mueller‐matrix imaging polarimeter in transmission mode. Sixteen images corresponding to independent combinations of polarization states in the illumination and analyzing pathways are recorded. Spatially resolved Mueller matrices of the samples are calculated from them. Results show that the birefringence of the cornea is almost linear. Although the magnitude of retardation depends on the sample, it is approximately constant at the center and increases towards the periphery. Dichroism and polarizing power are negligible. Maps of the degree of polarization indicate that the cornea basically does not depolarize the totally polarized incident light.

Interferometric measurements of dynamic changes of tear film

Tear film stability plays an important role in the quality of vision. We present an interferometric method for assessing the stability of precorneal tear film in real time. A lateral shearing technique is applied as a noninvasive and sensitive method for investigating tear film stability and the smoothness of the tear film surface by quantitative evaluation of the interference fringe pattern. The evaporation of tears and the appearance of tear film break-up between blinks cause changes in the fringe geometry. For quantitative assessment of the fringe smoothness and consequently of the tear film structure, the fast Fourier transform (FFT) is applied. Four parameters are used to quantitatively estimate dynamic changes in the tear film stability of the cornea 20 s after the eye blink. Examples of examined interferograms recorded in patients with healthy eyes, patients suffering from dry-eye syndrome, and patients wearing contact lenses are given. Significant differences between the stability of the tear film in the healthy eye and that in the dry eye and the eye with a contact lens are observed. The favorable influence of artificial tears applied in patients with dry-eye syndrome or contact lenses is also discussed.

Linear birefringence measurements of the in vitro human cornea.

This paper presents results of an in vitro investigation of the optical anisotropy of the human cornea. Computer controlled imaging polarimetry and the Jones formalism were used to investigate the distribution of the birefringence and the azimuth angle across the surface of 12 corneas taken from the corneal bank. Each map of the birefringence and the azimuth angle has no rotational symmetry and is different for each cornea. The minimal value of the birefringence always appears in the corneal centre and varies from 9 to 43° for different corneas. Birefringence of the cornea increases monotonically more than one order in the direction of the corneal periphery. Close to the centre of the cornea the azimuth angle is almost constant and varies significantly away from the optical part of the cornea.

Ultrasonic system for accurate distance measurement in the air

This paper presents a system that accurately measures the distance travelled by ultrasound waves through the air. The simple design of the system and its obtained accuracy provide a tool for non-contact distance measurements required in the lasers optical system that investigates the surface of the eyeball.

Generalized algorithm for photoelastic measurements based on phase-stepping imaging polarimetry

A general method for measuring the birefringence of nondichroic, linear retarder media has been presented. The method is based on phase-stepping imaging polarimetry and permits the azimuth angle, phase retardation, and transmission coefficient of a sample to be calculated. The method uses a simple setup, a sample at rest, and permits fast acquisition of data. With the mathematical description applied, various algorithms for different optical configurations can be used and any number of intensity patterns can be generated. Experimental results for photoelastic samples and the results of measurements of the birefringence of optical components and biological samples are also presented.

Interferometric measurements of the tear film irregularities on the human cornea

The pre-ocular tear film is the most anterior refractive surface of the eye. Its stability plays an important role in the condition of vision from the optical and physiological point of view. If the eye is opened for a significantly long time or suffers from an anormalities in tear production, there appear isolated dry islands - break-ups - with a random distribution in the continuous lacrimal film. We applied an interferometric method - Lateral Shearing Technique for investigating the tear film stability and the smoothness of the tear film surface. This method is non-invasive and it is characterised by the high accuracy and sensitivity. Interferometry allows dynamic measurements of the tear film stability in real time by observation of interference fringes. The evaporation of tears and appearance of the breakups causes changes in the fringe geometry. Fast Fourier Transform has been used for quantitative assessment of the fringe smoothness and as a consequence of the tear film surface geometry. This paper presents the method used for quantitative evaluation of the tear film distribution on the cornea. Examples of interferograms recorded on eyes of patients with healthy eyes, suffering from dry eye syndrome and wearing contact lenses are also given. With our technique we were able to observe distinct differences in stability of the tear film between healthy and dry eyes, and the tear film on contact lenses.

Interferometric measurements of fine corneal topography

The cornea is the most refractive element in the eye. Its refractive power is about 70% of the power of the whole eye. The shape of the cornea is aspheric, and almost always has no rotational symmetry. Even small surface irregularities can cause a perceptible reduction in visual acuity. Standard methods for evaluation of the corneal topography used in clinical practice include keratometry, photokeratoscopy, and computer assisted videokeratography. All of these methods used the principles of geometrical optics, and their accuracy is about 0.25 D. An application of interference phenomenons to examine the corneal contour map significantly increase the accuracy. Using the interferometric inspection of the corneal shape one can easily observe the fine corneal topography, the fast, dynamic changes of the corneal surface, and the topology of the tear film and its irregularities. The paper presents the Twyman Green interferometer, used in experiments, an example of sequence of interferograms and their 3D presentations.

Novel double path shearing interferometer in corneal topography measurements

The paper presents an approach for measurements of corneal topography by use of a patent pending double path shearing interferometer (DPSI). Laser light reflected from the surface of the cornea is divided and directed to the inputs of two interferometers. The interferometers use lateral shearing of wavefronts in two orthogonal directions. A tilt of one of the mirrors in each interferometric setup perpendicularly to the lateral shear introduces parallel carrier frequency fringes at the output of each interferometer. There is orthogonal linear polarization of the laser light used in two DPSI. Two images of fringe patters are recorded by a high resolution digital camera. The obtained fringe patterns are used for phase difference reconstruction. The phase of the wavefront was reconstructed by use of algorithms for a large grid based on discrete integration. The in vivo method can also be used for tear film stability measurement, artificial tears and contact lens tests.

Application of phase stepping imaging polarimetry technique in ophthalmology

The cornea is the outermost segment of the eyeball. Due to its lamellar structure the cornea indicates the optical anisotropy and effect of birefringence. We have applied phase stepping imaging polarimetry to measure birefringence of the human cornea in vivo and in vitro. Investigation of the corneal birefringence could be useful for examining the inner corneal structure, its lamellar arrangement and in medical diagnosing of corneal pathologies. There are also some potential applications of this method in transplantation of human corneas and refractive surgery procedures. The phase stepping imaging polarimetry technique used here, allows calculating azimuth angle, phase retardation and transmission coefficient of the sample. The method uses simple setup, sample at rest, and enables fast and accurate acquisition of data. The theory of the method is included. Experimental results of azimuth angle and phase retardation distribution for human cornea in vivo and in vitro are also presented.

Numerical and experimental study of the corneal anisotropy

An anisotropy of optical elements of the human eye is examined. A theoretical model of the corneal birefringence is considered. Ray tracing through such a model depending on different approximation of the corneal topography is calculated. In the paper photographs of the polarization patterns of the cornea in vivo with linearly polarized light are presented. Numerical and experimental results are compared and discussed.