PURPOSE: The goal of this study was to determine age-related variation in the elasticity of the human cornea using nondestructive means METHODS: Organ cultured human corneoscleral buttons were studied Changes in strain were measured with a radial shearing speckle pattern interferometer after an increase in intraocular pressure from 150 to 155 mm Hg Changes in central corneal displacement were calculated by integration, and a bulk corneal Young's modulus was derived by mathematical analysis RESULTS: Fifty corneas, including 17 pairs, were studied Donors were aged between 24 and 102 years (mean, 731); 29 (58%) specimens were from male donors and 21 from female donors Young's modulus of the cornea increased with age, with the line of best fit indicating an approximate doubling from 027 MPa at age 20 years (95% confidence interval, 022-031) to 052 (050-054) MPa at age 100 years (R² = 070) CONCLUSIONS: The stiffness of the human cornea increases by a factor of approximately two between the ages of 20 and 100 years This variation is relevant to the algorithms used to predict the response to incisional and ablative refractive surgery and will also affect the formulas used to calculate intraocular pressure by applanation

Age-related differences in the elasticity of the human cornea.

A new type of interferometer is described by means of which the asphericity of an optical wavefront can be measured, by testing it against itself with lateral displacement or shear. Continuous control of the amount of this shear, and of the meridional or sagittal fringes is obtained in white light.

A wavefront shearing interferometer

A new method for recording Fresnel transformations of two- and three-dimensional scenes illuminated by spatially incoherent light is described. The technique is based on the properties of the triangular interferometer and the afocal optical system. Experimental results with one- and two-point objects have verified the basic principles of the method.

New Method of Making Fresnel Transforms with Incoherent Light

Measurement of Freeform Optical Surfaces: Trade‐Off between Accuracy and Dynamic Range

It is difficult to test aspheric surfaces with a Twyman-Green interferometer because the interferogram frequently contains too many fringes. A simple way of overcoming this problem is to use a lateral-shearing interferometer, in which case the number of fringes in the interferogram can be controlled by varying the shear. However, this has the drawback that two interferograms with orthogonal directions of shear are required; in addition, the accuracy with which the shape of the surface can be evaluated from measurements on photographs of the fringes is limited. In this paper it is shown how these difficulties can be overcome by using a microcomputer-controlled digital radial-shear interferometer. The values of the phase difference in the interferogram at a matrix of points covering the pupil are processed directly in the same microcomputer to give the actual shape of the surface. Typical results obtained with an off-axis paraboloid are presented.

Measurement of Aspheric Surfaces Using a Microcomputer-controlled Digital Radial-shear Interferometer

A new type of wave front shearing interferometer is described in which two images of the wave front under test which are of different sizes are made to interfere. When the centres of the two images coincide, this results effectively in shear along the radial direction. It is shown that the interpretation of the resulting interferogram is comparatively easy. In addition, the instrument is extremely convenient to handle, since all the adjustments can be made with a white light source.

Radial shearing interferometer

https://iopscience.iop.org/article/10.1088/0950-7671/38/11/305/pdf

D. Sen

Papers

Radial shearing interferometer

Radial shearing interferometer