Astigmatism

Astigmatism is a refractive error caused by abnormal curvature of the cornea thereby causing blurred vision. It might occur along with myopia or hyperopia. Some persons suffer astigmatism from birth. Astigmatism can be identified with the routine eye tests. Visual acuity test, keratometry and refraction might be undertaken to diagnose the astigmatism or any other vision problem. Mild astigmatism is not usually corrected. Corrective lens is prescribed after noting the extent and axis of the astigmatism. Orthokeratology is undertaken to implant specially designed rigid contact lenses to gradually reshape the curvature of the cornea. Laser surgery can be done to alter the corneal shape.

Keratoscope

Keratoscope is a medical instrument used to examine the cornea, especially to detect the irregularities in its anterior surface. A keratoscope fitted with a video camera is videokeratoscope which is commonly employed in ophthalmic surgical procedures. Also called Placido's disk, keratoscope uses light to project rings on the cornea. It is a non invasive procedure. One can observe through a keratoscope, reflection of light from the cornea. An inspection of the shape and spacing of the rings which are concentric provides the viewer information about the degree of astigmatism. While in a regular shaped cornea there should be equally spaced symmetric reflections, in patients suffering from astigmatism, the rings will be distorted revealing corneal dystrophy.

In modern methods of sight correction including microsurgical operation of keratotomy and contact lens fitting, it becomes imperative to know the exact shape of the anterior surface of the cornea. For successful use of these methods, keratoscope is employed. Two new types of keratoscopes have evolved. One is the reflective type and the other transparent type. Transparent type of keratoscope is particularly useful in controlling corneal astigmatism during intra ocular surgery.

Such surgical keratometers enable the surgeons to monitor corneal astigmatism during wound closure and adjust suture tension accordingly. From the complex and expensive Terry Keratometer to the simple metal and plastic device of Karickoff, keratometers and scopes are varied, although these devices operate on the basic principle wherein the reflected image of a circular light source show an elliptical shape if significant astigmatism is present. Perhaps the most modern development of the keratoscope concept is corneal topography. Here, the analysis of the reflected image is passed on to a computer. The automated instrument is capable of producing color coded contour maps of the topology of the eye and even a three dimensional visualisation of its surface.

Orthokeratology

Orthokeratology is a process that reshapes the cornea using hard contact lens so as to correct or reduce refractive problems such as astigmatism, hyperopia and myopia. This is a non-surgical and non-invasive process that involves wearing specific lenses each night so as to achieve ideal corneal shape. This allows the person suffering the vision problem to be free of spectacles or glasses throughout the day. Those with high myopic error have seen some reduction in the error while teenagers how are recently myopic can help stabilize the progression of the vision defect. But the person needs to visit the optometrist many times in a period of about 6 months.