Essay About Contact Lenses

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Leonardo da Vinci, 1508 There is a traditional claim, much repeated in optometry and ophthalmology text books (and more latterly on websites, many copying from each other), that Leonardo da Vinci described and illustrated contact lenses in 1508, thereby giving birth to the study of their theoretical priniciple if not, at this stage, their practical application.

The latest scholarship, particularly the work of Professor Robert Heitz of Strasbourg (2003), demonstrates how this myth is of relatively recent origin (from the late 1950s) and how it has been distorted and extended by subsequent authors who haven’t gone back to the original sources.

If only he had concentrated upon the corneal lens idea he might have invented contact lenses far sooner than they were.

Both a physician and a physicist he embodied the unique link between ophthalmologists and optometrists to be detected subsequently in this branch of optics.

I take, out of a small botanical microscope, a double convex lens, of eight tenths radius and focal distance, fixed in a socket one fifth of an inch in depth; securing its edges with wax, I drop into the socket a little water, nearly cold, till three-fourths full, and then apply it to my eye, so that the cornea enters half way into it, and it is every where in contact with the water.

My eye immediately becomes presbyopic, and the refractive power of the lens, which is reduced by water to a focal length of about 16 tenths, is not sufficient to supply the place of the cornea, rendered inefficacious by the intervention of the water; but the addition of another lens, of five inches and a half focus, restores my eye to its natural state, and somewhat more., published in two volumes, 1807. Young discovered both that the cause of astigmatism and the fact that the cornea was not involved in accommodation.In other words this would be a completely impractical bioptic contact lens.It is doubtful however that the unit could have been hermetically sealed as required and the participant in the experiment would have been at risk of drowning because it covered the whole face.The reference comes in the seventh discourse of his essay (On Means of Perfecting Vision) in which he suggests, theoretically, that enlargement of the retinal image may be achieved by lengthening the ocular globe.Already we can assert that modern contact lenses do not work by increasing the axial length and are not concerned with enlarging an image, merely with correcting a refractive error...the experiment described in the discourse relates to a normal (emmetropic) eye, not one with an error.Franz Resisinger, 1824 In Germany in 1824 Franz Reisinger (1787-1855) mentioned the technique of corneal grafting suggesting its potential application from animal donor to human recipient.He also coined the term ' Keratoplasty' but the surgical solution was to be delayed for the time being.In this we certainly seem to be encountering the concept of corneal neutralisation.The length of the tube was adjustable so the device, if it had ever been made, would have had some historical parallel with the telescope but not so much with contact lenses since it was an afocal device and was not worn under the eyelids but had to be held in place by constant external pressure.The water-filled tube in direct contact with the eye was only the first and most readily dismissed step in his argument. Levene was perhaps the first modern scholar to challenge the idea that this was a contact lens, crucially identifying that many of the illustrations reproduced from the Discourse failed to show that it was a telescopic (extending) device.Thus we can conclude that it was never put forward as a serious practical suggestion and that the allusion to corneal neutralisation was incidental at best. The illustration shows Descartes' water-filled tube as illustrated in the 3rd edition of (1668) in our historical books collection.

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