Essay About Contact Lenses

The point of this experiment was to demonstrate that a transparent convex surface filled with water allowed rays of light from the peripheral visual field to focus on the pupil after refraction, as they passed through two media of different refractive index.From a close analysis of his notes, some of which appear to have been amended, possibly years after first being written, Leonardo seems to have realised that the surface of what he called ‘the luce of the eye’ has been transferred, so-to-speak, to the edge of the bowl through the action of the water contained in the bowl which is in direct physical contact with both eyes and had effectively neutralised the refractive power of the eye surface itself.In this discourse Descartes described and illustrated an extending water-filled tube which would serve the purpose of lengthening the eye's axis.

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 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.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.The year before he had moved into his late uncle's house in London and thus had the time and space to devote to his studies.Three of the other subjects he investigated would find applications in twentieth century contact lens materials: The size of molecules, the surface tension in liquids and the elasticity of materials (which is still defined by Young's modulus).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.Indeed, Descartes wrote that placing the water right in front of the eye would also be impractical which is why he went straight on to describe a glass tube closed at both ends - in effect describing the principle of the Galilean telescope.As with all Cartesian reasoning he was outlining a series of steps towards solving a problem. Levene FBOA attempted unsuccessfully to recreate Descartes' tube in 1977.

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