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Focimetry. When a patient is dispensed a pair of glasses is important to make sure that the lenses are done according to the patients prescription. To ensure that the patient is getting the right spectacles, the lenses should be checked before th

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Introduction

Reflection on the process of focimetry When a patient is dispensed a pair of glasses is important to make sure that the lenses are done according to the patient's prescription. To ensure that the patient is getting the right spectacles, the lenses should be checked before the patient is collecting them. A method of checking the prescription of a patient's spectacles is by measuring the powers on a focimeter. According to the British Standard Institute (2003, p49), a focimeter is "an optical instrument for determining the vertex powers, axis direction and centration of ophthalmic lenses". There are three types of focimeters: the projection focimeter, the computerized focimeter and the telescopic focimeter. The projection focimeter allows the user to view a screen from a distance of about 0.50 meters. The user can use both eyes which can be more comfortable fore some users. However, the screen can be difficult to see in a brightly lit room. The computerised focimeter is the most automated focimeter and is often seen in optical practices, hospitals and eye clinics. The operator only needs to rest the spectacles up on the centre and to push a button. ...read more.

Middle

During the steps mentioned above is important to keep both of the eyes open to ensure that the target is viewed with the accommodation relaxed. (Jalie and Wray, 2002). In the process of focimetry, the focimeter used is a telescopic one with the ring of dots target. During the process of focimetry three steps were followed to read the spectacles powers and the Optical Centres: * First, it was adjusted the angle of focimeter on the workbench so the eyepiece is in a comfortable position. * Then it was checked if the eyepiece is focused on the eye * Finally, both eyes were open when looking through the eyepiece. It should be used the dominant eye to look through the eyepiece with the dominant eye as it is much easier to ignore the image in the non dominant eye. According to David Wilson (1999, p140), to find the dominant eye the subject needs to focus at a distant object such as a door frame with both eyes open. A finger is hold at an arm's length and lined up with the distant object as though it were the sight of a gun. ...read more.

Conclusion

The higher sphere reading is recorded as the sphere power and the smaller reading minus the higher reading will give the cylinder power. When reading prescription of lenses with sphere and cylinder incorporated, an error of +/- 0.25D was made. The reasons why can be that the lens was not aligned flat on the table of the focimeter or the eyes are accommodating with the focimeter and the reading will be wrong. These errors can be overcome by having both of the eyes opened and making sure that the lens sits flat on the table of the focimeter. The focimeter is an important tool to read the power of the spectacles. In my practice I found that by using the focimeter many problems can be avoided, problems like giving the wrong prescription spectacles to the customer or giving the right prescription but with the optical centres wrong. At the beginning of the process of focimetry I found that the power of the spectacle lenses were not exactly as the power on the dispense record. But later I realised that if one of the steps in reading a prescription is missed, like calibrating the focimeter, or making sure that the eyepiece is sitting straight and aligned to me, the readings can be wrong. ...read more.

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