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3 Sight Measurement

Learning Objectives

The science of the measurement of the properties of sight is an advanced medical and engineering discipline. From a medical viewpoint, sight measurements are a means to diagnosis and route to prosthesis prescription. The engineering challenge in this measurement science is the application of precision engineering to quantify sight parameters using non-invasive methods.

The classical sight parameters are acuity and field of vision. Acuity is quantified over a range of distances (far, intermediate and close) whilst field of vision measures the image spread of the eye. These two test groups commonly support the prescription of lenses to correct for vision deficiencies.

A more modern and recent group of diagnostic tools include those to measure intraocular pressure and eye electrical potential gradients and those tools used to photograph the retina. These all use some advanced engineering methods. Finally, there is now equipment that automates some of the classical sight measurements; some of this equipment is now commonly found in opticians dispensaries.

Clearly there is continuing development of the science and equipment for sight measurement involving a substantial medical engineering input; this is described in this chapter for which the learning objectives are:

To understand the principles of the measurement of classical and diagnostic sight parameters.

To appreciate the engineering construction of selected items of sight measurement equipment.

To review the general trend of current and future research and development for sight parameter measurement equipment.

3.1 Introduction

A wide range of complementary tests is available for assessing an individual’s vision. Subjective tests such as visual acuity or visual field measurements rely on a response from the patient to a particular test condition. This response can be