ABSTRACT
Contents 8.1 Introduction 103 8.2 Instruments for the examination of the anterior segment 104
8.2.1 Keratometers 104 8.2.1.1 Principles of keratometry 104 8.2.1.2 One-and two-position keratometers 105 8.2.1.3 Automated keratometry 105
8.2.2 Corneal topography 106 8.2.2.1 Basic topographic principles 106
8.2.3 Slit lamp 107 8.2.3.1 Fundamentals of slit-lamp biomicroscopy 107 8.2.3.2 Slit-lamp accessories 108 8.2.3.3 Goldmann applanation tonometer 108
8.2.4 Noncontact tonometers and the ORA 108 8.2.4.1 ORA 109
8.3 Retinal imaging instruments 109 8.3.1 Direct ophthalmoscope 109 8.3.2 Indirect and binocular ophthalmoscope 110 8.3.3 Retinography (fundus cameras) 111
8.4 Objective refraction tests 111 8.4.1 Retinoscope 112
8.4.1.1 Illuminating systems 112 8.4.1.2 Viewing system 112 8.4.1.3 Neutralization of the reflex: Relationship between refractive error and the working distance 114 8.4.1.4 Retinoscopy of astigmatic eyes 114
8.4.2 Optometers and autorefractors 114 8.4.2.1 The Badal optometer and the Scheiner disc 114 8.4.2.2 Modern autorefractometers 115
8.5 Subjective refraction equipment 116 8.5.1 Visual acuity testing devices, visual acuity test charts, and optotype projector and displays 116 8.5.2 Phoropters and trial case lenses 117 8.5.3 Contrast sensitivity tests 119
References 119
The examination of the anterior segment involves several instruments of different characteristics. On the one side, instruments such as keratometers and corneal topographers are intended for the optical characterization of the cornea, mainly its refractive power. On the other side, slit-lamp biomicroscopes are utilized for the observation of external ocular structures. The Goldmann applanation tonometer is included in this section as a slit-lamp accessory, and, for completeness, we also describe the noncontact tonometers and the ocular response analyzer (ORA).
