Which instrument is used primarily for the indirect examination of the fundus?

The indirect ophthalmoscope is the instrument specifically designed for the indirect examination of the fundus, which is the interior surface of the eye, including the retina, optic disc, and macula. This instrument allows the clinician to view a wide field of the fundus easily and provides a three-dimensional view, enabling better assessment of any potential retinal abnormalities.

When using an indirect ophthalmoscope, the examiner can adjust the lens and light source to gain a detailed view, which is essential for diagnosing conditions such as retinal detachment, diabetic retinopathy, and other retinal diseases. The use of a handheld lens, combined with the light from the indirect ophthalmoscope, allows for enhanced visualization and a broader exploration of the fundus compared to other instruments.

Other tools mentioned, like the pinhole, otoscope, and slit lamp, serve different primary purposes. The pinhole is primarily used to assess refractive errors, the otoscope is designed for examining the ear, and the slit lamp is mainly used for detailed examination of the anterior segment of the eye and some aspects of the fundus in a direct manner. Thus, the specific design and functionalities of the indirect ophthalmoscope make it the correct choice for this task.