What type of instrument is used to document visual field defects?

The correct choice is a visual field instrument, which is specifically designed to assess and document visual field defects. This instrument evaluates the entire scope of vision, including peripheral vision, allowing practitioners to identify any areas of vision loss or abnormalities. The visual field test can reveal conditions such as glaucoma, retinal diseases, or neurological issues that might affect visual function.

In contrast, a visual acuity chart is used to measure the sharpness of vision but does not provide information about the visual field. An ophthalmoscope is utilized to examine the inside of the eye, focusing on structures like the retina and optic nerve, which is important for diagnosing certain eye diseases but does not directly assess visual field defects. A slit lamp is a microscope that provides a magnified view of the eye's front structures, including the cornea and lens, but again is not designed for visual field assessment. Thus, the visual field instrument is the only choice that directly fulfills the requirement of documenting visual field defects.