If a patient is unable to read the largest letter on the Snellen chart, what is the first step you should take?

When a patient is unable to read the largest letter on the Snellen chart, the first step to take is to count fingers. This method allows you to quickly gauge the patient's approximate visual acuity and determine whether they have any functional vision beyond mere light perception. Counting fingers can be a straightforward, practical examination that provides clear insight into the level of vision a patient possesses, which is essential for deciding next steps in assessment or treatment.

Using a pinhole occluder could also be useful, but it is typically employed after confirming that a patient has some form of usable vision; the pinhole test helps to clarify whether the visual problem is due to refractive issues. Measuring visual fields and assessing color vision are important parts of a comprehensive eye examination, but they are not immediate priorities when a patient clearly cannot read the largest letters on the Snellen chart. Immediate assessment focuses on understanding the patient's basic visual capabilities, making counting fingers the most appropriate initial response.