In visual assessments, what can influence a patient's ability to read from a Snellen chart?

In visual assessments using a Snellen chart, several factors can significantly influence a patient's ability to read the letters displayed. The correct answer encompasses multiple aspects that affect the clarity and visibility of the chart.

The angle of illumination plays a crucial role because proper lighting ensures that the letters on the chart are clearly visible and not obscured by glare or shadows. Insufficient or excessive lighting can compromise the patient's performance, as it may cause distress for the eyes, making it challenging for them to discern the letters accurately.

The patient's distance from the chart is another vital factor. The Snellen chart is calibrated to be viewed from a specific distance, typically 20 feet in a standard clinical setting. If the patient is too close or too far away, it can distort the perceived size of the letters, leading to inaccurate visual acuity measurements.

By recognizing that both the angle of illumination and the patient's distance from the chart are integral to optimal visual assessment, one can understand how these factors combine to affect test performance.