MRD1

MRD1, or marginal reflex distance 1, is an ophthalmologic measurement used to quantify the position of the upper eyelid. It is defined as the vertical distance in millimeters between the corneal light reflex (the reflection of a light source on the cornea) and the margin of the upper eyelid when the patient looks straight ahead. The metric helps assess eyelid drooping (ptosis) and is a standard part of evaluating eyelid function.

Measurement is typically performed with the patient gazing forward at a distant target. A ruler or caliper is aligned from the corneal light reflex to the upper lid margin. The result can be influenced by examiner technique, eye position, lighting, and eyelid contour. MRD1 is often considered alongside other eyelid measurements, such as MRD2 (distance from the corneal reflex to the lower lid margin) and levator function.

Normal values are commonly cited as about 4.0 to 4.5 mm in adults, with some normal variation. Values significantly lower than this suggest ptosis, while unusually large values may indicate eyelid retraction. MRD1 is used in diagnosing ptosis, planning and assessing ptosis surgery (for example, levator resection or procedures involving the Müller muscle), and monitoring changes in conditions that affect eyelid position, such as Horner’s syndrome or myasthenia gravis.

Limitations include inter-examiner variability and factors such as lighting, fixation, and tear film. MRD1 is one component of a comprehensive eyelid assessment used to determine surgical candidacy and to track functional outcomes.