The correct option is Pattern of blood vessels on the retinal surface.

The Pattern of blood vessels on the retinal surface is what retinal scanners capture by projecting a safe low intensity light into the eye and mapping the vascular pattern at the back of the eye. The retinal vasculature is internal and highly distinctive and it remains stable over many years which makes it suitable for identity verification.

Pattern of photoreceptor cells on the retina is incorrect because photoreceptor distribution refers to microscopic rods and cones and is not the biometric pattern that retinal scanners use for matching. Scanners target the vascular pattern rather than cell layouts.

Amount of light reflected from the retina is incorrect because a simple measure of overall reflectance does not provide the unique spatial detail needed for identity verification. Retinal systems analyze the spatial vascular pattern rather than a single brightness value.

Iris surface texture is incorrect because iris recognition examines the external colored ring around the pupil and its surface features while retinal scanning probes the internal blood vessel pattern at the back of the eye. These are distinct biometric modalities.

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