Blind spot (vision)

Area of the retina without photoreceptors

Blind spot (also known as the optic disc) refers to a specific area on the retina of the eye where the optic nerve exits the eye. This region lacks photoreceptor cells, meaning it cannot detect light, resulting in a gap in the visual field. Despite this, the brain typically compensates for the blind spot, so it is not usually noticeable in everyday vision.

Anatomy and Physiology

The blind spot is located approximately 15 degrees temporally from the point of fixation in each eye. It corresponds to the location where the ganglion cell axons exit the eye to form the optic nerve. This area is devoid of rods and cones, the photoreceptors responsible for detecting light and color.

Distribution of photoreceptors in the human retina, showing the absence of photoreceptors at the optic disc.

The optic disc is approximately 1.5 mm in diameter and is situated nasally in the visual field. The absence of photoreceptors in this region means that any light that falls on the optic disc is not detected, creating a "blind" spot.

Compensation by the Brain

The human brain uses information from both eyes to fill in the blind spot. When both eyes are open, the blind spots do not overlap, allowing the brain to use visual information from one eye to fill in the missing information from the other. Even with one eye closed, the brain can use surrounding visual cues to "fill in" the blind spot, making it unnoticeable under normal circumstances.

Testing for the Blind Spot

The blind spot can be demonstrated using a simple test. By closing one eye and focusing on a specific point, an object placed at a certain angle from the point of fixation will disappear from view when it falls on the blind spot. This test highlights the area of the visual field that corresponds to the optic disc.

Clinical Significance

While the blind spot is a normal anatomical feature, changes in its size or shape can indicate pathological conditions. For example, swelling of the optic disc, known as papilledema, can occur due to increased intracranial pressure and may affect vision.

Also see

• Retina
• Optic nerve
• Photoreceptor cell
• Visual field
• Papilledema

References

Diagram showing the night blind spot, which is different from the optic disc blind spot.