Which part of the eye is lacking visual receptors?

The optic disk, also known as the blind spot, is the correct answer because it is the point on the retina where the optic nerve fibers exit the eye. This area does not contain any photoreceptors—neither rods nor cones—therefore it cannot detect light, resulting in a lack of vision in that part of the visual field. When an image falls on the optic disk, it cannot be perceived, which is why it's referred to as the blind spot.

In contrast, the macula is a region of the retina that contains a high concentration of cones and is responsible for sharp central vision, making it crucial for tasks like reading and recognizing faces. The neural tunic refers to the inner layer of the eye, which includes the retina and its associated structures, all of which have photoreceptors that facilitate vision. The palpebral fissure, being the opening between the eyelids, is simply an anatomical feature and not related to the presence or absence of visual receptors.