Cross Section Of The Right Eye From Above Showing A Portion Of The Fundus Commonly Seen With The Ophthalmoscope

The posterior part of the eye that is seen through an ophthalmoscope is often called the fundus of the eye. Structures here include the retina, choroid, fovea, macula, optic disc, and retinal vessels. The optic nerve with its retinal vessels enters the eyeball posteriorly. You can find it with an oph thalmoscope at the optic disc. Lateral and slightly inferior to the disc, there is a small depression in the retinal surface that marks the point of central vision. Around it is a darkened circular area called the fovea.. The roughly circular macula (named for a microscopic yellow spot) surrounds the fovea but has no discernible margins. It does not quite reach the optic disc. You do not usually see the normal vitreous body, a transparent mass of gelatinous material that fills the eyeball behind the lens. It helps to maintain the shape of the eye.

Visual Fields. A visual field is the entire area seen by an eye when it looks at a central point. Fields are conventionally diagrammed on circles from the patient's point of view. The center of the circle represents the focus of gaze. The circumference is 90° from the line of gaze. Each visual field, shown by the white areas below, is divided into quadrants. Note that the fields extend farthest on the temporal sides. Visual fields are normally limited by the brows above, by the cheeks below, and by the nose medially. A lack of retinal receptors at the optic disc produces an oval blind spot in the normal field of each eye, 15° temporal to the line of gaze.

Temporal Field VisionCross Examination

LEFT EYE RIGHT EYE

Visual Fields Right And Left Eyes

When a person is using both eyes, the two visual fields overlap in an area of binocular vision. Laterally, vision is monocular.

Visual Pathways. For an image to be seen, light reflected from it must pass through the pupil and be focused on sensory neurons in the retina. The image projected there is upside down and reversed right to left. An

Light Shining Person Eye

image from the upper nasal visual field thus strikes the lower temporal quadrant of the retina.

Nerve impulses, stimulated by light, are conducted through the retina, optic nerve, and optic tract on each side, and then on through a curving tract called the optic radiation. This ends in the visual cortex, a part of the occipital lobe.

Pupillary Reactions. Pupillary size changes in response to light and to the effort of focusing on a near object.

The Light Reaction. A light beam shining onto one retina causes pupillary constriction in both that eye (the direct reaction to light) and the opposite eye (the consensual reaction). The initial sensory pathways are similar to those described for vision: retina, optic nerve, and optic tract. The pathways diverge in the midbrain, however, and impulses are transmitted through the oculomotor nerve to the constrictor muscles of the iris of each eye.

The Near Reaction. When a person shifts gaze from a far object to a near one, the pupils constrict. This response, like the light reaction, is mediated by the oculomotor nerve. Coincident with this pupillary reaction (but not part of it) are (1) convergence of the eyes, an extraocular movement, and (2) accommodation, an increased convexity of the lenses caused by contraction of the ciliary muscles. This change in shape of the lenses brings near objects into focus but is not visible to the examiner.

Autonomic Nerve Supply to the Eyes. Fibers traveling in the oculomotor nerve and producing pupillary constriction are part of the parasympathetic nervous system. The iris is also supplied by sympathetic fibers. When these are stimulated, the pupil dilates and the upper eyelid rises a little, as if from fear. The sympathetic pathway starts in the hypothalamus and passes down through the brainstem and cervical cord into the neck. From there, it follows the carotid artery or its branches into the

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