The Structures of the Retina
The retina is an incredibly complex structure. This entry will be about the larger structures involved in processing an image.
To learn how an image is focused on the retina, check out anterior eye anatomy. If you want to learn about the individual cells of the retina, check out phototransduction (conversion of a light ray into a chemical message for the brain). For information on the utilization and regeneration of vitamin A in the retina, check out the biochemistry of the visual process.
The goal of glasses, contact lenses or refractive surgery is to get images focused on the fovea of the macula. The macula is the general pigmented area surrounding and supporting the fovea. The fovea is the specific structure that processes all of the detailed (letters, print) visual information we see.
The fovea is a small structure, seen on examination only as a small pinpoint of light. In this small space, the fovea packs in over 100,000 cones (red and green cones only, no blue). Macular degeneration is the most common cause of damage to the macula and fovea. Patients with macular degeneration lose central vision and their ability to see detail.
Images received at the macula pass along a dense network of nerve fibers to the optic nerve. The optic nerve is the structure that connects the eye and brain. Anatomically, the optic nerve is composed of a collection of all the nerve fibers of the retina. It comes to a head as the fibers are bundled together to exit the eye and travel to the brain for processing. The head of the optic nerve is what we see on examination, it resembles an orange-yellow donut.
The larger the hole in the "donut" the more concerned we are about glaucoma which is the most common cause of damage to the optic nerve. Glaucoma is an excavation or erosion of the nerve fiber layer over time. Damage to the optic nerve creates a blindspot in the opposite area of the visual field (damage to the superior part of the optic nerve leads to a blindspot in the inferior visual field.
The optic nerve is also where the central retinal artery and vein enter the eye. The retina is one of the few places in the body we are able to see bare blood vessels. This is very helpful for our diabetic and hypertensive patients.
In diabetes, if a patient's blood sugar gets too high, the sugar thickens the blood. Thicker blood results widening of the blood vessels (which thins the blood vessel walls). Also, excess blood sugar has a shearing effect, cutting into the blood vessel walls. If enough damage occurs, blood will leak out of the blood vessels into the retina.
In hypertension, the arteries of the retina cross over the veins of the retina. Arteries are thicker and have higher pressure within them, than veins. If blood pressure gets to high, the arteries apply pressure to the vein and can pinch them off. This can cause veins to swell and rupture if the resulting pressure is great enough.
The last part of the retina to be examined in the peripheral retina. We have to dilate patients' eyes to see this portion of the retina. The peripheral retina is a much larger space than the central retina (space between the macula and optic nerve). In the peripheral retina we can identify threats to vision (retinal holes, tears, detachments). We can also identify eye cancers that can threaten a patient's life. Fortunately, these eye cancers are very rare.
A more common finding is a freckle or nevus (found in roughly 30% of patients). This spots should be monitored over time to make sure they don't take on a cancerous form, but this is very rare (6 in 1,000,000 become cancerous). Getting your eyes dilated can definitely be an inconvenience, but it is important to rule out possible causes of death or vision loss.
Summary
The macula captures the detailed images of the retina.
The optic nerve is the structure damaged in glaucoma.
Retinal blood vessels provide important information for diabetic and hypertensive patients.
Changes in the peripheral retina can indicate dangers to a patient's life or risk for vision loss.
The only way to see the peripheral retina is by dilating the eyes.
To learn how an image is focused on the retina, check out anterior eye anatomy. If you want to learn about the individual cells of the retina, check out phototransduction (conversion of a light ray into a chemical message for the brain). For information on the utilization and regeneration of vitamin A in the retina, check out the biochemistry of the visual process.
The goal of glasses, contact lenses or refractive surgery is to get images focused on the fovea of the macula. The macula is the general pigmented area surrounding and supporting the fovea. The fovea is the specific structure that processes all of the detailed (letters, print) visual information we see.
The fovea is a small structure, seen on examination only as a small pinpoint of light. In this small space, the fovea packs in over 100,000 cones (red and green cones only, no blue). Macular degeneration is the most common cause of damage to the macula and fovea. Patients with macular degeneration lose central vision and their ability to see detail.
Images received at the macula pass along a dense network of nerve fibers to the optic nerve. The optic nerve is the structure that connects the eye and brain. Anatomically, the optic nerve is composed of a collection of all the nerve fibers of the retina. It comes to a head as the fibers are bundled together to exit the eye and travel to the brain for processing. The head of the optic nerve is what we see on examination, it resembles an orange-yellow donut.
The larger the hole in the "donut" the more concerned we are about glaucoma which is the most common cause of damage to the optic nerve. Glaucoma is an excavation or erosion of the nerve fiber layer over time. Damage to the optic nerve creates a blindspot in the opposite area of the visual field (damage to the superior part of the optic nerve leads to a blindspot in the inferior visual field.
The optic nerve is also where the central retinal artery and vein enter the eye. The retina is one of the few places in the body we are able to see bare blood vessels. This is very helpful for our diabetic and hypertensive patients.
In diabetes, if a patient's blood sugar gets too high, the sugar thickens the blood. Thicker blood results widening of the blood vessels (which thins the blood vessel walls). Also, excess blood sugar has a shearing effect, cutting into the blood vessel walls. If enough damage occurs, blood will leak out of the blood vessels into the retina.
In hypertension, the arteries of the retina cross over the veins of the retina. Arteries are thicker and have higher pressure within them, than veins. If blood pressure gets to high, the arteries apply pressure to the vein and can pinch them off. This can cause veins to swell and rupture if the resulting pressure is great enough.
The last part of the retina to be examined in the peripheral retina. We have to dilate patients' eyes to see this portion of the retina. The peripheral retina is a much larger space than the central retina (space between the macula and optic nerve). In the peripheral retina we can identify threats to vision (retinal holes, tears, detachments). We can also identify eye cancers that can threaten a patient's life. Fortunately, these eye cancers are very rare.
A more common finding is a freckle or nevus (found in roughly 30% of patients). This spots should be monitored over time to make sure they don't take on a cancerous form, but this is very rare (6 in 1,000,000 become cancerous). Getting your eyes dilated can definitely be an inconvenience, but it is important to rule out possible causes of death or vision loss.
Summary
The macula captures the detailed images of the retina.
The optic nerve is the structure damaged in glaucoma.
Retinal blood vessels provide important information for diabetic and hypertensive patients.
Changes in the peripheral retina can indicate dangers to a patient's life or risk for vision loss.
The only way to see the peripheral retina is by dilating the eyes.
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