Anterior Eye Anatomy
My favorite part of each eye exam is getting the slit lamp (microscope) out and studying the various structures of a patient's eyes. The eye is a structure with many beautiful features. Each component of the eye plays a role in capturing images from the external environment and preparing that visual information for its journey through the brain.
The first structures examined are the eyelids and eyelashes. These structures work to protect the eye from debris in the air and reset the tear film with each blink. A major contributor to our natural tears, the meibomian glands, are located just behind the eyelashes. Our major concern when looking at the eyelid are various skin cancers (basal cell carcinoma, squamous cell carcinoma, sebaceous gland carcinoma).
Past the eyelids the tear film is observed. The tear film lubricates and protects the front surface of the eye, the cornea, and plays a vital role in keeping images clear on the way to the retina. The tear film is composed of three layers. The bottom layer is a sticky, mucousy layer produced by the goblet cells of the conjunctiva.
The largest volume of the tear layer is the middle, watery portion secreted by the lacrimal gland. The top, oily layer prevents evaporation and is produced by the meibomian glands. A defect in the tear film leads to dry eye and corneal scarring if the dryness is severe enough.
The tear film covers the conjunctiva and cornea. The conjunctiva contributes to producing the tear film, functions as a barrier to debris and bacteria and provides a mucous membrane capable of initiating an immune response.
Conjunctiva covering the eye itself is called bulbar conjunctiva and conjunctiva covering the eyelids is called palpebral conjunctiva. The most common disease of the bulbar conjunctiva is a pinguecula, or callous-like structure resulting from sun exposure. Papillae are the most common finding in the palpebral conjunctiva. Papillae indicate an allergic response.
For clear vision, the most important structure for the (anterior) front part of the eye is the cornea. The cornea is the clear structure on the front surface of the eye. To focus images on the retina, the cornea possesses nearly two thirds of the total focusing power of the natural eye. The cornea is made up of five layers. The most important layer is the bottom or endothelial layer.
The corneal endothelium regulates the fluid balance across the 5 layers of the cornea, which determines corneal clarity, which influences image clarity. Damage to the cornea can result in scarring which clouds the cornea and can cause patients debilitating glare and haloes or to lose the ability to see detail. The cornea can be damaged by improper contact lens wear, trauma, infection, genetic condition or chemical burn.
Behind the cornea, the next structure to be examined is the anterior chamber (AC). The AC is the space between the cornea and iris (colored part of the eye). This space is so important because of its influence on intraocular pressure (pressure inside the eye). Aqueous humor (fluid in the AC) drains into the trabecular meshwork on its way out of the eye. If the AC is too narrow or if an obstruction is present eye pressure spikes which can cause glaucoma or stop blood flow in the retinal blood vessels.
The most posterior portion of the AC is the iris. The iris is the colored part of the eye. Color of the iris is determined by the amount of pigment present on its anterior pigmented epithelium. The pupil or opening in the iris plays a major role capturing clear images and providing neurological information.
Blood vessel growth or neovascularization on the iris is the most concerning sign we see on the iris. Neovascularization of the iris indicates the drainage structures of the eye are obstructed and the retina and optic nerve are at risk for significant damage. Closed drainage structures are termed synechiae. A peripheral anterior synechiae involves the iris attaching to the cornea or other AC structure and closing off the trabecular meshwork.
Posterior synechiae involve the iris attaching to the lens. This prevents aqueous produced in the posterior chamber from reaching the anterior chamber for drainage. Posterior synechiae also damages the eye due excess intraocular pressure.
The lens is the last structure examined in the anterior chamber. The lens is a clear, round ball located just behind the iris. For the AC, the lens is the second most important structure for clear vision. The lens makes up about one third of the natural eye's focusing power. When reading, the ciliary muscle changes the shape of the lens to allow us to focus up close.
The lens also absorbs UV light entering the eye to protect the retina from damage. Enough UV exposure causes the lens to yellow. This yellowing is called a cataract. Once the yellowing becomes dense enough surgery is required to remove it. Sun exposure is the most common cause of cataracts. However, cataracts can be caused by medications or trauma. Some patients are even born with cataracts (congenital cataracts). Sunglasses and vitamin C consumption are the best methods for slowing cataract development.
Summary
The eyelids are a common site for skin cancer.
Clear vision is most influenced by the cornea, lens and tear film (in the AC).
Intraocular pressure is most influenced by proper iris location and function.
Avoid improper contact lens use to keep the cornea clear.
Wear sunglasses and get plenty vitamin C to delay the onset of cataracts.
The first structures examined are the eyelids and eyelashes. These structures work to protect the eye from debris in the air and reset the tear film with each blink. A major contributor to our natural tears, the meibomian glands, are located just behind the eyelashes. Our major concern when looking at the eyelid are various skin cancers (basal cell carcinoma, squamous cell carcinoma, sebaceous gland carcinoma).
Past the eyelids the tear film is observed. The tear film lubricates and protects the front surface of the eye, the cornea, and plays a vital role in keeping images clear on the way to the retina. The tear film is composed of three layers. The bottom layer is a sticky, mucousy layer produced by the goblet cells of the conjunctiva.
The largest volume of the tear layer is the middle, watery portion secreted by the lacrimal gland. The top, oily layer prevents evaporation and is produced by the meibomian glands. A defect in the tear film leads to dry eye and corneal scarring if the dryness is severe enough.
The tear film covers the conjunctiva and cornea. The conjunctiva contributes to producing the tear film, functions as a barrier to debris and bacteria and provides a mucous membrane capable of initiating an immune response.
Conjunctiva covering the eye itself is called bulbar conjunctiva and conjunctiva covering the eyelids is called palpebral conjunctiva. The most common disease of the bulbar conjunctiva is a pinguecula, or callous-like structure resulting from sun exposure. Papillae are the most common finding in the palpebral conjunctiva. Papillae indicate an allergic response.
For clear vision, the most important structure for the (anterior) front part of the eye is the cornea. The cornea is the clear structure on the front surface of the eye. To focus images on the retina, the cornea possesses nearly two thirds of the total focusing power of the natural eye. The cornea is made up of five layers. The most important layer is the bottom or endothelial layer.
The corneal endothelium regulates the fluid balance across the 5 layers of the cornea, which determines corneal clarity, which influences image clarity. Damage to the cornea can result in scarring which clouds the cornea and can cause patients debilitating glare and haloes or to lose the ability to see detail. The cornea can be damaged by improper contact lens wear, trauma, infection, genetic condition or chemical burn.
Behind the cornea, the next structure to be examined is the anterior chamber (AC). The AC is the space between the cornea and iris (colored part of the eye). This space is so important because of its influence on intraocular pressure (pressure inside the eye). Aqueous humor (fluid in the AC) drains into the trabecular meshwork on its way out of the eye. If the AC is too narrow or if an obstruction is present eye pressure spikes which can cause glaucoma or stop blood flow in the retinal blood vessels.
The most posterior portion of the AC is the iris. The iris is the colored part of the eye. Color of the iris is determined by the amount of pigment present on its anterior pigmented epithelium. The pupil or opening in the iris plays a major role capturing clear images and providing neurological information.
Blood vessel growth or neovascularization on the iris is the most concerning sign we see on the iris. Neovascularization of the iris indicates the drainage structures of the eye are obstructed and the retina and optic nerve are at risk for significant damage. Closed drainage structures are termed synechiae. A peripheral anterior synechiae involves the iris attaching to the cornea or other AC structure and closing off the trabecular meshwork.
Posterior synechiae involve the iris attaching to the lens. This prevents aqueous produced in the posterior chamber from reaching the anterior chamber for drainage. Posterior synechiae also damages the eye due excess intraocular pressure.
The lens is the last structure examined in the anterior chamber. The lens is a clear, round ball located just behind the iris. For the AC, the lens is the second most important structure for clear vision. The lens makes up about one third of the natural eye's focusing power. When reading, the ciliary muscle changes the shape of the lens to allow us to focus up close.
The lens also absorbs UV light entering the eye to protect the retina from damage. Enough UV exposure causes the lens to yellow. This yellowing is called a cataract. Once the yellowing becomes dense enough surgery is required to remove it. Sun exposure is the most common cause of cataracts. However, cataracts can be caused by medications or trauma. Some patients are even born with cataracts (congenital cataracts). Sunglasses and vitamin C consumption are the best methods for slowing cataract development.
Summary
The eyelids are a common site for skin cancer.
Clear vision is most influenced by the cornea, lens and tear film (in the AC).
Intraocular pressure is most influenced by proper iris location and function.
Avoid improper contact lens use to keep the cornea clear.
Wear sunglasses and get plenty vitamin C to delay the onset of cataracts.
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