What is Bowman’s Layer?
Bowman’s layer is the second layer of the cornea, which is the clear outer covering of the eye. Bowman’s membrane is also known as Bowman’s membrane. Bowman’s membrane is between the corneal epithelium and the corneal stroma. Bowman’s membrane of the eye is made up of a network of collagen fibers. The collagen fibers are important to maintain the structure of the cornea. Bowman’s membrane does not regenerate if it is damaged from eye disease or eye surgery.
- Bowman’s membrane is the second layer of the cornea, located between the outermost epithelium and the middle stroma.
- Bowman’s layer is composed of a dense network of collagen fibers that reinforce the structure of the cornea.
- Eye conditions such as pterygium, recurrent corneal erosion, band keratopathy, or photorefractive keratectomy (PRK) surgery can damage Bowman’s layer.
Understanding Bowman’s Layer
The cornea is the clear dome-shaped tissue that covers the front of the eye. The cornea is an important tissue to maintain the clarity of vision: it is transparent to allow light through, and it bends light rays so the eye can focus clearly. The human cornea has six layers:
- Epithelium: the outermost layer, regenerates quickly after surface damage
- Bowman’s Membrane: a collagen sheet that provides structural support, but cannot regenerate
- Stroma: regular collagen that makes up 90% of the cornea
- Descemet’s layer: elastic, trauma resistant, regenerates after injury
- Endothelium: has metabolic pumps that prevent corneal swelling, but cannot regenerate
Bowman’s membrane is a densely woven sheet made of collagen fibers. It is acellular, meaning it does not have any cells and it only has collagen fibrils. It is approximately 10 microns thick, which is about the thickness of a strand of spider web silk. Type 1 collagen is in Bowman’s layer, which is also the type of collagen found in skin, tendons, teeth, and bones. The role of Bowman’s layer is not entirely known, but it is thought to serve as structural support and as a protective barrier to the inner corneal layers.
Development of Bowman’s Membrane
Bowman’s membrane is produced due to interactions between the corneal epithelial cells and keratocytes. Keratocytes produce collagen, a protein that provides structural support and stretchiness to many of the bodily tissues. Bowman’s membrane develops between weeks 13 and 19 of gestation. Bowman’s layer thins with age in the normal cornea, losing approximately 30% of its thickness by 80 years of age.
The Function of Bowman’s Membrane
The role of the Bowman’s membrane remains unclear. However, recent research has postulated that the Bowman’s layer acts as a protective barrier to prevent bacterial invasion. It also is a barrier against the penetration of ocular drugs, so it reduces drug side effects and absorption. It may also provide structural support to the cornea and maintain the corneal shape.
Bowman’s Membrane Pathologies
The Bowman’s membrane can become damaged by the following eye conditions:
- Pterygium (Surfer’s Eye)
This condition involves the formation of a wing-shaped, elevated area due to growth of the conjunctiva, the white part of the eye. It is caused by excessive sunlight exposure. A pterygium disrupts Bowman’s layer once it starts to grow onto the cornea..
- Recurrent corneal erosion
This condition involves recurrent sloughing off of the epithelium overlying Bowman’s membrane. It is usually due to injury of the eye, which prevents epithelium from properly attaching to the underlying Bowman’s membrane.
- Photorefractive Keratectomy (PRK)
This refractive surgery, an alternative to LASIK refractive surgery, removes Bowman’s membrane. Bowman’s membrane is permanently destroyed in PRK using a laser. This is done to reshape the cornea and correct for refractive errors like farsightedness, nearsightedness, and astigmatism.
- Band keratopathy
In this condition, there are excess levels of calcium, and a thick white band of calcium grows across the eye. The calcium is deposited in Bowman’s membrane.
- Reis Buckler Dystrophy
This rare hereditary corneal dystrophy involves disintegration of Bowman’s layer, corneal haziness, and reduced vision.
Examining Bowman’s Layer
Most corneal diseases can be detected by an eye exam where the eye doctor will check for abnormalities in the cornea and its layers, including Bowman’s membrane. An eye doctor will use a specialized instrument called a slit lamp biomicroscope, which allows for a magnified view of the cornea and its tissues.
Because Bowman’s layer is so thin, it may be difficult to visualize even using a slit lamp microscope. A scan of the eye may be taken to examine the cornea’s microscopic structure. This scan is called an anterior segment optical coherence tomography (OCT). The OCT allows a clinician to determine what exact layer of the cornea is being affected by an ocular condition. Using the OCT device, an eye doctor can definitively determine if the eye condition is in the Bowman’s membrane or another layer.