The cornea is comprised of transparent tissue that covers the iris and the pupil. It is the outermost lens of the eye. The cornea permits light to enter the eye and bends or refracts the incoming light onto the crystalline lens. The lens focuses the light onto the retina at the back of the eye, initiating the translation of light into vision.
The cornea functions as a physical barrier and shields the inside of the eye from harmful matter such as germs and dust. As the human eye’s window onto the world, the cornea also filters out ultraviolet (UV) rays from the sun protecting the crystalline lens and the retina from injury due to UV wavelengths.
A cornea of normal shape and curvature permits light to refract with precision and accuracy to the crystalline lens. If the cornea is curved too much, distant light waves will refract imperfectly on the retina causing faraway objects to appear blurry; as is the case with nearsightedness. Asymmetric curvature of the cornea cause light to refract unequally. This results in a slight distortion of the visual image creating what is known as astigmatism.
Conjunctivitis (Pink Eye)
When the conjunctiva or protective membrane lining the eyelids becomes red and inflamed, causes can be linked to a bacterial or viral infection, a drug allergy, or a contact lens product. Treatment is needed for some forms of pink eye such as epidemic keratoconjunctivitis. If treatment is delayed and the infection is allowed to worsen it can lead to corneal inflammation and possible vision loss. Treatment usually consists of steroid and antibiotic eye drops.
Like other herpetic infections, herpes of the eye remains a serious problem. Ocular herpes is usually caused by the virus responsible for cold sores – herpes simplex I virus; although ocular herpes can result from the sexually transmitted herpes simplex II virus. Prompt treatment will help stop this virus from multiplying and destroying epithelial cells. Ocular herpes presents as a painful sore on the surface of the cornea and is treated with anti-viral drugs. If the infection remains untreated it can spread into the stroma. This more serious infection – herpes simplex stromal keratitis – can produce inflamation on the inside of the eye, as well as scar the cornea and cause vision loss after recurrent, untreated attacks.
Keratitis (Microbial Infections)
When a foreign object penetrates the epithelium, bacteria or fungi can pass into the cornea causing inflammation and infection. This condition has symptoms such as severe pain, reduced visual clarity and corneal discharge. If left untreated, it could erode the cornea. It is important to note that microbial infections are the most serious complication of contact lens wear. Corneal infections are treated with anti-fungal or anti-bacterial eye drops to eliminate the infection. The patient may also need to take steroid eye drops to eliminate inflammation.
Herpes Zoster (Shingles)
Shingles can occur in anyone exposed to the varicella-zoster virus (chicken pox), but two general risk factors for the disease have been established: advanced age and/or a weak immune system. In some patients with shingles present in the head and neck region, the virus infects the cornea resulting in corneal lesions. Without early anti-viral treatment the virus could infect cells deep in the tissue causing inflammation and corneal scarring. Corneal complications may arise months after the shingles are gone, so it is important that patients schedule follow-up eye examinations.
This disorder arises when the middle of the cornea thins and gradually bulges outward, forming a rounded cone shape. This abnormal curvature changes the cornea’s refractive power – producing moderate to severe distortion (astigmatism) and blurriness (near and farsightedness) of vision. Keratoconus usually appears in puberty. Sometimes the disease can be managed with contact lenses. If this is not effective, Inland Eye Institute now offers a progressive treatment called corneal collagen cross-linking (CXL) to strengthen the cornea. The process combines the application of riboflavin (a form of vitamin-B2) to the eye and ultraviolet A light exposure. Learn more about CXL by clicking here.
More advanced cases require a surgical treatment such as Intacs corneal implants to reshape the curve of the cornea or in severe cases may require a transplant. In up to 20% of people with keratoconus, the cornea becomes scarred and the diseased tissue needs to be replaced with a donor cornea. The corneal transplant surgery, called keratoplasty, is highly successful in patients with advanced keratoconus.
Routine eye examinations are important even if our eyes and vision are fine – because many blinding eye diseases have few or no warning signs until we experience vision loss. Contact us today to schedule a comprehensive eye exam.