Cornea

What is the cornea?

Your cornea is the clear, dome-shaped covering at the front of each of your eyes. It’s like your eye’s version of a windshield. It keeps debris, germs and more out. Its specific shape plays a key role in how your eyesight works and filters some ultraviolet (UV) rays.

Your corneas are just in front of a fluid-filled chamber of your eye called the anterior (forward) chamber, which contains the aqueous humor. Behind the anterior chamber are your iris and pupil, followed by the lens. Surrounding your cornea is the sclera (the white part of your eye).

Because corneas are the first line of defense for the surface of your eye, they’re also prone to injuries and damage. Fortunately, your corneas also have fast, effective self-repair abilities.

Layers of the cornea

Your cornea has six layers. They are:

• Epithelium. This is the outermost layer of the cornea. It’s a physical barrier between the inside of your eye and the outside world, and it’s incredibly sensitive to pain. Researchers estimate the cornea has about 300 to 600 times as many pain receptors as your skin. That sensitivity is protective. It makes you react strongly to stop or remove whatever’s hurting your eyes.
• Bowman’s layer. This is a tough layer made mostly of collagen. It’s there to provide structure and help your cornea hold its shape.
• Stroma. This is the thickest layer of your cornea. It strengthens your cornea structure and helps bend (refract) light and focus it onto your retinas.
• Pre-Descemet’s layer (PDL). Another name for this is “Dua’s layer.” Research indicates it’s airtight, which means it’s a very strong barrier separating the fluid inside your eye and the air from the outside world.
• Descemet’s layer. This layer is thin and stretchy but also remarkably strong. It’s important to your eye structure and helps protect the inside of your eye from injury and infection.
• Endothelium. This layer is mainly responsible for fluid balance in your cornea and the inside of your eye. It helps make sure there’s just enough water and fluid in the stroma for your cornea to work as it should.

Each layer has a specific job, but your cornea’s true strength comes from how the layers work together. The layers work like laminate glass (also known as “safety glass”) in car windshields. Laminate glass is two layers of glass with a sheet of thin, clear plastic between them. The plastic layer makes the whole piece much stronger (and sometimes, there are additional alternating glass and plastic layers to make it even stronger).

Since when does the cornea have six layers?

The pre-Descemet’s layer is a relatively recent discovery. The first research paper describing it came out in 2013. There’s still some disagreement among experts on whether or not it’s a layer on its own or if it’s part of the stroma (which is what experts thought before newer research suggested that might not be the case).

Available research shows several important differences between the PDL and the rest of the stroma. And eye surgeons now take the PDL into account (regardless of whether or not they think it’s a separate layer) when planning corneal surgeries.

What are common corneal disorders?

Your corneas are vulnerable to injuries, infections and other diseases. Examples include:

• Dry eye: The epithelium of your corneas needs tear fluid to work properly. Tear fluid provides lubrication for your eye surface and helps the epithelium absorb oxygen from the air. Dry eye is painful, and it can disrupt your eyesight.
• Infections: Damage to your cornea’s surface makes it easier for germs — including viruses, bacteria, fungi and parasites — to cause infections. One example is the parasitic infection acanthamoeba keratitis.
• Cornea inflammation (keratitis): Many conditions and issues can cause keratitis, including infections, injuries and diseases.
• Injuries: Just like the windshield on a car, your cornea is vulnerable to damage from outside objects and events. That can cause scratches (abrasions), lacerations (rips), sores (ulcers) and erosions (worn away areas).
• Environmental damage: Your corneas are vulnerable to extreme cold and heat. Corneal burns (either from heat or ultraviolet radiation) are common examples. Your corneas are also vulnerable to chemicals (either in liquid or gas form).
• Structural diseases (dystrophies): Some diseases affect the structure of your corneas, how they bond and move together, or both. The umbrella term for these conditions is “corneal dystrophies.” There are more than 20 such diseases, including keratoconus and Fuchs’ dystrophy.

What treatments are available for corneal conditions?

Some of the common treatments for cornea-related conditions include:

• Over-the-counter remedies. Simple issues affecting your corneas, like eye irritation or dry eyes, may only need simple treatments that you can buy at the pharmacy or grocery store.
• Medications. Several cornea conditions, especially infections, are treatable with medications. Many of these medications come in ointment or eye drop forms you apply directly to your eye, while others come in pill form you take by mouth.
• Coverings or wearable treatments. A simple example is wearing an eye patch to protect an eye and keep it closed while your cornea heals. More complex treatments include scleral lenses, bandage contact lenses and amniotic membrane grafts.
• Laser surgeries. These are vision correction surgeries that use a laser to change the shape of your cornea so it refracts light differently. LASIK is one of the more common laser procedures.
• Eye surgeries. These procedures can help in many ways, especially repairing damage or correcting certain corneal conditions.
• Cornea transplant or artificial cornea placement. Over time, your corneas can become cloudy or stop refracting light correctly. When these issues are severe, you may need surgery to replace your corneas.

Many factors influence the treatments that can help corneal conditions. The possible factors include your specific condition(s), medical history, personal circumstances and many more. Because so many factors can play a role, your eye care specialist or healthcare provider is the best person to tell you more about treatment options for your case.

How can I protect my corneas from injuries?

The most important way to protect your corneas from injury is to use safety glasses or goggles, even if you’ll only need them for a moment or two. A split second is all it takes for an eye injury to happen.

You should wear eye protection anytime you’re:

• Working with tools and machines. This goes for simple hand tools and power tools alike. Even something as simple as using sandpaper for smoothing wood without proper protection can lead to unwanted eye irritation or an injury.
• Doing yardwork and gardening. Leaves, grass clippings, pebbles and dirt are all hazards to your eyes when you’re working in the yard or garden. This also goes for tools and machines that help with yard work and gardening, like lawnmowers, string trimmers (also known as “weed-eaters” or “strimmers”), chainsaws, leaf blowers, etc.
• Using compressed air or water. Two examples are pressure-washing pavement and using compressed air to clear dust from the internal components of a computer or other electronic device. The pressure from either can easily turn grit, debris or dust into a hazard.
• Using chemicals at home or work. Common chemicals like bleach or drain cleaner can easily splash and get in your eyes, even if you’re being careful.
• Working around heat sources and open flames. The pain receptors in your eyes are more sensitive to heat than the receptors in your skin. Eye protection can help you avoid irritation from smoke or damage from fumes put off by a fire.
• Potentially exposed to UV radiation. Bodies of water and snow-covered surfaces can reflect UV rays and burn your corneas, causing corneal flash burns or photokeratitis.
• Playing sports. Protective eyewear can shield you from fast-moving objects. That goes for sports like baseball, tennis, hockey, pickleball, racquetball and more. And you should always use eye protection for target shooting sports (archery, trap shooting, skeet shooting, etc.).

Other important injury prevention tips include:

• Read the instructions. This goes for machines and chemicals alike. Chemical instruction labels tell you what to do if you get them in your eyes (and the labels are easier to read if you don’t have anything in your eyes). It’s tempting to dive right into the activity, but pausing to read the label could make a big difference.
• Use the right type of eye protection. Safety glasses with side panels or shields can protect against ricochets and debris from others working nearby. Goggles with soft plastic edges that rest snugly against the skin of your face are best for preventing chemicals and fumes from getting into your eyes.
• Make sure your eye protection can do the job. Protective eyewear is useless if it isn’t strong enough to protect you, so make sure your eyewear is appropriate for what you’re doing. And in environments with a lot of reflected sunlight, make sure your sunglasses have polarized lenses. They’re more effective at blocking UV rays than simple tinted lenses.
• Wash your hands frequently when cooking or using tools or chemicals. Whether it’s in the kitchen with spicy ingredients or working around the house, it’s easy for chemicals, particles and residues to get in your eyes from unwashed hands.
• Burns to and around your eyes ALWAYS need medical attention. Even seemingly minor burns close enough to or on your eyes need proper treatment. Always err on the side of caution when it comes to getting medical care.
• Don’t take a risk by driving with a possible eye injury. If you’re experiencing any kind of vision changes or eye symptoms that could be due to an injury, don’t drive. You don’t want to endanger yourself or others.

How do I keep my corneas healthy?

You can do the following to protect your corneas from diseases and certain conditions:

• Get regular eye exams. These may catch issues affecting your corneas (and your eyes in general) before you develop symptoms.
• Wash your hands often (even when not handling things that could irritate your eyes). That can keep your eyes free of unwanted germy hitchhikers.
• Don’t share cosmetics and similar items. Sharing items like this can spread eye infections.
• Wear, store and maintain contacts properly. This is important because it protects your eyes from serious infections, some of which can cause serious eye damage and even permanent vision loss.
• Avoid rubbing or touching your eyes. This includes rubbing your eyes through your eyelids. These can cause unintended damage to or weakening of the cornea’s surface.

What are the eye symptoms that mean I need medical care?

Several things — either symptoms or visible changes — can mean you need medical care. They include:

• Vision changes, including double vision, clouding, blurring or distortion.
• Sudden vision loss.
• Foreign object sensation (the feeling that something is in your eye — regardless of whether you can see the object — ranging from mild discomfort to severe and overwhelming pain).
• A foreign object you can see but can’t get out of your eye using proper techniques (see the table below).
• Eye pain.
• Watery eyes (epiphora).
• Light sensitivity (photophobia).
• Eye redness or irritation.
• Bleeding or fluid visible behind or inside your cornea, but in front of or outside of your iris or pupil.
• Getting hit directly on or immediately around your eye.
• A visible puncture, tear or wound on your cornea or eye surface.

This list isn’t comprehensive, though. When in doubt, err on the side of caution. Doing so could make a big difference in preserving your eyesight.

What should I do if something is stuck in my eye?

If you feel like something’s stuck in your eye, take a deep breath and try not to panic.

Here are some dos and don’ts:

Can you still see without a cornea?

No. Your cornea plays a key role in bending light so it focuses properly on the retina at the back of your eye. And your cornea is also there to protect more delicate parts inside your eye. So, without them, your eyes can’t see properly.

How long does a damaged cornea take to heal?

Your corneas have tremendous repair abilities. Minor corneal injuries heal within hours. Some injuries may take a few days to heal. In unusual or under specific circumstances, it could take longer. An eye care specialist is the best person to tell you the timeline for recovery that’s most likely for you, and what you can do to make your recovery as smooth as possible.