Cornea & External Diseases

What is the Cornea?

The cornea is the clear outermost layer of the eye, the part that you look through.  It serves as a protective cover against dirt, germs and other things that can cause damage to the eye.  The cornea also functions like a window that lets light into the eye and focuses it. 

The three main layers of the cornea are the:

  • Epithelium – the epithelium is the surface layer, like skin, that stops dirt and germs from entering the eye. Your tears keep this surface moist.
  • Stroma: The stroma is the main and thickest layer of the cornea. It is made up mostly of water and proteins that give it an elastic but solid form.
  • Endothelium: The endothelium is a single layer of cells located on the inner surface of the cornea. The endothelium works as a pump which keeps the cornea from swelling to keep it clear.

Below are some of the most common conditions that can affect the cornea. 


What is Blepharitis?

Blepharitis is an inflammatory condition of the eyelid margin, the eyelashes and oil producing glands (melbomian glands).  This condition can be an isolated problem or may be associated with bacterial infections or skin conditions.  It can occur at any age and is typically a chronic condition.  If left untreated, blepharitis can cause scarring and thickening of the eyelids. It can also trigger loss of eyelashes or their growth in the wrong direction which causes them to rub against the cornea and lead to loss of vision, corneal irritation and infection.

Blepharitis Image

Symptoms of Blepharitis

Blepharitis is a very common problem, in some ways like other common conditions such as teenagers with acne, people with dandruff, etc.  Many people have blepharitis without any symptoms and without knowing it.  Some symptoms can include:

  • Burning, irritation, itching and redness of the eyelids
  • Crusting around the eyelashes

Treating Blepharitis

While there is currently no cure for blepharitis, in most cases it can be controlled with relatively safe and simple treatment.  The goals of treatment are to reduce the eyes redness and discomfort and prevent corneal changes that can lead to permanent scarring or loss of vision.  Fortunately, these more serious changes are not common.

  • Warm Compresses – placing warm compresses combined with cleansing and scrubbing of the eyelashes are often enough to control the symptoms of blepharitis
  • Antibiotic or Antibiotic/Steroid Combination Ointment or Drops – This may be applied to the lid and eyelashes or instilled in the eye to promote more rapid control of the symptoms and reduce the possibility of corneal scarring.
  • Oral Antibiotic – In more severe cases, an oral antibiotic such as tetracycline or doxycycline may be prescribed

Conjunctival/Corneal Tumors

Tumors of the conjunctiva and cornea are usually grouped together because lesions from one area will frequently involve the other.  Most are relatively rare.  These lesions can be divided into several categories including:

  • Congenital tumors –These tumors are present at birth and tend to enlarge gradually and typically do not have any harmful potential.  Treatment may range from simple observation of the tumor to surgical removal.
  • Non-pigmented tumors – These may be subdivided into those that are completely benign and those that have some potential to become malignant.  Conjunctival cysts and viral papilloma are benign.  Pre-cancerous and cancerous lesions often develop in the area right at the edge or the cornea.  This region is called the limbus.  To determine if lesions here are benign, pre-cancerous, or cancerous, a tissue biopsy may be recommended.  If pre-cancerous or cancerous, we have medical and surgical options for treatment.  Fortunately, even for tumors that are determined to be cancerous, they typically respond well to therapy and rarely spread beyond the ocular and lid surfaces.
  • Pigmented tumors – Nevi and freckles are pigmented conjunctival tumors that have very low malignant potential.  Many are present at birth or develop prior to or during puberty.  Most pigmented lesions should be carefully documented by photographs or drawings over time.  If pigmentation of the conjunctiva is noted for the first time after early adulthood, or if they show an unusual growth or change, they should be biopsied or removed.  On occasion, a pigmented conjunctival lesion may turn out to be a melanoma and these are of great concern because they can cause significant damage to the eye and can spread to other parts of the body.

Corneal Dystrophies

Corneal dystrophies are rare genetic disorders that are associated with a buildup or change in specific layers of the cornea.  They are not associated with any prior condition or other underlying diseases.  Corneal dystrophies can: run in a family, often affect both eyes, affect both men and women, don’t affect other body parts and can happen even in good health.

Symptoms and Treatment of a Corneal Dystrophy

Many dystrophies are subtle and have minimal or no effect on vision.  These require no specific treatment.

In other cases, one may experience blurred or distorted vision and pain due to irregularity of the surface or repeated surface breakdown.  Drops and ointments are used to reduce the symptoms.  However, in some cases, surface changes may need to be scraped or peeled away to improve vision or comfort.

Some of the more dramatic dystrophies can cause swelling and/or clouding of the cornea resulting in considerable loss of vision.  In these cases, corneal transplantation may be required to restore vision to a normal level.

There are many different corneal dystrophies.  The following are some of the more common corneal dystrophies:

  • Anterior basement membrane dystrophy
  • Granular dystrophy
  • Lattice dystrophy
  • Macular dystrophy
  • Schnyder crystalline corneal dystrophy
  • Posterior polymorphous dystrophy
  • Endothelial or Fuchs’ dystrophy

Corneal Edema

In corneal edema, the cornea swells with fluid. which can lead to cloudy vision.  Cornea edema happens when the inner surface layer of the cornea, the endothelium, is unhealthy or damaged.  This can be caused by aging, trauma, inflammation, glaucoma, eye surgery, and some corneal dystrophies such as Fuchs’ dystrophy or posterior polymorphous dystrophy.

Symptoms of Corneal Edema

  • Cloudy, foggy, or blurry vision – especially in the morning
  • Glare
  • Haloes around lights
  • In more advanced cases, foreign body sensation or eye pain

Treatment for Corneal Edema

The type of treatment depends on the severity of the condition.  If it is mild, you may not need any treatment.  However, it may be recommended that you reduce the swelling using concentrated salt drops or ointment.

If the condition progresses and worsens, you may require surgery to replace the unhealthy or damaged layers of the cornea.  This surgery usually is a corneal transplant using a cornea that has been donated by someone who has passed away.  The main types of cornea transplant include:

  • Penetrating Keratoplasty (PK) – This type of cornea transplant involves replacing the full thickness of the cornea.
  • Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) – This is a partial thickness type of cornea transplant that is primarily used when there is swelling of the cornea.
  • Descemet Membrane Endothelial Keratoplasty (DMEK) – This is also a partial thickness type of cornea transplant.  With DMEK the donor tissue is extremely thin and can potentially allow for improved visual outcome and quicker recovery, but perhaps with some increased risk.
  • Your doctor will discuss the pros and cons of the various types of cornea transplant options to help determine what is best for you and your situation. Learn more about cornea transplants.

Corneal Ulceration

Corneal Ulceration refers to the breakdown of the surface of the cornea along with inflammation and then tissue loss.  It is a serious condition that is usually caused by an infection from bacteria, virus or fungus.  It can spread very quickly and can result in permanent loss of vision or even loss of the eye.  The most frequent causes of infection are from contact lens wear, or trauma to the cornea, like a fingernail injury or foreign body.  Dry eye, blepharitis, loss of normal neurologic sensation, or eyelid abnormalities are also frequent causes of ulcers.  Less frequent causes include rheumatoid arthritis and Parkinson’s disease.

Treatment of Corneal Ulceration

Once a corneal ulcer is diagnosed, aggressive treatment is necessary.  In some cases, your doctor may obtain a culture from the ulcer to determine what type of infection is causing it.  The type of infection will determine the type of antibiotic (either drops, oral or injections) and the frequency they are administered.

The patient with an ulcer will be examined frequently until it is determined that they are responding well to the treatment and are healing.  Most corneal ulcers respond well to therapy.  However, there are instances where the infection may be difficult to control and result in permanent damage to or even loss of the eye.

Dry Eye

Dry eye is a common, chronic condition in which a person either does not produce enough tears, has unhealthy tears, or has a problem causing the tears to evaporate too much. Enough and healthy tears are necessary for maintaining the health of the cornea and for providing clear vision.

Symptoms of Dry Eye

  • A burning feeling in the eye
  • Irritation or a foreign body sensation in the eye
  • Blurred vision
  • Ironically, some patients with dry eyes will complain of episodic tearing.

These symptoms can also be aggravated by exposure to wind, air conditioning and antihistamines.

Treatments for Dry Eye

While dry eyes can’t be cured, the symptoms can usually be controlled and any serious complications that can be caused by dry eyes prevented.

  • Drops – one of the primary treatments is the use of artificial tear drops.  These can be applied as needed, even as often as every thirty minutes depending on the severity of the individual’s condition.  With frequent usage, it is recommended that a preservative-free artificial tear be used.  The thickness of the artificial tears also depends on how severe the condition and symptoms are.
  • Ointments – Thicker lubricating ointments can also be used.  Ointments have the advantage of lasting longer since they do not evaporate or drain as rapidly as artificial tears.  However, they do blur one’s vision because of their thickness.  Many patients use ointment at bedtime.
  • Steroids – For some, low level inflammation may be the cause or a contributor to their dry eye problems.
  • Prescription topical medications – There are now several prescription eye drops that have been approved specifically for the treatment of dry eyes.  Your doctor will discuss whether a prescription medication may be beneficial in treating your dry eye condition.
  • Omega 3/6 Fatty Acids – Another option that may helpful to patients with dry eyes is taking omega 3/6 fatty acid supplements, such as flaxseed or fish oil supplements.
  • Autologous serum eyedrops – Although it may seem a bit odd at first, sometimes, arrangements will be made to draw your blood to make eye drops out of the fluid (serum).  Serum has hormones, growth factors and other components that have been beneficial to some dry eye patients.
  • Procedures – For some patients with dry eye, they may benefit from an office procedure that involves putting a plug into the channel in the eyelid where tears drain out.

It is important to remember that while dry eye can be a chronic and frustrating condition, the symptoms can usually be improved with maintaining a treatment regimen prescribed by your doctor.


The sclera is the white outer portion of the eye and is made of collagen.  The episcleral is a thin, normally clear layer of tissue that covers the sclera.  Both function to protect the delicate structures inside the eye and provide structural support to the eyeball.  Episcleritis and Scleritis are conditions where the outer wall of the eye is inflamed.

Causes of Episcleritis/Scleritis

While there is usually not a known cause, these conditions, especially scleritis, often occurs in people who may have an underlying inflammatory disease such as lupus, rheumatoid arthritis, Crohn’s disease, or colitis.

Symptoms of Episcleritis/Scleritis

  • Redness in either one or both eyes
  • Mild pain with episcleritis or more severe pain with scleritis


While episcleritis tends to be a mild condition that can go away on its own, scleritis can be more serious and, if left untreated, can lead to vision loss and even blindness. Your physician will conduct a careful review of your medical history to determine any conditions that may be contributing to the problem and a workup may require coordination with an internist, rheumatologist or other specialist.  The treatment is focused mainly on the inflammation and will depend on its severity.  Types of treatment your doctor may recommend include:

  • Steroid eye drops
  • An oral non-steroidal anti-inflammatory medication like aspirin or ibuprofen
  • Steroid pills
  • Immunosuppressive drugs

Your doctor will consider your condition, your general health and other factors when making a recommendation for the best treatment option.

Herpes Simplex

Herpes simplex virus (HSV) type 1 is a very common condition as nearly all adults have been infected by it.  Usually the initial infection is associated with minor flu like symptoms or no symptoms at all.  After the initial infection, the virus remains in the body in an inactive state.  At times, the virus can re-activate.  Cold sores on the lips are one very common manifestation of the virus when it becomes active again.

Sometimes, the herpes simplex virus infections can involve the eye.  Common symptoms include redness, tearing, irritation, tearing and sores on the eyelid usually involving only one eye.  These infections can be serious because they can result in scarring and inflammation leading to permanent damage to the eye or loss of vision.  In addition, once an eye has been infected by HSV, recurrences can occur.


  • Medicated drops/gel – a topical prescription antiviral drop or gel is typically used to treat herpes simplex and may sometimes be combined with an anti-inflammatory drop if the inflammation is severe.
  • Oral medication – an oral prescription antiviral medication may be prescribed as treatment of active episodes or for suppression of the virus in patients with frequent recurrences.
  • Surgery – in rare situations, if corneal scarring from HSV infections causes significant vision loss, corneal transplantation may be needed. Learn more about cornea transplant procedures.

Most patients with ocular herpes simplex respond well to treatment and maintain good vision.  It is important that patients with a history of ocular herpes simplex notify their ophthalmologist immediately if they develop any sign of a flare-up of the condition.

Herpes Zoster Ophthalmicus (Shingles)

The chickenpox/herpes zoster (also known as shingles) virus is a common virus that can affect both the skin and eyes. Chickenpox causes itchy blisters that might start on your back, chest, and face and spread to the rest of your body. Shingles is a reactivation of the virus that presents as a rash with shooting pain and usually shows up on one side and in one area of your body. Approximately 25% of people who get shingles will be affected in one eye.  This is called herpes zoster ophthalmicus.


  • Sudden onset of tingling and numbness over the scalp and forehead, primarily on one side
  • Headache
  • Fever & chills
  • Blistering rash that erupts in small groups or occasionally large groups over the forehead, brow, scalp and may extend downward to the eyelids and nose.  Sometimes, this may occur in the cheek area also
  • Redness, irritation, tearing, blurred vision, light sensitivity of one eye.  These symptoms may be delayed by days or weeks compared to the other symptoms.

Herpes zoster ophthalmicus can cause the following conditions:

  • Conjunctivitis – inflammation of the white part of the eye
  • Keratitis – inflammation in the cornea, which becomes rough, irritated or cloudy.  There may be some tendency to ulcers on the cornea.
  • Iritis – inflammation inside the eye


Treatment depends on how long the virus has persisted and how much the eye has been affected.  It has been shown that early treatment during the first couple of days can be beneficial to many patients.

  • Oral antiviral medications – these are the most frequently used during the early and most severe phase of the disease
  • Topical anti-inflammatory gels and drops – These may also be used for some patients as necessary

While the condition can resolve and be treated successfully, some patients may experience complications such as permanent scarring of the lids, dry eyes and corneal ulcers and scarring.  The inflammation following herpes zoster ophthalmicus tends to smolder and recur, so some patients may need low dose maintenance treatment for months or even years.


Keratoconus is a condition when the cornea of your eye becomes thin and begins to form an irregular cone shape.  The changing shape of the cornea can cause your vision to become blurry and distorted. The condition often begins when people are in their teens to 20s and often progressively worsens over time.  We think that this condition may be due to weakened structural proteins in the cornea.  Typically, a person will have it in both eyes, though not always symmetrically. It is unknown what causes keratoconus; however, it has occasionally been associated with a family history of keratoconus, certain allergic and arthritic disorders, Down’s syndrome, chronic eye rubbing and contact lens wear.


Symptoms can differ in each eye and may change over time.  Common symptoms include:

  • Blurred vision
  • Distorted vision (straight lines look bent)
  • Sensitivity to light
  • Nearsightedness or astigmatism


Treatment for Keratoconus can be discussed by asking 2 questions:

What can be done to improve vision?

  • Glasses – for mild keratoconus, a person’s vision can usually be corrected with glasses.
  • Contact Lenses – as the cornea becomes more irregular and glasses no longer correct the vision adequately, contact lenses, usually toric, rigid gas permeable, hybrid or scleral ones, can be very helpful.
  • Corneal Transplant Surgery – this is required when the condition is severe and other treatments no longer provide adequate vision. With this surgery, your ophthalmologist will replace the distorted part of your cornea with healthy cornea tissue donated by someone who has passed away. Learn more about cornea transplant surgery.

Is there anything that can be done about the keratoconus problem itself?

  • Do not rub your eyes!  The additional mechanical stress from rubbing on a weakened cornea can make the keratoconus worse than it would be on its own.
  • Corneal Cross-linking – Corneal cross-linking, also referred to as corneal collagen cross-linking, is an exciting new technology that can treat and strengthen the weakened cornea to prevent stabilize it and prevent further worsening.  A special UV light and eye drops are utilized to carry out this minimally invasive outpatient procedure that is done in your doctor's office.  This procedure may be recommended if your keratoconus is still worsening. Learn more about Corneal Crosslinking.


Pterygium is a growth of pink or white tissue that begins in the white part of the eye and grows onto the cornea.  It often remains small, but in some cases, it can grow larger and can affect one’s vision if it covers the cornea or gets close to the center of it.  It is believed that the condition is caused by a combination of excessive exposure to UV light from the sun, wind and dust.   To reduce the chance of a pterygium growing larger, it is important to wear sunglasses with UV protection when outdoors and exposed to sunlight.


These common symptoms of pterygium can range from mild to severe:

  • Redness and swelling of the white part of the eye
  • A yellow spot or bump on the white of the eye
  • Dryness, itching and burning in the eye
  • Blurred vision


If the pterygium does not affect your vision or cause any discomfort, no specific treatment is necessary.  However, if it causes discomfort or grows progressively over your cornea, you may need treatment.  Some treatment options include:

  • Lubricating drops: these can provide soothing and comfort to an irritated pterygium
  • Steroid drops – these will relieve the redness, swelling and inflammation that is caused by the condition.  Steroid drops must be used with caution and may not be a long-term option.
  • Surgical removal – if the pterygium is large enough to cause unrelieved discomfort, or threaten or cause vision problems, surgical removal may be beneficial.  Once removed, your ophthalmologist may transplant a thin layer of healthy tissue to the affected area to help reduce the chance of it coming back.

Recurrent Corneal Erosion

Sometimes, the epithelium (skin or membrane) over the cornea can be disrupted by trauma or injury such as a fingernail scrape.  Unfortunately, even after healing, sometimes the epithelium can repeatedly break down and develop recurring erosions of the cornea.  Because the cornea is very sensitive, these episodes can cause significant irritation, tearing and pain.


The most common symptom is pain and feeling like there is something in your eye.  Some other symptoms include eye redness, sensitivity to light, blurred vision, tearing and stabbing pain.  In many patients with recurrent corneal erosions, the symptoms may be worst upon awakening from sleep.


The simplest treatment is to prevent a recurrence or minimize the severity by using artificial tears during the day and lubricating eye ointment at night.  Another treatment option is a placement of a soft contact lens which functions as a bandage to help protect the surface so that the erosion can heal.  If the erosions continue, a scraping treatment may be recommended to remove the detached cells on the cornea and promoting new growth of the epithelium of the cornea.

Other treatment options may include:  use of steroid drops or ointment, doing a procedure called micropuncture to try to strengthen the attachment of the epithelium, oral antibiotics, PTK (a laser treatment to the corneal surface), and others.   Treatment may be short or long term depending on the severity and number of recurrences.  Your doctor will assess and determine which treatment options may work best in your individual circumstances.

Viral Conjunctivitis

A number of things can cause conjunctivitis, also known as “pink eye”, which is inflammation of the membrane over the white part of the eye.  These include viruses such as the common cold, bacteria, allergic reactions, or irritants like shampoos, dirt, smoke and pool chlorine.  Often this is caused by viruses and can be quite contagious.


Symptoms tend to start in one eye and usually will involve the other eye within days. They include:

  • Lots of tears and a watery discharge
  • Lid swelling and redness
  • Foreign body sensation and light sensitivity
  • Blurred vision
  • In some rare cases there can swelling of the eyeball and even some bleeding into the tears


Viral conjunctivitis can be treated with cold compresses and drops that sooth and whiten the eye, but, like the common cold, there is no specific and definitive treatment.  Also like the common cold, it generally must resolve on its own.  It typically takes 1-2 weeks for this to occur and for the patient to no longer be contagious.  If your symptoms become intolerable, your doctor may recommend steroid eye drops to help with the inflammation.  As viral conjunctivitis is contagious, it is important to take extra precautions to reduce the chance of spreading it to others.

  • Wash your hands frequently, especially after touching your eyes or face.
  • Use tissues when wiping your eyes and throw them away immediately after.
  • Do not share soap, toiletries, cosmetics, towels or pillows with anyone else.
  • Try to minimize your physical contact, such as shaking hands or hugging, with others.

In some severe cases, there can be inflammation of the cornea causing light sensitivity and blurred vision which, unfortunately, can go on for months or even years.  If yours is one of these cases, some measures can be taken to reduce the severity of your symptoms.