Refractive errors and common eye infections

Diseases & disorders of the eye

The following sections discuss the common diseases and disorders of the eye, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

Refractive errors

Four major types of refractive errors result when the eye is unable to focus light effectively on the retina. Refraction is the ability of the lens of the eye to bend parallel light rays coming into the eye so that the rays are focused simultaneously on the retina. An error of refraction means that the light rays are not refracted or bent properly and consequently do not focus correctly on the retina. Defects in the shape of the eyeball can cause a refractive error. Most refractive errors can be corrected with corrective lenses, contacts, or surgery.

Hyperopia (farsightedness)

When light enters the eye and focuses behind the retina, a person has hyperopia. This disorder occurs when the eyeball is too short from the anterior to the posterior wall. An individual with hyperopia has difficulty seeing objects that are close, at reading or working level. A convex corrective lens helps the eye’s internal lens place objects directly on the retina and creates a sharp, detailed image, or refractive surgery may be done to correct the shape of the lens.

Myopia (nearsightedness)

Myopia occurs when light rays entering the eye focus in front of the retina, causing objects at a distance to appear blurry and dull. Objects viewed at reading or working level are seen clearly. This disorder causes the eyeball to become elongated from the anterior to the posterior wall, and images cannot be sharpened by the internal lens of the eye. A concave corrective lens is used to focus the light rays on the retina, or surgery can be done to change the shape of the cornea. However, the surgery is performed only on adults who have had a stable eye prescription for at least 1 year.

Presbyopia

As people age, the lens of the eye becomes less flexible, and the ciliary muscles weaken; consequently, changing the point of focus from distant to near becomes difficult. This is called presbyopia. The condition results in difficulty seeing at reading level. A combination corrective lens, known as a bifocal lens or progressive lens correction, is used to focus both distal and proximal objects directly on the retina. Presbyopia actually starts at approximately age 10, but most people do not report an alteration in vision until their early 40s. Conductive keratoplasty is a laser surgical procedure used to treat presbyopia.

Astigmatism

Astigmatism occurs when light rays entering the eye are focused irregularly. This usually occurs because the cornea or the lens is not a smooth sphere but rather has an irregular shape. Ophthalmologists describe the lens as being shaped like a football rather than a sphere, such as a basketball. This causes light rays to be unevenly or diffusely focused on the retina, resulting in blurred vision. It is like attempting to focus on objects seen through a wavy piece of window glass. Astigmatism can be corrected with glasses, contacts, or surgery. Surgical correction attempts to reshape the cornea into a more spherical or uniformly curved surface.

Signs and symptoms of refractive errors

Refractive errors in vision can lead to squinting, frequent rubbing of the eyes, and headaches. The individual notices blurred vision, fading of words at reading level, or both. Some refractive errors are familial in nature.

Treatment of refractive errors

Eyeglasses and contact lenses are the traditional treatments for visual acuity problems caused by refractive errors. However, problems with the shape of the lens can be corrected surgically. Surgery is performed on an outpatient basis and requires only a short stay in the facility. Medical assistants employed in an outpatient eye surgery facility must be trained to fulfill this specialized role.

Surgical correction of refractive errors

Most types of health insurance do not cover surgery for refractive corrections. On average, each eye costs $1500 to $3000. The following are some of the surgical procedures performed to correct refractive errors:

• Photorefractive keratectomy (PRK): The first surgical procedure developed to reshape the cornea with a laser. The same type of laser is used for PRK and LASIK. The major difference between the two types of surgery is how the middle layer of the cornea is exposed before it is vaporized with the laser. In PRK, the top layer of the cornea (the epithelium) is scraped away to expose the stromal layer underneath. In LASIK, a flap is cut in the stromal layer.
• Laser-assisted in situ keratomileusis (LASIK): LASIK uses an excimer laser to reshape the central cornea to treat myopia, hyperopia, and astigmatism. A thin, hinged flap of the cornea is created, the flap is lifted, and the exposed surface of the cornea is reshaped. After the corneal curvature has been corrected, the flap is replaced, and the area heals without stitches.
• Laser-assisted epithelium keratomileusis (LASEK): In LASEK surgery, the surface epithelial cells of the eye are softened with an alcohol solution, allowing the epithelial layer to be rolled back and the cornea to be exposed. A laser is then used to reshape the cornea and treat myopia, hyperopia, and astigmatism. The epithelial flap is returned to its original position, and a contact lens is placed on the cornea as a bandage for several days to aid healing and reduce pain.
• Conductive keratoplasty (CK): CK uses heat created by a laser to reshape the cornea. Heat is applied to the cornea’s outer edge to tighten and steepen the cornea. CK is used in patients older than 40 years of age who need correction for hyperopia, presbyopia, and myopia. The procedure causes little or no discomfort and improves vision almost instantly. The corneal changes are not permanent, and retreatment may be required.

Strabismus

Strabismus is failure of the eyes to track together, which means that both eyes do not look in the same direction at the same time. Adults can develop strabismus because of a condition or disease elsewhere in the body, such as diabetes mellitus, muscular dystrophy, or hypertension, or as the result of a head injury. In children, strabismus is caused by weakness in the muscles that control eye movement. If the condition appears in infancy or childhood, it is most commonly associated with amblyopia. Treatment involves having the child wear a patch over the unaffected eye so that the muscles of the “lazy” eye are strengthened or administering atropine eyedrops to the unaffected eye to medically decrease visual acuity in the “sound” eye, thereby forcing the amblyopic eye to compensate. It was once standard therapy that an eye patch would be worn up to 6 hours per day, but getting young children to comply with this treatment is very challenging. In children with moderate amblyopia, research shows that patching daily for 2 hours is as effective as patching for 6 hours daily, and daily atropine is as effective as daily patching. Children older than 7 years may still benefit from patching or atropine, particularly if they have not previously received treatment for amblyopia. Amblyopia recurs in 25% of children after patching is discontinued; however, slowly reducing the amount of time the patch is worn each day at the end of treatment reduces the risk of recurrence. The main symptom in all age groups is diplopia (double vision).

Nystagmus

A constant, involuntary movement of one or both eyes are called nystagmus. The eye can move in any direction, and the movement is accompanied by blurred vision. A child may be born with the problem (congenital nystagmus), or the condition may be acquired as a result of a brain tumor, an inner ear lesion, multiple sclerosis, or substance abuse. Nystagmus is caused by an abnormal function in the part of the brain that controls eye movements. Congenital nystagmus is more common than acquired nystagmus, is usually milder, does not worsen over time, and is not associated with any other disorder. A patient with signs and symptoms of nystagmus should initially have a neurologic evaluation to determine the cause of the disorder, with treatment based on those findings. However, congenital nystagmus has no cure. Affected individuals typically are not aware of the eye movements, but they may have a decrease in visual acuity that can be corrected with surgery or corrective lenses.

Infections of the eye

Many acute disorders of the eye are seen in the ophthalmologist’s office. These include the following:

• **Hordeolum **(sty): A localized, purulent infection of a sebaceous gland of the eyelid. The area is inflamed, swollen, and painful. The infection usually is caused by staphylococci, and it is treated with warm compresses and topical or systemic antibiotics.
• Chalazion: A small cyst that results from blockage of a meibomian gland (sebaceous gland) and lubricates the posterior margin of each eyelid. The cyst can become infected, inflamed, swollen, and painful. It may disappear spontaneously or may need to be removed surgically.
• Keratitis: Inflammation of the cornea that results in superficial ulcerations. It can be caused by the herpes simplex virus, bacteria, or fungi, or it may develop as a result of corneal trauma (e.g., intense light). Symptoms include inflammation, tearing, pain, and photophobia. The condition is treated with ophthalmic ointments, eye drops, and use of an eye patch.
• Conjunctivitis: Inflammation of the conjunctiva caused by irritation, allergy, or bacterial infection. Bacterial conjunctivitis (pinkeye) is highly contagious and produces a purulent discharge. Symptoms include inflammation, swelling and itching of the sclera, photophobia, and tearing. Bacterial infections are treated with antibiotic ophthalmic preparations.
• Blepharitis: Inflammation of the glands and lash follicles along the margins of the eyelids that may be caused by staphylococcal infection, allergies, or irritation. Symptoms include itching and inflammation along the eyelash margins; the condition is treated with antibiotic ophthalmic ointment.

Disorders of the eyeball

The following sections discuss the common disorders of the eyeball, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

Corneal abrasion

The cornea, the transparent outer covering of the eye, is prone to abrasion because of its location. Symptoms of corneal abrasion include pain, inflammation, tearing, and photophobia. The abrasion is usually caused by a foreign body in the eye or by direct trauma, such as from poorly fitting or dirty contact lenses. A corneal ulcer may form and become infected.

Diagnosis is based on the patient’s signs and symptoms, but it can be confirmed with the instillation of fluorescein stain. After instillation of the stain, the provider uses a cobalt blue filtered light to visualize the abrasion, which appears green. If the abrasion is caused by a foreign body, it must be removed first; the eye can then be treated with antibiotic ophthalmic ointment to prevent infection. Although patching the affected eye has been recommended in the past, studies now show that patching does not reduce the patient’s pain and may actually prolong healing time. Corneal abrasions are quite painful, so the patient may be prescribed topical nonsteroidal anti-inflammatory ophthalmic drops, such as diclofenac (Voltaren) and ketorolac tromethamine (Acular), in addition to oral analgesics. Most corneal abrasions heal in 24 to 72 hours, but the patient should be aware that symptoms can worsen if the affected eye is exposed to bright light, if excessive blinking occurs, or if the patient rubs the injured surface of the cornea against the inside of the eyelid. Because the patient may develop a secondary infection from the corneal injury, topical antibiotics, including ciprofloxacin 0.3% (Ciloxan) ointment or drops and gentamicin 0.3% ointment or drops may be prescribed. Patients with contact lenses may be prescribed oral antibiotics and should not wear their contacts until the abrasion has healed and the course of antibiotics has been completed.