Eye Diseases (General)

Refractive Error

People with emmetropic vision have no refractive error. In these patients, the cornea, which provides two-thirds of refractive power, and the lens, which provides the remaining one-third of refractive power, perfectly focus an image on the retina. By contrast, people with ametropic vision require corrective lenses in order for the image to be in proper focus.

Color Blindness

Color blindness is usually an X-linked recessive condition affecting retinal photoreceptors that affects about 10 percent of the male population. There are several forms of color blindness, ranging for asymptomatic types to the most common type where the patient may confuse red with green. Cone dystrophy can also induce diminished color vision. Physicians commonly use the Ishihara or Hardy-Rand-Rittler pseudoisochromatic color vision plates to assess color vision of each eye individually.

Diplopia

Diplopia, or double vision, can be divided into two subtypes—monocular or binocular—and can be intermittent or constant. In monocular diplopia, patients have double vision when closing one eye. In binocular diplopia, patients have double vision only with both eyes open, and closing one eye causes the double vision to disappear. Some causes of monocular diplopia include corneal irregularities, astigmatism, cataracts, and refractive error. A common cause of binocular diplopia is strabismus (misalignment of the eyes) or neuromuscular disorders.

Common Disorders of the Eyelids

A hordeolum, commonly referred to as a sty, is an infection of the hair follicles or meibomian glands, usually due to Staphylococcus aureus. A chalazion is a chronic, granulomatous inflammation of a meibomian gland, which unlike a hordeolum, does not have acute inflammatory signs. Treatment consists of warm compresses and antibiotic ointment, and surgical drainage and excision if unresponsive to medical treatment.

Blepharitis, or inflammation of the eyelid margin, is a very common condition that can be subdivided into anterior and posterior blepharitis. Patients with blepharitis usually have symptoms of burning, itching, redness, and tearing. Anterior blepharitis can be further subdivided into staphylococcal or seborrheic blepharitis. Usually, both types of blepharitis are present. Posterior blepharitis is usually secondary to meibomian gland dysfunction, and patients may have frothy or greasy tears.

A xanthelasma is a common lesion that affects the upper eyelid more often that the lower eyelid. This lesion, while sometimes associated with elevated lipids, can also be found in patients with normal serum lipids.

Dry Eye Syndrome

In patients with dry eye syndrome, they may have a foreign body sensation with sandy, scratchy, burning, or red eyes. Some of the many causes of dry eye syndrome include hypofunction of the lacrimal gland due to congenital, acquired, infectious, traumatic, or medication-induced causes; mucin deficiency due to chemical burns, medications, chronic conjunctivitis, and Stevens-Johnson syndrome; lipid deficiency due to blepharitis; or defective spreading of the tear film secondary to eyelid abnormalities, lagophthalmos, proptosis, or conjunctival abnormalities. Some diagnostic measures include Schirmer test and assessing tear film breakup time with a slit-lamp examination. Fluorescein staining and slit-lamp examination will show the corneal irregularities present.

Other conditions that can cause foreign body sensation include corneal abrasions, trichiasis (this occurs when eyelashes grow in the wrong direction, touching the conjunctiva), and corneal foreign bodies.

...