mirror of the soul

When people are asked which of their five senses they would least want to lose, vision is the most frequently picked. Humans have excellent vision compared to many other animals. We see in color, have good depth perception and good distance vision. In truth, the eyes see nothing. The eye is simply a mechanism to gather and focus light on the retina. The rods and cones of the retina when stimulated by photons of light, send this information to the visual cortex. This part of the cerebrum or higher brain, interprets the information from the eyes into what our conscious mind perceives as vision.

The ER treats several types of problems with the eye. These problems are pain, with or without redness, visual changes or loss, and traumatic injuries to the eye. The triage nurse will check the patient's vital signs, and often perform a visual acuity using the familiar Snelling chart (with the big E on the top line). Visual acuity is rated from: none through light perception, movement perception, finger counting and a measurement of the actual acuity (20/20-20/400). Blood sugar determination may be checked if a history or suspicion of diabetes is obtained by the triage nurse. Diabetic retinopathy (disease of the retina) is the most common cause of blindness in the USA. High blood pressure and irregular heart rythyms may give information as to the cause of changes or loss of vision.

Injuries to the eye are frequent and usually not serious. Abrasions and foreign bodies of the cornea are diagnosed with some type of magnification and fluorescein dye to highlight the injury. The cornea can heal the abrasion usually with in 24 hours. Many foreign bodies can be removed with a cotton swab or eye spud. Pain medications and antibiotic drops are all the patient requires. Penetrating injuries to the globe (eyeball) are always refered to an opthalmologist or eye surgeon. X-ray or CT (CAT scan), antibiotics, tetanus prophylaxis and a shield to protect the eye are the ER docs responsibility.

Thermal and especially chemical injuries to the eye must be treated rapidly and aggressively. Anesthetising drops and copious irrigation often with a Morgan lens are employed to remove the offending chemicals. The pH of the chemical is determined, as acidic and alkaline chemicals cause different types of injury.

The painful red eye includes a number of diagnoses. Infections from viruses, bacteria and parasites can all present with a painful red eye. Glaucoma, a disease characterized by increased pressure in the eye, can present as a painful red eye with sudden change in visual acuity. A tonometer is used to measure the intraocular pressure. Medications and an urgent referral to an opthalmogist is needed to treat this form of glaucoma. Certain types of vasculitis, an inflammation of the blood vessels also presents as a painful red eye. Diagnosis can be difficult. Special blood tests and an examination with a slit lamp (binocular device for viewing the anterior portion of the eyeball) help to confirm this diagnosis.

Sudden loss of visual acuity or a complete loss of vision is a true emergency. Minutes may count as the cause of the loss must be determined and treated to try and preserve vision. Strokes involving the visual cortex or the retina itself can cause visual loss. Detachment of the retina or bleeding into the retina require urgent treatment by an opthalmologist. Blockages in the retinal artery or vein will also cause visual loss.

Our vision is divided into visual fields. The right half of both eyes take in light from the left visual field, and the left half of the eye from the right visual field. The optic nerves carry the information from the eyes. These nerves divide into branches that split and cross at the optic chiasm, just above the pituitary gland deep in the front of the skull. The ER doc will cover one eye or the other and check perception to movement in the entire visual field to try and ascertain where the visual loss arose. Loss of vision in one only one eye, strongly suggests a problem in that eye. A visual field cut involving both eyes implies a problem with the visual cortex from a stroke or injury or tumor.

The ER doc uses an opthalmoscope to look through the pupil and lens to visualize the retina and optic nerve. When looking at the optic nerve the ER doc is getting a hint of the condition of the brain. Swelling of the brain will cause the optic nerve to bulge. Dislocation or clouding of the lens (a cataract) can also be checked by using the opthalmoscope. A darkened room and even dilating drops may be used to facilitate the examination of the posterior of the eye.

This posting is but a taste of the complexities of the eye and vision. The specialty of opthalmology is devoted to the diagnosis and treatment of the diseases of the eyes and vision. I didn't include problems with the eyelids (chalazion, hordeolum, meibomian duct and gland problems), tear ducts, or the six muscles that move the eye.

The take home message is simple. Protect your eyes and vision. Use appropriate safety glasses. Wear sunglasses. Control your diabetes and hypertension. Head to the ER for any sudden change or loss of vision. Immediately irrigate any acid or alkaline chemical that gets into your eyes, as you go to the ER.