ANISOCORIA , ANISOKONIA & ANISOMEROPIA

by Dr Sarhan Tue Jan 01, 2008 1:50 pm

Anisocoria:
It means that the pupil in the right eye and left eye are not the same size. A small amount of anisocoria or difference in pupil size is normal. On some days, a person’s right pupil might be larger than the left and on other days, the pupils might be the same size or the left might be larger than the right. But if more than a small difference in pupil size is present and persists, you may have a neurologic problem.

The iris is the colored (brown, blue, etc.) portion of the eye and the pupil is the black, circular area in the center of the iris.
The pupil is actually a hole in the iris which controls the amount of light that gets into the eye. In dim light, the hole, or pupil, gets larger (dilates) to let in more light, while in bright light, the pupil gets smaller (constricts) in order to protect the eye from too much light.
The size of the pupil is controlled by muscles in the iris
– the iris dilator and the iris constrictor muscles. The
muscles are controlled by nerves from the brain to the eye.
Problems with these nerves cause the size of the pupil to be abnormal. A problem with the nerve that normally dilates the pupil in the dark, causes a small pupil. A problem with the nerve that normally constricts the pupil, produces an abnormally large pupil.

An Abnormally Small Pupil
The nerve that dilates the pupil in the dark, the oculosympathetic nerve, also controls a little muscle that holds the eyelid open. When the oculosympathetic nerve is not working, the pupil on that side is abnormally small and the upper eyelid droops a bit. This is called Horner Syndrome.

Although having Horner Syndrome by itself will not damage the eye or cause loss of vision, it may be a signal of damage to one of the structures along the nerve. The nerves that dilate the pupils in dark come in contact with many structures. They begin in the brain and pass down to the spinal cord. They exit from the spinal cord and run up over the lung and into the neck, where they travel with the
carotid artery. They follow the carotid artery back into the
brain, from where they enter the eye and go to the dilator
muscle of the iris. Damage anywhere along this path will cause Horner Syndrome. It is important to find out where the damage is and what is causing it because sometimes it can be serious. Examples of serious conditions causing
Horner syndrome are a stroke in the brain or a tumor in the lung or a break in the wall of the carotid artery called a carotid dissection. In other cases, the Horner syndrome is due to birth trauma. Sometimes no cause can be found and the patient remains well.
Your doctor may do one or two eye drop tests to confirm that a Horner Syndrome is present and to determine the location of the nerve damage. Detailed radiologic studies, usually magnetic resonance imaging (MRI), are done to look at the places the nerves pass through for possible causes of the damage.
An Abnormally Large Pupil
The nerve that goes to the constrictor muscle is part of the IIIrd cranial (oculomotor) nerve. The IIIrd cranial nerve controls several of the muscles that move the eye. It also controls the muscle that opens the eyelid and the muscle that constricts the pupil. A problem with the IIIrd nerve can result in a droopy eyelid, double vision and/or enlarged pupil.

Pupil enlargement in addition to lid droop and eye muscle weakness may signal an aneurysm and is a medical emergency. The patient should immediately have neuroimaging (CT, MRI, MRA, and/or angiogram) to look for the aneurysm.

When only the pupil portion of the IIIrd nerve is not working, the pupil is large and does not constrict in bright light. This might be caused by a medicine or chemical that dilates the pupil. Examples include motion-sickness patches, chemicals used in the garden, and certain eye drops. The patient often is unaware of what she touched that caused the problem but careful questioning by the doctor may reveal the cause. A pupil that is chemically dilated will return to normal size as the chemical wears off and eventually will react normally to light. Depending on the specific chemical, this can take hours or days.
Adie Pupil is another type of pupil that is large and constricts poorly in light.

An eye with an Adie pupil initially has difficulty focusing on objects held close, for example, for reading. Adie pupil is commonly seen in young adult women but men can develop it, too. In most cases, the cause of the damage is unknown and radiology studies rarely show any abnormality.
A person can have Adie pupils in one or both eyes. Adie syndrome is the combination of Adie pupils and reduced reflexes such as knee jerks. The cause of Adie syndrome, like Adie pupil, is unknown. There is no treatment for Adie pupils. With time, the ability to focus up close usually returns. The Adie pupil may remain enlarged but more often
shrinks in size gradually over several years, even becoming smaller than the normal pupil in the other eye. The Adie pupil will never react well to a light shined in the eye. It is important that you remember this for future eye exams.

Anisometropia:
is a condition where there is a significant difference in the
refractive errors of the two eyes. If this condition is present in infancy and is
undetected or untreated, it often results in the development of lazy eye or amblyopia in the more hyperopic (far-sighted) eye. The greater the amount
of the difference, the more likely the development of lazy eye will be.Another problem can occur when glasses are made for an anisometropic individual. The difference in the powers of the lenses induce a prismatic difference that can cause double vision in off-center areas of the lens, which can be compensated for by the use of slab-off prism.
A brighter right reflex indicates the need for glasses

Unequal refractive errors in the two eyes result in unequal vision. A brighter right reflex indicates the need for glasses

Anisokonia:
A difference of the image size on the retina of each eye. It is due to anisometropia.