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Afferent Pupillary Defect  (Also referred to as:  Marcus Gunn Pupil) from http://www.eyemdlink.com

An afferent pupillary defect (APD) occurs when the nerve pathways to the brain fail to properly transmit messages.  It can occur from a number of disorders, and ranges from mild to severe.  The finding is a sign of an underlying disorder and is not specifically associated with any particular disease. 

An afferent pupillary defect is identified by examining the eyes with a bright light.  In normal circumstances, when a light is shone in one eye, both pupils constrict.  However, when a light is shone in the abnormal eye of a patient with an APD, the pupil of the affected eye paradoxically dilates rather than constricts.  This abnormal response signifies the brain is not receiving the message properly.    

A mild APD (slight constriction of the affected pupil), may be a sign of underlying amblyopia, vitreous hemorrhage, retinal scars, severe age related macular degeneration, branch retinal vein or artery occlusion, or retinal detachment.  If an APD is severe (dilation of the affected pupil), it generally indicates optic nerve disease such as ischemic optic neuropathy, optic neuritis, severe glaucoma, central retinal artery or vein occlusion, or in rare cases, a lesion of the optic chiasm or tract due to a pituitary tumor or stroke. 

Ptosis (Also referred to as:  Droopy Eyelid Dermatochalasis) from http://www.eyemdlink.com

Droopy eyelids basically fall into one of two categories: dermatochalasis or ptosis. Each of these conditions is described below.   

Dermatochalasis

Dermatochalasis is the presence of excessive and redundant eyelid skin, almost always progressive with aging. This condition may be treated with the surgical procedure known as blepharoplasty.  

Ptosis (pronounced "tosis") is the term applied to a wholly droopy eyelid. In this case, the eyelid itself is situated over more of the eye, sometimes occluding the pupil. Redundancy of eyelid skin is not a characteristic of ptosis, though that may also be present. The condition may be either congenital or acquired.   

Congenital Ptosis

Congenital ptosis is most commonly caused by a dystrophy of the levator muscle, which elevates the upper eyelid. If the condition results in occlusion of the pupil, the infant or young child will almost certainly develop amblyopia (lazy eye). Treatment is prompt ptosis repair (surgery) to elevate the lid.   

Involutional Ptosis

Involutional ptosis is an aging phenomenon resulting from laxity of certain tissues in the upper lid. This condition may also be associated with brow ptosis (droopiness of the eyebrow). One or both conditions may be repaired surgically. 

Nystagmus from http://www.eyemdlink.com

Nystagmus is the condition characterized by repetitive oscillations of the eyes. Parents of children with nystagmus often refer to this as "jerking" or "jiggling" eyes. Nystagmus is a general term, as there are many different types of nystagmus, and many more causes of nystagmus. 

Congenital Nystagmus

Congenital nystagmus presents with oscillating eye movements by 2 to 3 months of age. The eyes usually move in a horizontal direction in a swinging fashion. A null point may develop, which indicates a position of gaze in which the child has the least amount of nystagmus. Most individuals with congenital nystagmus have "dampening" of the swinging eye movements when their eyes converge to view a near object. Vision is typically reduced and sometimes poor, depending on the underlying cause. The cause of congenital nystagmus is frequently unknown. However, the most frequent known causes of this disorder include albinism, Leber's congenital amaurosis, aniridia (congenital absence of the iris), optic nerve hypoplasia (underdeveloped optic nerves), and other disorders that result in poor vision or blindness at birth, such as congenital cataracts and macular disorders.

Spasmus Nutans Spasmus

nutans is a related form of nystagmus, which presents between 6 months and 3 years of age, and resolves spontaneously between 2 and 8 years of age. Patients with spasmus nutans have head nodding and a head turn, and the eyes may move in any direction (i.e., vertical, horizontal, or torsional). This condition does not require any treatment.

Acquired Nystagmus

Acquired nystagmus, that is, nystagmus that presents in later childhood or adulthood, has a myriad of potential causes. In general, the causes of acquired nystagmus may be categorized as unknown, inherited, or secondary to central nervous system disorders, metabolic disorders, toxicity from alcohol and drugs, and physiologic. Depending on the type of nystagmus, patient history and symptoms, and physical exam findings, an extensive medical evaluation may be required to fully evaluate the condition. A complete discussion of nystagmus, which is a exceedingly complex subject, is beyond the scope of this site.