The iris acts as the diaphragm of the eye, regulating the amount of light entering. The pupil, the dark opening at the center of the iris, is the gateway through which light travels to the retina. This system ensures clear vision across various lighting conditions. While most people have a single, centrally located pupil, a few individuals are born with a highly unusual variation involving the presence of multiple pupils within one eye.
Defining Polycoria and its True Rarity
Polycoria is characterized by the presence of two or more separate pupillary openings in a single iris. To be considered true polycoria, each pupil must possess its own complete and functional sphincter muscle tissue. This allows each pupil to independently constrict and dilate in response to light stimuli, much like a normal pupil.
This condition is an extremely rare congenital anomaly, often cited as one of the rarest developmental defects of the iris. Only a handful of verified cases have ever been documented in medical literature worldwide. In true polycoria, the multiple openings are typically smaller than a single normal pupil and are separated by a bridge of iris tissue.
Causes of Multiple Pupils
True polycoria is a congenital developmental anomaly, meaning it is present from birth. The exact mechanisms causing this duplication of pupillary structures remain largely unknown. One proposed theory suggests the condition results from an issue during the embryonic development of the iris, where the pupillary margins fail to fuse correctly. This defect leads to the formation of separate, functional sphincter muscles around each opening.
The condition is often associated with other ocular defects, suggesting a broader issue in anterior segment development. Associated conditions can include polar cataracts or the development of glaucoma. Its presence can sometimes be a sign of a more complex underlying developmental syndrome.
True Polycoria Versus Pseudopolycoria
The term “polycoria” is frequently misused, as most reported cases of multiple pupils are actually pseudopolycoria, or false polycoria. The distinction is based entirely on the presence or absence of a functional sphincter muscle surrounding the openings. In pseudopolycoria, the extra openings are merely holes or defects in the iris tissue.
These accessory openings lack their own sphincter muscles and therefore cannot constrict or dilate actively in response to light. While they may visually resemble a second pupil, they are non-functional and simply allow extraneous light to pass through. Pseudopolycoria is often associated with conditions like Axenfeld-Rieger syndrome or Iridocorneal Endothelial (ICE) syndrome, which cause generalized defects in iris structure.
Management and Visual Outcomes
The presence of multiple functional pupils affects vision because light enters the eye through more than one aperture, creating multiple focal points on the retina. Patients commonly experience symptoms such as reduced visual acuity, glare, and light sensitivity (photophobia). The uncoordinated light input can also lead to visual disturbances like monocular diplopia, or double vision in one eye.
Management is aimed at improving visual function and alleviating symptoms caused by the multiple light paths. When vision is significantly impaired, treatment involves surgical intervention known as pupilloplasty. This procedure involves cutting the iris tissue bridge that separates the pupils, joining them to create a single, larger, and more centrally located pupil. The visual prognosis after surgery depends on whether any associated conditions, such as glaucoma or cataracts, are also present and managed.