A lens coloboma is a congenital anomaly of the lens due to the absence of zonular attachments, causing a thicker lenticular area, but a ciliary body, choroid, iris, optic nerve and eyelid abnormalities may coexist. It is usually located in the inferior nasal quadrant of the eye and is caused by the failure of an embryonic fissure to close (due to toxic or inflammatory factors) during the third or fourth months of intrauterine life, but genetic transmission has also been postulated.
A lens coloboma presents as a wedge-shaped abnormality that is due to the existence of a peripheral flattening, indentation or defect, usually located in the inferomedial portion of the lens, but superior nasal quadrant involvement has also been described . The structure has an equatorial notch . This can be an only anomaly, being called a primary coloboma, or underlying structures like the uvea may also be affected- and then it is called a secondary coloboma. A typical coloboma occurs at the exact same location where an embryonic fissure is present, whereas an atypical one does not  and may be caused by a ciliary body tumor like a medulloepithelioma or following congenital glaucoma surgery . The neighboring area of the lens may become opaque and the lens capsule may become thicker.
The patient presents with visual abnormalities caused by astigmatism, that is, in turn, due to the lens shape abnormality . Lens contraction and dilation are also impaired, due to the absence or loose character of zonules in the affected area.
A lens coloboma may be associated with other ocular abnormalities: retinal detachment, iris, optic disk or choroid colobomas. Abnormalities may also be bilateral, but usually, only one eye is affected .
Ophthalmologic assessment reveals the presence of astigmatic refractive error  , as well as the possible involvement of underlying structures, such as the choroid, optic disk or optic nerve  . The optic disk may be hypoplastic . Other unrelated visual anomalies like cataract may sometimes be diagnosed by the ophthalmologist. Moreover, the general appearance of the patient may be suggestive of Marfan or Marshal syndromes  . In these cases, a genetic consultation may be in order. Aside from observing the patient's clinical traits, the genetician may order transforming growth factor β (TGFβ) levels which may be increased . A genetic syndrome may be absent, even if facial dysmorphism is present . Lens colobomas have also been reported in association with Alport-like glomerulonephritis , therefore a urinalysis may be in order if history and clinical examination point to that diagnosis.
If the visual abnormality is severe and not immediately addressed, the patient will experience visual decline due to amblyopia, that can be anisometropic, meridional or refractive. If the eyelid is affected by ptosis, the prognosis is even more grim. Overall, visual outcome depends on the presentation timing and the patient's desire to undergo surgery and rehabilitation.