The optic fissure is a temporary groove that forms during the early stages of eye development. This transient structure forms as an indentation in the optic stalk and optic cup, precursors to parts of the adult eye. Its proper formation and closure are important for the correct development of various ocular components.
Formation and Purpose
Eye development begins around day 22 of embryogenesis with the formation of optic vesicles, which are outgrowths from the developing brain. Around five weeks into gestation, these outpouchings undergo an auto-invagination process, creating a double-walled structure called the optic cup. The optic fissure, also known as the choroid fissure, forms as a groove along the ventral (bottom) aspect of this optic cup and stalk.
This groove provides a pathway for the hyaloid artery to enter the developing eye. The hyaloid artery supplies blood to the inner chamber of the eye during its formation, providing necessary nutrients without directly penetrating the neuroectoderm. Nerve fibers from the developing retina also exit through this region, forming the optic nerve.
Beginning around the fifth week of gestation, the edges of the optic fissure start to fuse. This closure process continues, completing by the seventh week of development. The most distal part of this fusion eventually forms the pupil. Once the optic fissure closes, the two layers of neuroectoderm comprising the optic stalk continue to grow and merge, leading to the formation of the optic nerve.
When Development Goes Wrong
When the optic fissure does not close completely during embryonic development, it results in a condition known as coloboma. Coloboma is a congenital defect, meaning it is present at birth, characterized by a gap or hole in one or more structures of the eye. This incomplete closure can vary in size and location, leading to a spectrum of presentations.
Colobomas are located in the inferonasal (lower-inner) quadrant of the affected eye structure. They can affect various parts of the eye, including the iris, which may result in a keyhole-shaped pupil. Other affected areas include the ciliary body, choroid, retina, and optic nerve. The severity of coloboma can range from a small, often unnoticeable defect to a large gap that significantly impacts vision.
Diagnosing and Managing Related Conditions
Conditions like coloboma are diagnosed during a comprehensive eye examination, sometimes in infancy. An ophthalmologist may use an ophthalmoscope to examine the internal structures of a baby’s eyes. As children get older, visual acuity tests and other assessments can determine the extent of vision impairment.
The visual impact of a coloboma varies depending on its size and location. Some individuals may experience no noticeable effect on their vision, especially if the coloboma is small or located in a less visually significant area. However, larger colobomas or those affecting the retina, choroid, or optic nerve can lead to significant vision impairment, including issues with central vision or specific visual field defects.
While coloboma cannot be “fixed” or reversed, management focuses on addressing its symptoms and any associated complications.
- Corrective lenses, such as glasses or contact lenses, may be prescribed to manage refractive errors like nearsightedness or farsightedness.
- For cosmetic concerns or light sensitivity related to an iris coloboma, colored contact lenses can be used, or surgical repair of the iris may be an option.
- Patients with posterior colobomas, particularly those involving the retina, are at an increased risk of retinal detachment, which requires urgent surgical intervention if it occurs.
- Regular eye examinations are recommended to monitor for potential complications like retinal detachment or glaucoma, which can also be associated with coloboma.
- Low vision aids and vision therapy can also be beneficial in maximizing the remaining visual potential.