Related Experiment Videos
The development of the eyelids. Part I. External features
Insights
Human eyelid development progresses through distinct embryonic stages, beginning with the lens placode formation and culminating in complete eyelid closure. This detailed timeline maps key events in embryonic eye development.
Area of Science:
- Developmental Biology
- Embryology
- Ophthalmology
Background:
- Eyelid formation is a critical aspect of human embryonic development.
- Understanding the precise sequence of events is essential for identifying developmental abnormalities.
Purpose of the Study:
- To describe the sequential developmental stages of human eyelids in embryonic development.
- To provide a detailed timeline of eyelid formation from early embryonic stages to complete closure.
Main Methods:
- Observation and description of staged human embryos.
- Documentation of morphological changes related to eyelid development.
Main Results:
- The lens placode forms by week four, followed by the development of the lens pit and vesicle.
- Eyelid grooves appear around 37 days, leading to the formation of eyelid folds.
- Eyelid folds develop into complete eyelids, with the palpebral fissure forming and canthi establishing between stages 19-20.
- Complete eyelid closure is observed by Stage 23.
Conclusions:
- Human eyelid development follows a predictable sequence of morphological changes.
- The study provides a detailed staging of eyelid formation crucial for embryological studies.
Abstract:
The sequence of developmental events leading to the formation of the eyelids is described in staged human embryos. By the end of the fourth week the optic vesicle lies close to the surface ectoderm. The surface ectoderm overlying the optic vesicle, in response to this contact, has thickened to form the lense placode (Stage 13). A few days later (about 32 days, Stage 14) the lens placode is indented by the lens pit. A day or two later (about 33 days, Stage 15) the lens pit is closed: however, the lens vesicle and optic cup lie close to the surface ectoderm and appear to press against the surface. Prior to the development of the eyelids, one small sulcus or groove forms above the eye (eyelid groove) and another below it (stage 16, 37 days). As these grooves deepen, in Stages 17--19, eyelid folds develop, first below, and then above, the eye. In Stages 19--22 the eyelid folds develop into the eyelids and cover more of the eye as the palpebral fissure takes shape. The upper and the lower eyelids meet at the outer canthus in Stage 19. The inner canthus is established a few days later in Stage 20. Closure of the eyelids is complete in Stage 23.