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Related Concept Videos

Accessory Structures of the Eye01:17

Accessory Structures of the Eye

Optical perception, or vision, is an extraordinary sense dependent on converting light signals received via the ocular organs. These organs, known as eyes, are securely positioned within the bony cavities of the skull, called orbits. The orbits serve a dual purpose: a protective shield for the ocular globes and a stable attachment point for the soft ocular tissues. The eye's external protective mechanisms include the eyelids, which are edged with lashes that act as a barrier against foreign...
Anatomy of the Eyeball01:20

Anatomy of the Eyeball

The eye is a spherical, hollow structure composed of three tissue layers. The outer layer — the fibrous tunic, comprises the sclera — a white structure — and the cornea, which is transparent. The sclera encompasses some of the ocular surface, most of which is not visible. However, the 'white of the eye' is distinctively visible in humans compared to other species. The cornea, a clear covering at the front of the eye, enables light penetration. The eye's middle layer, the vascular tunic,...

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Related Experiment Video

Updated: May 10, 2026

Whole-mount Retinal Organoid Visualization with Cellular Resolution
09:20

Whole-mount Retinal Organoid Visualization with Cellular Resolution

Published on: June 20, 2025

Accessory Inner Segment-Like Structures Develop in Human Retinal Organoids.

Kristen E Ashworth1,2, Cassandra D'Amata2, Brian G Ballios3,4,5

  • 1Institute of Medical Science, University of Toronto, 6 Queen's Park Crescent, Toronto, ON, Canada.

Stem Cell Reviews and Reports
|May 8, 2026
PubMed
Summary
This summary is machine-generated.

Human retinal organoids successfully recapitulate the accessory inner segment (aIS), a novel structure found in rod photoreceptors. This finding enables in vitro studies of aIS in retinal diseases.

Keywords:
Electron microscopyInner segmentOrganoidOuter segmentPhotoreceptorRetina

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09:47

Generation of Retinal Organoids from Healthy and Retinal Disease-Specific Human-Induced Pluripotent Stem Cells

Published on: December 9, 2022

Area of Science:

  • Ophthalmology
  • Cell Biology
  • Developmental Biology

Background:

  • A novel structure, the accessory inner segment (aIS), has been identified in human rod photoreceptors.
  • The aIS is a microtubule- and mitochondria-rich extension of the inner segment, located externally to the outer segment.
  • Human retinal organoids mimic human retinal development and cellular features.

Purpose of the Study:

  • To determine if human retinal organoids exhibit aIS-like structures.
  • To establish a model for in vitro studies of aIS function and its role in retinal diseases.

Main Methods:

  • Human induced pluripotent stem cells were differentiated into mature retinal organoids.
  • Immunohistochemistry and confocal microscopy were employed to identify aIS-like projections.
  • Transmission electron microscopy (TEM) was used for ultrastructural evaluation.

Main Results:

  • Retinal organoids displayed stratified photoreceptor layers with inner and outer segment-like processes.
  • Microtubule- and mitochondria-rich projections, consistent with aIS morphology, were observed extending from inner segments.
  • TEM confirmed the presence of aIS-like structures with microtubules and mitochondria adjacent to the outer segment.

Conclusions:

  • This study provides the first evidence of aIS-like structures in human retinal organoids.
  • These organoids serve as a valuable in vitro model for studying photoreceptor structure.
  • This research opens avenues for investigating photoreceptor vulnerabilities in retinal degenerations.