Ellipsoid Zone (EZ) is a highly reflective band indicating which part of the photoreceptors?

• A. The mitochondria-rich part of the photoreceptors
• B. The barrier between inner and outer segments
• C. The site of phototransduction in cones
• D. The boundary between retina and choroid

Answer: (A)

The Ellipsoid Zone represents the mitochondria-rich portion of the photoreceptor inner segments. This region contains a high density of mitochondria, which makes it especially reflective on OCT because the densely packed organelles scatter light effectively and support the energy needs of the photoreceptors. While phototransduction—the light-activated process—occurs in the outer segments, the EZ reflects the inner segment ellipsoid, not the outer segment where phototransduction actually takes place. The boundary between inner and outer segments is a different feature (the IS/OS junction), and the boundary between retina and choroid is the Bruch’s/RPE interface, not the EZ. A healthy EZ indicates intact mitochondrial-rich inner segments and correlates with photoreceptor health and visual function.