What is the Difference Between Choroid and Retina

The main difference between choroid and retina is that the choroid is a vascular layer of the eye, lying between the retina and sclera, whereas the retina is a thin layer of cells at the back of the eyeball where the light is converted into neural signals.

Choroid and retina are two types of anatomical structures that occur in the human eye. Their function is to receive and process visual details.

Key Areas Covered

1. What is Choroid
     – Definition, Structure, Function
2. What is Retina
     – Definition, Structure, Function
3. Similarities Between Choroid and Retina
     – Outline of Common Features
4. Difference Between Choroid and Retina
     – Comparison of Key Differences

Key Terms

Choroid, Retina

What is Choroid

Choroid is a part of the uvea, the vascular tissue of the eye. It occurs between the retina and the sclera. It also contains connective tissue. The thickness of the choroid is around 0.2 mm, while in outlying areas, the thickness is less than 0.1 mm. The main function of the choroid is to provide oxygen and nutrients to the outer layers of the retina. The choroid also forms the uveal tract along with the ciliary body and iris. Moreover, there are four layers of the choroid. They are the Haller’s layer, Sattler’s layer, choriocapillaris, and Brunch’s membrane.

Figure 1: The Choroid

Haller’s layer is the outermost layer of the choroid, containing blood vessels of larger diameter. Sattler’s layer contains medium-diameter blood vessels. Meanwhile, choriocapillaris is a layer of capillaries. Whereas, Brunch’s membrane is the innermost layer of the choroid. Furthermore, there are two types of blood supplies to the eye. They are the retinal and uveal blood supplies. The choroid is a part of the uveal circulation, supplying blood to the uvea and the outer and middle layers of the retina.

What is Retina

The retina is the innermost, light-sensitive layer of the eye of most vertebrates. The optics of the eye create a two-dimensional image on the retina. Then, the retina processes the image and sends nerve impulses along the optical nerve to the visual cortex of the brain, creating visual perception. The retina contains several layers of neurons connected by synapses. The retina also contains primary light-sensing cells that are the photoreceptor cells in two types: rods and cones. Rods are active in dim light and provide monochromatic vision, while cones are active in well-lit conditions, precepting colors. They use a range of opsins to provide color perception.

Figure 2: Retina

Moreover, there is a third type of cell called photosensitive ganglial cells that entrain circadian rhythms and reflexive responses. Overall, the main function of the retina is to strike a light to send nerve impulses to the brain through the optic nerve.  

Similarities Between Choroid and Retina

• Choroid and retina are two structures of the eye.
• Their function is to receive and process visual details.

Difference Between Choroid and Retina

Definition

Choroid refers to the pigmented vascular layer of the eyeball between the retina and the sclera while retina refers to a layer at the back of the eyeball that contains cells sensitive to light, which trigger nerve impulses that pass via the optic nerve to the brain, where a visual image is formed.

Significance

The choroid is a vascular layer of the eye lying between the retina and sclera, while the retina is a thin layer of cells at the back of the eyeball where the light is converted into neural signals.  

Anatomy

Moreover, the choroid is a thin, variably pigmented vascular tissue forming the posterior uvea, while the retina is made of two parts: the macula and the peripheral retina.

Function

The main function of the choroid is to bring oxygen and nutrients to the eye, while the main function of the retina is to capture incoming photons and transmit them along the neuronal pathway to the brain.

Conclusion

In brief, the choroid and retina are two structures of the eye that receive and process visual details of the body. The choroid is the vascular layer that occurs between the retina and sclera. It is a thin, pigmented, vascular tissue that occurs in the posterior uvea. The main function of the choroid is to bring oxygen and nutrients to the eye. Meanwhile, the retina is a thin layer of cells at the back of the eyeball, capturing incoming photons and transmitting them to the brain. The two parts of the retina are the macula and the peripheral retina. Therefore, the main difference between choroid and retina is their structure and function.

References:                     

1. Stewart, S. “Choroid. “Kenhub. 
2. Nguyen KH, Patel BC, Tadi P. Anatomy, Head and Neck: Eye Retina. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan

Image Courtesy:

1. “Blausen 0388 EyeAnatomy 01” By BruceBlaus. – Own work (CC-BY 3.0) via Commons Wikimedia
2. “Human eye cross-sectional view grayscale” By NIH National Eye Institute- Own Work (Public Domain) via Commons Wikimedia