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Rod Cells: Anatomy, Function, and Associated Eye Problems
Published on March 6th, 2024
Rods are photoreceptor cells in the retina of the eye that help with vision during low-light conditions. There are roughly between 91 and 120 million rod cells in the retina and are distributed in its external regions. Between rods and cones, rods are the most sensitive to light as they can process a single photon of light that enters the eye during dim-light conditions. A rod’s anatomy consists of an elongated structure, with four unique sections that include an outer segment, an inner segment, a cell body and the synaptic region.
What are the Rod Cells in the Eye?
The rod cells in the eye are photoreceptor cells that help process light, to aid vision during low-light conditions. Rod cells are located in the outer areas of the retina and work by changing visual stimuli in the form of light particles into electrical signals, for the central nervous system to process according to Britannica.
Are Rod Cells also Known as Photoreceptors?
Yes, rod cells are also known as photoreceptors. Photoreceptors refer to the cells in the retina that convert light into signals, which are then sent to the brain to enable night vision through rod cells and colour vision through our cone cells.
What is the Structure of Rod Cells?
The structure of rod cells consists of an elongated, cylindrical shape with four segments, which include an outer segment, an inner segment, a cell body and the synaptic region. The function of the outer segment involves changing incoming light into electrical stimulus according to Gorman, N. (2023) in an article on Photoreceptors.
The image below depicts the elongated structure of the rod cell, which consists of the outer segment, inner segment, a cell body and the synaptic region.
What are the Regions of Rod Cells?
The regions of rod cells are the outer segment, the inner segment, the cell body and the synaptic region. According to Brittanica, the outer segment holds the phototransduction apparatus, which is the process of transmitting light that enters the eye into electrical signals. The outer segment of rods can convert incoming light into electrical signals through its light-sensitive pigments.
Where are Rod Cells Located?
Rod cells are located across the retina except in the fovea. According to the American Academy of Ophthalmology, rod cells are located in the outer areas of the retina, which is the light-sensitive layer found at the back of the eye.
How is the Rod Cell Connected to the Retina?
The rod cells are connected to the retina as they are located in the external areas of the retina. The retina is the layer of photoreceptor cells located at the back of the eye, which responds to incoming light by changing them into electrical signals that go through the optic nerve. The electrical signals travel from the optic nerve to the brain and enable us to see images. The rods in the retina are what allow us to see in dim-light conditions.
What is the Function of Rod Cells in the Eye?
The function of cells in the eye is to help enable clear vision during low-light conditions. The rod cells function by reacting to the light that focuses on the retina and processes them into signals to send to the brain. Rods are able to work effectively in low light while the other type of photoreceptor known as cone cells work better in more light.
What are Rods Cells Sensitive To?
Rods cells are most sensitive to light as they only require a single photon of light to be activated. Rods respond to light by changing it to signals to send to the brain, which occurs through the photosensitive chemical known as rhodopsin. Rhodopsin is a protein located in the discs of the outer segment of rod cells and is triggered by light exposure.
How Many Rod Cells are in the Human Eye?
There are roughly between 91 and 120 million rod cells in the human eye according to the National Institutes of Health.
Are Rod Cells Responsible for Night Vision?
Yes, rod cells are responsible for night vision. Rod cells are able to detect dim light and activate when exposed to a single photon of light, therefore, making them more effective during the night.
Do Rod Cells Detect Colours?
No, rod cells do not detect colours. Rod cells do not assist with colour vision as they only come in one type of light-sensitive pigment and respond to low levels of light. Therefore, rod cells are only able to provide clear vision when there are limited sources of light. Cone cells come in three different types to detect different wavelengths of light, which helps us with our colour vision.
How are Rod Cells Activated?
Rod cells are activated when they are exposed to light. Rod cells have outer segment discs that contain the protein known as rhodopsin, which primarily contributes to phototransduction and the health of photoreceptors. Rhodopsin changes the light that enters the eye into electrical signals, therefore, enabling the activation of the rod cells during light exposure. Phototransduction is the term that refers to the process when a photon of light is converted into an electrical signal according to Science Direct.
What are the Eye Problems that Can Affect Rod Cells?
The eye problems that can affect rod cells include retinitis pigmentosa, usher syndrome, photokeratitis and cone-rod dystrophy. The eye problems that can affect rod cells and their definitions are listed below.
- Retinitis Pigmentosa: Retinitis pigmentosa is the term for a group of eye diseases that cause damage to the retina and can lead to loss of vision, loss of colour vision and light sensitivity.
- Usher Syndrome: Usher syndrome is a genetic disease that can cause vision and hearing loss.
- Photokeratitis: Photokeratitis is an eye condition that can lead to eye pain as a result of ultraviolet light exposure from sources such as the sun, arc welding and certain lamps.
- Photokeratitis: Photokeratitis is an eye condition that can cause eye pain as a consequence of ultraviolet light exposure, typically from the sun.
- Cone-Rod Dystrophy: Cone-rod dystrophy is a category of rare eye diseases that can result in symptoms such as decreased visual acuity, lack of colour perception and light sensitivity.
1. Retinitis Pigmentosa
Retinitis pigmentosa is a group of eye diseases that results in the cells of the retina to deteriorate over time. Retinitis pigmentosa can be inherited from your parents and can produce symptoms such as poor night vision, peripheral vision loss and light sensitivity. There is no treatment for retinitis pigmentosa, however, it may be helpful to use low-vision aids and rehabilitation programs.
2. Usher Syndrome
Usher syndrome is a rare genetic disease that damages hearing and leads to the development of retinitis pigmentosa. Type one of Usher syndrome causes significant hearing loss, night vision loss and balance problems. Type two can lead to moderate to severe hearing loss during early childhood and vision loss by the teenage years. Type three can result in the onset of hearing loss in childhood with normal hearing at birth, loss of night vision by teenage years and normal balance, according to the National Eye Institute. Symptoms of Usher syndrome can include difficulty moving around in the dark, longer need to adjust to lighting changes and stumbling over objects in their path. Early treatment such as low vision aids or hearing aids and cochlear implants may help optimise their hearing and vision.
3. Photokeratitis
Photokeratitis is an eye condition that can stem from overexposure to ultraviolet light rays from the sun, welding arcs, light reflection from snow and UV lamps. Photokeratitis may similarly feel like having a sunburn in the eye and may bring on severe eye pain as one of the early signs. Other symptoms that can develop along with the eye pain may include sensitivity to light, reduced vision and teary eyes. Similar to corneal abrasions, photokeratitis may heal on its own within 24-72 hours. However, other cases may require topical antibiotic ointments or topical pain relief ointments, according to the American Academy of Ophthalmology.
4. Cone-Rod Dystrophy
Cone-rod dystrophy refers to a group of genetic eye disorders that affect the cone and rod cells in the retina, causing vision loss over time. Cone-rod dystrophy can lead to symptoms during childhood and include loss of visual acuity, the inability to see or differentiate between certain colours, blind spots in central vision (scotomas) and light sensitivity. According to the National Centre for Advancing Translational Sciences, patients with cone-rod dystrophy may likely experience blindness by mid adulthood.
Does Damage to the Rod Cells Cause Colour Blindness?
No, damage to the rod cells does not cause colour blindness. The rod cells of the eye are responsible for sending electrical signals to the brain during low-light conditions. Therefore, damaged rod cells may result in loss of night vision or poor vision during low-light conditions. It is damage to the cone cells that causes colour blindness as cone cells are what help us to see colour.
How to Take Care of Rod Cells?
To take care of rod cells in the eye, it can be helpful to have your eyes regularly tested by an optometrist. If you do not already have vision conditions or concerns, you should get your eyes tested at least once every two years. If you require prescription glasses or have any other eye problems, you may need to have an eye test once a year to two years. If you are 65 years or older, it may be necessary to have your eyes examined every year. To take care of rod cells, it is recommended to maintain the consumption of nutritional meals and a routine of regular exercise. You may not be able to take care of your rod cells specifically. However, receiving comprehensive eye tests regularly or as advised by the optometrist can significantly aid with overall eye health.
How Important is a Regular Eye Exam For the Rod Cells?
Receiving regular eye exams is very important in sustaining the optimal health of rod cells. Regular eye exams with an optometrist can help ensure that any changes to your vision are identified early enough to start a suitable treatment plan. Early detection of any vision changes may also aid in preventing further complications and delay the progression of vision loss.
Does Wearing Polarised Glasses Protect Rod Cells?
Yes, wearing polarised glasses may be capable of protecting rod cells as they can protect your eyes from UV light to certain degrees. Polarised glasses are designed to reduce excessive glare and increase the contrast of images during bright and sunny conditions. Therefore, polarised glasses may not necessarily offer more protection than standard sunglasses. However, wearing any sunglasses that offer UV protection when outdoors can help ensure overall eye protection from overexposure to UV light rays.
Is Eating Carrots a Good Way to Take Care of Rod Cells?
Yes, eating carrots and other certain foods can be a good way to take care of rod cells as a healthy diet in general can be a helpful way to care for your overall vision health. Certain foods that are rich in lutein and zeaxanthin may be beneficial to consume for optimal vision health according to El-Sayed M. Abdel-Aal et al., 2013 in their journal article published in the National Library of Medicine. According to the National Eye Institute, consuming a diet that has a good balance of fruits, vegetables and fish such as salmon and tuna may promote overall healthy vision including healthy internal structures of the eye such as rod cells.
What are the Differences Between the Rod Cells and the Cone Cells?
The differences between the rod cells and the cone cells are their functions for vision. Rods and cones are both referred to as photoreceptors, which are defined as cells in the retina that respond to light. Rod cells are responsible for our vision, the ability to see shapes during low-light conditions or night and can detect a single photon of light. Cone cells are what allow us to see different colours and come in three different types that include L cones, M cones and S cones, which help detect different colours and wavelengths of light. There are significantly more rod cells than cone cells in the retina with the rods located in the outer areas of the retina and the cones being in the centre of the retina, known as the macula.
