Retina Flashcards
What is the retina?
The inner layer of the eye
What are the layers of the retina?
Inner neurosensory layer
Outer pigmented epithelial layer
What does the outer pigmented layer contain?
Melanin
What is the function of melanin in the outer pigmented layer of the retina?
Absorb scattered light in the eye
Reducing reflection of light in the eye
Allows light to be focussed in one area of the retina
What causes albinism?
Partial or complete absence of melanin
What is the inner neurosensory layer made up of?
Photoreceptor cells
- rods
- cones
What is the distribution of rod and cone cells in the retina?
Rod cells are abundant towards the periphery
Cone cells are most concentrated in the macula
What are the functions of rod cells?
Responsible for vision in low intensity light
See in black and white
What are the functions of cone cells?
Colour vision
High acuity
What is the macula?
Refer to the area of the retina onto which light from the centre of vision falls onto
Centre of vision meaning what the gaze is directed towards
How can the macula be visualised?
Fundoscopy
What does the macula look like on fundoscopy?
Slightly dark area of the retina
What is the relative position of the macula on the retina?
Lateral to the optic disc
What is the fovea?
Refers to a depression at the centre of the macula
What is the fovea made up of?
Only cone cells at this point on the retina
What is retinal detachment?
Refers to the inner neurosensory layer detaching from the outer pigmented layer in certain areas
What causes retinal detachment?
Can occur spontaneously
Head trauma
What is a sign of retinal detachment?
Visual disturbances
Why doe retinal detachment cause visual disturbances?
Photoreceptors in the neurosensory layer lose their blood supply, which comes from the choroid layer of the eye
Photoreceptors do not function
What are the types of cone cells?
Red
Blue
Green
How do cone cells see in colour?
Red, blue and green cone cells respond to different wavelengths of light
What causes colour blindness?
Absence or dysfunction of any of the types of cone cells
What is the function of horizontal cells?
Lateral inhibition
What is lateral inhibition?
Refers to stopping photoreceptors next to the macula from generating impulses
As these impulses would result in distorted images of vision
What is the visual pathway till the optic nerve?
Photoreceptor cells synapse with bipolar cells
Bipolar cells synapse with ganglion cells
Ganglion cells converge to the optic nerve
What is the optic disc?
Refers to where the optic nerve leaves the retina
What is the optic disc commonly known as? Why?
The blind spot
Because no photoreceptor cells at this point
How can the optic disc be visualised?
Fundoscopy
What does a swollen optic disc look like on fundoscopy?
Enlarged
Blurring outline
What are the causes of optic disc swelling?
Raised intracranial pressure
Why does raised intracranial pressure cause optic disc swelling?
Because the optic nerve is surrounded by meninges
So raised intracranial pressure extends around the optic nerve also
What is the blood supply of the retina?
Central retinal artery
What happens if the central retinal artery is blocked? Why?
Loss of vision
Due to loss of blood supply to photoreceptor cells, don’t function
Because the central retinal artery is an end artery, meaning it’s the only blood supply to the retina
