How we see - Refraction, Accommodation, and Transduction Flashcards
What is refraction?
Bending of light when it passes from one optical medium to another
What provides nutrition to the retina?
Choroid
Which components of the eye are involved in bending light?
Cornea and lens
What is the difference between the cornea and lens in terms of refraction?
The “bending power” of the lens can be altered, unlike the cornea
How does the lens change shape?
Ciliary muscle contracts Ciliary body bulges Space in the middle decreases Suspensory ligaments become lax Lens is no longer under stretch Lens becomes thicker
What is myopia?
Short sight caused by a long eye ball
What is hyperopia?
Long sight
What is astigmatism?
Non-spherical curvature of the cornea or lens
What is presbyopia?
Long sight from old age
What is emmetropia?
Perfect sight
How does myopia present?
Headache
Not being able to see blackboards
Divergent squint in infants and preverbal children
Loss of interest in sport
More interest in things up close, like books
How is myopia managed?
Biconcave lenses
How does hyperopia present?
Eye strain after reading or using a computer
How is hyperopia managed?
Biconvex lenses
How does astigmatism present?
Different curvatures across different axes
How is astigmatism managed?
Cylindrical corrective lens (Toric)
How does presbyopia come on?
Lens becomes less mobile/elastic with age
Seeing closer becomes more difficult
How is presbyopia managed?
Biconvex lens
What are the wavelengths for visible light?
400-800 nanometres
What is the thinnest part of the retina?
Fovea
Which side of the visual field is seen by the right side of the brain?
Left, and vice versa
Describe the outer segment of the transductive apparatus.
Stacks of lamellae have photoreceptors and form either rods or cones
What happens to 11-cis retinal when light falls on it?
It isomerises to all-trans retinal
What is rhodopsin (the visual pigment) made of?
Opsin and 11-cisRetinal
What is rhodopsin derived from?
Vitamin A
What does vitamin A deficiency cause?
Night blindness
How does vitamin A deficiency present?
Bitot’s spots (white patchy spots in conjunctivae)
Corneal ulceration
How is vitamin A deficiency caused?
Malnutrition
Some malabsorption syndromes like coeliac’s disease