Lecture 12 - Anatomy + Eye Conditions Flashcards
What are the transparent structures of the eye?
Cornea
Aqueous and vitreous humour
Wher is the centre of our vision focused onto?
Macula
How does light change as it enters the eye?
Changes from being very divergent or be refracted and focused onto the retina
What is the condition that presents with a white cloudy lens?
Cataracts
Why does a patient with cataracts have blurry vision?
Degradation of lens proteins makes the ens cloudy and white instead of transparent
This leads to the light being scattered in the eye and not refracted/focused properly
What structure regulates the amount of light entering the eye?
Pupil
Where does most of the refraction of light occur?
Tear film surface of the cornea
How can the shape of the eye affect vision?
Different lengths of eyeball lead to the focal point being before or after the retina not on the retina
What is an eyeball that’s too long called?
What sight defect does this cause?
Myopic
Short sightedness
What is an eyeball that’s too short called?
What sight defect does this cause?
Hypermetropic
Long sightedness
Is the light from a closer object more divergent/scattered or focused?
More scattered/divergent
More refraction needed to focus light onto retina
What is the reflex called when additional mechanisms are employed to increased refractive capabilities due to the cornea being fixed?
Accommodation reflex
What are the 3 things that occurs in the accommodation reflex?
Pupils constrict
Convergence of eye towards middle
Lens gets fatter/thicker
What is the purpose of the pupils constricting in the accommodation reflex?
Reduces amount of light entering eye
What is the purpose of the convergence of eyes in the accommodation reflex?
Ensures image is focused Ono same area of retina in both eyes
What is Presbyopia?
Age related loss of near vision
Why does presbyopia occur?
The lens stiffens and become less elastic with age
This means theres a reduced ability to increase refractive capabilities on near objects making it difficult to focus on near objects
What are the 2 types of photoreceptor?
Cones
Rods
What is the function of Cones?
C in Cones = Colour
Colour vision and high definition at high light levels
Where part of the retina are there lots of cones located?
Macula + fovea
What is the function of Rods?
Non colour vision
Low acuity at LOW light levels
(Think rods on night vision goggles allow sight at night)
Where part of the retina are there lots of rods located?
Peripheral retina (not in macula)
How is light converted to action potentials?
Cones/rods detect light
Action potential sent along retinal ganglion cell along axons to the optic disc to the optic nerve
Optic nerve travels to occipital lobe of brain
What is visual acuity?
How clear our central vision is
Ability of eye to discern shapes and details
How is visual acuity measured?
Snellen chart
How does the Snellen chart measure visual acuity?
6m or 20ft from chart
Cover one eye and try and read from big line down to as small as you can go
Lines are numbered with the distance you should be able to read this line at
How are the results written for visual acuity?
Always 6 or 20 as numerator (distance away)
Then the line you can clearly read at that 6m distance as denominator
Perfect vision is 6/6 or 20/20
Explain what is meant by a visual acuity score of 6/12:
This means at a 6m distance you can only clearly read text that should be perfectly visible form a 12m distance
What are the 2 main broad causes of decreased visual acuity?
Transparency issue
Structural issue (refractive problem)
What can cause transparency problems?
Cataracts
What are some conditions causing reduced refractive ability of structures anterior to retina leading to decreased visual acuity?
Astigmatism (irregular corneal surface)
Presbyopia
Shape of eyeball
What other conditions can cause decreased visual acuity?
Retinal detachment
Macular degeneration n
Optic neuritis (inflam of CNII)
Glaucoma
What is the red reflex?
Using an ophthalmoscope see if the retina reflects back an orange light =healthy
What is a common condition in older adults that would have an absent red reflex?
Cataracts
What can an absent red reflex in young children be indicative of which is concerning?
How does the eye look?
Retinoblastoma
Bright white
What refractive issues can cause decreased visual acut?
Abnormal corneal surface
Inability of lens to change shape
Size of eyeball
What 2 structures have pathologies if decreased visual acuity is caused by a non refractive problem?
Retinal
Or
Optic nerve problem
What tool can be used to determine whether a decreased visual acuity is caused be a refractive or non refractive problem?
Pinhole occluded
How does a pin hole occluder help determine whether decreased visual acuity is caused by a refractive or non refractive problem?
Pin hole lets only light in that’s perpendicular to cornea and lens (straight line)
This means it doesn’t need to be refracted so it focuses on the macula
Therefore if its a refractive problem the visual acuity should improve with the pin hole
If no improvement then the problem isn’t with refraction (likely optic nerve or retina problem )
