Lecture 12 - Anatomy + Eye Conditions Flashcards by Callum Donoher

What are the transparent structures of the eye?

Cornea
Aqueous and vitreous humour

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Wher is the centre of our vision focused onto?

Macula

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How does light change as it enters the eye?

Changes from being very divergent or be refracted and focused onto the retina

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What is the condition that presents with a white cloudy lens?

Cataracts

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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

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What structure regulates the amount of light entering the eye?

Pupil

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Where does most of the refraction of light occur?

Tear film surface of the cornea

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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

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What is an eyeball that’s too long called?

What sight defect does this cause?

Myopic

Short sightedness

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What is an eyeball that’s too short called?

What sight defect does this cause?

Hypermetropic

Long sightedness

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Is the light from a closer object more divergent/scattered or focused?

More scattered/divergent

More refraction needed to focus light onto retina

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What is the reflex called when additional mechanisms are employed to increased refractive capabilities due to the cornea being fixed?

Accommodation reflex

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What are the 3 things that occurs in the accommodation reflex?

Pupils constrict
Convergence of eye towards middle
Lens gets fatter/thicker

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What is the purpose of the pupils constricting in the accommodation reflex?

Reduces amount of light entering eye

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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

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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 )