Vision 1 Flashcards
Define refraction [2], accommodation [4] and refractive errors [1]?
Refraction - Bending of light rays [1] as they move from one medium to another [1]
Accommodation - Altering lens shape [1], pupil size [1], eye convergence [1] to alter how much we refract the light [1]
Refractive Errors - Mismatches in light ray refraction [1]
What kind of lens causes convergence and what kind causes divergence? [2]
A biconvex lens converges light rays
A biconcave lens diverges light rays
What refractive media are in the eye? [4]
Compare the cornea and lens in terms of refractive ability [2]
- Cornea
- Aqueous Humor
- Lens
- Vitreous Humor
The cornea is the biggest bender [1] but the lens is capable of varying its refractive power (accomadation) [1]
At what distance will all light rays reaching the eyes be parallel? [1]
6m and beyond
How does lens thickness change as the object moves closer to the eye? [3]
It gets thicker [1] because:
- The closer the object the more divergent the rays are when it reaches the back of the eye [1]
- Accommodation is needed to change the shape of the lens for a greater refractive power [1]
How does the lens thicken? [6]
- > Parasympathetic stimulus
- > Ciliary muscle contracts
- > Makes ciliary muscle bulge
- > Causes suspensory ligaments to go lax
- > Lens stretch decreases and lens gets thicker
How does pupil constriction affect focus? [1]
The closer the object the more the pupil constricts to minimize the rays getting through
How does the pupil constrict? [3]
Cranial Nerve III (Oculomotor)
- > Parasympathetic fibres
- > Sphincter Pupillae Muscle Contracts
What causes our eyes to converge to focus on closer objects? [2]
Cranial Nerve 3 (Oculomotor)
-> Stimulates Both Medial Recti
Because we do so much close work our medial recti have become thicker than our lateral recti
What do we call the condition of having perfect eyesite? [1]
Emmetropia i.e. you are an emmetrope
List some common refractive errors and their laymen term? [4]
Myopia - Short Sightedness
Hyperopia - Long Sightedness
Astygmatism - Non-spherical cornea/lens
Presbyopia - Age related long-sightedness
What causes myopia? [3]
Risk factors [2]
Why does myopia worsen with age? [1]
The persons eyeball is slightly longer than normal [1]
Causes the refractive power of the eye to be excessive [1] and the rays converge before hitting the retina [1]
Genetic predisposition Ch 18p, 12q
Very close work in early decades of life leading to changes in synthesis of mRNA, conc of metalloproteinase matrix
Myopia worsens with age because the eyeball and lens curvature is not compensating for the eyeball as it grows
How does myopia affect close vision?
It doesn’t [1], because close up the excess refractive power of the eye [1] does the job without needing to use your lens
How does myopia affect distance vision? [2]
Further away objects are seen with less divergent rays so the over-refractive nature of the myopic eyeball [1] means you cant focus the image on the retina [1] even with the ciliary muscle fully relaxed
How could myopia present in kids? [4] How regularly should kids have their eyes checked? [1] Whats defined as pathological myopia [1] What are the sequelae [2] What is one cause of infantile myopia?
- Infants may show a divergent squint
- Toddlers may lose interest in sports/people and instead focus on books/pictures
- Difficulty seeing or losing interest in class
- Headaches
Important to have eyes regularly checked every 6m
Over-correction can worsen myopia
Pathological myopia: above 6 diopters
Consequences: retinal detachment, macular bleeding
Vitreous degen can cause myopia
How do you treat myopia? [2]
Need to reduce refractive power:
- Biconcave lenses or glasses
- Laser eye surgery
What causes hyperopia? [4]
Either the eyeball is too short [1] or the cornea/lens is too flat [1]
So the bending power of the eye is less than normal [1] and the light rays converge behind the retina [1]
How would Hyperopia show up in a kid? [2]
Convergent Squint
Symptoms of eyestrain after reading/working close up. The ciliary muscles contract, and the lens gets more convex to focus the object on the retina. This can produce tiredness of gaze
How would we treat hyperopia? [2]
- Biconvex Lens/glasses
- Laser Eye Surgery
Define an Astigmatism? [2]
Non-spherical curvature [1] of the cornea or lens [1]
I.e. the eye is more like a rugby ball than a football
How does astigmatism affect sight? [3]
Because the cornea/lens is no longer spherical, the bending of light will never line up in one axis with another [1], therefore all objects will appear hazy [1] regardless of distance [1]
How would we treat Astigmatism? [3]
- Toric Lenses (bifocal lenses)
- Laser Eye Surgery
- Cylindrical Glasses (curved in only 1 axis)
Define Presbyopia? [3]
Age related long-sightedness [1]
With age the lens gets less elastic/mobile [1] so the ciliary muscle isnt capable of relaxing and contracting as well as before [1]
Therefore you cant focus close up
How do we treat presbyopia? [2]
Biconvex “reading Glasses”
Most people in their 50s onwards have them.
Define phototransduction? [2]
The conversion of light energy to electrochemical signals
Explain the process of phototransduction? [4]
Opsins (a protein in cones) and rhodopsin (in rods) contain chromophore 11-cis retinal. [1]
When struck by a photon 11-cis retinal isomerizes to all-trans retinal. [1]
A signal transduction cascade is triggered that leads to closure of na/ca channels. [1]
Leads to hyperpolarisation of the photoreceptor cell which triggers an action potential [1]
How is the visual pigment regenerated? [1] What is its clinical significance [1]
All-Trans Retinal is recycled into 11-cis retinal.
However some is lost and some forms retinyl esters, this is replaced using dietary vit A
Presentation of vitamin A deficiency [4]
- Night Blindness
- Abnormal conjunctiva/corneal epithelium (Vit A important to epithelial health)
- Bitot’s spot (White/silvery) in conjunctiva
- Corneal Ulcer
Anisocoria
Unequal pupil size
Aphakia
State of having no lens
Chemosis
Edema of conjunctiva
Cyclopegia
ciliary muscle paralysis preventing accommodation
Dioptre
Units for measuring refractive power of lenses
Ectropion vs entropion
Ectropion: the lids evert
Entropion: the lids invert
Fundus
Part of the retina normally visible through the ophthalmoscope
Miotic
An agent causing pupil dilatation
Optic disc
Optic cup
Optic disc - part of the optic nerve seen ophthalmoscopically in the fundus
Optic cup - cup like depression in centre of optic disc
Ptosis
Drooping eyelids
Scotoma
Defect causing part of the field of view to go missing
Uvea - name its components
Iris
Ciliary body
Choroid
