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
