Flashcards in 1.43 Case 28 - The eye Deck (29)
In the visual acuity test, what does 6/6 vision mean?
At 6 meters the patient can see the letters normally visible at 6 meters.
In the visual acuity test, what does 6/60 vision mean?
At 60 meters, the patient can see the letters normally visible at 6 meters (top of chart)
What is the function of an ophthalmoscope?
An ophthalmoscope allows you to look through the pupil and onto the fundus of the eye, it is perfect for examining the health of the retina, the optic disc and vitreous humour.
What is the function of the slit lamp?
It has a high intensity light which allows you to examine the anterior and posterior segments of the eye, this includes the eyelid, the sclera, the conjunctiva, the iris, the crystalline lens and the cornea.
What is a natural cataract?
It is the more dense area found in the centre of the lens, which results in refractive changes of light
How does a posterior subscapular cataracts reduce vision?
By dispersing light, so the eye cant focus
What is aqueous humor and its function?
The aqueous humour is a clear, water fluid which provides nutrients to the anterior part of the eye, which must remain clear and hence cant have a blood supply for the delivery of nutrients.
How is aqueous humor produced?
It is produced from the ciliary body, it then flows in front of the lens through the pupil, it then drains out from the angle of the eye between the iris and the cornea, through the trabecular meshwork.
What happens if the aqueous humor pathway is disrupted?
Pressure in the eye can either become too low or too high
What makes up the uvea (middle coat) of the eye?
The uvea is made up of the iris, ciliary body and the choroid.
What makes up the outer coat of the eye?
Cornea, sclera and limbus
What forms the inner coat of the eye?
The retinal pigment epithelium and the retina
What is the sclera?
The sclera is a dense connective tissue, which is continuous with the dura mater, the episclera contains blood vessels. Type I collagen
What is the conjunctiva?
Thin translucent mucous membrane, there is bulbar and palpebral conjunctiva, they contain glands which secrete mucin.
What is the cornea?
The cornea is transparent and it merges with the sclera at the corneosclera limbus; it is avascular and acellular. If damaged it would cause permanent vision damage.
What are TDC and TAC cells and where are they found?
TDC = terminally differentiated cells; TAC = transiently amplifying cell (divide more frequently than stem cells but have a limited proliferative potential and considered the initial stem on the pathway that results in differentiation)
Found in the corneosclera limbus – if damaged cant regrow
What makes up the anterior and posterior uvea?
Anterior – iris and ciliary body; Posterior – choroid
What acts as a blood ocular barrier? And what does that prevent?
The aqueous humour – prevents antibiotics from the blood to enter the eye – medication has to be given through the intraocular
What is the function of the ciliary epithelium?
Active secretion plus ultra filtration of aqueous humor
How can the intraocular pressure be measured?
It can be measured using applanation tonometry, this is the force needed to flatten one area of the cornea. P=F/A
What is open angle glaucoma?
There’s resistance to outflow, which raises intraocular pressure, which causes optic nerve damage and hence visual loss.
What is trabeculectomy?
Trabeculectomy is performed in patients with glaucoma, it is the making of an artificial drainage, it involves removing a part of the trabecular meshwork to allpw the fluid of the eye to drain.
What is accommodation?
Accommodation is changing the refractive power of our lens by changing the shape in order to be able to focus on things in the distance and vice versa.
What is presbiopia?
10 Dioptres of accommodation means that an immetropic person can focus at an object 10cm (1/10th of a metre) from them. 3 Dioptres of accommodation means that a person can focus at an object 30cm (1/3rd) of a metre from them. After the age of 45 people have less than 3 dioptres of accommodation and they therefore need reading glasses for near. If they also have a distance prescription they may choose bifocals or varifocals.
When accommodation occurs, are the ciliary muscles contracted or relaxed?
What can cause myopia?
Myopia is when the eye is too long or the lens is curvy so the eye focuses at the wrong place – short sighted – concave lens needed
What is hypermetropia?
This is when the eye is too short – long sightedness – convex needed
What do zonular fibres contain?
They are high in sulphur and contain amino acids such as cysteine