Intro to ophthalmology Flashcards
What is the most common cause for being registered partially sighted or blind under the age of 65
Diabetes mellitus
What do eyes do?
Formation of a focussed image on the retina
Transduction of the image into an electrical signal
What is the formation of an image in the eye dependent on
Ocular shape - astigmatism
Transparency of the ocular media - cataract
Ability of the transparent structures to refract light
Basic eye anatomy
Cornea Iris Pupil Lens Vitreous Humour Retina Macula Fovea Optic disc
Function of the cornea
Maintain transparency
Refraction
Barrier to infection and trauma
How is transparency maintained in the cornea
Stroma is maintained relatively dehydrated by the impermeable epithelial barrier and active pumping mechanisms of the corneal endothelium
The regular spacing of individual collagen fibrils
Stasis of the fibres and regular spacing of fibres maintain transparency
What is the refractive role of the cornea
The cornea is the major refractive component of the eye - 48/58 dioptres
What is the sclera and what does it do
Outer coat of the eye
- opaque, mechanically tough
- forms the posterior 5/6 of the outer coat of the eye
- consists of irregularly arranged collagen fibres
Maintains the eye shape
Maintains the intraocular pressure
Barrier to infection and trauma
What is the aqueous humour
It is formed by the active secretion by the epithelium of the ciliary body
Drainage out of eye
- conventional - 85% drains through the trabecular mesh work into the canal of schlemm in the anterior chamber angle
- uveoscleral route - 15% drains through ciliary body into the and into ciliary circulation
What is normal intraocular pressure ?
Maintained at 10-21mm Hg
There is a dynamic balance between secretion and drainage of aqueous humour
What is high IOP
Glaucoma
Which leads to loss of visual fields and eventual blindness
Features of the crystalline lens
Transparent - orderly arrangement of the lens fibres, small difference in refractive index between the various components, absence of blood vessels
Fine focusing - age related , metabolic e.g. Diabetic, or congenital changes in lens fibres lead to structural irregularity with resistant opacification i.e. Cataract formation
Features of the vitreous humour
Transparent - collagen type II, arranged into fibrils, few cells ( hyalocytes) - secreting glycoaminoglycans
Protects the ocular structures - firm gel, 80% of the globe volume
Passive transport and removal of metabolites - nourish the retina and maintain shape and integrity of vitreous
Features of the retina
Transparent
Transducers light energy into nervous impulses
- at least 11 layers
- photoreceptors 120 million rods - monochromatic, 6 million cones colour vision
Features of the macula
Central vision of the retina
- lies lateral to the optic disc
- slightly darker that the rest if the retina due to yellow luteal pigment
Fovea is the centre of the macula and is rod free
Has higher visual acuity
Fovea has the most cones so has the highest visual acuity
Features of the optic nerve
Contains over 1 million fibres - non myelinated in eye myelinated as the leave the eye
Nasal fibres decussate at the optic chiasm
Optic disc - the entry of the optic nerve into the eye, corresponds to the blind spot of the visual field as does not contain any overlying photoreceptors
What is the visual pathway
Optic nerves Optic chiasm Optic tracts Lateral geniculate nucleus Optic radiations Visual cortex
How to take an ophthalmic history
HPC - general symptoms -- unilateral or bilateral -- onset and duration -- any pain, photophobia, redness discharge Vista symptoms Vision loss Sudden gradual distortion Field defect - unilateral bilateral, central peripheral Flashes floaters Diplopia Horizontal vertical, binocular, monocular Past ocular history Other disease Family history - glaucoma PMH Allergies Drug history General health Social history If a child include - obstetric, pregnancy, birth neonatal problems Developmental problems and milestones, immunisation history
Where is the problem is the eye is red
Front of the eye
Where is the problem is there is painless loss of vision
Back of the eye
Where is the problem if there is distortion of the vision/central scotoma
Macula
Where is the problem if there are flashes or floaters
Vitreous or retina
What are the types of refractive error
Emmetropia Ametropia - myopia - hypermetropia - astigmatism
What is emmetropia
There is no refractive error and light rays from infinity are brought into focus on the retina
What is Myopia
Short sighted
Light rays from infinity are brought to focus in front of the retina
- the eye is too long - axial myopia
- the lens is too strong from nuclear sclerotic cataract - index myopia
What is hypermetropia
Light rays from infinity are brought to a focus behind the retina - the eye is too short
Or
The converging power of the cornea or lens is too weak
What is astigmatism
The cornea is not spherical - rugby ball shaped rather than football shaped
What is Accommodation
Physiological mechanism that allows close objects to be focused on the retina
In the non accommodative state the circular ciliary muscle is relaxed - allowing the suspensory ligaments of the lens or remain taut
During accommodation the ciliary muscle contracts and the suspensory ligaments become lax causing the natural elastic lens to assume a more globular (convex) shape
What happens to accommodation with age
Usually 45 years + the lens gradually hardens and is unable to accommodate - called presbyopia
This can be corrected by a weak converging lens (plus) convex lens
What occurs in an ophthalmic examination
Vision: acuity
Pupils : reaction to light
Front of eye
Back if eye
How is the front if the eye examined
Pen Torch
Ophthalmoscope
Slit lamp microscopic
How is the back of the eye examined
Direct ophthalmoscope
Indirect ophthalmoscope
What is an ophthalmoscope
3 essential components Lenses Light Diaphragm See the back of the eye Asses red reflex and look at the retina
Features of an ophthalmoscope
Magnification approx x 15
Small field of view - 6.5-10 degrees
With an undilated pupil you will not see the macula
The disc will take up the whole field of view
Don’t ask the patient to look into your light as the Latimer will accommodate and together with the bright light it will make the pupils smaller
How to know what lens to set the ophthalmoscope to
If you wear glasses keep them on
Does the patient wear glasses need to set the ophthalmoscope to the patents refractive error
If got contacts lenses set to zero
How to do direct ophthalmoscopy
Remove patients glasses
Hold ophthalmoscope with your index finger on the lens dial, set ophthalmoscope to see the fundus
Angle of approach
- 15 degrees temporal to the patient
- Same height as the patient
- aim 15 degrees nasal and you’ll hit the optic disc - corresponds or their blind spot
Get close
Start with your dominant eye
Close non dominant eye
Use diaphragm dial to set the small white beam for an undilated pupil and observe the red reflex (yellow orange glow)
The greater the refractive difference between you and patient the more blurred the red reflex will be
What to look at in direct ophthalmoscopy
Optic disc - colour, cup: disc ratio and contour
New vessels if diabetic
Retinal blood vessels
Arterioles and veins
Claire
New vessels, collateral vessels
What is background retinopathy
Least problematic Scattered haemorrhages and hard exudates Not affecting the macula Non sight threatening Used as a marker of disease control
What is diabetic maculopathy
Haemorrhages and hard exudates in the macula
Leakage if fluid from the vasculature and macular oedema
Treated with a focal laser - fluid can be lipid and interfere with vision
Sight threatening
Needs treating
What is the pre proliferative retinopathy
It is the next stage from background
More than five cotton wool spots
Venous drainage - thickening tortuousity or beading
Indicated retinal ischaemia
Sight threatening
Can’t treat eye need to aggressively treat diabetes
What is proliferative retinopathy
New vessels NVD - Disc NVE - elsewhere New vessels bleed causing vitreous haemorrhage Requires extensive laser treatment Panretinal photo coagulation Where they grow threatens sight Intravitral injection to try to regress blood vessels
