Intro to ophthalmology Flashcards by Jade Fellows

What is the most common cause for being registered partially sighted or blind under the age of 65

Diabetes mellitus

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What do eyes do?

Formation of a focussed image on the retina

Transduction of the image into an electrical signal

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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

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Basic eye anatomy

Cornea
Iris 
Pupil 
Lens 
Vitreous Humour 
Retina 
Macula 
Fovea 
Optic disc

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Function of the cornea

Maintain transparency
Refraction
Barrier to infection and trauma

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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

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What is the refractive role of the cornea

The cornea is the major refractive component of the eye - 48/58 dioptres

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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

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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

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What is normal intraocular pressure ?

Maintained at 10-21mm Hg

There is a dynamic balance between secretion and drainage of aqueous humour

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What is high IOP

Glaucoma

Which leads to loss of visual fields and eventual blindness

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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

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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

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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

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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

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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

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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 ```