opthalmo test Flashcards
How do you measure visual acuity
Have the patient at 6m from the eye chart
Cover one eye at a time, starting with the weaker eye
Begin reading the letters from the top downwards
If the patient isn’t able to read the top line, move him 1m forward each time until he is able to
If patient is unable to read 1m, count fingers starting from 50cm to 10cm
If unable to count fingers, see if the patient can detect hand motion by moving the hand in front of their face
Then see if they are able to perceive light
If unable to perceive light= no light perception ( total blindness)
Visual acuity= Distance of patient from the chart/ the distance a patient with normal eyesight can see
It is the last row you are able to read 75% of the letters
What are the causes of decreased visual acuity
Refractive error
Opacities of ocular media
Neuro-retinal disorders
What are the types of refractive errors
Emmetropia Myopia Hyperopia Astigmatism Presbyopia
Define Emmetropia
This is the ideal refractive state. Light is refracted from the cornea and lens and converges directly onto the retina making objects look clear
Define Myopia
The light converges anterior to the retina as the refractive power of the cornea and lens is too strong. Commonly because the eyes are too big.
Keratoconus ( cornea thins and bulges out)
cataracts ( cloudiness increased thickness of lens)
How do you correct myopia
Use concave lens ( negative) to decrease the refractive power of the eye
Define Hyperopia
The light converges behind the retina as the refractive power of the cornea and lens is too weak.
Commonly because eyes are small and short
How do you correct hyperopia
Use convex ( plus) lens to increase the refractive power
Define astigmatism
…
Define presbyopia
Reduction of the elasticity of the lens due to aging decreasing the refractive power and the image is formed behind the lens ( they need plus lens reading glasses)
How do you prescribe glasses for presbyopia
1 D added for every 5 years after the age of 40 years old
How do you differentiate between the different causes of decreased visual acuity
Pinhole- +ve in refractive errors
If -ve either neuro-retinal disorder or opacity of ocular media
Red reflex- normally present
If absent- opacity of ocular media
How do you measure the refractive errors of the eye VA=1
Measure visual acuity
If visual acuity= 1 they are either hyperopic or emmetropia
Add +0.5D spherical lens
Patient sees worse= emmetropia
Patient sees better= hyperopia
Keep increasing power until good vision is achieved
How do you measure refractive errors of eye VA<1
VA<1 either myopic or hyperopic
If vision gets better with increasing minus lens= myopic
If vision gets better with increasing + lens= hyperopic
What are the normal values of intraocular pressure
10-21 mmHg
What are the different ways of measuring intraocular pressure
Goldmann applanation tonometer ( gold standard)
Tono-pen
Airpuff non contact tonometer
Method of Goldmann Aplanotonometry
- Put anaesthetic drops and fluorescein into the eye
- Use a wide blue light source on the slit lamp
- Move the tonometer forward until the prism rests on the center of the cornea
- Turn the dial on the tonometer clockwise until 2 fluorescein semi-circles form a horizontal S shape
- Note the reading on the dial, this is the force needed to flatten the cornea
How does corneal thickness affect the IOP
Corneal thickness> 550um = overestimation of 1mmHg for every 25um
Thickness< 550um = underestimation of 1mmHg for every 25um
How is the fluorescien test performed
- Fluorescein strip touches the surface of eye
- Patient blinks
- Doctor shines blue light at eye
- Green light is reflected displaying any problems with the cornea
How to do seidel’s test
- Apply fluorescein strip to the affected area
- Use blue light
- Fluorescein appears green
- If there is a penetrating lesion, aqueous humour dilutes the fluorescein
Why is seidel’s test done
To identify a penetrating injury
What is the order of an anterior segment examination
Eyelids( ptosis, ectropion, entropion , blepharitis, stye, chalazion)
Conjunctiva ( chemosis, ocular discharge, papillae, subconjunctival hemmorhage)
Cornea- florescein ( keratitis, corneal edema, leukoma)
Anterior chamber ( hypopyon, hyphema)
Iris ( aniridia, coloboma)
Pupil ( colour, shape, dimensions)
Lens
vitreous humour
pinhole examination
Pinhole testing device is used to see if the problem os visual acuity if because of refractive error , it is not improved for an organic eye disease (cataract, neuro-retinal)
In refractive error the light is scattered and is not focused on the retina, the pinhole only focuses straight beams of light directly onto retina =clear image
red light reflex examination
light goes to pupil and reflected off retina forming red glow
1) Turn off lights in room
2) make your eye height the same as patient’s
3) set opthalmoscope to 0 power/ to match your refractive error
4) hold opthalmoscope at a arms length away from patient’s eye and shine light in patien’s eye
5) Put light in each eye to see the red reflex
Red reflex pathologies
leukocoria- whitening of red reflex
causes:
retinoblastoma, cataracts, retinal detachment, corneal abrasion, vitreous hemorrrhage
colour vision definition
ability to retina to discriminate colour based on wavelength
colour vision tests
Lantern test- different colours projected onto screen, patient should recognise
wool test- distinguish colours from different wool
munsell 100 test - patient should arrange different coloured pills into 4 boxes, in order of tone progression
The examiner notes the number at the back of the colours and determines the colour defect.
ishihara plates - coloured circles with dots that form a number, used to detect red-green colour vision
Technique for ishihara plates
patients puts glasses if normally wears
1) cover one eye
2) patient reads numbers, first is the test plate that assesses contrast sensitivity not colour vision
3) ask patient to read number for each plate, document the number they read correctly
4) repeat in other eye
Plates 2-17 = only normal patients
plate 18-21= only colour blind patients
22-25 =deuteranopia 1st digit, protanopia 2nd digit
types of colour vision deficiencies
congenital- bilateral non progressive, patient is not aware
acquired- uni or bilateral, progressive, patient is aware of it
congenital colour vision deficiency
trichomacy- protanomaly, deutranomaly,tritananomaly. red, green, blue colour seen only if high saturation
dichromacy- protanopia, deutranopia, tritanopia- absence of one of colours
achromatopsia- absence of all colours( see only shades of grey)
acquired colour vision deficiency
dyschromatopsia - degenerative, inflammatory, toxic disorder of retina/optic nerve. Optic nerve damage= red/green axis affected retinal=blue-yellow axis
chromatopsia- perception of white surface as coloured
red colour- erythanopsy ( vitreous haemorrhage)
blue- ( aphakia- lens absenc)
yellow- xanthopsy ( ingestion of santonine)
define visual field
the area that can be seen when the eyes are focused on a single point
comparative method for visual field
1) examiner sits in front of patient
2) one eye is covered
3) examiner places object half way between them and moves in 4 quadrants from periphery to center
4) examiner asks when the patient first sees he object
If patient sees object at same time as examiner= same visual field
5) if patient sees later/earlier, they have narrow/wider visual field
goldmann perimetry for visual field
an instrument is used that has a space in the center of the dome for the patient to put their head
1) Patient fixates eyes at a target indicated by the instrument
2) in the background there are white spots that go from periphery , without moves the eyes, the patient should press a button when they see the white dot
static method ( humphrey visual field)
used to identify the threshold of retinal sensitivity at each point
1) a dull light is presented to the patient at a particular point, if the patient does not see it, it is gradually made brighter until the patient is able to see
2) test is done at several different locations
classification of visual field defects
istopteric( concentric constriction, peripheral amputations)
scotoma
causes of concentric constriction ( decrease in retinal sensitivity from the edge)
uncorrected refractive errors
small pupil diameter
opacities of transparent media ( cataract vitreous hemorrhage, pigmentary retinopathy, optic nerve pathology)
causes of peripheral amputations
non systemic ( no connection between eyes)- retinal detachment, vascular thrombosis, diabetic retinopathy
systemc ( optic pathway nesions)- hemianopia, quadranopias
scotoma definition
normal VF with areas of low/no vision
classification of scotoma
positive= patients aware of presence, negative= VF used to detect
intensity = relative/absolute loss of sensitivity
location=central ( macular lesion) centrocecal,( between blind spot and fixation point- inflammatory optic) paracentral ( glaucoma). paracecal ( around blindspot- papillary edema), peripheral
types of visual field defects + pathology
prechiasmal- ipsilateral monocular visual field defect
post chiasmal- homonymous contralateral
at optic chiasm= bitemporal hemianopia
optic radiation= homonymus contralateral quadrantanopia
what structures are in the posterior segment of the eye
vitreous humour retina choroid sclera optic nerve
methods of posterior segment examination
opthalmoscopy ( direct and indirect)
fundus examination in slit lamp ( non contact and contact)
describe direct opthalmoscopy
1) opthalmoscope is held at the level of the patient’s eye
2) look through the instrument, and ask the patient to look straight ahead ( identify optic disc and macula0
describe indirect opthamoscopy
1) dilate patient’s eyeball using drops, lie down patient flat
2) patient and examier at at a distance
3) fundus is seen through +20 condensing lens
advantage: can see peripheral retina, image less influenced by opacities in media but is hard to use and expensive
fundus examination at slit lamp technique
1) dilate patient’s pupil and put their head on chin rest
2) shine light at pupil , see red reflex
3) move slit lamp forward, you’ll see a retinal vessel and also move lens, continue moving forward until you see the retina
advantage: rapid, can see entire posterior segment, but indirect opthamoscopy gives better visibility in eyes
what are the paraclinical investigations of post segment
angiography ( inject constrast agent)
B-scan ultrasound
optical coherence tomography ( makes 3D images of retina)
electrophysiological tests ( measures electrical response of retina to light stimulus )
what are the uses for angiography
to see vascular filling defect, leakage, subretina neovascularisation, choroidal disease
what are the uses of ultrasound
when there are opacities, so it’s difficult to directly examine ( retinal detachment, vitreous haemorhage, intraocular tumour, intraocular foreign body)
uses of optical coherence tomography
diagnose and monitor disease of macula
use of electrophysiological test
electro-oculogram- determines function of outer retina, does not provide info about photoreceptors , finds ratio between dark and light potentials ( heridatory macular disease)
visually- evoked potential= measures electrical signal made in response to visual stimulation ( integrity of visual pathway)
differential diagnosis of red eye ( painful )
Painful acute angle closure glaucoma keratitis anterior uveitis trauma( foreign body,corneal abrasion) scleritis endopthalmitis oribital cellulitis pre-septal cellulitis
differential diagnosis of red eye ( painless)
conjunctivitis episcleritis subconjunctival haemorrhage blepharitis dry eye syndrome
types of examination for anterior segment of eye
diffuse light
side lighting
slit lamp
gonioscopy
finds the angle of anterior chamber, needed to drain aqueous humour
define strabismus
eyes do not properly align with each other when focusing on an object
classification of strabismus
phoria-occurs when cover is placed over eye
tropia- deviation when eyes are uncovered
duction- movement of one eye
version- movement of both eyes in same direction
vergence- movement of eye in opposite direction
comitant- ocular deviation present in all directions
incomitant- ocular deviation only present in specific directions
What are the names of tests for ocular motility
hirschberg krimsky cover test ( most common) alternate cover test cover,uncover with prisms
hirschberg test
1) ask patient to focus on a target half a meter away while you shine a light in both eyes
2) inspect corneal reflex in each eye
if ocular alignment is normal light reflex is positioned centrally and symmetrically in each pupil
deflection of corneal light reflex in one eye=strbismus
krimsky test
used in young children
prisms of increasing power are placed in front of the deviating eye/ fixating until corneal reflexes are symmetrical
cover test
1) patient fixates on a target
2) one of patient’s eye is covered, the noncovered eye is observed for a shift in fixation
if no shift = orthotropic ( normal alignment)
if there’s a shift= heterotropia
deviation of uncovered eye= tropia, deviation of covered eye=phoria when uncovered
alternate cover test
used to differentiate whether it’s a tropia or phoria
1) examiner covers 1 eye for 1-2s then removes to restore binocular vision
2) the eye that was occluded is observed for refixation
phoria= eye shifts back to orthotropic straight looking)
prism cover test
1) prism is placed on the non-fixating eye, cover placed on fixating eye
2) power of prism adjusted until the eye no longer shifts
treatment of strabismus
correct refractive errors- glasses
correct amblyopia - occlusion of the better eye
surgery- weakening ( recession) to decrease muscle pull, strengthening (resection) to enhance pull of muscle
digital method intraocular pressure
1) patient closes eyes, palpate both eyeballs using index finger from top to bottom, one eye at a time
provides info if it’s soft or hard, compare one eye to the other and to the IOP of the examiner
what are the results for digital method for measuring intraocular pressure
normotonic- firm to touch=normal
hypertonic - hard to touch( glaucoma, hypertensive uveitis)
hypotonic- indents easily ( retinal detachment, atrophic globe)
contraindicated- rupture of eyeball
lens recognition
- convergent lenses (+) : enlarge the image ; when the lens is moved in a vertical plane, the image moves in the opposite direction
- divergent lenses (-): shrink the image; when the lens is moved in a vertical plane, the image moves in the same direction
- cylindrical lenses: rotate the lens; if the image becomes deformed, starts to wobble, the lens is cylindrical
Find the dioptric power of the lens: the method of neutralization. Add lenses of opposite sign and known, increasing value over the lens that we study. Check the vertical movement of the image. When the movement of the image disappears, we have neutralized the lens.
