Important content to remember Flashcards
describe the optic disc, cup and macula and fovea.
describe arteries vs veins
and isnt rule
optic disc is nasal and the macula is temporal.
optic disc is the blind sppot. no photoreceptors.
pinky orange colour but not good if white.
arteries are thinner and lighter and veins are thicker and redder.
I>S>N>T follows isnt and if isnt then isnt glaucoma.
neuroretinal rim is the broadest in inferior and thinnest in temporal.
cup size= 0.3-0.4mm. can be different. normal in some people or indicator of damage.
macula= posterior retina that contains pigments and photoreceptors cells. responsible for colour and central vision. fovea is the depression of central inner macula=clearest vision.
when examining the eye what do you look for (10)
overall view of the eye
assess quality of fundus
assess disc appearence
colour (pink)
clarity disc margin (sharp edges)
cup to disc ratio
neuroretinal rim isnt rule
assess arteries and veins
repeat for each 4 quadrants
assess macula and fovea
high blood pressure vs high intraocular pressure
high blood pressure= can see it in the back of the eye.=hypertension screening.
high intraocular pressure= due to poor drainage of aqueous humour.
monocular
describe and
mag and fov numbers
using one eye to assess
views real and erect images
condensing lens required
greater fov and wd
lower mag
no stereopsis (3d)
mon indirect- 5 times mag
15 degrees fov
independent of patients Rx
no stereoscopic view
binocular
using both eyes to assess
stereoscopic, aerial
condensing lens
real inverted laterally reversed
greater fov than direct
direct vs indirect
direct- small fov, high mag, close wd, dim image, monocular, easy to use, mag image, erect image
indirect- high fov, low mag, far wd, need to dilate pupil, stereoscopic, inverted imag.
keeler wide angle vs Pan optic
monocular
10 times larger fov than direct
Pam optic- 5 times larger than direct
binocular
using both eyes to assess
stereoscopic, aerial
condensing lens
real inverted laterally reversed
greater fov than direct
higher power condensing lens= decreases mag= increases fov
indirect biomicroscopy( slit lamp) and compare to head mounted bio
and when to use
fov depends on lens power and diameter of lens
90 and 78D bi convex
60D and superfield unidirectional
less mag w stronger lenses.
lens used with slit lamp
short wd
gerater mag than head mounted bio
smaller fov than head mounted bio
when to use-
poor direct view
stereoscopic view
wider fov than direct
binocular indirect
head mounted bio
prinicples
properties
procedure
and when to use
principles-
stereoscopic view
hand held condensing lens
image inverted and laterally reversed
real image
condensing lens most common is +20
flatter side towards patients
lower powers have higher mag, smaller field of view, greater wd.
properties-
2.5 times mag
30 degrees fov
must dilate
procedure-
set up headbang
eye piece rx and pupil size
hold condensing lens in front of eye
pull lens back until fundus image fills lens
8 positions
remember inversions
when to use- poor direct view
stereoscopiv view
to see whole fundus
to assess for diabetes, rd symptoms or young children
digital fundus camera
large stand instruments
2 light sources- 1 to take flash photo and 1 to view fundus
optical design based on indirect opth
specialised low power microscope w an attached camera
immediate viewing
archive and monitor
images can be shown to patients
oct
most common used for routine imaging of retina and optic nerve in high resolution
non invasive cross sectional imaging of retina by measuring the backscatter and delay as it journeys through the ocular tissue comparign it to a known reference path
provides thickness data of retinal layers
used in med retina care, glaucoma care, primary health care and screening
equation for direct opthalmoscopy
M= Fe/4 times 1/1-wK
Fe= power of eye +60
w= working distance (negative and m)
k=ocular refraction
mag= Fe/4 therefore emmetropes its always times 15, if myope then power is higher than 60 then it will be more than 15
for hyperopes power is less so it will be less than 15
higher refraction of the patients eye is it easier or difficult to assess back of eye and why
more difficult it is to assess the back of the eye
as increased refraction= increased mag= decreases fov
if light doesnt focus on the retina but behind it
blur circle is formed on the retina
we can work out the size of this= field of view
j(m)=g(k-w)/Fe
j= blur circle of fov
g= pupil size (m)
k= ocular refraction
w= reciprocal of wd (m and negative)
Fe= dioptric power= 60D
factors affecting fov and mag
pupil size increases increases fov
sighthole size
wd closer increases fov
subjects ametropia. increasing decreases fov
good ophthalmoscope
clear uniform light patch
fov coincident w light patch
minimise corneal reflections
abscence of sighthole flare
range of target apertures
extra targets
for j= k-w equation
convert w to metres first and then make sure its negative
and then work out the reciprocal
and then do the equation
and then times by 1000 at the end!
Human eye refracts w 2 ocular structures
cornea = 2/3 refraction 40D
lens= 1/3 refraction 20D
overall= 60D
3 elements to focus light
shape of cornea,
power of lens
and length of eyeball
far point and near point
furthest distance a person can see without glasses or contact lenses. can be at infinity, behind or in front of an eye.
near point= closest point at which a person can see an object in perfect focus without glasses or cl
focal point
where parallel light meets after passing through the lens.
can be at the macula in front of the macula or behind the macula or retina.
myopia
focal point is in front of the retina
far point is in front of the retina
blur circle is formed on the retina
myopia and why
focal point is in front of the retina
far point is in front of the retina
blur circle is formed on the retina
if cornea is too curved or if the lens is too powerful (refractive ametropia)
or bc eye is too long or combination of these (axial ametropia)
hyperopia
focal point is behind the retina, far point is behind eye and image formed behind retina. blur circle on retina. corrected with positive lens.accom can fix this if young
could be bc cornea is too flat or if lens is too weak (refactive ametropia)
or bc eye is too short or combination (axial ametropia)
astigmatism
usually occurs with myopia or hyperopia
irregular curvature of cornea or lens. light rays focus in different locations.
theres 2 focal points 1st and second. use cylindrical lens to correct this
light can hit at one meridian and other.
2 types of astigmatism
against the rule (cornea more curved in horizontal meridian)
with the rule (cornea more curved in vertical meridian))
correction
amount of power in D needed to bring rays of light back onto focus on the retina
if + hyperopia
if - myopia
visual acuity
sharpness of vision measured by the ability to discern letters or numbers at a given distance according to a fixed standard.
distance= 6m for far
near= 40cm
visual acuity
sharpness of vision measured by the ability to discern letters or numbers at a given distance according to a fixed standard.
distance= 6m for far
near= 40cm
snellen chart= widely used
problem= scale is not linear, crowded, hard notation
minimum angle of resolution
reciprocal of snellen fraction
logMAR= log 10 of the minimum angle of resolution (MAR)
bailey lovie charts. same no of test letters but easier to use
how does the log mar thing work
each letter read correctly= -0.02 logmar
logmar- (0.2 times no of letters read)
picture snellen
lea symbol chart- based on logmar principles and uses shapes
unaided vision- check va with glasses and test worst eye first
n-notation- N= height of letter. 1/72 of an inch. N5= 5/72 inches/ etc
jaeger and m notation
if you cant recognise letters-
orientation of rotated snellen c
tumbling E orientation of prongs
key card point matching
picture or symbol charts
teller nad keller acuity cards
cardiff acuity cards
logmar acuity cards
vision in spherical ametropia and lens
lens and ciliary muscles and accom at near
Rx can affect va
accom and pupil size also afects va
lens- shape isnt fixed. its responsible for accomodation= eye changes its power by the lens changing its shape.
ciliary muscles are relaxed= lens zonules taut, lens flattened.
ciliary muscles contracted= lens zonules relax and lens surface becomes fat= power=accom
distant-cm relaxes
near- cm contracts lens fat= accom
vision in spherical ametropia and lens
lens and ciliary muscles and accom at near
Rx can affect va
accom and pupil size also afects va
lens- shape isnt fixed. its responsible for accomodation= eye changes its power by the lens changing its shape.
ciliary muscles are relaxed= lens zonules taut, lens flattened.
ciliary muscles contracted= lens zonules relax and lens surface becomes fat= power=accom
distant-cm relaxes
near- cm contracts lens fat= accom
(as age increases lens flexibility decreases and hence power decreases=presbyopia)
near vision triad
convergence- inward movement of eyes towards each other
pupil miosis- constriction as accom
acccomodation= increases lens power
emmetropia, hyper and myopia accomodation
not using accom for distant
near= closer distance= increases power of eye
accom= ray has to bend through a larger angle to focus them onto the retina.
hyperopia- can accom to bring it forward
near= accom all the time
myopia= cant as it brings it more forward
length of standard eye
22.22mm
longer then myopia
if shorter than hyperopia
power
+60D
if higher than myopia
if lower than myopia
ametropia what it does to pupil size and blur circle with va.
decreases pupil size decreases blur circle and increases vision.
large pupil= blur circles overalp and cant be resolved.
so we can use pinhole aperture to decreases pupil size of the retinal blur circle to get the best acuity. if vision does not improve w pinhole then vision loss is due to non refractive causes eg disease.
decimal notation
snellen numbers divided
Astigmatic ametropia if
The eye displays 2 different refractive powers in 2 planes when meridians are perpendicular to each other. 2 focal points instead of 1.
Cone or rugby ball shape. Steeper meridian more curved= light is refracted more by this curvature and least by the flattest curvature. (Ocular astigmatism)
Spherical ametropia
Same curvature over the entire surface
Light is refracted by the same amount when it passes= -> one sharp focus
Corneal, lenticular and ocular astigmatism, with and against and oblique
Corneal astigmatism- major source of astigmatism. Measured w keratometer.
Lenticular- astigmatism by anterior and posterior surfaces of lens being tilted. Calculated by taking corneal readings away from the total astigmatism.
Corneal and lenticular total astigmatism.
Ocular astigmatism- regular if meridians are 90 degrees apart
Irregular- meridians any angle apart not perpendicular Ocular can be with the rule or against. With- more curved in vertical and against is more curved in horizontal.
Oblique- one meridian lies between 120 and 80 and other between 30-60
What is the circle of least confusion
Dioptric midpoint between the anterior and posterior focal point. We need to move this onto the retina
This is the sphere power+ (cyl power/2)
Classification of astigmatism (regular)
Simple hyperopic astig - focal line 1 on retina and one behind. Plano and positive
Compound hyperopic- focal line 1 and 2 behind retina. Both positive.
Simple myopic astigmatism-focal line 1 on retina and one in front. Plano and negative.
Compound myopic- focal line 1 and 2 are in front of the retina. Both negative.
Mixed astigmatism- focal line 1 in front of retina and one behind retina, pos and neg.
Larger difference- larger distance between 1st and 2nd focal line.
Vision in uncorrected astigmatism and what is it affected by
Accommodation isn’t too useful as 2 focal points
Stretched or distorted
Affected by: amount of astigmatism, types of astigmatism, axis direction
Optimum vision
When circle of least confusion on retina. Can happen in simple or compound hyperopia if enough accommodation. Otherwise need to fix
Oblique is likely to affect vision more.
How to correct astig
1st= put 2nd focal line on the retina by adding + or - lenses
2nd= then add - cylinders to push the 1st focal line left to the retina
+lenses= pushes it left
- lenses= pushes it right
If you add + lenses it pushes both focal lines left. And then you need to push it right using negative lenses.
If you add - lenses moves it right then you put second focal line onto as well so add - again
Indirect vs direct mag and fov
Indirect-
typical M= times 2- times 5
Typical fov= 25-45 degrees
Direct-
Typical M= times 15
Typical fov= 10 degrees
What affects indirect
Pupil size effecting diameter
Condensing lens power
Distance from patient to lens
Distance lens to observer
Ametropia
retinoscopy used to to what
Objective
Used to measure patients Rx
Useful and accurate
Screen for ocular disease: keratoconus, media opacities
Specialist retiniscope- next year, accommodative stability, accommodative lag
Dynamic ret- next year
Wd= 67cm
Can put in drops to relax accommodation
Describe the retinoscope
Eyepiece- light source - spot/streak bulb.
Collar- needs to be kept down= divergent light rays
The ret reflex is normally red or orange. Trial lenses are addd till reversal. Estimate Rx. Remove working distance. 1/0.67= 1.50 so minus 1.50
Where is the ret reflex
Appears to be located in the patients pupil but it’s anywhere front or behind.
If accommodation is relaxed external image is formed at the far point of the eye.
Vergence of light rays
Dependent on patients Rx
Emmetrope= rays leave parallel far point at infinity
Myope- rays leave convergent far point In front of eye
Hyperope- rays leave divergent far point is virtual. Only converging light focuses on the retina.
Far point explaining the patient and examiner eye thing
If far point is behind patient= hyperope with
If between patient and examiner- myope and against
If behind examine low myope= with
Far point should be coincidental w examiners ret.
neutral- no movement. Bright. Fast.
If with and against and over correction snd neutral
Add positive lenses till neutral
Against= add negative lenses till neutral
Overcorrection= against
Neutral lean forward with lean back= against to check.
How to do ret
Accom relaxed= distance
Dim room illumination
Px observes target at 6m
Wd=2/3m
Both eyes open
Use ret in right hand when examining left eye
Keep the same wd
Adding lenses moves the far point to the examiners ret.
Fog the other eye = against
Neutral= fast, bright, no movement;
If -1D what does that tell us
1/ far point
So here far point is 1m in Front of patients eye
No movement
Wouldn’t add anything bc neutral
Far point is at the retina
If neutral does this mean the person is an emmetrope
No, it means the far point is at the examiners ret
This doesn’t mean the person is an emmetrope. Emmetrope= far point at infinity so you still need to bring this to the retinoscope to check the eye. And you add positive lenses to do this.
2 ways to vary the working distance
Add lenses to vary the far point plane
Vary wd, only do this if at neutral
If power is pos or Neg
You know if it’s in front or behind
How to correct w spherical sylindrical lenses
Correct slowest with first or fastest against
Variations in ret and cycloplegia and methods of ret
Can use trial frames, ret bar, or phoropter.
Cycloplegia- relaxed accommodation by relaxing ciliary muscles. Pupils get dilated. Ensures we know patients real Rx
Methods of ret- streak, Spot or static ( patient fixated on a distant target w accom relaxed)
Near fixation or Barrett’s method
Used when examiner is unable to do ret accurately with both eyes eg lazy eyes
Only one of practitioners eye is used
Perform ret on both eyes of Px whilst patient fixates the ret and then check spherical component
Ret at near- and ret at distance. Do near one for both eyes and then distant one for the eye that is good for examiner. Them work out difference and the And apply this difference in both eyes.
Mohindra
Useful in children that cannot fixate distant targets
Dark room
Fixates ret light
Wd=50cm monocular
Correc of -1.25D
How to do ret in opacities, large pupil and keratoconus
Opacities- if in centre can’t really do it but dilate pupil or move closer
Large pupil- focus at the centre
Keratoconus- cone shape, Sllit or scissor reflex, use lens step larger than 0.25D and use bracketing technique.
Increase room illumination to decrease pupil size
Factors affecting accuracy of ret
Intra-individual variation (same people)
Inter individual variation (between diff people)
Not concentrating on movement in centre of pupil
Age of px
Off axis errors
Wd errors
Blocking pxs errors of chart-> likely stimulating accom
Speed of reflex
Important in estimating neutral point
Dioptric power= reciprocal of distances
