Exam Questions Flashcards
Describe the design of the ishihara colour vision test
Colour confusion test
plates are phedu Isochromatic ( fake 1 colour)
1st plate in every test fake demo
4 Seconds per Plate
not every plate will have Something on it
only finds Red or green defect
in a 28 plate edition 4 wrong = fail
What lightening should be used to illuminate the ishihara test
daylight source of colour temperature 6500k tungsten no good
when using the Ishihara Colour vision test. what is the recommended working distance?
7 5 cm
Explain the meaning of the following terms related to colour vision
Dueteranomaly
Protanopia
Rod Monochromacy
-Deoteranormaly - Green definecy appears grey
Protanopia - Red definecy
Rod Monochromacy- only one photo pigment works.
what is the most Common type of congenital colour vision defect
red and green more common in males than in females
deuteranomaly
anomalous trichromacy
State 2 causes of aquired color vision defect(10)
Congenital - inherited photo pigments abnormalities
excessive use of therapeutic drugs
disease or Injury that damage optic neve
give 2 ways in which acquired colour vision defects may differ from Congenital defects
aquired - develops to Ocular Conditions- or Side effects of medications or toxic effects of Chemicals,trauma aging
Congenital - Inherited at birth In curable and do not Change
Define the terms depth perception and Stereopsis (10)
Death perception ~ visual ability to Perceive the world In 3D
Stereopsis - Perception of depth produced by the reception in the brain of usual Stimuli from both eyes In Combination
A monocular subject may use the following clues to experience depth perception
overlapping Geometric perspective Relative size Aerial perspective Parallax
In one Sentence give brief definition of each of these clues (25)
Overlapping - the object in the background obscured by objects in foreground Seem further Away
Geometric . parallel lines narrowing gues perception of been further Away
relative give . objects further away Seem to be smaller
Aerial - further away less contrast
Parallax - determine distance doe to Speed Something is travelling Slower Seems to be further Away
what range of values would be considered to be normal for stereoacuity
.20 - 40 Sec’s of Arc
How is stereoacuity affected by
Pupil distance
Amblyopia
PD - larger PD = better SA
Amblyopia - worse SA
Define Presbyopia (15)
loss of elasticity of the lens
loss of eyes ability to focus on near objects
starts to happen from age 40 +
state 2 changes that Occur within the eye that contribute to Presbyopia (10)
show on a diagram how amplitude of accommodation varies with age (20)
13 D at 13 years of age then less 0.25D Per year
Amp = 18 - ( 1/3 Patients age)
what’s meant by the term depth of field (10)
Distance between nearest and farthest objects that arein Sharp focus In an image
How does depth of field affect the value of the amplitude of accommodation as measured using the push- up method (5)
Increases
A Subject with a -1.00D of myopia has anamplitude of accommodation of +1.50D. what is the Power of the lens (to the nearest 0.25D) that would be required for close Work at 36cm (20)
Explain how astigmatism may be classified according to the positionof the focal lines formed by a distant Point object relative to the retina (25)
Simple Myopia 1 line on retina other in front
Simple Hyperopia 1 line on retina 1 line behind
compound Myopia both line in front
Compound Hypermyopia both behind
mixed 1 Infront 1behind
LV
compare the practical advantages and disadvantages of mounted Spectacles magnifiers + monocular Near vision Spectacles Telescopes include 4 points
spec Mounted telescopes Can provide longer working distance, Can provide higher amount of magnification
can be variable focus
have significantly restricted foV
easie to provide illumination to object for spec mounted telescopes
State criteria for registration as Sight impaired
3/60 → 6/60 full visual field
6/60→ 6/24 moderate field loss
6/18 or better + gross field defect
Explain what is meant by the terms
Myopia
Axial Hypermetropia
far point
myopia- light from a distant object is focused in front of the macula of an unaccommodated, uncorrected eye
Axial - the Power of the reduced Surface is standard while the axial length is Shorter than +22.22mm light from a distant object is focused behind the macula of an un accommodated,uncorrected eye
far point - the Point Conjugate by refraction with the macula of the uncorrected unaccommodated eye
A Patient has Snellen acuity of 6/36 explain what this fraction represents
6= testing distance 36 = Distance at which smallest letter CX can read Subtends 5' of Arc
What would 6/ 36 be as decimal
6/36 = 0. 16667
explain log Mar
logarithmic value of minimum angle of resolution in minutes
logmar acuity of 0.0 What Snellan acuity does this represent
6/6
3 advantages in using baily lovie chart Instead of a Snellen chart
equal number of letters on each line
works @ different working Distances still acurate each gaps different when going down chart
consistant 0.1 log until progression in letter height between rows
letter Spacing= letter height - reduce visual Crowding
Define near point and amplitude of accommodation
near point - Conjugate with the macular by refraction at the fully accommodated uncorrected eye (b)
Amp Of acc the maximum accomodation the eye can exert
amp = k-B
State 2 advantages applying to all prescriptions of contact lenses over spectacles
cosmetic Improved fov no magnification Sports Sunglass choice less aberrations no prismatic effect
State 2 Specific Conditions in which C L may be used for therapeutic reasons
Keratoconus - Improve VA through Corneal Surface +tear layer
Albinism - coloured CL reduces blordisc and photophobia
ectropian- bandage CL
High myopia - Reduction in Spectacle magnification
Briefly describe a typical Problem which a new wearer of RGP might experience during adaption
What advice
Problem- Discomfort due to lens and lid interaction
Problem- eyelids will touch lens when blinking
advice - increase Wear time slowly
if noticable look down for a few moments
use conditioning Solution to help with wetting
briefly describe shape of Cornea
oval in shape average measurements are 11mm horizontally
10mm vertically
radi average 8 - 8.5
explain terms edge lift when applied to RGP including reason for its presence
the final curve I’on the back surface of the contact lens is slightly flatter this Is to aid tear exchange + helps lens removal
name 2 preservaies currently used in RGP CL Soaking Solutions
Polyhexanide
Hydrogen peroxide
EDTA
list instructions which you would give to a CX when advising Safe removal of RGP lens which has moved onto the Superior bulbar Conjunctiva
wash+ Dry hands
look into mirror
Carefully reposition the CL onto Cornea through the eyelid
State 1 typical diameter of Scleral contact lens
21-25mm
State 1 typical diameter of f rigid contact lens
8.5-10.5mm
State 1 typical diameter of a soft contact lens
13.5 - 14.5mm
How does the BOZR of a rigid contact lens usually relate to the Central radius of curvature (k reading) of the cornea
The BOZR of an RGP Contact lens is the Same as the flattest k reading
How does the BOZR of a soft contact lens usually relate to the Central radius of curvature (k reading) of the cornea /
The BOZR of a soft cL is 0.8mm - 1mm flatter than the flattest K reading
State 1 typical K reading
8.00mm
State 2 advantages of rigid gas permable contact lenses over traditional (non - Silicone) soft contact lenses (30marks)
Improved VA Good for astigmatism VA + fit Improved hygiene myopia control Greater amounts of Oxygen High Rx range
list signs which maybe present in Someone who is suspected of having a microbial Keratitis
Signs closed eye Swollen eyelids Hyperaemia Lacimation Reduced VA wearing Sunnies + Photophobia corneal staining (SIit lamp) Central corneal ulcer ( Slit lamp) Anterior chamber Involvement
list Symptoms which maybe present in Someone who is suspected of having a microbial Keratitis
(40 marks fo Signs + Symptoms )
Symptoms pain Sudden onset Possibly on lens removal Red eye lacrimation Poor vision Photophobia
name a bacterium which is a common cause of microbial Keratitis
Staphylococcus aureus, pseudomonas aeruginosa
name a Virus which is a common cause of microbial Keratitis
Herpes Simplex
Zoster
adenovirus
name a fungus which is a common cause of microbial Keratitis
canidida Albicans
fusarium solani
name a protozoa which is a common cause of microbial Keratitis
Acanthamoeba
A contact lens wearer who appears to be displaying Signs + Symptoms for Keratitis
You are alone in practice
Describe course of action which you should take (40 marks)
Any painful + redeye should cease CL wear immediately but keep Cl in case as made need to determine cause
As a Do I would contact local opticians to try get CX in to See optom or clo if not - refer to local eye hospital Or A + E,would contact them ahead to make aware to expect cx,give referral letter with main details on and include Relevant history + Symptoms Signs VA On the day Take CL + case to hes
Name the document which a Prospective wearer must possess before anyone can commence a contact lens fitting Include 3 Criteria which this document must satisfy (40 mark)
the Eye Exam findings/ Prescription / Statement
Signed and in date (2 Years)
Patient details
state 2 advantages of scleral contact lenses over rigid Corneal contact lenses (40 marks)
Good for therapeutic fitting
can be used for instilling drugs
High Rx range
in traditional non Silicone Soft contact lenses
What is the main advantage of a high water Content material over a low water content material
Increases the amount of oxygen which reaches the Cornea
Improved comfort
easier to handle
state 1 disadvantage of a high water content material (30 marks)
can dry out more than lower water content lenses
name + describe two findings which might be recorded at an aftercare appointment following slit lamp examination (40 marks)
tear breakup time
Comeal and Conjunctival Staining
R GP lens fitting
State 2 reasons for the use of the Keratometer at a routine aftercare appointment (30 marks)
check for Pathological Conditions
check non - Invasive tear break up time
check Corneal Integrity
list 2 other elements of a routine contact lens after care (30 marks)
History and Symptoms contact lens compliance check vision + VA + over refraction check lens fitting + lens condition check Spectacle visual Acuity feedback + Future actions
Briefly describe the condition keratoconus (30 marks)
A collagen disorder of the Cornea
the Cornea thins and is displaced down and in from the Central position
the Cornea is distorted + Cone shape
onset is usually lateteens to early 20 ‘s
Describe an advantage,Specific to keratoconus of contact lenses over Spectacles and explainthe reason behind this advantage (30 marks)
contact lens give improved vision as the tear film can be used to correct the astigmatism and provide a Smooth refracting Surface
list 4 designs of CL that could be used in Keratoconus (40 marks)
Scleral C L
RGP
Hybrid CL
Piggy back
A man visits your practice with a red,Painful watery RE.He tells you that his eye Suddenly felt uncomfortable yesterday when he was walking in windy conditions,whilst wearing his RGP CL
state 2 Possible causes of his discomfort ( 30 marks)
foreign body (Corneal abrasion) Discomfort,lacrimation Microbial Keratitis - pain photophobia reduced VA
alone in practice cause for action
Remove cl ( keep +case)
Go to A + E
Record actions and advice
Describe 4 main advantages of RGP comeal lenses compared to Silicone hydrogel Soft lens
improved VA Corneal astigmatism Corrected with Spherical lens fewer deposits myopia Control more oxygen High Rx range less allergic reactions can be modified
Describe 1 advantage of modern RGP materials when Compared to the older PMMA material
improved oxygen transmission
Describe one disadvantage of modem RGP materials over pmma (15)
lenses are not as comfortable
more likely to break/damage
state 1 typical diameter of a Cornea (HVID) (15)
11 mm
for the cornea above (11mm) what would be a typical total diameter for Corneal RGP lens
Soft lens
Scleral lens
RGP = 9. 5mm
Soft . = 14.2mm
scleral = 22mm
according to uk legislation List 4 c lasses of Professionals who may legally fit contact lenses (20 marks)
Registered medical Practitioner
Registered optometrist
DO who holds an approved qualification and is registered on GOC
Trainee CLO or pre reg optometrist Under Supervision
if a patient is not from your practice requests contact lenses.what document must the Patient show you before you may supply lenses ?
include 3 items of info which must be contained in this document (40 marks)
contact lens Specification
Date fitting commenced
Date specification Expires
Patients details ( DOB if under 16)
Practice details
CL details from which CL can be replicated
Pr actioner details and registration number
give 2 examples of important information that fluorescein Sodium Can provide during on initial Contact lens assessment (30 marks)
check for Corneal Integrity and damaged cells
check for dry eye
tear breakup time
conjunctival Staining
name a Common finding which might be seen and noted after in stilling fluorescien at initial CL assement (30 marks)
Tear quality - Instill fluorescein - Ask Cx to blink count how many Seconds forthe tear film to start to break up
Record this as TBUT
corneal Staining - fluorescein stains any dry or damaged cells
This can range from dryness to a mechanical stain from CL wear ( previous wearer) Any Cornealdamage needs to be clear before CL fitting can Commence
name 4 Structures which are examined with the slit lamp during an Initial CL assesment ( 40 Marks)
Cornea epithelium,Stroma,endothium Conjunctiva - Bulbar,limbal,Palpebral and tarsal Lids + lashes limbal blood Vessels Tear film
List the advantages a patient with microphthalmos is likely to experience if they were fitted with contact lenses for distance compared to wearing spectacles include 4 advantages (20 marks)
increased field of view
reduced weight
fewer aberrations
reduced reflection
describe the symbol cane explain the purpose of this cane and describe how it is used by a visual impaired patient
foldable white cane indicates px is visually impaired extends cane and holds diagonally across body or keeps folded and holds across chest
state the defination of severely sight impaired as laid down by the national assistnce act (1948)
so blind as to be unable to perform any work for which eyesight is essential
what non optical aid can you advise to help a patient make a cup of tea safely. Describe this aid and explain how this aid works
Liquid level indicator
has 3 prongs hangs over edge of cup
middle prong shorter
when water hits prongs device will make noise and vibrate patient can add milk middle prong will activate once touches liquid
if a patient consents to having their name entered onto the register for severely sight impaired. what will happen next within the registration process
assesment of needs will be undertaken
3 advantages of spectacle magnifiers
hands free
larger field of view
not too expensive
psycholically more acceptable
explain how a telescope can be used to increase their Field of view for a patient with peripheral visual field loss
Reverse Galilean telescope
minifies image so remains on central part of retina
what does the pelli-robson chart measure
measures contrast sensitivity
name a non optical aid that may assist a patient seeing the dials on their cooker
enlarger numbers stickers or bumps ons
which is the form currently used in Britain to certify someone as serverly sight impaired
RVI form certificate of vision impairment
after certification of the patient list who recieves copies of the form
GP
Local Authority
college of optometrists
differentiate between a symbol cane and a long cane by stating the use of each
symbol cane used to indicate person has a visual impairment
long cane used for mobility
explain the term terrestrial telescope
/an astronomical telescope withan erector system
explain the term reading cap
positive lens placed in front of the telescope objective to adapt it for use with a near object
explain the term telemicroscope
A telescopic unit designed to view objects closer than infinity
explain visual field
the area in space that can be seen when fixating on a point
state if the following patients would be eligible to be certified as sight impaired. serverely sight impaired or not eligible for certification Patient with Va 3/60 full visual field VA 1/60 diagnosed with early AMD with VA of 6/18
sight impaired
severely sight impaired
not eligible
why can the measurement from the pelli-robson chart be considered more useful than snellan chart for the practitioner assessing the low vision patient (15)
snellan chart measures in high contrast and most LV patients have greater difficulty in low contrast. Pelli- robson assesses visual function in real life situation rather than black and white of sight test assesses effect of contrast and likely success with aids
Distinguish between heterophoria and hetertropia
Heterophoria- in normal binocular vision with both eye fixating there is no deviation. If 1 eye occluded or binocular vision prevented then 1 eye will deviate
Heterotropia- one eye will alwyas deviate. The 2 visual axis are never directed in the same place
with reference to heterotropia, explain the meaning of the follwoing terms convergent divergent unilateral alternating
Convergent -1 visula axis rotates nasally compared to the other axis
Divergent- 1 visual axis rotates outwards compared to other eye
unilateral- the deviation is always in the same eye
alternating- can switch/ change between each eye either eye can take up fixation
concomitant
incomitant
constant
intermittent
concomitant- when angle between 2 visul axis remains the same when viweing distance & near objects what ever position
incomitant- angle between 2 visual axis is compared to object distance position
constant- amount of deviation there all the time
intermittent- comes and goes under certain circumstances
what is meant by
dissociated
associated heterophoria
dissociated- 2 eyes presented with completly diff targets so that fusion reflex is presented
associated- the amount of phoria meassured usinga test in which part of the image is the same for both eyes (mallet unit)
explain the stage depression of loss model. include a minimum of 4 facts
lack of engaement with professional
feelings of worthlessness
poor memory of interaction
feelings of hopelessness of outcome
how will patients age influence the sucessful use of a low vision aid (4 facts)
less likely to accept
dexerity issues
more likely to have additional needs/health issues
difficult to learn new skills
what is the benefit of testing contrast sensitivity
(5marks answer) gages visual performance in real world
(15 mark answe)- allows us to predict the likely sucess of LVA’s allows us to gage weather contrast advise is warrented
describe the structure of pelli-robson chart
8 rows 6 letters per row in groups of 3 letters same size each triplet has different contrast varis from 89% - 0.5% use at 1m use in good lightling progress is logerithmic
other things to take into consideration other than visual Field and vA maybe to be registered as sight impaired
impact on life home situation other additional needs Age of onset emotional state physical ability
the patient is suffering from visual hallucinations. what is name of syndrome
charles bonnet
explain what is meant by the terms
myopia
axial hypermetropia
far point
Myopia- light from a distant object is focused in front of the macula an unaccommodated, uncorrected eye
axial hypermetropia- the power of the reduced surface is standard while the axial length is shorter than +22.22mm. Light from a distant object is focused behind the macula of an unaccommodated, uncorrected eye
far point -the point conjugate by refraction with the macula of the uncorrected unaccommodated eye
describe key features of a landolt ring
attends 5’ of arc at specified distance
presented to cx with gap at different positions
describe how a landolt ring used in practice
minimum angle between 2 objects so eye can resolve as seperate
move away from cx until no gap can be seen
move towards until gap detected
measure distance from cx to landolt C + size of gap
MAR =tan-1 (size of gap/distance to patient)
x by 60 to get minutes of ARC
an eye has an ocular ametropia of -1.00 and the nearest object that it is able to focus on is at 25cm from the reduced surface. What is the amplitude of accomodation of this eye
K=-1.00D
b=-25cm
AMp= k-B
B=n/b = 100/25= -4.00D
AMP = K-B = -1.00- -4.00= +3.00D amps of accommodation
caluculate the range of clear vision of the eye?
k= n/K = 100/-1.00=-100cm range = -25cm to -100cm
Give defininitions of the terms emmetropia and ametropia
Emmetropia - An unaccommodated, uncorrected eye will focus distant light ion the macula- far point lies at infinity and in conjugate with the macula
Ametropia - An uncorrected, unaccommodated ametropic eye will not focus distance light on the macula- eyes far point is not at infinity - some degree of refractive error
calculate the power of the lens placed at 12mm required to correct an axially ametropic reduced eye with an axial length of +20.83 (30Marks)
K’= 4/3 x1000 / 20.83= +64.01D
K=K’-Fe = +64.01 - (+60.00) = +4.01D
FSP = k/1+dK = 4.01/ 1+(0.012 x 4.01) = +3.83D
Define spectacle magnification
spectacle magnification is the magnification of the retinal image due to the spectacle lens
SM= height of retinal image in corrected ameetropic eye/
Height of retinal image in uncorrected ametroipc eye
=hc/hu’
a subject with a refractive ametropia of +10.00D is corrected for distnce vision by +9.00D. Assuming that it is a thin lens. What spectacle magnification does it produce
SM=hc/hu’
= +10.00/+9.00 = 1.11
The corrected eye in previous question view a distant object subtending 2 degrees calculate the size of the retinal image
K=+9.00
K’= +60.00
-1000 tan w /K’
= -1000tan(2)/60 = -0.58
hc’=hu’xSM = -0.58 x 1.11= -0.65
Define the terms orthphoria, heterophoria and hetertropia
Orthophoria= straight state eyes are in ideal position for distance and near objects -visual axes always remain directed towards fixation object even whe eyes dissociated
Heterophoria- other state-the visual axes are directed towards the fixation object when the eyes are associated but deviate when dissocaited
hetertropia - manifest squint- only the visual axis of the eye that can fixate will pass throughthe object of regard deviation always present angle can vary
A heterphoria can be described as uncompensated what does this mean
where the eyes are unable to align properly - causes strain on muscles as causes cx to correct over correct,compensate for misalignment
explain what is meant by fixation disparity
Twinned single oints on the retina are too simplistic. The retina has elliptical zones and if the images falls within these then there will be no diplopia
Why is it necessary to dertermine Weather a hetertropia is concomitnat or non concomitant? (10Marks)
concomitant means the angle between visual axis are the same , incomitant varis with direction of gaze.
state 2 forms of treatment that maybe used in heterotropia
mildest colour defect
Anomalous trichromacy all 3 photopigments are present but one is less sensitive
How is stereoacuity affected by
interpupillary distance
Amblyopia
PD = longer PD = better Stereo acuity Amblyopia = Worse Stereoacuity
Give definition for snellan acuity and Minimum angle of resolution (MAR) (20marks)
snellan based a chart around letter recognition as opposed to resolving gratings. Letter decreased in height allowing the patient to remain seated in a test room tested at 6m as eyes natural depth of field can over come this
The angle (meaursed in minutes of arc) subtended at the nodal point of the eye by 2 points which can just be distinguished as seperate
what is the height of a 12m snellan letter
tan5’ = letter height/ letter size therefore
letter height = tan5’ x letter size
=tan0’5’ x 12 x 1000 (mm) = 17.45mm
what is the purpose of an optometer
To measure ametropia . device that measures refractive error
explain the difference between a subjective optometer and an objective optometer
Subjective - Determines refractive error by analysing response from the patient ( eg Snellan)
objective - no response - (eg Autorefractor/ ret )
Name 3 signs of diabetic retinopathy
retinal haemorrhages hard exudates retinal oedema neovasucularisation cotton wool spots microaneuysm venous dilation
State 3 disadvantage of spectacle magnifiers
short WD
thickness
increased TCA
Problems with illumination
state 3 advantages of spectacle magnifiers
better FOV than telscopes
Hands free
look normal
define term low vision
THe WHO defines low vision as visual acutity less than 6/18 and blindness as visual acuity less than 3/60 or visual field < 10 degrees
state the definition of serverly sight impaired as laid down by the National Assistance Act (1948)
Blind so blind to be unable to perform any work for which eyesight is essential
Partially sighted there is no legal defination of partial sight provided by the act gives guidance of- Substantially and permanently handicapped by defective vision caused by congenital defect or illness or injury
6 psychological stages a cx may go through when recently diagnosed with sight loss
depression shock realistic acceptance denial disbelief Anxiety anger
What is the pathological term used for the absense of the iris
Aniridia
What is the pathological term used for when the eyeball is abnormally small?
Microphthalmia
short notes
Keratoconus (5 facts) (30 Marks)
Cornea cone shape
thinning of the cornea causes it to buldge into a cone shape
more common in males late teens to early 20’s
can occur in one or both eyes
can caused blurred vision due to astigmatism
write short notes iris coloboma (5facts 30marks)
occurs at birth part of the eye does not fully develop can cause light sensitivity can affecrt one or both eyes iris looks like a key hole shape does not affect vision
shorts notes on albinism (5 facts 30 marks)
lack of pigment in the iris photophobia nystagmus reduced VA due to development of retina poor depth perception abnomal curvature of eye causing astigmatism
A device intended to be postioned and supported by the users hand and without artifical support
hand magnifier
A magnifier in which the support is designed to position the optical system at a set or adjustable distance from the object to be viewed
stand magnifier
The distance from the magnifier surface nearest to the eye to the virtual image when the object is placed at teh designated position
exit image vergence
Agreed distance of 250mm between the anterior corneal vertex of the eye and the object observed
Reference seeing distance
Telescope mounted in or on a spectacle frame
Spectacle mounted telescope
An astronomical telescope to which has been added an erecting system
Terrestrial telescope
A Positive lens placed in front of a telcope objective to adapt the device for viewing a near object
Reading Cap
A negative lens placed in front of a near vision telescope/ telemicroscope objective to adapt the device for viewing distance object
Distance cap
Distance between the most anterior portion of a near-vision telescope/ telemicroscope and the object
free working distance
Device used by visually impaired persons to enhance vision
Low vision aid
state why the patient may suffer from asthenopia after prolonged use of the aid
Light is divergent when reaching the eye some accommodation will be required at an elderly age not much accommodation for prolonged periods of time
solve problem - cx to wera SVN specs
stand magnifiers may have various sources of power for internal illumination. Name 2 such power sources and name 2 such light sources. Name the most efficient light source currently available
Power sources- mains batteries rechargeable batteries
light sourses tungsten bulbs, halgen, fluorescent, LED
Most efficient - LED
List disadvantages of the Snellan chart for Low vision 6 facts (30 marks)
too few letters at lower acuties non logrithmic design no constant ratio between size of letters non consistant spacing = crowding not real life enviroments designed for use at 6 metres measures high contrast only
advantages of bailey lovie chart for assesment of low vision chart
logarithmic in design constant ratio of letter size line and spacing equal throughout can be used at any WD allows more accurate prediction of mag requirements each line has 5 letters
Why is the measurement of contrast sensitivity considered useful in the assement of low vision patient
measures in real life situation assesses likely success of visual aids
compare the practical advantages and disadvantages of monocular Spectacles Magnifiers + Monocular Near vision Spectacles telescopes
Spec mounted telescopes can provide longer working distance
Spec mounted telescope can provide higher amount of magnification
can be variable focus
have significantly restricted f. O.V
easier to provide illumination to object for Spec mounted telescopes
Badal Optometer
A Single high powered len’s around 16.00D
The lens is positioned So that he Second focal Point coincides with the plane of Spectacle lens which therefore measures Spectacle Prescription
one eye occluded the target is moved towards the Patient Until retinal Image appears clear
Scheiner Disc
opaque disc
38mm in diameter
2 Pinholes around 0.75mm- 1mm-
2-3mm Apart
what is meant by dissociated and associated
dissociated - 2 eyes Presented with completely different targets So that fosion reflex is presented
Associated - the amount of phoria measured using a test In which part of the image Is the same for both eyes ( mallet unit)
What is keratometry
measurereal - of radi of Curvature of the central Portion of the anterior surface of the Cornea
what is keratoscopy
examination of the shape of the corneal surface
Section C
give a definition of Relative Spectacle magnification
Is the ratio of the retinal Image size in corrected ametropic eye Compared with retinal Image Size
.what is meant - when a keratometer Is described as being a one Position instrument
Single Mire
uses 2 doubling Prisms Opposed to are another
can read both principal Median from one Position
Explain the difference between anisometropia and anti metropia
anisometropia unequal refractive errors in two eyes
antimetropia opposite refractive errors
what is meant by Indentation tonometry
measures the depth of corneal Indentation made by a Small plunger carrying a known weight.the higher the Iop the harder it is to push against and Indent Cornea
give definitions of Scotoma and hemianopia
Scotoma - blind spot or partial loss of vision
hemianopia - blindness over half the field of vision
a subject with re fractive Ametropia of + 6.50 D Is Corrected for distance Vision by + 6.00D.Assuming that this lens is thin.What Would Spec magnification Produce
6.50 / 6.00 = 1.0833
View distance object a 2 degrees - calculate Retinal image size
hu’ = - 1000 tan w / k ‘ =
-1000 tan 2 / 60.00 = -0.58
hc’ = hu’ x Sm= - 0.58 X 1. 0833 = -0.630
.How is the field of view affected by a Patients Myopia when examining the fundus using
Direct Ophthalmoscopy
indirect ophthalmoscopy
Direct - Reduced
indirect - Unaffected
define term Stereopsis
limit of Stereopsis
the perception of depth Produced by the reception in the brain of visual stimuli from both eyes
What range is normal for stereoacuity
2 - 40 Seconds of arc
what is the name of the early Colour Vision theory which states that there are 3 types of retinal receptor each responding to a different region ofthe Visible Spectrum
Trichromatic theory
name a test that can be used to determine Whether a Patients heterotropla is Comitent or Incomitant
mobility test or Hess Screen
accommodative esotropia meaning + treatment
is an Inward turn of one or both eyes can happen when child longsighted - they over focus
Prescribe glasses - helps eyes relax
Explain what is meant by refractive Surgery
Surgery to the eye to alter the patients refractive error
explain
version
Vergence
versions- conjugate Movement.the eyes move together binocularly and angles between the visual axis is constant
Vergences - Disjunctive Movements . eyes move in opposite directions
Grades of binocular vision
Simultaneous Perception lowest
fusion
Stereopsis
3 Types of Diplopia
Pathological
physiological
Prism Induced
simple optometer
consists of a sliding target and a high Positive lens mounted on a rod that's marked with Spec refraction eye placed at required Vertex distance relies or Image clarity
Disadvantages of Simple optometer
/ difficult to determine astigmatism
–non linear
Proximal accommodation will under correct hypermetropia and over Correct Myopia
retinal Image size varis
a maddox Rod placed in front ofthe left eye to be used to detect whether a Subject has exophoria or esophoria
What would be the the axis direction of the maddox Rod
Horizontal
if the left eye is looking through the Maddox Rod what would be used as a target for the right eye
Distance Spotlight
maddox Rod
In order to determine what type of heterophoria is present what question would the subject be asked
Is the line Image on the right or left
maddox Rod
what answer would the subject give if exophoria were present
line is on the right
Prisms can be used with the Maddox Rod to Measure the exophoria
what would the Subject see when the Correct Image is in place
the Spot and the line would be together
what would be the direction of the Prism used to measure the Exophoria
Base in
A heterophoria maybe described as Uncompensated what does this mean
Symptoms arise when fusion amplitudes are Inadequate to control deviation
muscular fatigue
eye strain
Push up method
using an RAF Rule
move the Slider for away from CX
instruct (x you will Slowly more Slider toward them along rule
at Some point the text will become blurry
when this happens they need to advise and you stop moving the Role
Read Position of the Slider on the Side of the ruler in distance/ dioptres
Repeat for other eye
explain what is meant by Convergence when related to eye movements
Aligns the visual axes with the object So two Images will fall on Corresponding retinal points
Define near point convergence
nearest point for which a subject can Converge whilst keeping Image on the fovea
A Subject with a PD of 66mom Views an object on the midline between the two eyes at a distance of 35cm from the Centres of rotation.calculate the Convergence required by each eye In Prism Dioptres
1/2 PD XMA
ma = 1/d = 1/ 3.5 = 0.28 X 33 = 9.43 Prism each eye
homonymous
hemianopia
heteronymous hemianopia
congruous
homonymous -Same
hemianopia -1/2 visual field loss
heteronymous hemianopia- left or right of both eyes
congruous- Same in each eye
fixation disparity
defined as the difference between the target vergence angle and ocular Convergence angle during binocular fixation
indirect ophthalmoscopy
exon of the inside of the back of the eye using a beam of light and hand held lens - gives wider view of inside the eye
f acultative hypermetropia
manifest hypermetropia
which of these is equal to the amplitude of accomodation
facultative- can not overcome by accomodation
manifest Cannot be overcome by accomodation
accommodative esotropia
is an Inward turn of oneor both eyes that can happen when a Child is longsighted
nystagmus
an involuntary rhythmic side to Side up+ down or Circular motion of the eye
Contact lens would move with the eye causing less distortion
Percervative In RGP lens
Polyhexamide
Define the terms near point and amplitude of accommodation
near point / The vergence required at the fully accomodated eye to form a clear retinal Image
AOA - maximum amount of accomodation an eye can exert
An eye has a Ocular Ametropia of -1.00D andthe nearest object that it is able to focus on is a 25cm from the reduced surface
What is the amplitude of accommodation
( 25cm - True near point )
Amp = K-B
B= n/ b = 100 / -25 = -4.00D
= - 1.00- -4.00 = + 3.00D
Keratometry
fixed doubling
variable doubling
fixed doubling- Power of prism is fixed
variable doubling- only one fixed object - Power /position of prism changes
placido disc
Corneal topography examines the weall shape of the cornea and is useful when more complex lenses are required
the simplest tool is the placido disc
it is made up of a Series of Concentric black and while circles with a sight hole in the centre
KeratoScope
3 advantages of a non- contact method of tonometry
eliminates Corneal contact
eliminates Risk of infection
Does not need topical anesthesia
Definition of relative Spec Magnification
the ratio of the retinal . image Size in the corrected aretropic eye compared with the retinal Image size in the Standard Emmetropic eye
list 5 ocular Structures
lids + lashes - bletharitis - Smooth eyes Cornea - conjunctiva - smooth eyelids Anterior chamber - blood cells Iris - melanomia- Limbus - Redness
Explain Inverse Square law
illuminance at a point on a Surface Perpendicular to a Source is In versely Proportional to the Surface of the distance from Source to Surface
E= I/ d2
cosine Square law
illuminance of a surface varies as the Cosine angle of Incidence
the greater the angle the Lower Illumination falling on Surface
E = I / d2 x cos ( angle)
luminous flux
rate of light flow from the Source in a given direction
illuminance
the amount of luminous flux falling on a surface
Symbol E
unit lux
Reflectance
A Ratio comparing the lomens of a flux leaving a surface to the lumens of a flox that were incident on the surface
Dry AMD
loss of central vision 3 stages early Intermediate,late no treatment for late certain medication may slow process may struggle to See peoples faces Colours are less bright regular check ups monitored at home using Amsler chart straight lines may appear wavey will more likely affect both eyes Progresses slowly over Sereval years
EVES
vary mag vary brightness / Contrast auto focus interact with image Save image to View later Portable Screen reading technology voice control no abberations improved FOV
PD: 62
calculate Convergence required in MA and Prism If the spec may of +12.00 D is fitted 27 mm from eyes centre of rotation
PD: 60
F: +12.00D
S= 27
100/ 12 = -8.33 cm
MA = 1 / WD = 1 / I - S = 100 / -8.33-2.7=9.066
P = MA X mono CD= 9.066 X 3.1 = 28.18 each eye
State 3 disadvantages of Spec magnifiers
short WD
Poor illumination
weight /thickness
State 3 advantages of Spec magnifiers
increased fov
hands free
more acceptable
other than a reduced field of view state 2 other Symptoms of retinitis pigmentosa
Poor dark adaptation
night blindness
another Patient Suffers from retinitis Pigmentosa Explain how a telescope can be used to increase their field at View
reverse telescope to minify Images so falls on central retina
state the 3 major causes of visual Impairment Certification in england and wales
ARMD
Glaucoma
diabetic Retinopathy
A Patient attends foa low vision assessment state how you would explain the Purpose of this appointment
Help cx use residual vision
enable required tasks to be Performed
aids independence
Improves qualily of life
structure of Pelli Robson chart
8 facts
8 Rows 6 letters Per row grouped into 2 triplets logarithmic design Used @ 1m 89% ~ 0.5% Contrast Same size + spacing Specific lighting needed high to low contrast left - right, Top - bottom
advantages of contact lenses for Iris coloboma and howthese advantages are achieved
cosmetically better - handpainted to match look of other eye
better VA
reduced Photophobia
opaque backing reduces Light Scatter
3 Signs of diabetic retinopathy
Retinal haemorrhages
micro aneurism
macular Oedema
Give 2 reasons Why the results obtained with he simple optometer may not be accurate
Difficult to determine astigmatism
Proximal accommodation will under/ over correct
