Bit Exam Questions Flashcards
What condensing lens would i use to examine a myopic 75 yo px -8.00 and why
78D
Need good fov to check peripheral retina for tears or detachment bc myopic greater chance of this
Good mag to observe microvasculature changes
Sharper image in presence of media opacities bc image formed anterior to the eye
Consideration of smaller pupils- elderly= smaller pupils. Cant use anything too big. So maybe use 90D for this reason as it is smaller than 78D and would provide a greater fov but it wouldn’t be as magnified meaning can’t see microvaculature changes as well.
Describe slit lamp technique for anterior eye
Diffuse with low mag 10x to get an overview of anterior eye and adnexa
Increase mag to x16 and use parallelpiped beam to view lids lashes cornea, conjunctiva manipulating upper and lower lids where necessary. View upper and lower fornices and tarsal plate.
Make at least 3 sweeps across eye to check for abnormalities of the cornea
Where abnormality spotted increase mag further to around 25 or 40x and use optic section to assess the position and depth of the abnormality
Nafl can be used here
Describe the filters- 5 marks
Diffuser- general overview of anterior eye and adnexa
Cobalt blue- used with sodium fluoroscein and excites it
Red free- enhances contrast between blood vessels and the surrounding ocular structures
Neutral density- if larger slit heights or widths are required it reduces the brightness
Yellow/ short wavelength- eliminates short wavelength light during fluoroscein examination
Trichromats use 3 primaries to match their colour experience, why do dichromats use two monochromats use only one
Use examples of absorption spectra to illustrate your points
Monochromats only have one functioning pigment either rods or just one cone for their colour experience.
Below i am going to draw an absorption spectrum for a hypothetical photo pigment
A photon of light wavelength a has the highest probability of being absorbed whereas wavelength b has half the prob
Eventhough wavelength a is 2x as likely to be absorbed than wavelength b pigment has no way of knowing which is which
There may be differences in brightness but this may be due to a difference in intensity but there is no actual way of discriminating colours
Thus, a monochromat is unable to distinguish between objects based on wavelength alone
For dichromats they have 2 functioning photopigments and draw it
Absorption spectrum for a hypothetical photo pigment
Spectra peak at diff wavelengths but overlap considerably
The quanta absorbed by the 2 photopigments is different therefore the photons are distinguishable by their wavelength
You examine a 12 yo boy who has been referred to you for advice following the detection of a cv problem with the ishihara test during a school vision screening assessment. He passed all other visual performance screening tests,
List the tests that could be performed to determine the nature and characteristics of this pxs colour vision-4
What is the most common type of inherited colour vision defect in males
What must we make sure
Assuming your px has this, comment type of colour vision defect, what advice would you give to him
D15, Waggner hrr test, 100 hue test, anomaloscope
Deuteranomaly most common in males
Important to ensure that this is congenital and not an acquired defect that may be associated with a more serious ocular or systemic condition
Advice-
Relatively mild case of cv deficiency
Defect is unlikely to get worse
May need to seek help at school when colours used eg geography or chemistry
Manage expectations for chosen career eg pilots or electricians require good colour vision
Will need to take care when working w electronic devices and printed circuit boards as there may be a health and safety risk
70 year old px presents to your practice reporting decrease in vision. Ret reflex not as bright and Rx -2.00DS 6/9 with and without pinhole.
You suspect cataract in re
What instrument would you use to assess this
How would you identify the type of cataract this px has
With the aid of a diagram describe how the pxs visual acuity and contrast sensitivity may be affected
Slit lamp biomicroscopy best to assess and localise location of cataract.
Retro illumination of retina or iris- short light beam directed through the pupil and reflects off retina to reveal lens opacities, best w dilated pupil.
And optic section to localise the location of the cataract for example nuclear cataract, subcapsular cataract and cortical cataract.
Spatial frequency on x axis cpd. 0.1,1,10,100. Contrast sensitivity on y from 1,10,100,1000. 3 curves high medium and low. Normal cataract and cataract and glare
Va impacted but more significant attenuation of the pxs mid sf contrast sensitivity
Addition of glare source will have a more significant effect on the pxs sf
A 6 yo boy px arrives at your practice, it is his first eye examination. Using bullet points describe what test you would use to assess his colour vision, how would you perform the test and describe how the full 38 plate ishihara test is designed to screen for cv deficiencies
Ishihara test bc it is a very efficient screening test for red green colour deficiencies and provides quick and simple measurements. At this age you would test for congenital colour vision deficiency
If screening for congenital measure cv binocularly
Test should be conducted in natural daylight or in artifical light that is as close to daylight as possible. Tungsten light is unstable but daylight fluoroscent light which is available in most consulting rooms is satisfactory if the illuminance is greater than 250 lux
The plates should be held at 75cm from the subject and tilted so the plane of the paper is at right angles to the line of vision
Subject should be encouraged to answer within 4 seconds of presentation and it is designed to give a quick an accurate assessment of cv deficiency of congenital origin
Full test contains 38 plates: 25 numerals and 13 contain pathways which may be used to test young children and enumerate subjects,
The abbreviated 24 plate ver is used generally.
Plate 1 should be seen by all subjects
Rest consist of transformation vanishing and hidden digit plates. Then classification plates are used.
For pre and post iop what are 2 things we should note
Pressures obvs
Note time of day
Note down anterior chamber depth
What technique would you use to examine someone presenting with flashers or floaters
Slit lamp biomicroscopyy
Describe what drugs you could use to increase vision and drug concentrations available to you and modes of action.
And what are the 4 ds
Mydriatic dilating agents
Antimuscarinic- tropicamide which is given in concs of either 0.5 or 1 percent. Role is to prevent any contractions of the sphincter pupillae to ensure dilator muscle works unopposed and if sphincter pupillae contracts this would reverse dilation
Sympathomimetics- phenylephrine which is given in concs of 2.5 percent and their role is to keep the eye open by initiating the dilator response without touching sphincter pupillae
Drug, dose, date, disposal
What additional checks would you conduct prior to and following topical drug instillation
If theres any blurred vision/ photosensitivity
Check intraocular pressure and note down the time it was taken
Repeat intraocular pressures 3 times to get an average
Check the anterior chamber of the eye
Using a diagram to illustrate your answer, outline the key characteristics of the CIE Chromaticity diagram (7 marks)
What are colour vision confusion lines
How are these lines used in the design of cv tests
Wherever possible provide worked examples of clinically available cv tests
Draw the 3 diagrams. Protans deutan tritan
Cv defects can be characteristised by the chromaticity diagrams drawn above. These are a 2d representation of colour space, xy coordinates relate to different colours. Spectral colours are arranged along the arc of the perimeter of the diagram and different colour vision defects confuse colours paled along certain orientations. The first diagram is for protans and they confuse colours which plot along those lines as shown above and they confuse red purple with grey. The second diagram is for Deutans who confuse colours placed along that orientation and they confuse blue purple with grey. Tritans confuse lines placed in an orientation of nearly 90 degrees.
Confusion lines are placed in different orientations on the diagram and different cv defects will confuse diff orientations along lines which relate to their colour vision defect.
Confusion lines are made use of in designing pseudoisochromatic colour vision tests eg ishihara. If they pass the plate they arent confusing lines but if they fail it then they are confusing lines that plot along certain confusion lines so they must be a protan deutan or a tritan. So confusion lines can be used to categorise dichromacy and also can categorise anomalous trichromacy in the same way by seeing which colours patients confuse.
This system offers more precision in colour measurement than other systems eg munsell because the parameters are based on the spectral power distribution of light emitted from a coloured object and are factored by sensitivity curves which have been measured for the human eye.
Then draw the ishihara plate and draw arrows pointing to cv orientation. Eg protan deutan and tritan.
The diagrams for protanopes and deutanopes are similar as they share a strong confusion on red and green colours, for tritanopes the confusion lines are at the blue end of the colour spectrum so the diagram looks different.
Describe the ishihara test for the 38 plate version
Plate 1 should be seen by all subjects
Plates 2-9 = transformation. Seen by normal another seen by cv defect
Plates 10-17= vanishing. Seen by normal not by cv defect
Plates 18-21= hidden digits. Not seen by normal only cv
Plates 22-25 differentiate between protan and deutan defects. Each plate contains 2 numbers printed against a background of grey dots and one number is made up of reddish purple dots while the other consists of more bluish purple spots. The former will be invisible or less visible to an individual with a protan defect whilst deutan have difficulty resolving the latter.
The rest contain pathways for those unable to read numerals so young children and enumerate subjects.
