CLINICAL TESTS - Optics ones Flashcards
What are the findings from the four worth dot test?
Red covers RIGHT EYE.
What are the 3 definitions of binocular vision?
- Simultaneous perception
- Fusion
- Stereopsis (perceive 3D)
What tests can be used to assess binocular vision?
- Worth 4 dot test / Bagolini glasses - Simultaneous perception and fusion
- Synoptophore
- Prisms - range of motor fusion
- Stereoacuity tests: Titmus, TNO, Lang, Frisby
What does the Maddox rod test?
Heterophories and heterotropias at near and far fixation distances.
Single maddox rod: horizontal and vertical
Double maddox rod: Torsional deviations?
What does the four diopter base out test measure?
Small central suppression scotoma / foveal suppression
Difference in minutes of arc between
Titmus
TNO
Lang
Frisby
Synoptophore
Ambylopia
Frisby 15-600 seconds of arc
Titmus - 40-3000 seconds of arc
TNO: 15-480 seconds of arc
Lang: 550-1200 seconds of arc
Synoptophore: 90-720 seconds of arc
Lang and Frisby do not need glasses (f’ng lewandowski)
Titmus needs polarised glasses
Frisby - 15 Frisbees fly at 600mph
TNO: 15 dynamites explode at 480mph
Titmus: 40 year old MILF with 30003ies
Lang: is bare long. 550-1200.
Synoptophore: Sleek 90 and Perfect 720.
Ambylopia= <250
What does the Worth Four Dot test test for?
Binocular vision
1. Suppression
2. Anomalous Retinal Correspondence (ARC)
What does a keratometer measure?
Measures curvature of anterior surface of cornea, across a fixed chord length (2-3mm) which lies within optical spherical zone of the cornea.
Used for
1. Non conact tear break-up test
2. Differentiation of corneal astigmatism
3. Detection of irregular astigmatism
Whats the difference between a Bausch & Lomb Keratometer and a Javal & Schiotz Keratometer?
They are both manual keratometers 36-52D can be measured.
B&L : one position keratometer - both horizontal and vertical meridian measured by keeping keratometer in same position
J & S: two position keratometer: after measuring one meridian, need to change position to measure other meridian.
- has variable object size
- A wollaston prism is used to achieve doubling of the image.
When is an extended keratometer used?
Anything higher than 52D
–> +1.25D lens (equal to 9D) placed over eyepiece
Anything less than 36D
—> A -1.00 lens (equal to 6D) placed over eyepiece.
What can the synoptophore be used to measure?
All three grades of BSV
Grade 1: Simultaneous perception (red slides) –> can map suppression scotoma and angle of deviation objectively and subjectively
Grade 2: Fusion (Green) –> sensory and motor fusion
Grade 3: Stereopsis (yellow)
What are the findings of the synoptophore in normal retinal corespondence?
What are the findings of the synotophore in anomalous retinal correspondence?
Normal retinal correspondence: Objective angle = subjective angle of deviation.
Anomalous retinal correspondence: Objective angle not equal to subjective angle - the patient does not perceive true fovea as fovea, adn they are moving one of the images to the pseudofovea.
When ARC is detected, you can determine angle of anomaly, which is distance of pseudo-fovea from true fovea. Nasal + sign, Temporal - sign.
What is used to eliminate chromatic aberration in the focimeter?
Green light is used.
What does the four prism diopter base out test detect?
Small central suppression or foveal suppresion.
What is the normal scenario after a 4D BO prism is placed in front of the right eye?
What are the abnormal pathological findings?
Normal
1. Levoversion of right eye - rays deviate towards base, so right eye moves left to refixate on fovea - indicates absence of foveal suppresion of RIGHT eye.
- Initial levoversion of left eye - Hering’s law
- Subsequent refixation of left eye to the right to avoid diplopia –> Absence of foveal suppression of the LEFT eye.
Foveal suppresion of right eye: no movement of both eyes.
Foveal suppresion of left eye: Levoversion of right eye, levoversion of left eye but NO RE-FIXATION.
When the synoptophore measures stereopsis, what does it measure? What can it not measure?
2 responses are
Stereopsis perceived or not perceived - cannot be used to measure the LEVEL of STEREOPSIS or minimal disparity patient can perceive.
Sheridan Gardiner - crowded or uncrowded test?
Uncrowded
Hirshburg test: Reflexes at the pupillary margin, the pupillary/limbal gap, and limbal margin cause how much mm of deviation?
1mm = 15 Diopters
Pupillary margin: 2mm deviation
Pupillary/limbal: 3mm deviation
Limbal margin: 4mm deviation.
Which visual acuity charts should be used for children < 1 years old?
Fixing and Following - after 3 months
Preferential looking: Keeler/Teller acuity cards, Cardiff acuity cards
Visual Evoked Potentials.
Which visual acuity charts should be used for children 1-2 years old?
Which visual acuity charts should be used for children 2-3 years old?
1-2 years old: Picture test, Cardiff Cards
2-3 years old: Cardiff Cards, Kay picture cards (single optotye)
Which visual acuity charts should be used for children >3 years old?
Kay picture cards
Keeler LogMAR/LogMAR.
Sheridan Gardiner
Sonsken-Silver.
What is the interpretation of Pelli-Robson Test?
> 2 - normal
< 1.5 - visual impairment
< 1 - visual disability
How do you test for Photostress recovery time?
Ask patient to gaze into bright light 2-3cm from eye for 10 seconds.
Then as soon as light is removed patient attempts to read larger snellen VA line above patients normal VA line
What is normal photostress recovery time?
Which conditions is associated with abnormal recovery?
30 seconds –> normal in optic neuropathy / neuritis.
Can differentiate between vision loss caused by macula lesion or ischaemia vs optic neuropathy.
Abnormal in:
1. AMD
2. Diabetic retinopathy
3. CSR
4. Digitalis toxicity
5. Severe ocular ischaemia / maculopathy.
Purkinje Image Table.
What is Kestenbaum’s rule?
Allows patient with low vision to read newsprint.
Power of lens = reciprocal of VA.
Images formed from prisms are…
- Erect
- Virtual
- Displaced towards apex
- Neither enlarged nor diminished
Object and Image in Mirrors
CONVEX - V E D (within)
CONCAVE
outside: R I D (between)
between: R I E (outside)
within: V E E (behind)
Object and Image in Lenses.
CONVEX
outside: R I D (within)
between: R I E (outside)
within: V E E (outside)
CONCAVE
V E D (between)
Schematic Eye and Reduced Eye.
Direct v Indirect
Indirect: Image size INCREASES as condensing lens is moved away from MYOPIC patients
Order of exposure time in lasers.
vs
Order of power density in lasers
EXPOSURE TIME:
photochemical > thermal > photoablation > photodisruption > plasma-induced ablation
CHADS –> Chemical, Heat/Thermal, Ablation, Disruption, Shockwave/Plasma.
POWER DENSITY:
Photodisruption > plasma-induced ablation > photoablation > thermal > photochemical
DSATC
How to minimise image jump
- Flat-top and executive-style segment
- Positioning the optical centre of the segment as close as possible to top of the segment
- Incorporating base-up prism in the near segment
What is the purkinje effect?
Dark adaptation where rod function takes over cone function.
Shift in spectral sensitivity from 555nm (yellow) to 505(nm)
What happens with surface tension force when there is decreased amount of surface area of contact in goldmann tonometry?
What happens with corneal rigidity when there is increased amount of surface area of contact in goldmann tonometry?
Surface tension: Increases with reduced amount of contact.
Corneal rigidity: Increases with amount of contact.
What is the difference between depth of field and depth of focus?
Depth of field - distance range of OBJECT.
Depth of focus - distance range of IMAGE of object.
Luminous flux definitions.
Condensing lens table.
What are base in prisms used for?
What are base out prisms used for?
Base-in: assessing fusional divergence
Base-out: assessing fusional convergence. Used for
1. assessing suppression scotoma of microtopias
2. for exercise to stimulate convergence reflex in patients with convergence insufficiency.
How do you calculate power of contact lens when you have power of spectacles?
Power (CL) = P (spectacles)
—————————————–
1 - (vertex distance x P(spectacles)
Relationship of back vertex distance with convex lens.
Increasing back vertex distance –> increases effective power of a convex lens
What is the image formed from a compound microscope?
What is the image formed from a galilean telescope?
Compound: V II E
Galilean: V E E
Compound - c’est la viie
What’s the difference between the position of minimum deviation and prentice position?
Prentince: All refraction occurs at exit surface
position of minimum deviation: angle of incidence is equal to angle of emergence
What are the positions of the Sturm’s conoid?
Horizontal oval
Horizontal line
Horizontal oval
Circle of least confusion (spherical equivalent)
Vertical oval
Vertical line
Vertical oval
HO / HL / HO / COLC / VO / VL / VO.
What is the SRK formula?
Power = A constant - 2.5 x (axial length) - 0.9 x (average keratometry)
