eeeeee Flashcards
Imbert fick law:
IOP = (force + Tear-film attraction - Corneal resistance) / Area
- from P=F/A equation on perfect sphere
Ishihara test plates:
Demo plates (4)
Transformation plates
- Colours on confusion loci present different numbers
Vanishing plates
- Confusion loci > loss of any number
Hidden plates
- Number is crowed by confusion loci (only seen by CVD)
Diagnostic plates
- One number is not seen by protan (red) or deutan (purple)
- Inaccurate
Colour vision test result interpretation:
Ishihara: Mono or Bino
- <=2 (normal)
- >2 on plates 2-15 (RG defect) 2% false pos.
- >4 Certain CVD
Medmont C-100:
- -1<>+1 (normal)
- <-1 (Protan)
- >+1 (deutan)
HRR:
- 2 on screening plates (probable CVD)
- >2 (definite CVD)
1. Classification plates 1>5 (mild), 6>8 (medium), 9>10 (severe)
Farnsworth D-15:
- Pattern of proten, deutan, tritan, rod monochromacy
- requires 2 major crossings (space of more than 2 caps)
Colour vision procedure:
- VA > Ishihara
- HRR / Medmont C100 / Farnsworth D-15
- L’anthonys desat. D-15
Educate Px on CVD
- Document and record Fx
Counselling/support groups/color identifying apps
Regular follow-ups
OCT evaluation for glaucoma:
RNFL thinning <80 microns
GCL thinning <70 microns
ONH
- CDR >0.5, or asymmetry of 0.2
- NRR (ISNT/Notching/Localised thinning)
- PPA (asymmetrical, pronounced B-PPA)
- Drance haem
- Vertical elongation
- Laminar dot sign
CVD causes:
Protan/Deutanopia: X-linked recessive
- Red (L-cones), or green (M-cones) completly missing
- P/D-anomaly > mild form where photopigments are altered
Tritanopia: Autosomal recessive
- Blue (S-cones)
Acquired:
- Cataract (contrast loss)
- Glaucoma/MS (blue yellow loss)
- AMD (contrast loss)
- DR (blue/yellow > red/green)
- RP
Keratometry:
Videokeratoscopy (placido discs) provide Corneal topography map
- Axial/tangential power/curvature
- Required for fitting CLs and detecting corneal diseases
- Pupil/cornea size
Ocular biometry:
Pachymetry: Ultrasound / OCT
- U/540um
Ultrasound biometry:
- A-scan: Axial length
- B-scan: RD, Tumors
OCT:
- Ant: CCT, Angle, Iris
- Pos: everything else
CL wearer clinic procedure:
Hx:
- PC, GH, CL compliance/use, lens handeling
VA (mono/bino)
Lens fit (Stain for RGP)
Ant. assessment without lens: (observe Px handeling lens)
- Stain+wratten
- Ocular surface > DEWS grading
- Tear assessment
- Lid eversion
Soft contact lens assessment:
15 minute settling period
VA + over refraction
Corneal coverage (TD) 1mm over limbus
Lens centration/position
Lens movement
- Primary blink (0.2-0.5mm)
- Up/horizontal gaze
- Push-up
Edge alignment
Lens surface biocompatibility (wettability)
Toric alignment
- Left of vertical requires adding to axis, otherwise:
- Acuvue oasys for astig (accelerated stabilisation design)
- Biofinity toric (Peri-ballast)
Soft contact lens selection & example order:
- Material > Spherical/aspheric
- Hydrogel: ^comfort for short term wear
- Silicone hydrogen: ^O2 permeability for long term wear - SCL 2mm larger than HVID (keratometry/slit)
- Base curve 0.6mm flatter than mean K (keratometry)
- Flat K + 0.6mm - BVP from refraction
- 4D > +0.25
- 6D > +0.50…
- If > 1 DC, use toric
Example order: Acuvue Oasys 8.4/14.0/-2.00D (BC/TD/BVP)
RGP parameters and rule of thumb:
TD 2mm less than cornea (9-9.8mm)
- BOZD (7.0-8.5) increases with TD, must be 1.5mm larger than pupil
BOZR (7.80-7.70mm)
- Fit to flattest (greater value) K meridian
- Increased by 0.5mm per 1DC
- If >2.5DC, consider toric back surface
BVP: 0.05mm increase in BOZR from corneal curvature = 0.25D tear lens power
- Tear lens power - refractive error
Design/brand/Material
Centre/edge thickness
ALTERING LENS PARAMETERS RULE OF THUMB (to retain stain pattern)
- Increasing BOZD by 0.5 requires flattening BOZR by 0.05
- Flattening (increasing) BOZR by 0.05 decreases tear power by 0.25
Fused cross cylider:
At Habitual
-0.50DC at 90 to project hortizontal lines anterior
- Clearer horizontal lines > lag of accom. > add plus lenses till equal
This seperates the meridians in the interval of strum
Clinical tests for children:
—Visual Acuity—
Visually evoked potentials: 0-2
Optokinetic nystagmus drum: 0-2
Keeler grating acuity cards: 0-2
Lea symbols: 2-5
- Match cards, threshold everything is a circle
- 3m (distance), then 25cm (near)
Kay pictures: 2-5
Tumbline E/Landot C: 4-5
- Broken wheel is a fun variation of landot C
Letter matching/Snellen: 5+
—Binocularity—
20PD BO > motor fusion
20PD BI > fixation preference
Red reflex: Symmetrical reflex from ophthalmoscope
Steriofly
—Cyclopentolate—
- Check RAPD and PERRLA prior
Retinoscopy: expect 1D of hyperopia
- Provide full prescription
- Atropine stronger eye in case of strab
Mohindra retinoscopy: if cannot cyclo
- ret at 50cm, and subtract 1D
Cause of deviations:
Comitant:
- Congenital strabismus (Tropia)
- Accomodative esotropia (hyperopia)
- Intermittent exotropia
- Genetic/anatomical factors
Incomitant:
- CN 3/4/6 palsy
- TED
- MG
- Chronic progressive external ophthalmoplegia
DED Hx and risk factors:
- Severity
- Assoc. (sjrogrens cotton mouth)
- Onset (infection/trauma)
- Vision change (blur on blink)
- Uni/Bilateral
- Itchy/pain
- CL wear
- Systemic conditions
DED risk factors:
^age, Female, asian
MGD, pterygium, DM
Sjogrens
CLs
Environment
Antihistamines
Clinical management of phoria:
Sheards criterion > Opposing fusional reserve must be at least twice the phoria
- If 6 exo
- PFV > 12 BO, phoria is compensated
- PFV = 8 BO, a 2 BI lens in required (is now a 4PD exo)
Percival’s criterion > PFV+NFV = 10
- PFV ~20 BO
- NFV ~ -10 BI
Incomitant deviation clinic:
Hx:
Diplopia: U/new acquisition
- Horizontal/vertical
Amblyopia: U/new
Head position change: U/long standing
1. Cover test: measure deviation of each eye while the other if fixing > Greater deviation in non paretic eye (herring’s law of equal innervation)
2. Hess screen: R/G dissociation > R fixation and G pointer > Px marks where the fixation light is
1. Smaller chart is parietic eye
2. Degree of disparity gives angle of deviation
3. Parks 3 step: determines parietic muscle from Rectus or Oblique muscles
1. Which is hyper (Hyper eye’s IR/SO, or Hypo eye’s IO/SR)
2. Worse on R/L gaze (Gaze’s IR/SR, or opposite’s IO/SO)
3. Worse on R/L tilt (Tilt’s SR/SO, or opposite’s IO/IR)
Dissociated phoria tests:
Cover-uncover:
- Tropia > uncovered eye moves
- Phoria > covered eye moves when uncovering
Alternating cover:
- Determines degree of phoria
Phi phenomenon: subjective
Prism cover test:
- amount of prism required to remove phoria or tropia
Maddox rod: Vertical streak (horizontal phoria) or horizontal streak for vertical
- Used in case of suppression
- Eso if Px sees line left of light source
Vone graefe: 6BU and 15BI
- Decrease horizontal OR vertical to determine horizontal or vertical phoria
Howel phoria card
DED management:
DEWS step 1:
- Educate: DED lifelong
- Environment (masks, computer time)
- Diet change
- Cease offending medications
- Ocular lubricants
- Lid hygiene, warm compress
- 45’ towel, reheated every 2 mins for 10 mins
Step 2:
- Non-preservative tears
- Tea-tree oil for demodex
- MG expression
- short term cortico.
- FML QID shown to reduce symptoms and increase goblet density
- Immunomodulatory drugs
- Ciclosporin to prevent T-cell activation
Step 3:
- Autologous serum drops
- BCL
- Soft > comfort
- RGP scleral > tear repository
Step 4:
- Long term cortico.
Fixation disparity:
Vergence error within panums fusional area <10minutes of arc
- causes strain, asthenopia, poor near/distance (exo/eso)
Mallet unit test: polarized septum dissociation
- Each eye sees either top of bottom line
- Prism added to align lines
Measuring fusional vergence:
Prism bar until blur/break/recovery
Risley prism on phoropter is easier
- BO > Convergence
- BI > Divergence
- BU/BD if needed
Repeat for NFV
Vergence facility:
3BI/12BO flippers, cycle once 40cm target cleared
Normal > 15cmp
Poor BI > convergence insuf
Poor BO > Divergence insuf
AC/A:
Gradient AC/A: (PD deviation with lens - Prism deviation without)/Lens power
- The difference between values divided by lens required to create deviation
Calculated AC/A: AC/A = (Convergence demand + near esophoria - distance exophoria)/Accom. demand
- Stimulus to accommodation at 40cm = 2.5
- Convergence stimulus at 40cm = 15
