TEST ROOM Flashcards
how does corneal thickness affect IOPs?
thin corneas have pressures that are underestimated (lower)
thick corneas have pressures that are overestimated (higher)
parasympathetic efferent pathway
brain to eye
- Edwinger-Westphal nucleus
- Cranial nerve III (oculomotor nerve)
- iris sphincter muscle
sympathetic efferent pathway
brain to eye
- hypothalamus
- ciliospinal centre
- iris dilator muscle
horner’s syndrome
problem with sympathetic nerve supply (dilator affected)
miotic pupil, ptosis on same side, failure to sweat on affected side
urgent referral
adie’s tonic pupil
anisocoria greater in light conditions - affected pupil cannot constrict
affects parasympathetic nerve supply
dilated pupil with poor light reaction, reacts better when accommodating
argyll robertson pupil
bilateral miosed + irregular pupils, dilate poorly in darkness
accommodates but not reactive to light
caused by neurosyphilis
CNIII palsy pupil signs
impaired parasympathetic efferent innervation
impaired direct + consensual response
diplopia, ptosis - eye down + out
presbyopia
gradual loss of the eyes ability to focus on things up close
when you are younger, the lens is very flexible and can easily change shape depending on whether looking at something near or far away
as time goes on the lens becomes less flexible making it more difficult to focus on near objects
domestic waste
paper, cardboard, used tissues/paper towels, disposable CLs
disposed in normal black bag waste stream
sector specific non-hazardous healthcare waste
e.g., disposable tonometer probes, expired CLs, empty CL solution bottles which don’t present a risk of infection
disposed of as offensive waste (tiger stripe bags)
non-hazardous pharmaceutical waste
used or expired minims - need to be incinerated and discarded in medicine disposal box (usually yellow)
hazardous waste
computer monitors, fridges, batteries, chloramphenicol - special requirements
dichromat vs anomalous trichromat
dichromat have an absent cone (e.g., protanope has same number of cones as everyone else but instead of red cones they have green cones)
anomalous trichromat - defective cone
S-cone
short wavelength = blue (tritan)
M-cone
middle wavelength = green (deutan)
L-cone
long wavelength = red (protan)
ishihara test
- uses pseudoisochromatic plates
- doesn’t grade severity, classification only
- present in random order
- 3-4 secs per plate
- test distance 75cm
ishihara plate types
transformation = CVD sees diff figure
vanishing = CVD doesn’t see number
hidden digit = CVD sees figure (normal doesn’t)
classification = differentiates protan from deutan
city university test
- colour confusion test (10 plates)
- can be used to detect protan, deutan or tritan defects
- grades severity
- pages shown for 3 secs @ 35cm
dichromats
absent cone - 2/3 present
protanopia - L cone missing (red deficient) - 1% of males
deuteranopia - M cone missing (green deficient) - 1% of males
tritanopia - S cone missing (blue deficient) - 0.001% of males
anomalous trichromacy
defective cone - 3/3 present but 1 anomalous
protanomalous - 1% of males
deuteranomalous - 5% of males
tritanomalous - 0.0001% of males
SIGN referral guideline for IOPs
IOPs >25mmHg irrespective of CCT
IOP 21-25 + CCT <555nm + 65 or under
IOP <26 + CCT equal or > 555 = monitor
why is only 1 measurement required for Goldmann?
Goldmann takes ocular pulse into account
NCT requires at least 3 readings to take an average so ocular pulse is accounted for
outer lipid layer
secreted my meibomian glands
prevents tear evaporation
acts as a lubricant to smooth eyelid movement on globe
middle aqueous layer
secreted by lacrimal glands
supplies oxygen to avascular cornea
contains antibacterial enzymes
washes away debris from ocular surface
inner mucin layer
mucous secreted by conjunctival goblet cells
converts corneal surface to hydrophilic surface and allows wetting
afferent pupil pathway
eye to brain
retina —> optic nerve —> optic chiasm
—> optic tract —> pretectal nucleus
if affected RAPD present
efferent pupil pathway
from brain to eyes
controlled by autonomic NS
sympathetic - fight or flight (iris dilator)
parasympathetic - rest + recovery (iris sphincter)
absent direct vs absent consensual
absent direct = significant ocular or neurological disease (either afferent or efferent pathway affected)
absent consensual = if direct present then afferent pathway unaffected + must be impaired parasympathetic efferent pathway to affected eye
hand magnifier advantages
- low cost
- compact, lightweight, portable
- can have long eye-to-magnifier
distance - used with DV rx as emergent light
parallel
hand magnifier disadvantages
difficult for px with arthritis etc
increased distortions as lens held further from eye
hand magnifier px instructions
lay magnifier on page + slowly pull away until image clear
use SVD rx
larger FOV holding magnifier closer to eye
stand magnifier advantages
- incorporated illumination
- good for px with hand tremors
- small and portable
- relatively inexpensive
stand magnifier disadvantages
can be bulky
limited field of view
px must have adequate accommodation or suitable SVN
bar/ flat field magnifiers advantages
normal reading posture possible
very bright - light gathering
useful for px with hand tremor
clear image across while lens (minimal aberrations
bar/ flat field magnifier disadvantages
large lenses (heavy)
low mag
reading material must be flat + on firm surface
must wear SVN or accommodate
CCTV advantages
- aberration free
- max mag up to 70x
- zoom control
- contrast reversal
- binocular viewing
- normal viewing distance/ posture
CCTV disadvantages
- cost to buy + service/repair
- size can be large/bulky
- practice required
- depth of field limited by focal length of camera, reading material needs to be flat
corneal arcus
white/grey crescent shape made of lipid deposits that curves around outer edge of cornea
occurs in ~60% of those aged 50-60yrs
can be related to HBP, high cholesterol
AVERAGE RX + VA FOR 1 YR OLD
+2D and approx 6/24
AVERAGE RX FOR 3 YR OLD
+1D and 6/9
AVERAGE RX FOR 4-6 YR OLD
+0.50D and 6/6
STEREO 1YR OLD
170-210 Frisby
STEREO 3YRS
55-85 Frisby
STEREO 5YRS
20-30 Frisby
STEREO 6YRS
5-10 Frisby
SAME DAY EMERGENCY REFERRAL
- Acute angle closure glaucoma
- retinal detachment
- acute 3rd nerve palsy (pupil involved)
- papilloedema
- penetrating/ chemical injury
- CRAO
- hypopyon/ hyphaema
- endophthalmitis
- sight threatening keratitis
- pre retinal haemorrhage
DIURNAL IOP VARIATION
higher IOPs in the morning
diurnal variation usually 4-5mmHg
ARMY/ NAVY/ PILOT COLOUR VISION
army - ishihara test pass is 2 or less on screening plates
navy - impaired CV = restricted branches
pilot - pass first 15 plates (random order) without error or further CV testing required
POLICE/ ELECTRICIAN COLOUR VISION
police - mild anomalous trichromat acceptable
electrical engineer - some companies allow no more than 2 errors on ishihara
how common is congenital CVD?
1 in 12 males (~8%) and 1 in 200 females (~0.5%)
congenital CVD
caused by variants in genes on X chromosome (male XY, female XX)
one altered copy of the gene is sufficient to cause CVD whereas female variant must occur in both copies of gene to cause CVD
fathered cannot pass X-linked recessive conditions to their sons
CCTV
closed circuit television
EVES
electronic vision enhancement systems
AMBLYOPIA CAUSES
- stimulus deprivation (ptosis, cataract)
- strabismus (manifest)
- anisometropia
- ametropia (high degrees)
- meridional (uncorrected astigmatism)
amblyopia mechanisms
light deprivation - no stimulus to retina
form deprivation - retina received defocused image
abnormal binocular interaction - non-fusible images on foveae
prisms for heterotropia
only prescribed when px symptomatic
long term solution when stable angle of deviation - prescribe smallest amount that relives symptoms
sheards criterion
is more than half fusional reserves need to be used to control the phoria then visual system will be under stress and phoria decompensates - manifest
