TBL2 Flashcards
(25 cards)
when do px complain of flare ?
- small BOZD
- significant lens decentration
- large pupil size in dim condition
- tear film deficiency
- poor lens wettability
3 types of rgp lens and when do we select them
spherical (<1.5CA)
aspheric (ca1.5- below 3.5)
toric (ca 3.5 and above / presence of internal astigmatism)
initial rgp definition
rgp that we think will fit cornea well
what measurement do we need to select initial rgp
keratometry / cornea topo
HVID and pupil size measurement
selecting initial bc
flattest k - ( flat-step)/3
selecting lens diameter
hvid-2
2 type of fitting assessment
static: nafl staining looking at central, mid , peripheral zone
dynamic: centration , lag , primary gaze ( blink)
2 types of rgp wearing scenario
inter- palpebral lid attach ( less sensation)
types of acceptable fitting
- slight tight but acceptable
- slight flat but acceptable
- optimum fit
Characteristics of flat fitting
Decentration: > 0.5 mm movement : >2 dynamic of movement: rocky, apical rotation,2 parts unstable lag : cross limbus centre : touch mid periphery: pooling (clearance ) edge clearance : >0.5 mm
characteristics of optimum fit
decentration: less than 0.5 movement : 1-2 mm dynamic : fast (up down) lag: uncross centre: alignment evenly green mid periphery : even/ slight touch edge clearance : 0.3-05 mm
characteristics of steep fit
decentration: less 0.5
movement: 1mm
dynamic: slow (up down)
lag: uncross
centre: pooling
mid periphery: touch
edge clearance: <0.3
excessive: air bubble
What is sag and it’s relationship with cl
sag - vertical space between a curved surface from the apex of the surface to a horizontal line circumscribe by lens diameter
lens behaviour is related closely with cl sag
relationship of sag and bc n diameter
increase sag: increase diameter, steep bc
decrease sag : decrease diameter ,flatten bc
bad centration and it’s remedy
bad centration - flat fit
to improve centration: make lens tighter
-decrease bc
-increase diameter
if centration is good but movement too little , increase bc (in 0.05 step ) (diameter in 0.4 steps )
maintaining sag
steepened bc : increase sag to offset this effect decrease diameter
Tear lens
formed by back surface of RGP contact lens and front surface of cornea account for astig <3.5 ca cyl as it neutralise 90% of regular and irregular astigmatism
Types of tear lens
positive- steeper than flattest k
plano - on k
negative- flatter than flattest k
SAM FAP
power of tear lens
difference between bc n k for every 0.05 mm diff =0.25 D sign depends if it’s a positive or negative tear lens
final lens order power
cornea rx: over refraction plus trial lens plus tear lens
equivalent balance equation
RGP indication
high astigmatism
orthokeratology
dry eyes
unsuccessful scl - vx/ complication
rgp contra indication
contact sport
dusty environment
occasional wearer
advantages of rgp
corrections of astigmatism
low risk of cl complication
suitable for extended wear
less hydration
disadvantage of rgp
require adaptations
easier to dislodge from cornea
complaint of flare
