scleral lenses Flashcards
Scleral lens diameter can range between ..
15-25mm
Average corneal diameter is 11.8m
what are scleral lenses
Large diameter GP that vault over the entire cornea and rest on the sclera
-Minimum or no contact on the cornea
-Can be used to treat a number of diff conditions by vaulting over an irregular or diseased corneal surface
Different scleral categories
-corneo-scleral
-semi-scleral
-mini-scleral
-scleral
function of scleral lens
-maintains corneal hydration
-masks irregularities in corneal shape
-reduce pain from corneal diseases
features of scleral lenses that make them different from GPs
-The large size makes them more stable on the eye which contributes to increased comfort
-does not touch the cornea / sits on sclera instead
-diameter is much bigger
-less movement
canidadtes for scleral lenses
-corneal ectasias
~keratoconus
-altered corneal shape
-severe dry eyes
-high refractive errors
why are scleral lenses not popular?
-lack of comfort or expertise to fit
-lack of appropriate technology to fit accurately
-expensive
-fragile
3 zones of scleral lens design
-haptic surface AKA landing zone
-optical zone
-transitional zone
optical zone
-contains the refractive correction
-can be customized for optical vision: aspheric front surface. wavefront guided
-responsible for the creation of a vault - a liquid filled space over the cornea
what is the term for vault
sagittal depth
-space between the scleral lens and the cornea
-increase the sag depth causes the lens to “lift” off the eye, which increases the vault of the lens
transitional zone
-connects the optic and landing zones
-may contain multiple curves
-can be customized to adjust the fluid reservoir depth over the mid-peripheral cornea and limbus
landing zone / haptic zone
-contacts the conjunctival tissue overlying the sclera
-the size and angle can be customized
~influences characteristic like seal off, centration, suction
technology for sclera lens fitting
-anterior segment OCT
-scleral topography and tomography
-impression based lenses
anterior segment OCT
-most practitioners would NOT fit scleral lenses w/o an anterior segment OCT
-the fitting relationship cannot be fully evaluated with biomicroscopy alone
what can anterior seg OCT assess?
-sag depth
-limbal clearence
-landing zone position
-corneal health
scleral topography and tomography
-maps out the shape of the sclera
-allows for the creation of a customized scleral lens
-results in a highly accurate scleral lens fit
-topography = 2D image
-tomography= 3D image
impression based lenses
creates an exact replica fo the corneal surface from an impression
intial lens selection based on two things..
-diagnostic fitting
-empirical fitting
diagnostic fitting
Must consider
-overall lens diameter
-sag depth
-posterior lens surface profile
empirical fitting
-provide clinical finding using clinical software or speaking with a consultant and they design the lens for you
4 steps to scleral lens evaluation
- central clearance
- limbal clearance
- landing zone alignment
- edge lift
central clearance or vault evaluation
-OCT
-target 200-300 micrones of central clearance but can go higher.
-slit lamp
-use scleral lens fit scales
-adjust sag depth as needed
-increased sag depth = increased clerance / making a lens “steeper”
limbal clearance
-adequate limbal clearance is necessary to protect the hydrate and protect limbal cells
two types of limbal clearnece
- Adequate
-fluroscein at limbal area - Inadequate
-beraing - black at limbal area
