CLM - Irregular Cornea Fitting II - Week 7 Flashcards
What are three indications for contact lenses after a corneal graft?
Ametropia
Irregular astigmatism
Refractive anisometropia
-difference of >4.00D
What percentage of grafts with >5.00D astigmatism had irregular astigmatism?
22%
What spectacle and surgical refractive procedure can correct irregular astigmatism?
No spectacle correction or surgical refractive procedure can correct irregular astigmatism apart from regrafting
List three possible causes of irregular astigmatism. What do all three result in and where?
Excessive and variable suture tension
Poor suture alignment
Significant asymmetric host thinning
-all three result in irregular healing at the graft margin
What suture technique generates the most astigmatism and why? Name an advantage of this technique over others.
Single interrupted sutures
-uneven distribution of tension
-surgeons have more control of astigmatism by removing individual sutures
What are five components to assessing a corneal graft for contact lenses?
History
Topography
Slit lamp examination
Slit lamp photography
Pachymetry
List three general graft shapes and describe them.
Prolate - steeper centrally, flatter peripherally
Oblate - flatter centrally, steeper peripherally
Mixed
Describe the C, C, and E mneumonic for RGP lenses.
C - centre - base curve - central fluorescein pattern
C - centration
E - clearance
What is a good base curve to begin with when trialling RGPs?
2/3rds towards the flattest K reading
i.e. 8.1/7.2 - try 7.8
What is a good diameter to begin with when trialling RGPs?
11.2mm
What is considered a small RGP for a corneal graft?
One that fits within or on the graft
List three potential problems that can occur with small RGPs (for corneal grafts). Explain why for each.
Stability - may easily be displaced off the graft
Small optic - may have flare difficulties especially at night
Small diameter - if the lens is displaced, the edge may be visible again, especially at night
What is considered a medium RGP for a corneal graft?
One that fits over the graft
What does the larger diameter of a medium RGP lens allow for vs a smaller one and what does this improve?
Allows for lid attachment with better stability
What may need adjustment with medium RGPs for corneal grafts and why?
May need to adjust peripheral curves to control edge clearance
What does the larger optic of a medium diameter RGP reduce vs smaller RGPs (2)?
Larger optic reduces flare, less interaction with the pupil, especially at night
Is the back surface toric of a medium RGP lens for a corneal graft generally considered? Explain. What is the host astigmatism generally like vs the corneal graft?
Generally not, unless the graft astigmatism is ?5.00D
-generally the host cornea has much less or no significant astigmatism
What is considered a large RGP for a corneal graft?
Corneo-scleral
What does the larger design of large diameter RGPs for corneal grafts allow for the elimination of and how?
Eliminates superior edge interaction via significant lid attachment
What should be aimed for regarding bearing and edge clearance with large RGP lenses for corneal grafts?
Moderate area of central bearing and edge clearance that allows adequate tear exchange
What can excessive edge lift in large diameter RGPs cause?
May cause the lens to displace on excursions
What is a disadvantage of sclerals and minisclerals?
Expensive and time consuming
List some advantages of scerals and minisclerals.
Comfortable
Good vision
Hard to lose
Hard to break
What should you look for at the edge of the lens with sclerals and minisclerals?
Compression of conjunctival blood vessels
-edge lift if so
