BCSC Refractive Surgery Flashcards
What are the two main classes of refractive surgical procedures?
1) Corneal
2) Lenticular
What are 3 types of maps produced in corneal topography?
1) Axial power and curvature
2) Instantaneous power and curvature
3) Mean curvature
What parameter is used to described the asphericity of a cornea?
Q-value (Q=0 for spherical cornea, Q < 0 for prolate cornea, Q > 0 for oblate cornea)
What is “forme fruste keratoconus?
Subclinical keratoconus
Are patients with keratoconus commonly considered for refractive surgery?
No, unpredictable and often negative responses to procedures usually preclude patients with keratoconus from refractive surgery.
Can irregular astigmatism be corrected with spherocylindrical lenses?
No (the principal axes, highest and lowest power, are not orthogonal to each other)
What is one indication of irregular astigmatism during a refraction?
Inability to identify the axis meridian of the astigmatism
Where does corneal protrusion occur in a patient with Pellucid Marginal Degeneration?
The thinning occurs at the superior or inferior margin of the cornea, and the thinning occurs above the thinning in both cases.
Where does corneal protrusion occur in a patient with Keratoconus?
At the point of maximal thinning.
Defocus (positive or negative) and astigmatism are considered aberrations of what order?
2nd order
Does myopia produce positive or negative defocus?
Positive. (Hyperopia produces negative defocus)
Do the lamellae of collagen fibrils comprising the cornea slide easily over one another?
Yes
Does the corneal stroma distribute tensile stress equally throughout its thickness?
No
Which lamellae of the corneal stroma take up the strain in the healthy or edematous state?
anterior lamellae
Which lamellae of the corneal stroma take up the strain in the dehydrated state?
posterior lamellae