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Management Options for Keratoconus and Irregular Corneas
Abstract: This course will introduce practitioners to the use of specialty contact lens
designs, including large diameter and reverse geometry, as well as soft and hybrid
lens designs to manage patients with keratoconus, pellucid marginal degeneration,
post-PK, post-LASIK, and post-RK. Surgical management options will also be
discussed.
I.
Goals of GP Lens Fit
A. Good visual rehabilitation
B. Patient comfort
C. A centered lens
D. No areas of harsh corneal bearing or excessive clearance
E.
Proper tear exchange
II. Base Curve Determination
A. By keratometry
1) Readings are difficult secondary to corneal distortion
2) Range extension with trial lenses (-1.00,+1.25,+2.25 diopters)
B. By topography
1) Provides information on steep/flat areas
2) Provides information on where GP lens will probably position
a. Lens tends to position over steepest portion of cornea
3) Provides a starting point for the selection of diagnostic lenses
C. By fluorescein pattern analysis
1) Use to select subsequent diagnostic lenses
2) Balance between minimal corneal bearing and minimal corneal clearance
3) Aim for acceptable peripheral clearance
III. Lens Parameter Determination
A. Base curve radius
1) Final base curve determination based on:
a.
Fluorescein pattern analysis
b.
Lens position
c.
Lens movement
2) Make changes during follow-up visits based on:
a.
Fluorescein pattern analysis
b.
Corneal staining
c.
Patient’s symptoms
i.
Excessive lens movement
ii.
Lens edge awareness
B. Contact lens power
1) Determine by over-refracting the endpoint diagnostic contact lens and adding
the vertexed equivalent diopter sphere to the power of the diagnostic lens
2) SAM-FAP
3) Residual astigmatism
a.
Bitoric
b.
Front surface toric
c.
Spectacle over-correction
C. Overall diameter
1) Generally larger (10.5mm – 11.2mm) and beyond
a.
To improve lens centration and stability (for example, post-PK & post-RK
cases)
b.
To place the OZD over the visual axis in pellucid marginal degeneration
cases
D. Optic zone diameter
1) Dependent on lens position, lens movement and pupil size
2) Large enough to vault corneal graft
3) Slightly larger than graft diameter in reverse geometry lens designs
E.
Peripheral curve(s)
1) Aspheric design
2) Reverse geometry design for oblate corneas
3) “Flat-steep” design
3) Junction blends
F.
Material selection
1) Post-surgical corneas should be prescribed with high Dk materials, for example
Dk 100
IV. Piggyback lens systems
A. Silicone hydrogels, hydrogels and upcoming products
1) To enhance GP lens centration
2) To improve optics
3) To enhance patient comfort
4) To reduce/prevent 3-9 o’clock corneal staining
B. Hybrid lenses
V. Patient management
A. Corneal health assessment
1) Corneal graft rejection signs
2) RK incision splitting
3) Sodium fluorescein corneal staining
B. Ocular health assessment
1)
IOP measurement, DFE
C. Co-managing with ophthalmologist
VI. Surgical Options
A. Intracorneal segment rings (Intacs)
B. Penetrating keratoplasty
C. Corneal collagen cross-linking with Riboflavin