My Fashion Blog

.

Oxygen Permeability of Different Materials (Dk/t)


  • Glass = 0 Dk/t
  • PPMA = 0 Dk/t
  • Boston EO = 31-61 Dk/t
  • Boston XO = 61-100 Dk/t
  • Fluoroperm 151 = 151-200 Dk/t
  • Scleral Lens = 10 – 36.7 Dk/t in center

What if you don’t have an OCT?

An OCT or Optical coherence tomography makes fitting Scleral CLs easier; however, it is not necessary. If you have the pachymetry reading of your patients’ cornea you can use that as a guide to estimate the corneal clearance of the scleral contact in the slit lamp.

If clearance is too low you need to either increase the sagittal depth by steeping the base curve or increasing the diameter. You should always start steep and back down from there approximately 1.00 D STEEPER than patients’ STEEPEST curvature.

You have learned from your own fitting experience that it is important in the initial fit that you leave about 400 um clearance. The reason for this is the scleral elasticity of every person is different. These lenses can settle anywhere between 50 ums to 250 ums in a 4h period and can continue to settle up to 8h.

Limbal clearance – complete and generous limbal clearance ensures good tear circulation. If there is a low limbal clearance, then you must pick a large-diameter lens. If there is too much limbal clearance, then large bubbles will form and a smaller diameter should be used.

Peripheral Curves need to be adjusted to either tighten or loosen the fit of the CL. If the PCs are too tight this can lead to vessel blanching, hyperemia, difficulty removing the lens, fogging and discomfort for the patient. If the PCs are too loose then the seal may come off which cannot be maintained and the lens will not stay on the cornea.

Why would we use Scleral Contacts?

  • Dry Eye
  • Ocular Surface disease
  • Keratoconus
  • High refractive error
  • Irregular Corneas
    • Post Lasik
    • Post RK
    • Post PKP
    • Injury/Scarring

You also have an option of sharingan contact lenses, which are also known as theatrical contact lenses. As the name suggests it is used in theatre mostly and are in no way intended to improve the vision.

Dry Eye/Ocular Surface Disease

  • Advantage – since the scleral contact is filled with preservative-free saline the cornea is constantly bathed in fluid throughout the day.
  • Advantage – since the scleral contact is vaulted over the cornea instead of touching the cornea it does not compromise the integrity of the corneal surface.
  • Disadvantage – lenses are large and difficult to handle.
  • Disadvantage – cost 300 dollars per lens

Keratoconus

  • Keratoconus is a progressive thinning of the cornea secondary to the loss of the collagen fiber integrity. Thinning causes a bulging of the cornea resulting in an irregular corneal surface.
  • Treatment for keratoconus:
    • Rigid Gas Permeable contacts
    • Hybrid Contacts (Duette)
    • Specialty Contacts (Rose K, Rose K2IC, Rose K Post)
    • Scleral Contacts
    • Surgery (Corneal Cross-linking, Intacs, PKP)
  • Advantage – corneal vaulting reduce risk of corneal scarring since the lens does not touch the cornea.
  • Advantage – excellent visual outcome even with advanced keratoconic patients.
  • Disadvantage – difficult to handle
  • Disadvantage – cost
  • Advantage – wide range of powers
  • Advantage – does not compromise corneal integrity
  • Advantage – gives an excellent visual outcome
  • Disadvantage – difficult to handle
  • Disadvantage – Cost
  • Scleral lenses are not difficult to fit if you follow some simple rules.
  • Scleral lenses have improved materials and oxygen permeability to make them safe to fit.
  • They can be a lifesaver for that difficult dry eye patient or irregular cornea.
  • They are usually difficult to handle due to their large size
  • They are not expensive, but worth it for the right patient.



Leave a Reply

Your email address will not be published. Required fields are marked *