Collagen Crosslinking

Question 1

Reasons why you’d WANT crosslinking done:

Answer 1

• STOPS the progression of KC, PMD
• KC pts who had KP (keratoplasty/corneal replacement) still needed special correction
• reduces the overall need for surgery/PK

Question 2

PROGRESSION of KC in regards to ASTIGMATISM is manifested of at least ___D w/i a year OR,

a change in the STEEP K of more than ___D w/i a year

Answer 2

1 diopter of astig/yr

1 diopter steeper K/yr

Question 3

T/F: the cornea softens as we age.

-goal of CXL is to increase the ____ of the KC cornea

Answer 3

FALSE - it becomes more STIFF.

-softening may occur a bit in a normal KC patient though - the goal of CXL is to increase the STIFFNESS by about 1.5X

Question 4

ENZYMATIC OXIDATIVE DEAMINATION - describes the natural process of the crosslinking of ____ fibers

• how does GLYCATION relate to this?
• T/F: diabetes DECREASES the rate of KC

Answer 4

collagen

glycation: also causes crosslinking; and is more prevalent in DIABETIC patients (hence faster thickening rates to their corneas)
- true. because it increases the thickening rate!

Question 5

what’s the process of crosslinking?

• full effect of the crosslinking procedure takes anywhere from ___hours to ___ weeks
• in the IMMEDIATE part of the process, products released/produced have (inc/dec) resistance to MMP (which would normally breakdown stuff)

Answer 5

UVA hits riboflavin

• ROS generated/released
• free ROS makes AMINO group required for strengthening collagen bond…that’s it!

24 hours - 12 weeks (involves apoptosis and repopulation of keratocytes and epithelium)

-INCREASED resistance - d/t STRONGER bond

Question 6

minimum thickness required on corneal pachy?

Answer 6

400 microns

-effective crosslinking takes place in the anterior 250-300 microns

Question 7

Dresden protocol (epi-OFF): constant drops ____ drops (to soak the cornea) followed by ____ light for ~30 minutes

-Transepithelial (epi-ON) is not as common but is used when?

Answer 7

dresden: drops RIBOFLAVIN, hit w/ UVA light x30 mins

TEP (transepithelial): done when there’s

Question 8

post-op CXL: see the patient on day __, __, and __

-you can expect to see an initial (flattening/steepening) ~1-2 months after the procedure, followed by (flattening/steepening until about 12 months after the procedure

Answer 8

1,3,7 (then 2 wksk, 1 month, 3 and 6 months)

-STEEPENING after 1-2 months, subsequent FLATTENING after that (2-12) months - stroma becomes more compact

Question 9

complications of CXL?

Answer 9

EPI HEALING FAILURE
other:
-delayed epi healing
-hypertrophic epi healing
-remarkable SPKs
-corneal infiltrates
-later: corneal HAZE (central toxic epitheliopathy)

Question 10

GP lenses post-CXL: good idea?

Answer 10

not really…2X INCREASED RISK OF CORNEAL SCARRING (ESP if used prior to full healing), and they have to bear on the cornea somewhere

• use smaller lens w/ apical clearance fit if you must
• larger lenses increase risk of dimple veiling d/t decreased o2 transmissibility
• corneal hypoesthesia up to 3 months is also possible (you have no idea an infection is developing)

Question 11

A bandage CL will be on the eye for __-__ weeks s/p CXL; it should be ___ modulus and well-____ to prevent corneal infiltrates

Answer 11

1-2 weeks

LOW
WELL-CENTERED

Question 12

steep corneas/compromised surfaces are best treated post-CXL with which lens type?

-other lens types available for use post-CXL?

Answer 12

scleral lens - be sure to CLEAR the limbus (epi regeneration) - ensure proper fluid ventilation!

-Sihy mini sclerals, piggybacks, hybrids, and mini-sclerals also available

Question 13

can you perform CXL on a keratoGLOBUS cornea?

Answer 13

no - it’s the whole cornea that’s bulging - CAN do TEP

Question 14

OVERALL GOAL IN CL FITTING AFTER CXL?

Answer 14

DON’T INTERFERE W/ THE NORMAL BIOLOGICAL RECOVERY OF THE CORNEAL SURFACE