Post LASIK Ectasia

7/25/2019 Post LASIK Ectasia

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Prevention of Post-LASIK Ectasia:What Do We Really Know?

VICTOR

L. CAPARAS

,MD MPH

3rd Asia Cornea Society Biennial Scientific Meeting

Sofitel Philippine Plaza Hotel, Manila, Philippines

29 November 2012


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28-year old/F+0.50 sph 1.50 cyl @170

42.5 X 44.5 @101

609 !m

25.9 !m ablation depth


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Post-LASIK Ectasia Incidence

Number %

Reinstein, 2006 6/5215 0.12

Pallikaris, 2001 19/2873 0.66

Rad, 2004 - 0.2

Condon, 2007 3/140 0.8

Binder, 2007 3/9283 0.01

Sergey, 2006** 13/23,990 0.05

Oliviera, 2006** 6/2500 0.24

Stulting, 2006* >1:5000 -

ESCRS Ectasia Registry, 2006 72 -

Binder, P. Analysis of ectasia after laser in situ keratomileusis: Risk factors. J Cataract Refract Surg 2007; 33:1530-1538.*Data presented at the AAO Meeting 2006

**Data presented at the ESCRS Meeting London 2006

Spadea, 2012 23/4027 0.57

American Eye Center Manila, 2010! 28/25,200 0.1!Unpublished data of LASIK cases using microkeratome, 1995-2010


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The importance of post-LASIK ectasia has to do less with the frequency

with which it occurs but by the threat it poses to the patient's vision

People come in as well patients -- not sick patients -- and to cause such a

destructive, sight threatening condition is unimaginable and is

unforgivable.

The challenge for us is to detect and predict the risk of ectasia before any

procedure is performed

"One of the most controversial issues in refractive surgery"


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Pathophysiology

Refractive surgery alters the biomechanical properties of the corneaSchmack I et al. J Refract Surg 2005; 21:433445 Guirao A. J Refract Surg 2005; 21:176185

" Creation of corneal flap and subsequent tissue ablation, weakens

the anterior stroma, which normally confers more biomechanical

strength to the cornea than the posterior stroma Randleman JB, et al. JRefract Surg 2008; 24:S85S89 Dawson DG, et al. J Refract Surg 2008; 24:S90S96

" Interlamellar and interfibrillar biomechanical slippage occurs in

the postoperative stress-bearing regions of the corneal

stroma, similar to that seen in keratoconus (delamination and

interfiber fracture) Dawson DG, Randleman JB, Grossniklaus HE, et al. Ophthalmology. 2008;115: 21812191

" Continuous stresses, which are caused by intraocular (IOP)

pressure, extra-ocular muscles action, blinking, eye rubbing and

other forces result in unstable stromal bed


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Assessing Ectasia Risk

"Conventional" risk factors:

" Thin corneas

" Thin residual stromal bed: lower limit 250 !m

" Deep ablations

" Thick flaps

" Enhancement treatments

" Preoperative topographic abnormalities

" Young age

Randleman J, Woodward M, Lynn M, Stutling. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology 2008


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Renato Ambrsio, Jr, MD, PhD; Daniel G. Dawson, MD; Marcella Salomo, MD; Frederico P. Guerra, MD; Ana Laura C. Caiado, MD; Michael W. Belin, MD. Corneal Ectasia

After LASIK Despite Low Preoperative Risk: Tomographic and Biomechanical Findings in the Unoperated, Stable, Fellow Eye. J Refract Surg. 2010;26(11):906-911.


-6.00 sph 1.00 cyl @180

45.20 X 46.30 @86

528 !m

-5.75 sph -1.25 cyl @10

45.70 X 47.10 @94

528 !m

31-year old


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ParameterPoints

4 3 2 1 0

Topography pattern FFKC Inferior steepening/SRA ABT Normal/SBT

RSB thickness (!m) 300

Age (yrs) 18-21 22-25 26-29 >30

CT (!m) 510

MRSE (D) > -14 > -12 to -14 > -10 to -12 > -8 to -10 -8 or less

Cumulative Risk

Scale ScoreRisk Category Recommendations Comments

0 to 2 Low risk Proceed with LASIK or surface ablation

3 Moderate risk

Proceed with caution; consider special

informed consent; safety of surface ablation

has not been established

Consider MRSE stability,

degree of astigmatism,

between-eye topographic

asymmetry, family history

4 or more High riskDo not perform LASIK; safety of surface

ablation has not been established


Ectasia Risk Factor Score System


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-6.00 sph 1.00 cyl @180

45.20 X 46.30 @86

528 !m

-5.75 sph -1.25 cyl @10

45.70 X 47.10 @94

528 !m

! Symmetric bow tie = 0

# RSB: 285 m = 1

# Age: 27 years = 1

! CCT: 528 m = 0

! MRSE


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Challenge: deriving predictive model from rare disorder with limited

data

" Pre-op topography was available in only a subset of cases

" Only 11% of cases had intra-op RSB thickness measurement

" Estimation of RSB rather than measurement, done

" Different practice patterns

" Surgical technique

" Diagnostic technology


Ectasia Risk Factor Score System


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Category Ectasia (n=86) Controls (n=133) P value

Low risk 6 (7%) 117 (88%)


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Belin-Ambrosio Enhanced Ectasia Display

" Comprehensiveectasia screening

display to determine

ectasia susceptibility

" utilizes 3-Dtomography

" anterior elevation

" posterior elevation

" pachymetricdistribution

" other indices


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"Enhanced" Ectasia Screening

BAD: Increased sensitivity of as high as 94% Ambrosio R. et al. Evaluation of corneal shapeand biomechanics before LASIK. INTERNATIONAL OPHTHALMOLOGY CLINICS Volume 51, Number 2, 1138

" However, ectasia may occur without any pre-operative risk factorsBinder PS. J Cataract Refract Surg 2007; 33:15301538 Klein RS et al. Cornea 2006;25:388Y403)

Those corneas that develop ectasia "unexpectedly" are the result of:

" Acceptedsuspected risk factors

" Currentinability to identify corneas at risk

" Unmeasured and unknown factorsthat affect the individual

corneas biomechanical stabilityBinder PS. Analysis of ectasia after laser in situ keratomileusis: Risk

factors. J Cataract Refract Surg 2007; 33:15301538

Those "unknown factors" are not a consequence of changes in corneal

thickness, geometry or IOP but are probably the differences in the

changes in constituent properties of the cornea, i.e., corneal

biomechanics Carlos Dorronsoro et al. Dynamic OCT measurement of corneal deformation by an air puff in normal and cross-


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Corneal Biomechanics: Ocular Response Analyzer

Most significant attempt to date to

provide clinical instrument to monitor

biomechanical response of cornea

" Measures changes in light

intensity reflected from corneaduring applanation produced by

air-puff impinging cornea.

" Derives values of inward and

outward pressure obtained

during dynamic applanation,

" Viscous damping of the

cornea, produces delayed

response, i.e., corneal

hysteresis


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Air pressure

P1: inward applanation

P1: outward applanation

Rebound peak

CRF: 7.5 mmHgmean normal: 10.411.74 mmHg

CH: 8.6 mmHgmean normal: 10.231.88 mmHg



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Reports in the literature raise questions on the sensitivity of the technique

to monitor changes in the biomechanical properties of the cornea DA Luce, JCataract Refract. Surg. 31(1), 156162 (2005). B. M. Fontes et al. J. Refract. Surg. 27(3), 209215 (2011). Y. Goldich, et al. Cornea

28(5), 498502 (2009).

" CH: sensitivity 82%, specificity 72%

" CRF: sensitivity 79%, specificity 85% Ambrosio R et al. INTERNATIONAL OPHTHALMOLOGY CLINICSVolume 51, Number 2, 1138

ORA does not provide a direct measure of corneal deformation upon

applanation, nor a direct measurement of standard biomechanical

parameters that describe the mechanical behavior of a material

" CH values may be specific to measurement method and conditionsrather than representing an unequivocal corneal property

" ORA CH finding may not represent the "true"CH, but instead represents

a hysteresis value better described as central, applanation-derived

hysteresis, which is based on a very short unloading/loading sequenceMcMonnies CW.Assessing corneal hysteresis using the Ocular Response Analyzer. Optom Vis Sci. 2012 Mar;89(3):E343-9.

http://www.ncbi.nlm.nih.gov/pubmed?term=McMonnies%20CW%5BAuthor%5D&cauthor=true&cauthor_uid=22198797


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Long-term safety and efficacy follow-up of prophylactic higherfluence collagen cross-linking in high myopic laser-assisted insitu keratomileusis AJ Kanellopoulos. Clinical Ophthalmology 2012:6 11251130

Methods: !" $%$& '( ()$ *+,-.$(/+0 +1 23456 )'7 *8+&&9./0:/0; ()8+6D myopia, >1D astigmatism,


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Accelerated corneal crosslinking concurrent with laser

in situ keratomileusis H. Ugur Celiket al. J Cataract Refract Surg 2012; 38:14241431

Method: Patients had LASIK with concurrent accelerated CXL in 1 eye and LASIKonly in the fellow eye to treat myopia or myopic astigmatism.

" 12-month follow-up

" Attempted correction (spherical equivalent) -5.00 to -8.50 D in LASIKCXL

group and from -3.00 to -7.25 D in LASIK-only group" Main outcome measures: manifest refraction, uncorrected (UDVA) and

corrected (CDVA) distance visual acuities, and the endothelial cell count.

" Used KXL System(Avedro Inc.): 30 mW/sec for 3 minutes

Results: Eight eyes of 3 women and 1 man (age 22-39 years old) enrolled

" At 12-months, LASIKCXL group had UDVA and manifest refraction equal toor better than those in the LASIK-only group.

" No eye lost 1 or more lines of CDVA at the final visit

" Endothelial cell loss in the LASIKCXL eye not greater than in the fellow eye

" No side effects associated with either procedure.


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Post-LASIK "prophylaxis"

Long-term studiesof corneal CXL to treat keratoconus show riboflavin-

mediated CXL can stabilize diseased corneas for more than 3 years

" One may anticipate that the application of riboflavinUVA CXL in a

healthy eye would result in similar stabilization.

With LASIK flap already open, application of riboflavin to stromal bedbypasses epithelial barrier and allows rapid diffusion of riboflavin into

surrounding stromal tissue.

Did not appear to affect efficacy and efficiency

" Accelerated CXL did not appear to affect the LASIK algorithms, and

LASIKCXL patients had similar or better outcomes than patients having

LASIK only

" The use of a uniform, high-powered UVA light source provides rapid

activation of CXL with little interruption in the flow of the procedure.

AJ Kanellopoulos. Clinical Ophthalmology 2012:6 11251130

H. Ugur Celiket al. J Cataract Refract Surg 2012; 38:14241431


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How sure are we of the long-term benefit of CXL?

Are we sure that there are no long-term adverse effects of CXL?

Does the benefit of routine use of CXL outweigh the risks, especially

since ectasia is a relatively rare occurrence?

What parameters do we use in applying the prophylactic treatment?

Post-LASIK "prophylaxis"


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Conclusion

Despite improved detection with current screening protocols, there is a

definite need for further development of better screening tests

Current and evolving diagnostic techniques such as three-dimensional

corneal tomography and biomechanical measurements aid therefractive surgeon and lead to more accurate identification of risk for

ectasia

The ultimate goal is to identify Individualized level of susceptibility or

predisposition for developing ectasia

While interesting and promising, prophylactic collagen cross-linking at

the time of the LASIK procedure needs additional information about the

long-term effects of CXL, and its effects on the visual results of LASIK


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Thanks for your attention

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Post LASIK Ectasia