Effect of waiting time on corneal thickness and visual outcome after intralase flap creation in pati

1
Effect of waiting time on corneal thickness and
visual outcome after intralase flap creation in
patients with opaque bubble layer

• Priti Manjunath MRCO,DOMS1
• Hung Ming Lee (HML) FRCSEd, MMed(Ophth), FAMS 1
• Poh Wei Ting Eugenie MRCSEd,MMed(ophth) 1
• Manjunath KP FRCSEd, MS,DNB 2
• Chan Siew Pang Phd(Hon)3
• 1 Department of Ophthalmology, Tan Tock Seng
  Hospital, Singapore
• Department of Ophthalmology, National University
  Hospital, Singapore
• 3 Clinical Research Unit, Tan Tock Seng
  Hospital, Singapore.

2
Introduction

• Intralase (femtosecond laser) is a new technology
  for flap creation in LASIK.
• Interaction between the femtosecond laser and
  corneal tissue occasionally forms a bubble layer
  - Opaque Bubble Layer (OBL).
• In such cases the surgeon has to wait for OBL to
  resorb before initiating excimer laser.

3
Objective

• To determine if there is a change in the corneal
  thickness due to this waiting period.
• To determine whether the waiting period affects
  the post op visual outcome in terms of -
• UCVA (un corrected visual acuity),
• BCVA (best corrected visual acuity),
• MR(manifest refraction)
• Predictability

4
Methods

• Randomized prospective study, recruiting 114 eyes
  of 63 patients, operated by a single surgeon
  (HML), between June/July 2006.
• An online ocular coherence pachymetry (OCP) (4
  optics AG) was used to measure corneal
  thickness - in all the patients before flap
  creation.
• Intralase(FS 60) flap created in all patients.
• Depending on the formation of OBL, patients were
  assigned to two groups Group 1-without OBL
  Group 2- with OBL.
• Online OCP repeated in group 1 after flap
  creation and in group 2- after resorption of
  OBL.
• Change in the corneal thickness (pre flap and
  post flap corneal thickness) was compared
  between two groups.
• UCVA, BCVA, MR and predictability was assessed at
  3 months.

5
Materials-pre op patient profile
Group 2 OBL
Group 1 No OBL
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Results-change in corneal thickness
Change in corneal thickness mean pre cut
corneal thickness mean post cut corneal thickness
p0.15
7
Discussion-UCVA (3 months post op)
p 0.14
8
Discussion-BCVA (3 months post op)
p 0.59
9
Discussion-Safety Profile
p 0.95
10
Discussion-Safety Index
Safety indexpost op BCVA/pre op BCVA
Fishers exact test
p0.80
Efficacy index
Efficacy indexpost op UCVA/pre op BCVA
Fishers exact test
p0.16
11
Discussion-Predictability at 3 months post
procedure
p 0.53
Ransksums test
12
Conclusion

• It is safe to wait for the OBL to resorb.
• The waiting time does not significantly
  thicken the cornea and does not have any adverse
  impact on the visual outcome .