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Perspective Volume 6 Issue 2
Femtosecond Assisted Lasik for Post PKP Myopic Astigmatism
Bahaa Al Din Jaber
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Department of Cornea Refractive Surgery Bahaa Eye Clinic Jordon
Correspondence: Bahaa Al Din Jaber Department of Cornea Refractive Surgery Bahaa Eye Clinic Amman Jordan
Received: January 23, 2017 | Published: February 8, 2017
Citation: Jaber BAD (2017) Femtosecond Assisted Lasik for Post PKP Myopic Astigmatism. Adv Ophthalmol Vis Syst 6(2): 00175 DOI: 10.15406/aovs.2017.06.00175
Introduction
High residual refractive error can be a disappointing end point to an otherwise successful penetrating keratoplasty, it can prevent the patient attaining satisfactory visual acuity.
Causes of astigmatism post PKP
- Size and shape difference between donor and host
- Eccentric placement
- Scarring at graft host junction
- Asymmetric forces in the cornea resulting in altered shape
Astigmatic patterns
- According to ESCRS istanbul (Dr Rudy niujts)
- 4 to 5 D and anisometropia
- 30% shows > 5 D
- 25% regular
- 75% irregular
Vision correction options after keratoplasty
Non surgical
- Spectacles.
- Contact lenses
- Surgical
- PRK … (disadvantage) haze and scar.
- Corneal relaxing incision, wedge resection, along with ± compression sutures…….. (disadvantage) Wound dehiscence, corneal topographic changes, low predictability of the results, lack of internationally accepted nomograms.
- Lasik using microkeratome or femtosecond laser.
- Implantable contact lenses.
- ICRS
- Femtosecond laser–assisted
- Intrastromal corneal ring
- Segment implantation for high
- Astigmatism correction after
- Penetrating keratoplasty
- Carlos Lisa MD, Miriam García-Fernández MD, David Madrid-Costa PhD, Leonardo Torquetti MD, PhD, Jesús Merayo-Lloves MD, PhD, José Fernando Alfonso MD, PhD correspondence mail
Femtosecond laser
Ultra-short pulse duration (10-15 sec.) has the ability to deliver laser energy with minimal collateral damage to the adjacent tissue (1µm).
Femtosecond laser
- Mechanism of action
- Photo disruption
- FSL energy is absorbed by the tissue, resulting in plasma formation.
- This plasma of free electrons and ionized molecules rapidly expands, creating cavitation bubbles.
- The force of the cavitation bubble creation separates the tissue (Figure 1).
Figure 1 Femto laser.
Femto laser
Why femto?
The only reliable and predictable way of creating the flap within the graft.
Why femto (cont’d)
- Reduced incidence of flap complications like buttonholes, free caps, irregular cuts etc.
- Control over flap diameter and thickness; side cut angle, hinge position and length.
- Increased precision with improved flap safety and better thickness predictability.
- Capability of cutting thinner flaps to accommodate thin corneas and high refractive errors.
Why femto (cont’d)
- Stronger flap adherence.
- Better contrast sensitivity.
- Decreased incidence of epithelial in growth.
- Extremely low incidence of graft wound dehiscence secondary to less increase in IOP required. (20 to 35 mm) compared to microkeratome (55 to 70).
- NB. The fibrotic edge of the graft was also an additional safety factor for us for the prevention of a possible transplant wound rupture.
Why femto (cont’d)
- Lesser incidence of dry eye due to higher epithelial stability.
- Lesser hemorrhage from limbal vessels.
- The ability to retreat immediately if there is incomplete FS laser ablation.
Why Femto?
- It is capable, to a certain extent, of passing through optically hazy media, such as an edematous cornea.
- The laser may be applied in multiple geometric patterns including vertical, spiral, or zigzag cuts.
- It can be focused anywhere within or behind the cornea.
Why Femto?
It is not a blade! (Figure 2).
Figure 2 It is not a blade!
Aim of the study
The purpose of this study is to determine the efficacy and stability of LASIK for the correction of post keratoplasty myopic astigmatism using a femtosecond laser for flap creation.
Study design
- Retrospective study, 40eyes of 35patients
- Time between PKP and femtosecond lasik 18 to 65months mean (41.5)
- Interval at least 8months after suture removal
- AGE: 25years TO 54years MEAN 39.5
- Follow up 1, 3 and 12months
Study design (Cont’d)
All patients were examined pre & post operatively for:
- UCVA
- BSCVA
- Autoreffraction and cycloreffaction(cyclo pre only),
- Corneal topography(TMS4),
- Corneal tomographhy (allegretto occulizer),
- IOP,
- ORA,
- And Pachymetry.
Study design (cont’d)
- Contraindications for refractive intervention include peripheral corneal vascularization, thin host tissue, wound ectasia and significant graft override or malapposition.
- The patient should have a minimal corneal thickness of at least 500μm.
- The possibility of graft rejection was considered and addressed by the use of topical steroids post operatively.
Pre op
- Pre op myopia -3.50 to -7.75D
- Pre op astigmatism -3.00 to -6.00D
- Pre op UCVA CF 3mtr to 0.30
- “The attempted spherical equivalent correction ranged between 60 to 90% of the measured pre op refraction.”
Post op
- Myopia -0.75 to -1.75 D
- Astigmatism -1.25 to -2.25
- UCVA 0.40 TO 0.90
Discussion
- In 3month follow up 75 to 92% reached the attempted correction (±1.00D).
- (Mean increase is 4lines) 3months.
- And in 1 year follow up all of the examined eyes (31 out of 40) gained at least 3lines on snellin acuity tests.
- No pt has lost one line of his original visual acuity.
- One eye exhibited peripheral flap epithelial in growth which didn’t require any flap re lifting.
Data analysis
Se pre op vs post op (Figures 3‒6).
Figure 3 Data Analysis: Se pre op vs post op.
Figure 4 Data Analysis: astig pre vs astig post.
Figure 5 Data Analysis: UCVA pre vs UCVA post.
Figure 6 Effective procedure for pt with myopic astigmatism post PKP.
Conclusion
- Femto lasik is an effective procedure for pt with myopic astigmatism post PKP.
- It is also relatively a safe procedure with minimal complications regarding the surgery itself and the graft.
- However; more work should be done regarding the endothelial cell count and topographic changes over years.
Take home message
- Talk to the patient.
- Determine his needs, expectation
- Use the best and safest technology available to serve the best outcomes.
Acknowledgments
None.
Conflicts of interest
The authors declare that there is no conflicts of interest.
Funding
None.
©2017 Jaber. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and build upon your work non-commercially.