LASIK or Lasik (laser-assisted in situ keratomileusis), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, since it is in the cornea. LASIK surgery is performed by an ophthalmologist who uses a laser or microkeratome to reshape the eye's cornea in order to improve visual acuity. For most people, LASIK provides a long-lasting alternative to eyeglasses or contact lenses. The planning and analysis of corneal reshaping techniques such as LASIK have been standardized by the American National Standards Institute, an approach based on the Alpins method of astigmatism analysis. The FDA website on LASIK states, "Before undergoing a refractive procedure, you should carefully weigh the risks and benefits based on your own personal value system, and try to avoid being influenced by friends that have had the procedure or doctors encouraging you to do so." The procedure involves creating a thin flap on the eye, folding it to enable remodeling of the tissue beneath with a laser and repositioning the flap.

1. LASIK
(LASER ASSISTED IN SITU
KERATOMILEUSIS)
- Surg Lt Cdr (Dr) Prabhjot Singh
AFMC, Pune
1

2. REFERENCES
• Cornea by Jay H Krachmer MD- 3rd Ed
• Refractive Surgery- AAO
• Ophthalmology- Myron Yanoff, MD

3. PREVIOUS QUESTIONS
• LASIK – Principle, advantages and disadvantages. Summer 2009,2012
• Describe recent advances in laser refractive surgery. Winter 2016
• Describe recent advances in keratorefractive surgeries. Winter 2010
• Femtosecond laser in cataract and refractive surgery- Principle, technique, advantages and
disadvantages. Summer 2015
• Excimer laser- Indications. Summer 2010
• Femtolaser. Summer 2013, Winter 2010,2014,2015
• IOL power calculation. Describe IOL power calculation in post refractive surgery patients. Summer
2018, Winter 2016

4. THE SCIENCE OF REFRACTIVE SURGERIES
• Reduces dependence on contact lenses or spectacles
• Appropriate preoperative evaluation to determine the best technique

5. LASIK(LASER ASSISTED IN SITU KERATOMILEUSIS)
• Greek words for “cornea” (kerato) and “to carve” (mileusis).
• combines lamellar corneal surgery with the accuracy of the excimer
laser.
• Involves excimer laser ablation of corneal stroma beneath a hinged
corneal flap that is created with a microkeratome or a femtosecond
laser
• most frequently performed keratorefractive procedure
• because of its safety, efficacy, quick recovery of vision, and minimal
patient discomfort.

6. EXCIMER LASER
• Excited dimer of Argon and Fluoride - releases UV energy at 193nm for
corneal ablation
• photoablates or vaporizes tissue by breaking intramolecular bonds and
generating unstable smaller particles.
• The 193 nm wavelength - optimal for surgical use
• shorter wavelength lasers - technically difficult to produce
• longer wavelength lasers (200 nm and above)- produce undesirable
thermal effects
• MOA- Non thermal Ablative photodecomposition

7. PATIENT SELECTION
• >18 years
• Stable Refractive status for at least 1 year.
• Current FDA approval-
– Myopia upto -12D
– Hyperopia upto +6D
– Astigmatism upto 6D
however the results have been better in lower ranges than in higher ranges
of correction.
• Most surgeons limit levels of correction to less than 8.00–10.00 D of
myopia and 4.00 D of hyperopia

8. • CCT such that minimum safe bed thickness left (250-270µ).
• Post op Corneal thickness should not be <410µ.
• Cornea not too flat or steep <36D or >49D

9. CONTRAINDICATIONS
• Systemic factors-
– Poorly controlled IDDM
– Pregnancy/lactation
– Autoimmune / connective tissue disorders (RA,SLE,PAN etc)
– Clinically significant Atopy, Immunosuppressed patients
– Keloid tendency
– Slow wound healing- Marfans,Ehler-Danlos
– Systemic Infection-(HIV,TB)
– Drugs-Azathioprene,Steroids(Slow wound healing)

10. CONTRAINDICATIONS
• Ocular Factors-
– Glaucoma, RP (Suction Pressure-ON damage, Blebs)
– Previous h/o RD
– One eyed
– Pre-existing dry eye, Keratoconus, pellucid marginal
degeneration, Superficial corneal dystrophy, Uveitis, early
Lenticular changes
– h/o Herpetic Keratitis (one year prior to surgery)

11. PREOPERATIVE EVALUATION PRIOR TO
LASIK
• UCVA and BCVA
• Dry and wet manifest refraction (with 1% cyclopentolate)
• Pupillometry
Large pupil - increased glare
- Can change Optic Zone
• Slit Lamp Examination-
– Rule out blepharitis, miebomianitis, pingecula, Pterygium, corneal
neovascularization
– Other contraindications for LASIK.
• IOP by applanation
• Dilated Fundus Examination

12. • Tear film asessment- Schirmers, TBUT and Lissamine staining
• Blink Rate-(Normal---3-7/min)
• Corneal Topography-
– Stop RGP lenses 2 weeks prior and soft lenses I wk prior
– To rule out early Keratoconus and other ectasias
– For mean K values
• Pachymetry -For CCT
• Contrast Sensitivity testing for pre-operative baseline.

13. OPERATIVE TECHNIQUE
• Suctiion ring
• Flap Creation
• Excimer lase ablation
• Flap Repositioning

15. BASIC STEPS AND MACHINE SPECIFICATIONS
• Topical anasthesia
• Surgical Painting and draping
• Lid speculum with aspiration.
• Corneal marked with two circular markings of 3.0 mm and 3.5 mm, marked with gentian violet and
applied peripherally and inferiorly before creating the corneal flap with the microkeratome to more
easily realign the corneal flap in the event that a free flap is created.
• In addition, the two circles of different sizes provide four-point alignment that will prevent any chance
of the flap being placed epithelial-side down.

18. APPLICATION OF THE PNEUMATIC SUCTION RING
• lid speculum is depressed to proptose
the eye to allow better apposition of
the ring to the globe
• suction ring is then placed on the eye
•
• Patient is warned of a slight feeling of
pressure and discomfort.
• The suction ring is firmly and steadily
depressed downward , while the ring
is twisted slightly in clockwise and
counterclockwise fashion in order to
securely seat and seal the ring.

20. • If the position is adequate, the suction pressure is activated and the
patient is warned that the fixation and other lights may go out
completely and that vision will go dark.
• At this point, four helpful signs assure the surgeon that adequate
suction has been obtained:
1. The suction ring can be lifted toward the ceiling slightly and
the eye should come up with it.
2. The pupil will dilate slightly.
3. The patient will confirm that everything has gone dark.
4. The eye will feel firm to palpation.

22. CHECKING FOR ADEQUATE INTRAOCULAR
PRESSURE
• Raise the IOP to 65 mm Hg which is necessary for the
microkeratome to create a pass and resect the corneal flap.
• This is crosschecked with Barraquers tonometer.

23. INSERTION OF THE MICROKERATOME HEAD
AND CREATION OF THE KERATECTOMY
• Adequate lubrication
• Resection of corneal flap
• Several different
microkeratomes are
available
Microkeratome
Femtosecond Laser
(Intralase)

24. MICROKERATOME
– Uses Disposable blades
– If using a two-piece microkeratome, the head is slid onto the the
suction ring and advanced until the gear on the microkeratome head
engages the track.
– The surgeon then activates the microkeratome using forward and
reverse foot control, the suction is turned off after the microkeratome
pass, and then the suction ring can be carefully removed.

26. FEMTOSECOND LASER FOR FLAP
• uses laser pulses to cause microcavitation bubbles at a preset depth in
the corneal stroma
• The cavitation bubble is composed primarily of water and carbon
dioxide.
• Multiple cavitation bubbles coalesce, and an intrastromal cleavage
plane is created

27. • Creates photodisruption using femtosecond solid state laser with
wavelength of 1053nm.
• Needs lower vacum.
• Very short pulse with spot size of 3µ
• High precision cutting device.
• Any hinge can be made
• Can make flaps as thin as 100µ (Sub BowmannsKeratomileusis)
• Better LASIK outcomes

29. Typically, an applanation cone with an optical glass lens flattens the cornea and
maintains a precise distance from the laser head to the focal point, while a suction
ring provides a docking port on the eye for the applanation cone

30. FEMTOSECOND LASER
ADVANTAGES
• reduced patient anxiety.
• deep-set or small eyes, blepharospasm, or steep or flat corneas
• more control over flap centration, size, hinge location, and hinge
width
• Femtosecond incisions can also be used for lamellar keratoplasty,
penetrating keratoplasty, intrastromal corneal ring channels
Potential disadvantages
• include increased procedure time and expense, possible residual
adhesions
• cavitation bubble migration into the anterior chamber and resulting
interference with excimer ablation, and postoperative transient light
sensitivity syndrome (TLSS).

31. LIFTING OF THE CORNEAL FLAP AND PREPARATION
OF THE STROMAL BED
• Flap is reflected back with either a
blunt, fine tying forceps or a
cyclodialysis spatula
• Some surgeons reflect the flap back
so that the stromal surfaces are
opposed and the epithelial surface is
exposed in a ‘taco’ fashion

32. • Once the flap is reflected- stromal bed carefully inspected for
any irregularities
• A Microsurgical sponge is then used to removed excess fluid
from the bed and obtain uniform hydration.
• Nonuniform hydration would influence refractive predictability
• Assessment of the thickness of the residual corneal bed may
be performed by using ultrasound pachymetry

33. INTRASTROMAL ABLATION
• After flap is lifted, laser is applied to the stroma according
to the ablation profile calculated by the machine.
• Laser beam is delivered by the following ways depending
on the machine-
Beam Delivery
Broad Beam Scanning Slit Beam Flying Spot

34. • Most machines employ a flying spot to deliver laser with
the help of incorporated eye tracker.
• The laser eye tracker and iris registration are activated,
and the laser ablation initiated

37. REAPPROXIMATION OF THE CORNEAL
FLAP
• After irrigating interface ,flap
reposited
• Sweeping movements should be
performed from the hinge toward
the periphery of the flap.

38. FLAP ALIGNMENT
• Ends of the previously placed alignment marks carefully
reapproximated.
• Keratectomy gutter checked along its entire circumference to
ensure that the space between the edge of the flap and the
peripheral cornea is the same throughout
• If Misaligned- refloat the flap to attain better approximation.
• A flap compressor can also be used to smooth wrinkles by
compressing the cornea centrally
• Small misalignments can be easily managed by using a partially
moistened expanded microsurgical sponge to manipulate the flap
into the proper position

40. ADEQUATE ADHESION
• Wait for several minutes - allows for adequate adhesion
methods to ensure firm flap adhesion.
• Striae test - irrigating cannula or spatula is used to depress the peripheral
cornea adjacent to the edge of the keratectomy.
The presence of striae in the flap indicates adequate adhesion.
• Blink test-have the patient blink several times while observing the flap
- if no movement- adhered

41. POSTOPERATIVE CARE
• Topical prophylactic antibiotics and corticosteroids QID for 1–2 weeks.
• Preservative-free lubricating drop
• POD-1 , careful evaluation of the corneal flap
• may resume most activities

42. LASIK FOR MYOPIA
• The normal cornea has a prolate shape (greater curvature centrally than
peripherally
• LASIK for myopia reverse this prolate cornea and decrease the central
corneal curvature to create an oblate shape
• different for hyperopia - ablation is directed toward the periphery of the
underlying stroma with minimal ablation occurring at the center of the
cornea.

43. LASIK FOR HYPERMETROPIA
• More than 4 -5 D - major challenge to the refractive surgeon
• Consider the age of the patient in surgery for hyperopia
• must consider manifest, latent, and facultative hyperopia in planning surgery and to
anticipate the long-term efficacy of the procedure
• It is common for a young patient to have latent hyperopia of 3.0 to 4.0 diopters
exposed by cycloplegia.
• The amount of correction that should be provided during surgery is controversial in
such cases.

44. • Treat 50–75% of the difference between the cycloplegic and manifest refraction
on the top of the manifest refraction
• Or 100% of the hyperopia obtained by cycloplegic refraction
• If partial correction- pt informed about a return of hyperopia after the onset of
presbyopia

45. • Excimer laser profile is different for hyperopia
• Ablation directed toward the periphery
• The corneal refractive power must be increased to treat hyperopia, whereas it must
be decreased to treat myopia.
• higher risk of developing LASIK-induced neurotrophic epitheliopathy (LINE)
• The higher risk d/t larger flap in hyperopia.

46. INDICATIONS FOR LASIK FOR HYPEROPIA
• 1-4 D of spherical equivalent hyperopia with or without astigmatism.
• Attempted correction for consecutive hyperopia after LASIK for myopia should
be decreased by 0.5 diopter, there is a high risk of overcorrecting the eye back
to low myopia.
• LASIK can also be used effectively to correct consecutive hyperopia after radial
keratotomy (RK).

47. TECHNIQUE AND INSTRUMENTATION FOR
LASIK FOR HYPEROPIA
• requires a large flap diameter, typically larger than 9.0 mm.
• For both primary and consecutive hyperopia, the VISX S2™ or VISX
S3™ excimer laser is used with a 9-mm ablation zone

48. LASIK IN COMPLEX CASES
• LASIK after radial keratotomy
- LASIK to be safe and effective in treating residual myopia and RK- induced
hyperopia.
- However preference is to utilize PRK with MMC as the primary procedure when
dealing with patients after RK
• LASIK after photorefractive keratectomy
- treating eyes with no or low haze after PRK
- typically utilize PRK for the enhancement procedure also

49. LASIK after penetrating keratoplasty
• primary goal - allow spectacle correction.
• risk of corneal dehiscence during the creation of the flap
• as early as 8 months after PKP
• while others advise a minimal period of 2 to 3 y
• careful prep attention to the graft as well as the GHI
• All sutures should be removed prior

50. LASIK enhancements
• Performing Re LASIK
• Undercorrection is the m/c problem following LASIK
• Before enhancement, refractive stability should be present
• use the preoperative refraction in diopters to indicate the number of months to
wait after the initial LASIK
• example- wait for at least 6 months in a patient with a preoperative refraction
of 6 D

51. LASIK AFTER INTRAOCULAR
LENSES
• The surgeries can be staged-with the lens surgery performed first, followed later
by PRK or LASIK
• Alternatively, the LASIK flap can be made at the time of the lens surgery and
lifted several weeks later for the laser ablation

52. INTRAOCULAR LENS CALCULATIONS AFTER
LASIK
• use of postoperative average standard k readings in std IOL power formulas -
substantial refractive errors
• hyperopia being the unexpected surprise in patients who undergo myopic
refractive procedures and vice versa
• The keratometer is inaccurate
- because it measures only the paracentral region, ignoring flatter (after myopic
refractive surgery
- or steeper (after hyperopic refractive surgery )

53. • Methods of calculating corneal refractive power in patients who have had
corneal refractive surgery include
the clinical history method
contact lens over-refraction
videokeratography
corneal tomography/Pentacam
the double-K method
Gaussian optics formula.
• Pentacam software can accurately calculate the front and back surface
powers of the cornea and adjust for any power overestimate and report a
term called equivalent keratometric reading (EKR), which can then be
used in IOL calculations

54. • Clinical history method*
Gold std
algebraically add the surgically induced refractive change to the preoperative K-readings
K = Kpre + Rpre – Rpo
Kpre = preoperative corneal power, Rpre = preoperative refraction, and Rpo = postoperative
refraction
This method cannot be used if
• presurgical K-readings and refractive correction unknown
• postoperative refraction affected nuclear sclerosis-induced or axial length progression myopia
*IOL Power Calculations After LASIK and PRK Giacomo Savini, MD; Kenneth J. Hoffer, MD, FACS;
and Maurizio Zanini, MD https://crstodayeurope.com/articles/2007-apr/0407_09-php/

55. https://iolcalc.ascrs.org/wbfrmCalculator.aspx
Online software

56. COMPLICATIONS OF LASIK
• satisfaction rate of 95.4%,
• with the most common reasons for dissatisfaction being residual refractive error, dry eyes, older age,
and night vision symptoms.
• divided into intraoperative, early postoperative, and late postoperative complications

57. INTRAOPERATIVE LASIK COMPLICATIONS
1. Femtosecond laser flap complications
• Cavitation air bubbles
Rx- gentle massage of corneal stroma
• Epithelial breakthrough
• Suction loss during flap creation -
stops the laser creation of the lamellar interface causing an incomplete flap

59. 2. Microkeratome complications
Buttonhole flaps
when the keratectomy perormed without
adequate suction
evident immediately
irregular circle in the center
representing the buttonhole
Management
flap should not be lifted
Gentle interface irrigation
eye is allowed to heal for at least 3 months

60. Thin flaps
tend to roll along the distal cut edge
Management-
If smooth- LASIK can be performed
If not smooth or perforations or buttonholes in the flap- flap should
then be replaced and the cornea allowed to heal for 3 months.

61. Free flap
when the microkeratome does not stop to
create a hinge
but continues across the cornea, severing
the flap from the bed
Management-
If suctionis low and the stromal bed is
irregular- flap replaced and allowed to
heal without performing the excimer laser
ablation
If stromal bed smooth and free cap of
normal thickness- ablation can be
continued

62. C. Corneal perforation
• most feared and rare complication
• Without the depth plate , blade would cut straight into the
cornea,
• causing penetration into the AC
• With extrusion of the intraocular contents due to IOP
• obvious during the advancement of the microkeratome
• sudden release of a jet of fluid as the cornea is penetrated
• followed by a loss of suction with beeping from the suction
pump
• could be a/c extruded iris and/or lens material
Management-
-preserve as much intraocular tissue as possible,
-suturing the corneal incision to restore the AC

63. 3. Laser-related complications
• Incorrect laser programming
• obvious postoperatively - patient does not achieve a good UCVA
• double check programming prior to performing LASIK.
Ablation complications
• Irregular astigmatism
• Beam profile abnormalities
• irregular hydration
• particulate material falling onto the cornea may block subsequent laser
pulses
• Decentration

64. 4.Epithelial defects
• l/t prolonged visual recovery
• postoperative pain
• diffuse lamellar keratitis (DLK)
epithelial ingrowth
Management-
• -continue with the laser treatment,
replace the LASIK flap
• place a BCL if greater than 3 mm
• If extremely large, dont proceed with
the treatment of the second eye

65. 4. Neovascular bleeding during LASIK
occurs immediately after keratectomy along the superior flap edge.
Management
• downward pressure from the suction ring - tamponade
• be dried with a dry Murocel spear.
• Continuous bleeding that could extend into the ablation area, dry rectangles
of instrument wipe
• Iopidine is used as it is an alpha-2 agonist with a vasoconstrictive effect
without the pupillary dilatio.

66. • Prevention- ring can be switched to the 8.5-mm ring so that the neovascular
bleeding can be minimized

67. EARLY POSTOPERATIVE COMPLICATIONS
1. Flap striae-
occur when it is folded onto itself.
Normally-oriented horizontally .
Displaced flaps-oblique striae.
Retroillumination -accurate localization of
striae
Fluorescein staining of the cornea - identifies
subtle striae.

70. Indications for M/nt-
striae that extend through the visual axis
M/nt-
• stretch and smooth technique
• flap hydration with hypotonic saline
• epithelial debridement
• flap applanation
• phototherapeutic keratectomy
• flap suturing

71. 2. Dislodged flap
• extremely blurred vision
• Painful eye
• Patients with a dislodged flap
should be treated as urgently
as possible

72. 3. Infectious keratitis
- infiltrates be cultured prior to starting therapy
- flap lifted- infiltrate removed
- interface irrigated with antibiotic and flap replacement.
- m/c organism- MRSA
Symptoms - pain, photophobia, watering, or decreased visual acuity.
Slit lamp examination- ciliary injection, epithelial defect, AC reaction, or hypopyon
Mycobacteria and fungi- seen in the interface, with a feathery or indistinct margin

73. 4. Diffuse lamellar keratitis
• aka Sands of Sahara
Sands
nonspecific diffuse interface keratitis
LASIK interface keratitis (LIK)
• interface inflammation that occurs in the 24–72-
hour postoperative period
RISK FACTORS-
bacterial endotoxins
Epithelial defects
ocular inflammation
ocular trauma
Other causes - cleaning solutions, talc from gloves,
meibomian gland secretions, microkeratome oil, rust
on instruments, blade debris, iodine skin cleaners,
and CMC drops.

74. • confined to the flap interface
• subtle DLK difficult to differentiate postoperative SPK or mild interface
debris.
• SPK is always on the corneal surface and will stain with fluorescein.
• DLK is at the level of the interface and does not stain with fluorescein.
• There is no AC reaction DLK except in the most advanced cases.

75. Grade 1 DLK
Focal granular material in the LASIK flap
interface
Rx- Intensive topical steroids
Grade 2 DLK
Diffuse granular material
Rx- Interface irrigation, Intensive topical
steroids
Grade 3 DLK
Diffuse, confluent granular material
Rx - Grade 2 Plus Topical steroids and
antibiotics can been placed on the stromal
bed
Grade 4 DLK
Grade 3 plus Inflammation localized
Rx- as Grade 3

77. 5. Transient light sensitivity syndrome
• unusual photosensitivity 2- 6 wks after LASIK performed with FSL
• D/t pulse energy used during flap creation
• Visual acuity is unaffected,
• slit lamp findings are minimal
• steroid therapy

78. LATE POSTOPERATIVE LASIK COMPLICATIONS
1. Epithelial ingrowth
d/t Epithelial cells trapped under
flap
Risk factors -
anterior BM dystrophy
h/o recurrent erosions
Peripheral epithelial defects
Poor flap adhesion
Buttonholed flaps
Repeat LASIK

80. 2. Postoperative keratectasia following LASIK
- after 1 to 12 months
- corrections of over 8 D.
- final corneal thickness of less than 400 µm
- with less than 250 µm of presumed posterior corneal
stroma
Rx-
- hard contact lenses
- PKP
Prevention
- Patients with keratoconus or other corneal thinning
disorders identified on topography should not have LASIK

81. 3. Central islands
area of higher refractive power of more than 1.5 D and 2.5 mm
Rx- Customized wavefront laser correction
4. Night vision disturbances: halos and glare
5. Irregular astigmatism
6. Post-LASIK dry eyes-
-creation of a temporary neurotrophic cornea by severing the corneal nerves
- The cause of the dry eye is decreased corneal sensation withdecreased feedback
to the lacrimal gland with reduced tear production
Rx- frequent lubrication, Punctal plugs in upper punctum , silicone plugs in
the upper punctum, bedroom humidifier and protective sunglasses

82. 7.Vitreoretinal Complications after LASIK
- theoretical risk of increased occurrence of RD after LASIK due to the
alteration of anterior retina by the suction ring
- lattice degeneration (0.3%), posterior vitreous detachment (0.1%),
macular hemorrhage (0.1%), retinal tear without retinal detachment
(0.1%),and choroidal neovascularization (0.1%).

83. EPILASIK / LASEK
• Anterior stroma of cornea (ant. 1/3 rd) has stronger interlamellar connections than
post. 2/3rd.
• So surface ablation preserves the structural integrity better than LASIK especially in
the correction of moderate to high myopia.

84. • LASEK-Camellins Technique-
– 20% absolute alcohol used for 20-35s To raise epithelial flap.
– Flap reposited after ablation

85. EPILASIK
Epithelial keratome used to lift epithelial flap of about
60-80µ thick.

86. THIN-FLAP LASIK
• also referred to as sub Bowmans keratomileusis
• allow LASIK to be done more safely with regard to
ectasia and corneal hypoesthesia
• pendular mechanical microkeratomes
• Femtosecond lasers

87. THANKYOU