preoperative evaluation for LASIK & PRK. Lecture by Dr.Mohammad Mousa in Ibn Alheatham Eye Teaching Hospital, Iraq.2013

1. Preoperative
evaluation for
lasik and prk
By
Dr. Mohammad Mousa
Page 1

2. Introduction
• The purpose of the pre-operative
assessment is:
1. • To determine by physical measurement
whether it is possible to correct a patient’s
individual refractive error.
2. • To determine by examination whether the
ocular health is adequate for this procedure.
3. • To identify if there is any increased risk of
complications specific to that patient.
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3. Evaluation
• History
– Age
– Sex
– Occupation
– Stability
– expectation
– General health
– Ocular health
Page 3

4. • Absolute general health contra-
indications
• Relative general health contra-
indications
• Absolute ocular health contra-
indications
• Relative ocular health contra-
indications
Page 4

5. Absolute general health
contra-indications
• Auto-immune disease e.g. RA,SLE, Thyroid
disease.
• Immune suppression – HIV or immune
suppression drugs.
• Pregnancy-wait 6 months after giving birth or
cessation of breast feeding.
• Systemic steroids
• Amiadarone
• 5-Hydroxy-tryptamine e.g. sumatriptan –
there is an increased risk of vascular
occlusion when the intraocular pressure is
raised during treatment.
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6. Relative general health contra-
indications
• Tricyclics or lithium-based medication-the need
for such medication indicates that the patient
may have obsessive or compulsive personality
or is suffering from a significant level of
depression. These patients can have
expectations of surgery that are too high and
are unlikely to be satisfied following surgery.
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7. Relative general health contra-
indications
• Diabetes – diabetics can have an increased
risk of epithelial complications after Treatment.
Eyes which have signs of diabetic retinopathy
are contra-indicated.
• Active atopy – any active or uncontrolled
atopic disease would be contraindicated until it
is well controlled.
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8. Relative general health contra-
indications
• Epilepsy – the patient must be able to remain
relatively still during the procedure. Therefore,
only patients that have not had an epileptic
episode for 12 months or more may be
considered for treatment.
• • History of frequent fainting – these patients
may have a low threshold for vasovagal attack.
Patients that have a low oculocardiac reflex
would also be unsuitable.
• • Hepatitis B and C – patients with these
conditions will not be considered for surgery in
many clinics due to the potential risk to surgical
staff.
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9. Absolute ocular health contra-
indications
• Diabetic retinopathy – this is an absolute
contra-indication as it can accelerate the
progression of diabetic retinopathy.
• Glaucoma – During LASIK treatment, the
intraocular pressure (IOP) is raised to above 65
mmHg which may cause further damage to the
optic disc. The topical steroids used
postoperatively may also affect IOP
• Corneal thinning dystrophies e.g.
keratoconus – in dystrophies where the cornea
is abnormally thin, LASIK would reduce the
corneal thickness.
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10. Absolute ocular health contra-
indications
• History of ocular inflammatory diseases.
• Herpatic ocular disease
• Sjogren’s syndrome – these patients will have acute dry eye
and their symptoms will be exacerbated by treatment.
• Fuch’s endothelial dystrophy – endothelial decompensation
and poor flap adhesion has been associated with this
condition.
• Unstable refractive error – the prescription must be fairly
stable before treatment is considered. A change of more
the 0.50 D equivalent in 12 months or less is deemed
unstable.
• Visually significant cataract – in cases where there is a
significant lens opacity, cataract surgery with IOL implant
provide good alternation to laser procedure.
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11. Relative ocular health contra-
indications
• Dry eye – in some patients their condition may
be temporarily worse after Treatment.
• Blepharitis – all signs of blepharitis must be
absent prior to treatment as it may induce
postoperative inflammation.
• Nystagmus – not all lasers have a tracker that
can keep up with the involuntary eye
movements associated with nystagmus.
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12. Contra-indicated eye examination
findings
• Unaided vision – patients with very good
unaided vision and who only need spectacles
to correct presbyopia are not suitable .
• Binocular vision status – if the patient has
prism controlled diplopia or where
decompensate heterophoria is corrected by
the use of prism in spectacles.
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13. Ophthalmic examination
• Vision assessment - VA - the level of vision
achieved with and without spectacle correction.
• Refraction – manifest and cycloplegic
refraction where necessary.(young)
• Focimetry of spectacles – together with the
refraction results, it can be used to check
prescription stability over a period of time.
• Ocular dominance testing – this is carried out
on all patients but is particularly relevant with
presbyopic patients who are considering
monovision.
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14. Ophthalmic examination
• Tonometry – the IOP is measured as part of the
examination to check for suitability for treatment and
as baseline data.
• Tear film assessment – the patient’s tear quality and
quantity will be evaluated.
• Anterior eye examination and dilated fundoscopy.
• Pupillometry – the pupil size in scotopic conditions.
• Pachymetry – the corneal thickness is measured
• Specular microscopy. For corneal endothelial state
• Orbit Configuration: Patients with small or
Deep-set orbits and narrow palpebral fissures should
be discouraged from having LASIK
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15. Ophthalmic examination
corneal curvature: Several different methods
are available to analyze the corneal curvature.
 Wavefront aberrometry – is a technique that
can provide an objective refraction
measurement and used in measure the optical
aberrations of the eye. Certain excimer lasers
can use this wavefront analysis information
directly to perform the ablation, a procedure
called wavefront-guided, or custom, ablation.
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16. Near vision
 presbyopic patients must understand that
reading spectacles will still be necessary after
LASIK/PRK to correct their distance vision
unless they opt for monovision.
 Myopes, aim is to undercorrection of the less
dominant eye.
 hypermetropes it would mean overcorrection,
which will probably worsen the unaided distance
vision in the eye that has been corrected for
near vision tasks.
 If the patient refuses to accept these options,
then they are not suitable for LASIK/PRK.
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17. K- reading
 Lenticular astigmatism
 Flat corneas (flatter than 40.00 D) increase
the risk of small flaps and free caps.
 steep corneas (steeper than 48.00 D)
increase the risk of buttonholeflaps.
 Excessive corneal flattening (flatter than
approximately 34.00 D) or excessive corneal
steepening (steeper than approximately 50.00
D) after refractive surgery may increase the
risk of poor-quality vision. Page 17

18. Postoperative
keratometry
 Postoperative keratometry for hyperopic
patients is estimated by adding 100% of the
refractive correction to the average
preoperative keratometry reading.
 Postoperative keratometry for myopic
patients is estimated by subtracting
approximately 80% of the refractive
correction from the average preoperative
keratometry reading
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19. Page 19

20. Residual Stromal Bed Thickness
(RSBT)
• Residual stromal bed thickness (RSBT) is
calculated by taking the preoperative central
corneal thickness and subtracting the flap
thickness and the calculated laser ablation
depth for the particular refraction
• Each 1 refractive error subtracting 10micro-
m from SBT.
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21. Page 21

22. THANK YOU
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