Preoperative evaluation for LASIK & PRK

Preoperative evaluation for lasik and prk

ByDr. Mohammad Mousa

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.

Evaluation

• History

– Age

– Sex

– Occupation

– Stability

– expectation

– General health

– Ocular health

• Absolute general health contra-indications

• Relative general health contra-indications

• Absolute ocular health contra-indications

• Relative ocular health contra-indications

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.

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.


• 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.


• 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.

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.

Absolute ocular health contra-indications

• History of ocular inflammatory diseases.

• Herpatic ocular disease

• Sjo ِgren’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.

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.

• 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.

Contra-indicated eye examination findings

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.


• 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


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.

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.

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.

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

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.

THANK YOU

Preoperative evaluation for LASIK & PRK

Health & Medicine

Transcript of Preoperative evaluation for LASIK & PRK