Pre op corneal laser

Pre op corneal laser

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  PRE OPERATIVE ASSESMENT FORCORNEAL LASERS PRESENTER:SUMEGHA TOMAR CHAIRPERSON: DR BALMUKUND AGARWAL
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  Introduction • The purposeof 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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  PATIENT SELECTION CRITERIA •Motivated patient • Age >18 years • Optimal range of refractive error • Informed consent • Inappropriate expectations • Ocular abnormalties
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  Inappropriate expectations
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  Ocular abnormalties Absolute contraindications •Keratoconus • Chronic steroid and antimetabolite use for immunosuppression • Glaucoma • Herpes simplex keratitis • Connective tissue disease Relative contraindications • Blephritis • Dry eye • History of uveitis • Chronic eye rubbing • Other ocular surface disease • DM • Single eyed
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  EXAMINATION
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  Ophthalmic examination • Visionassessment - 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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  Ophthalmic examination • Slitlamp biomicroscopy – evaluation of anterior segment • Pupillometry – the pupil size in scotopic conditions. Pupil size both in light and dark (<5 lux) should be measured, preferably with an infrared pupillometer such as the Colvard Pupillometer. • 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. • Posterior segment evaluation.
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  • 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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  • 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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  TOPOGRAPHIC ANALYSIS Keratometry &Computerized Videokeratography Corneal topography can help in the evaluation of extreme corneal curvatures since central keratometry readings flatter than 35D or steeper than 50D after LASIK is felt to be associated with a decrease in quality of vision.
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  K- reading • Lenticularastigmatism 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 button hole flaps.
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  TOMOGRAPHY • ANTERIOR CURVATURE (TOPOGRAPHY ) • ANT. & POST. CORNEAL SURFACE ELEVATION DATA • REGIONAL CORNEAL THICKNESS • BELIN / AMBROSIO DISPLAY FOR EARLY DETECTION OF ECTASIA The Oculus Pentacam is a device that measures lens density and can help define whether or not there is early lens pathology. When used in conjunction with dilated wave front testing it can be helpful in assessing lenticular clarity PENTACAM GOLD STANDARD GIVE ALL ABOVE DATA
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  • wave frontanalysis showed a significant amount of HOAs • Oculus Pentacam lenticular density analysis showed a significant amount of increased nuclear density • It was recommended he need not to undergo refractive surgery with this diagnosis of early cataract formation.
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  Ray tracing aberrometry overallelliptical spot distortion is caused by oblique regular astigmatism, whereas the asymmetrical spot repartition is due to coma-like aberrations.
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  PACHYMETRY measuring thickness ofcornea ULTRASONIC PACHYMETRY Minimum bed thickness (300µ)
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  • After liftingthe flap (typically 110-180 μm) and performing the laser keratectomy in a primary LASIK procedure there is at least 300 μm of corneal tissue posteriorly that has been left untouched. • Going below 250 μm increases the risk of iatrogenic keratoconus which may require corneal transplantation to visually rehabilitate the patient
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  CAUTION
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   All cornealrefractive surgical procedures reduce corneal strength to varying degrees  Excessive corneal weakening can result in non progressive irregular astigmatism or progressive corneal ectasia
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  ECTASIA RISK SCORESYSTEM
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  THANKYOU