Astigmatism correction methods Alireza Peyman, MD .
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Transcript of Astigmatism correction methods Alireza Peyman, MD .
Measurement of astigmatism
• Auto-refraction and retinoscopy• Subjective refraction
• Astigmatic dial• Cross cylinder
• Wavefront PPR• Keratometry
• Automated or manual
• ORA could be calculated
Correction methods
• Glasses• Contacts
• Soft (toric)• RGP• orthokeratology
• Incisional methods• Traditional• FS assisted• full thickness paired incisions
• Intra-corneal inlays• Excimer ablation• Toric pIOLs• Toric IOLs
Glasses
• Easy and difficult!• Cause distortion of images and depth due to dissimilar meridional
magnification in eyes
Easy cases
• Persons that have had astigmatic glasses for years or from childhood• Minor vertical or horizontal astigmats• Monocular patients, and children
Most difficult ones
• New glasses with > 2.5 diopters of oblique astigmatism and enantiomorphism
• Impaired proprioception (diabetics in some stages)
Incisional methods
• AK• Arcuate• Straight
• LRI• Induced wound dehiscence
• After PKP or improperly sutured wounds
• Compression sutures & wedge resection• Paired full 3.2 incision• FS assisted
• Incisional methods mostly used during or after a major intra-ocular surgery like cataract extraction or PKP
Excimer ablation
• Case selection• R/O lens problems
• Lens tilt or subluxation• Lenticonus
• R/O KC
Evaluations
• Inquiry about recent refractive change and FHx of KC are important
• Check both Placido based topographies and elevations
• In Pentacam check • 4 map• Front & Back elevations in detail• Belin enhaced ectasia map• Refractive map for KC indices
• Use front and back Pentacam elevation maps with “toric ellipsoid fixed” reference if you have decided to proceed to surgery.
Measurements
• Always look at autorefraction
• Check subjective refraction and BCVA
• Consider keratometric astigmatism • Amount• Axis
• Check PPR and optical aberrations
• Decide for the amount and axis of the correction seeing all measurements
• Under-correct the power for at least 5% to decrease induced astigmatism due to angle of error of corrections.
• Check, check, and recheck the numbers at each stage.
Determine ablation protocol
• Conventional (Plano-scan)• Tissue Saving• Aspheric• Customized WF guided
WF guided ablation(APT)
• Best for moderately aberrated corneas• Not suitable for highly aberrated eyes
• Removes much higher amount of tissue• Post-op hyperopia may arise
• Not appropriate for patients with non-corneal aberrations
• Crystalline lens opacities• Cloudiness of vitreous
• No benefit in eyes with low aberration
Errors of angle of correction
• Exact alignment of measured angle of astigmatism with angle of correction is of paramount importance for best results in astigmatic correction.
Basis of error in angle alignment
• Position of head and eyes are different in upright measurement phase and supine correction stage.
• Incorrect position of head compared to body in operation cradle.• Misaligned and unlucked operating bed.
• This type of rotation does not occur in supine position.• This phenomenon cause error even if the amount of tilt were similar in
upright and supine positions
Rotational registration
• Manual• Mark 90, 180, and 270 in upright• Re-align with axes in operating bed
• Automated• Iris image registration
Automated Iris registration
• Takes iris image in sitting position• Takes another image immediately before Sx and compensate rotation
comparing two images
Iris registration tips
• Add another image taken in exam room with room lights on• Turn off lights in OR• Align with pupil center exactly• Don’t move head until beginning of ablation
Tips (cont.)
• If registration unsuccessful:• Turn off all lights even of monitor and red green target lights• Use both of two LED IR light sources
• I prefer to remove epithelium before registration for quick continuing of the surgery.
Toric pIOLs & IOLs
• Available options:• Toric phakic artisan• Toric Artiflex• Toric ICL• Toric IOLs of multiple brands• Toric supplement IOLs for sulcus
Drawbacks
• Cost• Availability• Imaginable complications with intra-ocular surgery• Problems with stability of lens