✍️ Most patients have excellent results after refractive surgery.
✍️ A small minority of patients have
☝️ visual complications
☝️ unsatisfactory visual outcomes.
✍️ unsatisfactory visual outcomes can be minimized by
☝️ careful patient selection
☝️ meticulous preoperative evaluation.
✍️ Patients with unrealistic expectations or unwilling to accept any level of risk should be excluded.
✍️ Identify patients with relative or absolute contraindications to refractive surgery.
✍️ Age Lower limit 18–21 yrs
✍️ refractive stability (no change or < 0.50 D in 2yrs ) otherwise retreatment is necessary.
✍️ No theoretical upper age limit, but presence of cataract would make laser surgery inappropriate.
✍️ In younger patients (accommodation normal), aim for perfect distance vision.
✍️ In older patients (reduced accommodation), consider
☝️ monovision correction
☝️dominant eye perfect for distance
☝️fellow eye low myopia for near vision
✍️ treatable Refractive error range
☝️ varies according to patient corneal thickness and needs.
☝️ On average, +6 D to –12 D covers main range for LASIK, PRK, and .
☝️ up to 5 D astigmatism can be treated.
✍️ All patients undergo subjective refraction (and cycloplegic refraction, if necessary, especially young hypermetropes).
✍️ Pachymetry (Cornea thickness ) a limiting factor for the degree of possible laser correction, especially LASIK.
✍️ A minimal residual stromal bed of >250 microns is an accepted figure but not absolute.
✍️ Corneal topography is Mandatory in all patients undergoing excimer laser.
✍️ Eyes with features of ectatic disease on topography (keratoconus, pellucid marginal degeneration, and forme fruste keratoconus) excluded, since laser ablation can cause further weakening of cornea, leading to further ectasia.
✍️ Scoring systems exist to help evaluate risk of post-laser ectasia , the Ectasia Risk Scoring System based on
☝️ topography pattern( forme fruste Keratoconus)
☝️ residual stromal bed thickness( less than 250 microns)
☝️ age( young age below 34 yrs )
☝️ preoperative corneal thickness( below 500 microns)
☝️ preoperative spherical manifest refraction ( high myopia > 8 D)
☝️ PTA ( percent of tissue altered > 40% )
• PTA = (FT+AD)/CCT
• FT( flap thickness)
• AD( ablation depth )
• CCT( preoperative central corneal thickness)
✍️ Keratometric power
☝️ Myopic treatments cause corneal flattening, and hypermetropic treatments cause corneal steepening.
☝️ Optical quality is significantly degraded beyond certain limits of post-operative keratometry.
☝️ Accepted values are a minimum of 36 to 38 D after myopic ablations and a maximum of 48 to 50 D after hypermetropic ablations.
✍️ Pupil size
☝️ Pupil size measurement under mesopic conditions is mandatory.
☝️ large pupils in mesopic conditions (6 to 7 mm) tend to be associated with increased optical aberrations, and so a larger laser treatment zone may be preferable.
✍️ Full ophthalmic examination
☝️ Particular attention to ocular surface
☝️ evidence of dry eye
☝️ presence of cataract
☝️ retinal examination.