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Home التعليم الطبي المستمر تعليم أطباء طب وجراحة العيون
Refractive laser preoperative assessment

Refractive laser preoperative assessment

Dr.Reda Gomah El Garia by Dr.Reda Gomah El Garia
18 فبراير، 2022
in تعليم أطباء طب وجراحة العيون
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المحتويات إخفاء
1 ✍️ unsatisfactory visual outcomes can be minimized by
2 ✍️ In older patients (reduced accommodation), consider
3 ✍️ treatable Refractive error range
4 ✍️ Scoring systems exist to help evaluate risk of post-laser ectasia , the Ectasia Risk Scoring System based on
4.1 ✍️ Keratometric power
4.2 ✍️ Pupil size
4.3 ✍️ Full ophthalmic examination

270d✍️ Most patients have excellent results after refractive surgery.

270d✍️ A small minority of patients have

261d☝️ visual complications
261d☝️ unsatisfactory visual outcomes.

270d✍️ unsatisfactory visual outcomes can be minimized by

261d☝️ careful patient selection
261d☝️ meticulous preoperative evaluation.

270d✍️ Patients with unrealistic expectations or unwilling to accept any level of risk should be excluded.

270d✍️ Identify patients with relative or absolute contraindications to refractive surgery.

270d✍️ Age Lower limit 18–21 yrs

270d✍️ refractive stability (no change or < 0.50 D in 2yrs ) otherwise retreatment is necessary.

270d✍️ No theoretical upper age limit, but presence of cataract would make laser surgery inappropriate.

270d✍️ In younger patients (accommodation normal), aim for perfect distance vision.

270d✍️ In older patients (reduced accommodation), consider 

261d☝️ monovision correction
261d☝️dominant eye perfect for distance
261d☝️fellow eye low myopia for near vision

 Refractive laser preoperative assessment
Refractive laser preoperative assessment
 Refractive laser preoperative assessment
Refractive laser preoperative assessment

270d✍️ treatable Refractive error range

261d☝️ varies according to patient corneal thickness and needs.

261d☝️ On average, +6 D to –12 D covers main range for LASIK, PRK, and .

261d☝️ up to 5 D astigmatism can be treated.

270d✍️ All patients undergo subjective refraction (and cycloplegic refraction, if necessary, especially young hypermetropes).

270d✍️ Pachymetry (Cornea thickness ) a limiting factor for the degree of possible laser correction, especially LASIK.

270d✍️ A minimal residual stromal bed of >250 microns is an accepted figure but not absolute.

270d✍️ Corneal topography is Mandatory in all patients undergoing excimer laser.

270d✍️ 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.

270d✍️ Scoring systems exist to help evaluate risk of post-laser ectasia , the Ectasia Risk Scoring System based on

261d☝️ topography pattern( forme fruste Keratoconus)

261d☝️ residual stromal bed thickness( less than 250 microns)

261d☝️ age( young age below 34 yrs )

261d☝️ preoperative corneal thickness( below 500 microns)

261d☝️ preoperative spherical manifest refraction ( high myopia > 8 D)

261d☝️ PTA ( percent of tissue altered > 40% )

• PTA = (FT+AD)/CCT
• FT( flap thickness)
• AD( ablation depth )
• CCT( preoperative central corneal thickness)

270d✍️ Keratometric power

261d☝️ Myopic treatments cause corneal flattening, and hypermetropic treatments cause corneal steepening.

261d☝️ Optical quality is significantly degraded beyond certain limits of post-operative keratometry.

261d☝️ Accepted values are a minimum of 36 to 38 D after myopic ablations and a maximum of 48 to 50 D after hypermetropic ablations.

270d✍️ Pupil size

261d☝️ Pupil size measurement under mesopic conditions is mandatory.

261d☝️ 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.

270d✍️ Full ophthalmic examination

261d☝️ Particular attention to ocular surface
261d☝️ evidence of dry eye
261d☝️ tonometry
261d☝️ presence of cataract
261d☝️ retinal examination.

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