Finite element analysis of blunt foreign body impact on the cornea after PRK and LASIK.

PURPOSE: To investigate the effect of blunt foreign body impact on a human cornea after photorefractive keratectomy (PRK) and LASIK using a simulation model. METHODS: Computational simulations were performed using a finite element analysis program (LS-Dyna, Livermore Software Technology Corp). The blunt foreign body was set to impact at the center of the corneal surface models (after PRK and LASIK) with thicknesses of 500, 450, 400, 350, and 300 µm. Corneal rupture was assumed to occur at a peak stress of 9.45 MPa and at a strain of 18%. The foreign body projectile was blunt in shape, made from aluminum, contained plastic-kinematic properties, and had a density of 2700 kg/m(3). RESULTS: The projectile was launched at the center of the cornea with velocities ranging from 20 to 60 m/s. The threshold of impact velocities creating rupture in corneal thicknesses of 500, 450, 400, 350, and 300 µm were 33, 32.8, 30.7, 27.9, and 22.8 m/s, respectively, in the PRK model. In the LASIK model, the thresholds creating rupture in the stromal bed of the corneas with thicknesses of 500, 450, 400, 350, and 300 µm were 40, 38.1, 35.6, 31.5, and 26.7 m/s, respectively. The 110-µm corneal flap in the LASIK model ruptured at all velocities. CONCLUSIONS: Ruptures occurred at lower velocities in the PRK cornea model than in the corneal stromal bed of the LASIK model following blunt foreign body impact.

Corneal endothelial cell changes after Ahmed valve and Molteno glaucoma implants.

BACKGROUND AND OBJECTIVE: Changes in corneal endothelial cell (CEC) indices 24 months after Ahmed valve (New World Medical, Inc., Rancho Cucamonga, CA) and single-plate Molteno implants (Molteno Ophthalmic Limited, Dunedin, New Zealand) were evaluated. PATIENTS AND METHODS: This cohort included Ahmed valve (29 eyes) or single-plate Molteno (28 eyes) implants. Preoperative and postoperative central CEC indices were compared. Main outcome measure was endothelial cell count. RESULTS: Twenty-four months postoperatively, no difference in visual acuity improvement or decrease in antiglaucoma medications was observed between groups. The Molteno group showed better postoperative intraocular pressure control (P < .001). An 11.52% (Ahmed) and 12.37% (Molteno) reduction in CEC density (cells/mm(2)) and 3.78 (Ahmed) and 2.48 (Molteno) increase in CEC area (mm(2)) was observed, but no significant between-group difference in CEC density and area or corneal thickness. CONCLUSION: Twenty-four months after Ahmed valve or Molteno implant, statistically significant quantitative (cell density) and minor qualitative (cell area) changes in central CEC were observed. Both groups appeared to have similar CEC damage.

Transition to phacoemulsification at the farabi eye hospital, iran.

PURPOSE: To provide objective evidence on the transition of cataract surgical care at Farabi Eye Hospital, Iran. MATERIALS AND METHODS: Two separate years, 2003 and 2006, were selected for evaluation. One thousand nine hundred fifty-seven surgical records of age-related cataract cases were randomly selected and reviewed. Three hundred fifty-three patients (405 eyes) in 2006 and 125 patients (153 eyes) in 2003 were selected randomly for a follow-up examination. The two phases were compared in terms of surgical routines, patient characteristics and outcomes for statistical differences. P <0.05 was considered statistically significant. RESULTS: The phacoemulsification rate increased from 25% to greater than 90% between 2003 and 2006, rates of corneal incisions and use of foldable intraocular lenses tripled, administration of general anesthesia dropped from 80% to 12%, the outpatient admission rate rose from 5.2% to 71%, 4% vs. 66% of the operations were performed by a senior phacoemulsification surgeon and the number of advanced surgeons changed from 6% to 38% (all P-values < 0.001). In 2006, more patients at the two extremes of age, more patients with poor systemic conditions and myopes underwent surgery (all P-values < 0.05); the cataract surgery volume increased by 49% and post-operative visual acuity improved (P = 0.03) while patient satisfaction was unchanged. CONCLUSION: We objectively documented the transition in cataract surgery technique to phacoemulsification at the Farabi Eye Hospital in the mid-2000s. This was accompanied by significant expansion of the spectrum of cataract surgery candidates and remarkable attainment of surgical skill.