To determine if the residual corneal stromal bed of 250 micrometer is enough to prevent iatrogenic keratectasia in laser in situ keratomileusis (LASIK), we studied 958 patients who underwent LASIK from April 2000 to October 2003 retrospectively. The estimated probabilities of the residual stromal bed, that was less than 250 micrometer, were calculated using the published flap thickness data of Moria C&B microkeratome. Then we calculated the ratio of the real incidence of keratectasia to the expected the percentage of the patients with less than 250 micrometer residual stromal bed in our study. Using the LASIK flap thickness data of Miranda, Kezirian and Nagy, the expected probabilities that the residual stroma would be less than 250 micrometer were 8.8%, 4.3% and 1.5% of the 1,916 eyes respectively, while keratectasia developed in both eyes (0.1%) of 1 patient in our study. The estimated ratio of the keratectatic eyes to eyes with less than 250 micrometer stromal bed were 1.2-6.9%. Compared to the number of eyes with residual stromal thickness less than 250 micrometer, the incidence of keratectasia was relatively low. The residual stromal bed thickness of more than 250 micrometer may possibly be safe, but further observations for long period are necessary.
Postoperative Complications/*prevention & control ; Middle Aged ; Keratomileusis, Laser In Situ/*adverse effects ; Iatrogenic Disease/*prevention & control ; Humans ; Dilatation, Pathologic ; Corneal Stroma/*pathology ; Corneal Diseases/etiology/*prevention & control ; Adult

Biomedical Research ; Blindness ; etiology ; prevention & control ; surgery ; Corneal Diseases ; complications ; prevention & control ; surgery ; Corneal Transplantation ; education ; methods ; Education, Medical, Graduate ; Health Promotion ; Humans ; Ophthalmology ; education ; Singapore

The purpose of this study was to compare the effects on astigmatism after penetrating keratoplasty with three different suture techniques. In this prospective study, 38 eyes of 38 patients underwent penetrating keratoplasty with three suturing techniques: interrupted, single running, and double running. Topographic astigmatism was measured at 2, 6, 12, and 18 months after keratoplasty. During 18 months after surgery, the interrupted suture group had higher astigmatism than the double running suture group. There was no significant difference in the amounts of astigmatism during the first year after keratoplasty between the single running and the double running suture group. However, at 18 months after surgery, when all sutures were out, the double running suture group (3.60+/-1.58 diopters) showed significantly less astigmatism than the single running group (5.65+/-1.61 diopters). In conclusion, post-keratoplasty astigmatism was the least in the double running suture group of the three suturing techniques at 18 months after penetrating keratoplasty.
Adult ; Astigmatism/etiology/*prevention & control ; Corneal Diseases/surgery ; Corneal Topography ; Female ; Humans ; *Keratoplasty, Penetrating ; Male ; Middle Aged ; Postoperative Complications ; Prospective Studies ; *Suture Techniques ; Time Factors ; Visual Acuity

This essay explains the essential principle for the determination of oxygen permeability by the FATT method, and introduces the specific testing procedure and the method for data processing.
Algorithms ; Contact Lenses, Hydrophilic ; standards ; Corneal Diseases ; etiology ; prevention & control ; Humans ; Materials Testing ; methods ; Oxygen ; metabolism ; Oxygen Consumption ; physiology ; Permeability