Photorefractive keratectomy after DMEK for corneal decompensation by phakic IOL

Purpose To provide the first description of photorefractive keratectomy (PRK) for the correction of mild residual refractive error after Descemet membrane endothelial keratoplasty (DMEK). Methods Case report. Results A 45 year-old woman presenting with phakic intraocular lens (PIOL)-related corneal decompensation underwent staged DMEK surgery following PIOL explantation and cataract surgery. Eighteen months after DMEK, uncorrected distance visual acuity (UDVA) was 20/60 and best-corrected visual acuity (BCVA) was 20/22, with a stable refraction. The patient requested refractive surgery to decrease spectacle dependance, and wavefront-optimized PRK was performed. At last follow-up observation thirty-three months after PRK (54 months after DMEK surgery), UDVA was 20/20, the cornea remained clear without signs of rejection or endothelial failure, and the endothelial cell loss rate was not accelerated after PRK. Conclusion Since long-term visual and refractive stability can be expected after DMEK, PRK may be a particular safe and effective approach for the correction of mild residual refractive errors after DMEK. However, we consider that surgeons must exercise caution when considering keratorefractive surgery in these eyes due to postoperative changes in corneal curvature and thickness, and further studies are encouraged.

Endothelial cell loss rate after penetrating keratoplasty: Optical versus therapeutic grafts

Background: This study aimed to compare the rate of endothelial cell loss (ECL) after penetrating keratoplasty (PKP) for optical versus therapeutic grafts at 3-, 6-, and 12-month postoperatively. Furthermore, the study aimed to investigate postoperative graft viability and the rate of graft rejection during the first year of follow-up for both indications. Methods: This was a prospective, observational, comparative study that included patients who sought medical advice at the cornea outpatient clinic of Ain Shams University Hospitals, Cairo, Egypt. The study recruited 60 patients: group 1 included 30 transplanted corneas of 30 patients who underwent optical PKP for various indications, while group 2 included 30 transplanted corneas of 30 patients who underwent therapeutic PKP for unhealed, resistant infectious keratitis. Specular microscopy was performed for all patients at the 3-, 6-, and 12-month follow-up visits using Nidek CEM-530 specular microscopy. Postoperative clinical examinations were performed at the same follow-up visits to detect graft rejection. Results: There were no statistically significant differences between the groups concerning the postoperative timing of graft clarity or the rate of ECL at 3- and 6-months postoperatively; however, the rate of ECL was significantly greater in group 2 than in group 1 at 12-months postoperatively (P = 0.03), although the difference was small from a clinical point of view. Moreover, there was no statistically significant difference between the groups in terms of the graft rejection rate. Conclusions: Therapeutic PKP results were comparable to optical PKP with respect to graft viability, the rate of ECL, and the rate of graft rejection 1 year after grafting. How to cite this article: Shams A, Abdelmoneim Gaafar A, Elkitkat RS, Omar Yousif M. Endothelial cell loss rate after penetrating keratoplasty: Optical versus therapeutic grafts. Med Hypothesis Discov Innov Ophthalmol. 2021 Summer; 10(2): 74-79. https://doi.org/10.51329/mehdiophthal1424

Endothelial cell density change in fully dislocated XEN Gel IMPLANT after trabeculectomy: A case report

Purpose: To report a case of fully dislocated XEN Gel Implant device into the anterior chamber, 18 months after its implantation and its impact on endothelial cell density. Result: A 75-year-old man with a history of multiple glaucoma surgeries during the last three years presented with an entirely dislocated XEN Gel implant into the anterior chamber. An endothelial cell density reduction was observed over 18 months. Thus, the implant was removed. In the short-term after surgery, the endothelial cell loss rate reduced. Conclusion: XEN Gel Implant can dislocate into the anterior chamber, increasing endothelial cell loss in an eye already underwent multiple surgical procedures with subsequent adverse events. Therefore, if the implant seems displaced, the endothelial cell density should be monitored, and the length of the free-tube segment within the anterior chamber should be measured, during the patient’s follow-up.

Performance of a new bus assignment algorithm for an ATM switch fabric

This paper presents the results of the performance evaluation, through analytical and simulation models, of a High Speed Packet Switch with a New Bus Assignment Algorithm, designed and developed at the Research and Advanced Studies Center of National Polytechnic Institute in Guadalajara, México (CINVESTAV-GDL). The analytical model is tested under two different arrival processes: Binomial and Poisson distributions. The simulation model is tested with two bus assignment algorithms: Fixed Start and Rotated Start . The performance parameters considered are: Cell Loss Rate, Delay and Throughput.