ABSTRACT
Objective:This paper studied the electromagnetic-driven pressure control system in the automatic measurement of intraocular pressure (IOP).The accuracy of pressure control directly impacts on the accuracy of IOP measurements,so it calls for precise pressure to achieve closed-loop control.Methods:According to the actual needs of IOP measuring,we got the structural and electromagnetic parameters of the electromagnetic drive system by combining the methods of numerical calculation and ANSYS simulation.Using the FC bus and digital-analog conversion,the microcontroller module controlled the drive current digitally and precisely in order to achieve closed-loop control of pressure.Results:The experimental results showed that in the electromagnetic pressure control system,the pressure range was 0 N～0.48982 N,the accuracy 0.00058 N,the drive current control error about 1% on average.Besides,the electromagnetic force and the excitation current showed a good linear relationship in the same stroke.Conclusions:The electromagnetic pressure control system achieved a good result in closed-loop control of pressure.The control pressure range and control accuracy were in line with the standard of Goldmann applanation tonometer.According to the results,this study laid the foundation for the further development of IOP automatically measuring instruments.
ABSTRACT
PURPOSE: To review the management of posterior segment metallic intraocular foreign bodies (IOFB) and to compare the use of an external approach using a large electromagnet and an internal approach using vitrectomy and its tools for their removal. METHODS: A retrospective review was performed on 49 eyes of 49 patients who underwent surgical removal of metallic IOFBs with either an internal or an external approach at a single institution between January 2003 and December 2006. We divided 49 eyes into two groups based on the type of approach: 26 external (n=26) and 23 internal (n=23). Visual acuity and the presence of any complications occurring with the two approaches were the main outcome measures studied. RESULTS: Thirty of 49 eyes (61%) showed improvements in visual acuity. When we compared patients treated with an external versus an internal approach, we found no statistically significant difference in regard to visual outcome. Preoperative vitreous hemorrhage and endophthalmitis were more common in the internal approach group. A trend toward a higher rate of reoperation was more common in the external approach group, but they were not statistically significant. Postoperative complications found to be significantly different between the two groups were the rate of postoperative endophthalmitis and retinal detachment, which were more common in the external approach group. CONCLUSIONS: Surgical removal of metallic IOFBs results in significant visual improvement regardless of the approach method. The internal approach by vitrectomy is recommended as the first choice in preoperative conditions such as severe cataracts, vitreous hemorrhage and endophthalmitis, as well as in groups at high risk for postoperative endophalmitis and retinal detachment.