Experimental Assessment of Common Crucial Factors That Affect LoRaWAN Performance on Suburban and Rural Area Deployments.

LoRaWAN networks might be a technology that could facilitate extreme energy-efficient operation while offering great capacity for suburban and rural area deployment, but this can be a challenging task for a network administrator. Constraints that deform the trade-off triangle of coverage, scalability and energy efficiency need to be overcome. The scope of this study is to review the limitations of the LoRaWAN protocol in order to summarize and assess the crucial factors that affect communication performance, related to data rate allocation, bidirectional traffic and radio spectrum utilization. Based on the literature, these factors correspond mostly to configurable payload transmission parameters, including transmission interval, data rate allocation, requirement for acknowledgements and retransmission. In this work, with simulation experiments, we find that collision occurrences greatly affect channel occupancy. In particular, it was evaluated that collision occurrence is increasingly affected by transmission intervals, which have the most significant negative impact on packet delivery rate (PDR). We then validated that clustering of end nodes in the vicinity of a gateway, taking into account distance and transmission settings, can improve network scalability. This can assure distribution of the total transmission time to end nodes with respect to application-related QoS requirements. Following this clustering approach, we achieved a PDR greater than 0.90 in a simulation setting with 6000 end nodes in a 10 km coverage.

Treatment of corneal dellen with a large diameter soft contact lens.

A 58-year-old man presented with corneal dellen twelve days after pterygium removal on his left eye. Initial treatment with lubrication and artificial tears was unsuccessful. The fitting of a conventional contact lens was not possible because of conjuctival chemosis. Additionally the patient denied eye patching due to professional reasons. As an alternative treatment a large diameter bandage soft contact lens approved for extended wear was applied ((David Thomas Contact Lens T74/85 Extended Wear/Bandage of 18mm diameter). The next day corneal dellen had already began to retreat and four days later the contact lens was removed since there was no sign of dellen in the slit lamp examination. In conclusion, the use of a large diameter soft contact lens was an effective alternative solution for the treatment of corneal dellen in our patient.

Efficacy of 2 types of silicone hydrogel bandage contact lenses after photorefractive keratectomy.

PURPOSE: To compare the efficacy of 2 types of silicone hydrogel bandage contact lenses with high oxygen transmissibility after photorefractive keratectomy (PRK). SETTING: Institute of Vision and Optics, Faculty of Medicine, University of Crete, Heraklion, Crete, Greece. METHODS: In this prospective study, 1 eye of patients having bilateral PRK was randomly fitted with a bandage contact lens of lotrafilcon A (Night & Day) and the fellow eye, with a bandage contact lens of lotrafilcon B (O(2)Optix). The patients and the examiner were masked to which bandage contact lens type was in which eye. Patients were examined on the day of surgery and 1, 3, and 5 days postoperatively. Postoperative examinations included uncorrected distance visual acuity and slitlamp biomicroscopy to assess epithelial defect size. Subjective evaluation of pain and vision was recorded 1, 2, 3, and 4 days postoperatively. RESULTS: The study enrolled 44 patients (88 eyes). The mean epithelial defect size immediately after surgery was 47.0 mm(2) with both types of bandage contact lenses. There was no statistically significant difference in epithelial defect size between the 2 lenses at any postoperative visit. Three days postoperatively, reepithelialization was complete in 75.0% of eyes in the lotrafilcon A group and 72.7% of the eyes in the lotrafilcon B group. CONCLUSION: There were no differences in corneal reepithelialization or subjective measurements after PRK between the 2 types of silicone hydrogel bandage contact lenses.

LASIK flap characteristics using the Moria M2 microkeratome with the 90-microm single use head.

PURPOSE: To evaluate the accuracy and consistency of corneal flap thickness, horizontal diameter, and hinge size with the Moria M2 90-microm single use head. METHODS: Fifty-two myopic patients (104 eyes), mean age 32.6 years, underwent bilateral LASIK with a superior hinged flap using the Moria M2 microkeratome (90-microm single use head). Prospective evaluation included flap thickness (subtraction method), diameter, hinge size, interface particles, intraoperative complications, and visual recovery. RESULTS: The mean preoperative spherical equivalent refraction was -5.72 +/- 2.59 diopters (D) (range: -2.88 to -10.75 D) and -5.84 +/- 2.73 D (range: -3.13 to -9.38 D) for right and left eyes, respectively. The mean preoperative central corneal thickness was 548 +/- 24 microm and 547 +/- 25 microm for right and left eyes, respectively. The mean preoperative steepest K was 44.12 +/- 1.28 D and 44.41 +/- 1.27 D for right and left eyes, respectively. Corneal diameter (white-to-white) was 12 +/- 0.4 mm and 11.9 +/- 0.4 mm for right and left eyes, respectively. The mean postoperative flap thickness was 109 +/- 18 microm (range: 67 to 152 microm) and 103 +/- 15 microm (range: 65 to 151 microm) for right and left eyes, respectively. The mean postoperative flap diameter was 9.4 +/- 0.3 mm (expected mean according to the nomogram given by the company was 9.5 mm). The mean postoperative hinge chord was 4.4 +/- 0.4 mm (expected mean 4.2 mm). No interface particles were detected on slit-lamp examination. CONCLUSIONS: The Moria M2 90-microm single use head is safe with reasonable predictability for LASIK flap creation.

Eleven-year follow-up of laser in situ keratomileusis.

PURPOSE: To report the long-term (11-year) outcomes (stability and complications) of laser in situ keratomileusis (LASIK) in patients with high myopia. SETTING: University refractive surgery center. METHODS: Seven patients (4 with bilateral treatment and 3 with unilateral treatment) who had myopic LASIK and completed 11 years of follow-up were included in the study. RESULTS: The mean age of the 2 men and 5 women was 41.7 years +/- 6.5 (SD) (range 34 to 50 years). The mean follow-up was 140.18 +/- 6.70 months (range 132 to 150 months). At 11 years, the spherical equivalent error was statistically significantly reduced, from a mean of -12.96 +/- 3.17 diopters (D) (range -19.00 to -10.00 D) before LASIK to a mean of -1.14 +/- 1.67 D (range -4.25 to 1.00 D) after (P<.001). Predictability of postoperative refraction 6 months and 11 years after LASIK showed that 6 eyes (55%) were within +/-1.00 D of intended correction. No late postoperative complications occurred. Five patients (8 eyes, 73%) were satisfied with the final outcome. CONCLUSIONS: Laser in situ keratomileusis was moderately predictable in the correction of high degrees of myopia. After the sixth postoperative month, refractive and topographic stability were obtained. No long-term sight-threatening complications occurred during the follow-up period.

Long-term follow-up of Intacs in keratoconus.

PURPOSE: To evaluate long-term follow-up of Intacs microthin prescription inserts (Addition Technology, Inc, Fremont, California, USA) for the management of keratoconus. DESIGN: A long-term (five years) retrospective, follow-up study. METHODS: Seventeen eyes of 15 patients with keratoconus ages 24 to 52 years (mean age +/- standard deviation [SD], 34.0 +/- 10.5 years) who had completed five years of follow-up (mean follow-up +/- SD, 67.2 +/- 7.5 months; range, 58 to 78 months) were included. Two Intacs segments of 0.45-mm thickness were inserted in the cornea of each eye, aiming at embracing the keratoconus area to try to achieve maximal flattening. RESULTS: No late postoperative complications occurred in this series of patients. At five years, the spherical equivalent error was statistically significantly reduced (pre-Intacs, mean +/- SD -5.54 +/- 5.02 diopters [D]; range, -12.50 to 3.63 D; -3.02 +/- 2.65 D; range, -8.25 to 1.88 D) (P = .01). Pre-Intacs uncorrected visual acuity (UCVA) was 20/50 or worse in all eyes (range, counting fingers to 20/50), whereas, at the last follow-up examination, 10 (59%) of 17 eyes had UCVA of 20/50 or better (range, counting fingers to 20/32). Six eyes (35%) maintained the pre-Intacs best spectacle-corrected visual acuity (BSCVA) and one eye lost 3 lines of BSCVA, whereas the rest of the 10 eyes (59%) experienced a gain of one up to 8 lines. CONCLUSIONS: After five years, intracorneal ring segments implantation improved UCVA, BSCVA, and refraction in the majority of the keratoconus patients. There was no evidence of progressive sight-threatening complications in this study.

Long-term follow-up of Intacs for post-LASIK corneal ectasia.

OBJECTIVE: To report long-term follow-up of Intacs microthin prescription inserts for the management of post-LASIK corneal ectasia. DESIGN: Long-term (5 years), retrospective, nonrandomized study. PARTICIPANTS: Eight eyes of 5 patients with post-LASIK corneal ectasia (3 men and 2 women) ages 31 to 54 years (mean age+/-standard deviation [SD], 41.60+/-9.24 years) who had completed 5 years of follow-up (mean follow-up +/- SD, 60.1+/-4.9 months; range, 57-68 months). INTERVENTION: Two Intacs segments, inserted in the usual fashion, were used for low myopia correction (1 each nasally and temporally), with thickness based on the residual refraction of the patients. MAIN OUTCOME MEASURES: Manifest refraction, uncorrected and best spectacle-corrected visual acuity, patient satisfaction, topography, and confocal microscopy analysis. RESULTS: No intraoperative or late postoperative complications occurred in this series of patients. At 5 years, the SE error was statistically significantly reduced (pre-Intacs mean+/-SD, -5.47+/-2.66 diopters [D]; range, -11.50 to -3.00 D) to -2.56+/-3.44 D (range, -9.50 to 1.5 D; P = 0.01). At the end of the first postoperative year, refractive stability was obtained and remained stable during the follow-up period with no significant changes between the interval meantime (P>0.05). Pre-Intacs uncorrected visual acuity was 20/100 or worse in all eyes (range, counting fingers-20/100), whereas at the last follow-up examination, 6 (75%) of 8 eyes had uncorrected visual acuity of 20/40 or better (range, counting fingers-20/25). Two eyes (25%) maintained the pre-Intacs best spectacle-corrected visual acuity, whereas the rest of the eyes (6 eyes; 75%) experienced a gain of 1 or 2 lines. At the end of the first postoperative year, uncorrected and best-spectacle corrected visual acuity and topographic stability were obtained and were shown to have remained stable during the follow-up period with no significant changes between the interval meantime. Lamellar channel deposits were observed in confocal microscopy at or adjacent to the intrastromal ring segment. CONCLUSIONS: Refractive stability was maintained for up to 5 years in the treatment of post-LASIK corneal ectasia after Intacs implantation. There was no evidence of progressive time-dependent corneal ectasia, late regression, or sight-threatening complications in this study.

Two-year follow-up of conductive keratoplasty for the treatment of hyperopic astigmatism.

PURPOSE: To evaluate the safety, efficacy, predictability, and stability of conductive keratoplasty (CK) for the treatment of hyperopic astigmatism. SETTING: University of Crete Medical School, Vardinoyannion Eye Institute of Crete, Heraklion, Greece. METHODS: In this prospective nonrandomized noncontrolled single-center study, 47 eyes of 34 patients (15 women and 19 men) were treated for hyperopic astigmatism (up to + 3.50 diopters [D]) with a Refractec ViewPoint CK system and followed for 24 months +/- 0.6 (SD). The treatment consisted of 4 to 36 spots applied to the periphery of the cornea. Mean age was 48.5 years +/- 9.7 years, range 25 to 68 years. All the treated eyes were analyzed for safety, efficacy, predictability, and stability. RESULTS: The mean patient age was 48.5 +/- 9.7 years (range 25 to 68 years). Preoperatively, the mean manifest refraction spherical equivalent (MRSE) was +2.11 +/- 0.88 D (range -0.50 to + 4.13 D); at 12 months, it was -0.52 +/- 0.73 D and at 24 months, -0.50 +/- 0.77 D. At 24 months, the mean MRSE was within +/-0.50 D in 61% of eyes, within +/-1.00 D in 83%, and within +/-2.00 D in all eyes. At 24 months, the uncorrected visual acuity was 20/20 or better in 37% of eyes and 20/40 or better in 97%. By the end of the follow-up period, no eye had lost > or =2 Snellen lines or had an induced cylinder > or =1.50 D. CONCLUSIONS: Conductive keratoplasty for low hyperopic astigmatism was a safe, effective, and stable procedure. Nomogram adjustments and careful patient selection should contribute to higher levels of predictability when treating hyperopic astigmatism.

Conductive keratoplasty: histological study of human corneas.

PURPOSE: To determine the morphologic changes in human corneas over time following radiofrequency-based conductive keratoplasty (CK) treatment. DESIGN: Prospective, observational case series. METHODS: In a single-center study six human corneas of six patients with localized peripheral keratoconus underwent CK treatment followed by penetrating keratoplasty. Three spots were applied in the periphery of each cornea (6 mm optical zone). Corneal buttons were examined with light and electron microscopy at different postoperative intervals up to 6 months post-CK. RESULTS: In samples assessed on day one post-CK, small areas of detachment between the basal layer of epithelial cells and Bowman's layer were observed. At 1 week after the CK procedure, the epithelium appeared almost normal. Endothelium and Descemet's membrane had no alterations. In all samples, thermally induced misconfiguration of collagen fibers, described as "crumpled" changes of collagen layers, was observed reaching 75% to 80% of the stromal depth. The area of alterations had a cylindrical shape with a diameter of 120 mum. CONCLUSIONS: The conductive keratoplasty procedure produced collagen "crumpling and splitting" changes in human corneas, which were observed during the follow-up of 6 months. Areas adjacent to treatment site were minimally damaged.

Long-term results of conductive keratoplasty for low to moderate hyperopia.

PURPOSE: To assess the long-term safety, efficacy, predictability, and stability of conductive keratoplasty (CK) for the treatment of low to moderate hyperopia and to evaluate the impact of the procedure on the quality of vision. SETTING: University of Crete, Medical School, Vardinoyannion Eye Institute of Crete, Crete, Greece. METHODS: In this prospective nonrandomized noncontrolled single-center study, 38 eyes of 26 patients (13 women and 13 men) were treated for hyperopia with a Refractec ViewPoint CK system and followed for 30 months. Preoperatively, the mean manifest refraction spherical equivalent (MRSE) was +1.89 diopters (D) +/- 0.6 (SD) (range +1.00 to +3.25 D), and the mean follow-up was 30.9 +/- 1.1 months. All eyes were treated with the regular CK nomogram for the treatment of spherical hyperopia. The treatment consisted of 8 to 32 spots applied to the periphery of the cornea. Mean age was 50.3 +/- 8.8 years (range 31 to 71 years). All treated eyes were analyzed for safety, efficacy, predictability, and stability. RESULTS: At 12 months, the MRSE was -0.06 +/- 0.8 D and at 30 months was -0.02 +/- 0.7 D. At 30 months, the mean MRSE was within +/-0.50 D in 68%, within +/-1.00 D in 92%, and within +/-2.00 D in all eyes. At 30 months, uncorrected visual acuity was 20/20 or better in 52.5% and 20/40 or better in 89% of eyes. No eye lost 2 or more Snellen lines or had an induced cylinder of 2.00 D or greater. The procedure did not cause statistically significant changes in contrast sensitivity. CONCLUSION: Results show that CK for low to moderate hyperopia is a safe, effective, predictable, and stable procedure.

Intraoperative management of partial flap during LASIK: a small case series report.

PURPOSE: To report the intraoperative management of incomplete microkeratome LASIK flaps. DESIGN: Small, retrospective, noncomparative, interventional case series. PARTICIPANTS: Five outpatients. METHODS: In 5 eyes of 5 patients, the premature stop of the microkeratome resulting from mechanical obstacles resulted in an incomplete flap that would not allow for the completion of the LASIK procedure. After the careful realignment of the partial flaps and the removal of the identified obstacles, the second pass of the microkeratome resulted in flaps of the intended size. MAIN OUTCOME MEASURES: Final creation of a flap as intended, completion of the procedure, and visual and refractive outcome of the operative eyes. RESULTS: The second pass of the microkeratome resulted in flaps as planned. All the procedures were completed, and the operative eyes that were followed up for at least 3 months had excellent visual and refractive results. CONCLUSIONS: The second pass of the microkeratome can successfully manage incomplete flaps resulting from microkeratome premature stop as a result of mechanical obstacles.

Intraocular pressure measurements after conductive keratoplasty.

PURPOSE: To determine the possible impact of conductive keratoplasty (CK) on intraocular pressure (IOP) measurements. METHODS: A prospective, single-center, noncomparative interventional case series was performed. Baseline and postoperative IOPs were measured by Goldmann applanation tonometry in 32 eyes of 18 patients who underwent CK for hyperopia correction. Mean follow-up was 11.9 months (range: 8 to 18 months). RESULTS: After CK, a statistically significant decrease in the measured IOP was observed (before CK: 14.22+/-1.64 vs after CK: 12.66+/-2.21, P<.001). The change in IOP readings postoperatively was not correlated with age, sex, keratometric readings, or attempted correction. CONCLUSIONS: Despite the limitations due to the small number of patients enrolled in this study, the applanation tonometer appears to underestimate the true IOP after CK.

Induced videokeratography alterations in patients with excessive meibomian secretions.

PURPOSE: To describe lipid-induced specific videokeratographic (VKG) corneal changes and subsequent resolution after eyelid washing. METHODS: VKG was performed with C-Scan corneal topography. In all patients an excessive meibomian gland lipid secretion was found with or without coexistent chronic posterior blepharitis. After the initial VKG, a meticulous cleaning of the lids with a mild alkali shampoo (10% Johnson's baby shampoo in sterile water) was done, first by gently scrubbing the closed eyelid fissure with the solution to mobilize and emulsify any Meibomian gland secretions followed by cleaning of the upper and lower margins individually, using Q-tip applicators soaked in the detergent. RESULTS: Three patients with tear film lipid layer excess (TFLE), which correlated with the presence of a superior or central corneal steepening in VKG, were studied. In two of the subjects, careful lid washing reversed either completely or partially this VKG effect, whereas in the last patient the VKG changes after artificially increasing the tear film lipid content is described. CONCLUSIONS: Meibomian gland lipid secretions may induce mainly superior and occasionally central VKG corneal steepening that is not correlated with any slit-lamp pathologic findings. Computerized corneal topography can help detect such corneal abnormalities, and their reversibility may distinguish them from other pathologic conditions (such as contact lens-induced warpage, eccentric ablations, irregular astigmatism, superior keratoconus).

Topographically supported customized ablation for the management of decentered laser in situ keratomileusis.

PURPOSE: To evaluate the efficacy, predictability, and safety of topographically supported customized ablations (TOSCAs) for decentered ablations following laser in situ keratomileusis (LASIK). DESIGN: Prospective nonrandomized clinical trial. METHODS: Nine patients (11 eyes) with LASIK-induced decentered ablations underwent TOSCA following flap lifting. Topographically supported customized ablation was performed using a corneal topographer to obtain a customized ablation profile, combined with a flying spot laser. RESULTS: Mean follow-up was 9.22 +/- 2.82 months (range 6-12 months). No intra- or postoperative complications were observed. Manifest refraction (spherical equivalent) did not change significantly (pre-TOSCA: -0.14 +/- 1.58 diopters [range, -1.75 to +3.00 diopters] to +0.46 +/- 1.02 diopters [range, -1.00 to +1.75 diopters]; P =.76), whereas there was a statistically significant reduction in the refractive astigmatism (pre-TOSCA: -1.55 +/- 0.60 diopters [range, -3.00 to -0.75 diopters] to -0.70 +/- 0.56 diopters [range, -2.00 to -0.25 diopters]; P =.003). Mean uncorrected visual acuity improved significantly (P <.001) from 0.45 +/- 0.16 (range, 0.2-0.7) to 0.76 +/- 0.29 (range, 0.2-1.2) at last follow-up. Mean best-corrected visual acuity improved from 0.74 +/- 0.22 (range, 0.4-1.0) to 0.95 +/- 0.20 (range, 0.6-1.2; P =.002). Eccentricity showed a statistically significant reduction after TOSCA treatment (pre-TOSCA: 1.59 +/- 0.46 mm [range, 0.88-2.23 mm]; post-TOSCA: 0.29 +/- 0.09 mm [range, 0.18-0.44 mm]; P <.001). CONCLUSION: In our small sample, enhancement LASIK procedures with TOSCA appear to improve uncorrected and best-corrected visual acuity as well as eccentricity in patients with LASIK-induced decentered ablation.

Conductive keratoplasty for low to moderate hyperopia: 1-year results.

PURPOSE: To assess the safety, efficacy, and stability of conductive keratoplasty in the treatment of low to moderate hyperopia and evaluate the impact of the procedure on the quality of vision. METHODS: Thirty-six eyes (25 patients; 13 female and 12 male) were treated for hyperopia up to +3.25 D with a Refractec ViewPoint CK system and followed for 1 year. Mean age was 50.2 +/- 8.7 years (range 31 to 71). RESULTS: Before surgery, mean spherical equivalent refraction was +1.90 +/- 0.60 D (range +1.00 to +3.25 D), decreasing at 1 year after conductive keratoplasty to -0.06 +/- 0.80 D, and was within +/- 0.50 D of emmetropia in 68% (24 eyes) and within +/- 2.00 D in all eyes. Twelve months after conductive keratoplasty, uncorrected visual acuity was 20/20 or better in 19 eyes (50%) and 20/40 or better in 32 eyes (89%). No eye lost > or = 2 Snellen lines or had induced cylinder > or = 2.00 D. The mean root mean square values for higher order optical aberrations were 0.060 +/- 0.039 before and 0.174 +/- 0.170 at 3 months after surgery. No statistically significant changes in contrast sensitivity were noted. CONCLUSIONS: Conductive keratoplasty for low to moderate hyperopia provided safe, effective, and stable results both in refraction and quality of vision.

Management of post-LASIK corneal ectasia with Intacs inserts: one-year results.

OBJECTIVE: To prospectively study the effects of the use of Intacs microthin prescription inserts (Addition Technology Inc, Fremont, Calif) for the postoperative management of corneal ectasia resulting from laser in situ keratomileusis (LASIK). METHODS: In this prospective nonrandomized clinical trial, 10 eyes of 7 patients with post-LASIK corneal ectasia (2 men and 5 women) aged 33 to 46 years (mean +/- SD, 40.67 +/- 5.99 years) were included. The follow-up ranged from 6 to 24 months (mean +/- SD, 15.0 +/- 6.5 months). Two Intacs segments of thickness depending on the residual refraction of the patients were inserted in each eye. MAIN OUTCOME MEASURES: Uncorrected visual acuity, best spectacle-corrected visual acuity, refractive outcome, and topographic findings after Intacs implantation. RESULTS: Intacs were successfully implanted in all eyes. Spherical equivalent error was statistically significantly reduced after Intacs implantation (pre-Intacs, mean +/- SD: -4.81 +/- 3.24 Diopters (D) (range, -13.75 to -2.50 D) to -0.96 +/- 2.93 D (range, -8.75 to 2.50 D) (P<.001). Pre-Intacs uncorrected visual acuity was 20/100 or worse in all eyes (range, counting fingers to 20/100) while at the last follow-up examination, 9 (90%) of 10 eyes had uncorrected visual acuity of 20/40 or better (range, counting fingers to 20/20). Three eyes maintained the pre-Intacs best spectacle-corrected visual acuity while the rest of the eyes (7) experienced a gain of 1 to 2 lines. The mean difference between pre-Intacs and last follow-up best spectacle-corrected visual acuity was a gain of 1.00 +/- 0.82 lines. CONCLUSIONS: Intracorneal ring segments implantation improved uncorrected visual acuity and best spectacle-corrected visual acuity in patients with post-LASIK ectasia. Even though the results are encouraging, concern still exists regarding the long-term effect of such an approach for the management of post-LASIK ectasia.