Tracking Optical and Electronic Behaviour of Quantum Contacts in Sub-Nanometre Plasmonic Cavities.

Plasmonic interactions between two metallic tips are dynamically studied in a supercontinuum dark-field microscope and the transition between coupled and charge-transfer plasmons is directly observed in the sub-nm regime. Simultaneous measurement of the dc current, applied force, and optical scattering as the tips come together is used to determine the effects of conductive pathways within the plasmonic nano-gap. Critical conductances are experimentally identified for the first time, determining the points at which quantum tunnelling and conductive charge transport begin to influence plasmon coupling. These results advance our understanding of the relationship between conduction and plasmonics, and the fundamental quantum mechanical behaviours of plasmonic coupling.

Tracking Optical Welding through Groove Modes in Plasmonic Nanocavities.

We report the light-induced formation of conductive links across nanometer-wide insulating gaps. These are realized by incorporating spacers of molecules or 2D monolayers inside a gold plasmonic nanoparticle-on-mirror (NPoM) geometry. Laser irradiation of individual NPoMs controllably reshapes and tunes the plasmonic system, in some cases forming conductive bridges between particle and substrate, which shorts the nanometer-wide plasmonic gaps geometrically and electronically. Dark-field spectroscopy monitors the bridge formation in situ, revealing strong plasmonic mode mixing dominated by clear anticrossings. Finite difference time domain simulations confirm this spectral evolution, which gives insights into the metal filament formation. A simple analytic cavity model describes the observed plasmonic mode hybridization between tightly confined plasmonic cavity modes and a radiative antenna mode sustained in the NPoM. Our results show how optics can reveal the properties of electrical transport across well-defined metallic nanogaps to study and develop technologies such as resistive memory devices (memristors).

A compact holographic optical tweezers instrument.

Holographic optical tweezers have found many applications including the construction of complex micron-scale 3D structures and the control of tools and probes for position, force, and viscosity measurement. We have developed a compact, stable, holographic optical tweezers instrument which can be easily transported and is compatible with a wide range of microscopy techniques, making it a valuable tool for collaborative research. The instrument measures approximately 30×30×35 cm and is designed around a custom inverted microscope, incorporating a fibre laser operating at 1070 nm. We designed the control software to be easily accessible for the non-specialist, and have further improved its ease of use with a multi-touch iPad interface. A high-speed camera allows multiple trapped objects to be tracked simultaneously. We demonstrate that the compact instrument is stable to 0.5 nm for a 10 s measurement time by plotting the Allan variance of the measured position of a trapped 2 µm silica bead. We also present a range of objects that have been successfully manipulated.

Epithelial downgrowth after descemet stripping automated endothelial keratoplasty.

PURPOSE: To report the clinical and histopathologic findings of 2 patients who developed epithelial downgrowth after Descemet stripping automated endothelial keratoplasty (DSAEK). METHODS: A 64-year-old woman (case 1) underwent DSAEK for corneal edema secondary to Fuchs endothelial dystrophy in left eye. However, the graft failed to attach, and a repeat DSAEK was performed 3 weeks later. After 4 months, the patient developed herpes simplex virus keratitis that resulted in anterior stromal scarring. A penetrating keratoplasty was performed 15 months after the initial DSAEK. Our second patient (case 2) was an 87-year-old female who underwent DSAEK for corneal edema secondary to Fuchs endothelial dystrophy in left eye. Six months later, she had an episode of graft rejection and developed secondary glaucoma. At 14 months postoperatively, a retrocorneal membrane was seen involving the temporal half of the endothelial surface of the graft. The retrocorneal membrane extended from the inferior thickened edge of the endothelial keratoplasty graft to the iris stromal surface. An Ahmed shunt implantation followed by repeat DSAEK were then performed. The excised corneal buttons were examined. RESULTS: Histopathologic evaluation showed multilayered epithelium on the interface and attenuated endothelium in the endothelial graft in case 1. The host cornea showed diffuse stromal scarring. Case 2 showed multilayered epithelium with early cyst formation at the edge of the graft. The epithelium extended to involve the endothelial surface without involvement of interface surface. Significant scar formation was observed between the edge of the endothelial keratoplasty graft and thickened host Descemet membrane. Some pigmented cells were present within the epithelial downgrowth. The epithelium stained positively with cytokeratin A1/A3 in both cases. CONCLUSIONS: Although rare, epithelial downgrowth can occur after DSAEK and can be associated with graft failure. Early recognition and surgical treatment of epithelial downgrowth is crucial in treating the complications of corneal decompensation and glaucoma.

Tandem scanning confocal microscopy of cornea after descemet stripping automated endothelial keratoplasty.

PURPOSE: To evaluate the changes in the corneal stroma after Descemet stripping automated endothelial keratoplasty (DSAEK) using tandem scanning confocal microscopy (CM). METHODS: Thirteen eyes of 13 patients who underwent DSAEK without preoperative corneal haze or scar obvious at the slit lamp, any ocular disease, and postoperative complication were included in the study. All patients were examined clinically and by CM 6 months after DSAEK. RESULTS: Six months after DSAEK, none of the eyes had clinically significant interface haze (i.e., haze affecting quantity or quality of vision) at slit lamp. The mean best spectacle corrected visual acuity was 0.18 +/- 0.12 (range 0-0.4) logMAR (Snellen 20/30). The CM revealed highly reflective particles in interface in six eyes, particles with mild surrounding increased reflectivity in four eyes, and no discernible interface in three eyes. The mean particles density at interface was 28.6 +/- 23.4 particles/mm. No significant keratocyte activation was seen in any case at the interface. The mean anterior stromal reflectivity was 431.2 +/- 269.1 confocal back scatter units (CBU) and the mean interface reflectivity was 65.9 +/- 46.9 CBU. The mean anterior stromal reflectivity was significantly greater than the mean interface reflectivity (P<0.01). Significant keratocyte activation with high reflectivity was seen in superficial anterior stroma in 8 of 13 eyes. CONCLUSIONS: Tandem scanning CM shows the presence of highly reflective particles at the level of the DSAEK interface that are morphologically similar to a laser in situ keratomileusis interface. The stromal reflectivity is more prominent in subepithelial layers than that of interface 6 months after DSAEK. However, the areas under the mean reflectivity peaks (CBU) corresponding to the flap interface and superficial anterior stroma do not seem to correlate with best spectacle corrected visual acuity results after the procedure.

A comparison of higher order aberrations in eyes implanted with AcrySof IQ SN60WF and AcrySof SN60AT intraocular lenses.

PURPOSE: To evaluate the efficacy of AcrySof SN60WF aspheric intraocular lens (IOL) in decreasing spherical aberration and total higher order aberrations (HOAs) after cataract surgery compared to the spherical SN60AT lens. METHODS: Wavefront analysis was conducted on 28 eyes of 28 patients that underwent un-complicated phacoemulsification with implantation of either SN60WF (15 eyes) or SN60AT lenses (13 eyes). Eyes with a history of uveitis, retinal diseases, and previous surgery were excluded. RESULTS: SN60WF eyes had less mean absolute spherical aberration than SN60AT eyes both at 4 mm (0.04+/-0.03 vs 0.11+/-0.03 RMS, p<0.0001) and 6 mm pupils (0.09+/-0.04 vs 0.43+/-0.12 RMS, p<0.0001). Mean total HOAs was lower in the SN60WF group at 6 mm pupils (0.44+/-0.14 vs 0.56+/-0.13 RMS, p=0.0274), while no difference was seen at 4 mm pupils (0.20+/-0.10 vs 0.25+/-0.08 RMS, p=0.160). There were no clinically significant differences between the SN60WF and SN60AT IOLs both at 4 and 6 mm pupils in terms of coma (0.16+/-0.07 vs 0.18+/-0.09 RMS, p=0.514 and 0.25+/-0.12 vs 0.23+/-0.12 RMS, p=0.664) and trefoil (0.14+/-0.09 vs 0.10+/-0.05 RMS, p=0.167 and 0.28+/-0.12 vs 0.23+/-0.07 RMS, p=0.199). There were no differences be-tween groups in mean age, axial length, postoperative spherical equivalent, IOL power, or corneal curvature. CONCLUSIONS: An aspheric posterior optic IOL design with thinner center effectively reduces the positive ocular spherical aberration observed in the pseudophakic and elderly eyes, especially at larger pupillary diameters (6 mm), with no notable increase in coma. However, reduction in total ocular HOAs was only significant at 6 mm pupils.

Patient satisfaction after LASIK for myopia.

PURPOSE: To determine satisfaction among patients treated with laser-in-situ-keratomileusis (LASIK) for various degrees of myopia (-0.75 D to -16.00 D) and myopic astigmatism (+0.50 D to +4.50 D) and assess factors which may affect satisfaction. METHODS: One-hundred seventy-four consecutive patients treated with LASIK between November 1, 1997 and October 31, 1998 were surveyed. Charts were reviewed to collect refractive data. RESULTS: Eighty-three patients (163 eyes) returned surveys for a response rate of 53%. Of the responders, 55% were female, the average age was 39.6 years (range 21-59), the mean preoperative sphere was -6.36 +/- 0.23 D, cylinder +0.94 +/- 0.07 D, and spherical equivalent-5.89 +/- 0.23 D. Ninety-six percent of eyes enjoyed freedom from corrective lenses following LASIK. Twenty-nine percent reported reduced night vision clarity following LASIK and 27% noted more eye dryness following LASIK. Overall, 84.8% were at least "very pleased" with the results of the procedure and 97% indicated that they would decide again to have LASIK. Uncorrected visual acuity and lower preoperative cylinder correlated positively with satisfaction, while increased postoperative dry eyes correlated negatively with satisfaction. CONCLUSIONS: This study demonstrates a very high level of patient satisfaction following excimer laser treatment for myopia and myopic astigmatism. A great deal of literature has evaluated objective outcomes of LASIK, but this is one of few studies to examine patient satisfaction.

Surgically induced astigmatism after hyperopic and myopic photorefractive keratectomy.

PURPOSE: To compare the axis and magnitude of surgically induced refractive astigmatism (SIA) after hyperopic and myopic photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, USA. METHODS: In this single-center retrospective study, the VISX Star S2 excimer laser was used to create a peripheral annular ablation profile to correct spherical hyperopia in 23 eyes of 16 consecutive patients. Attempted corrections ranged from +0.50 diopter (D) to +4.25 D with 0 to 1.00 D of astigmatism. The same laser was used to create a central ablation profile to correct spherical myopia in 25 eyes of 17 consecutive patients. Attempted corrections ranged from -2.25 to -6.50 D with 0 to 1.00 D of astigmatism. The absolute change in refractive astigmatism was calculated by taking the difference in magnitudes of astigmatism before and after laser treatment without regard to axis. Axis and magnitude of SIA were analyzed by vector differences. Magnitudes were compared using the Student t test, and axial shifts were compared using the chi-square test. All patients were followed for a minimum of 6 months. RESULTS: The mean changes in absolute astigmatism were 0.29 +/- 0.28 D at 3 months and 0.34 +/- 0.29 D at 6 months after hyperopic PRK and 0.40 +/- 0.35 D at 3 months and 0.39 +/- 0.36 D at 6 months after myopic PRK. The mean vectoral magnitudes were 0.49 +/- 0.29 at 3 months and 0.52 +/- 0.25 at 6 months after hyperopic PRK and 0.48 +/- 0.39 at 3 months and 0.44 +/- 0.38 at 6 months after myopic PRK. The mean values for SIA (the centroid) were 0.10 +/- 0.57 D x 113 degrees at 3 months and 0.15 +/- 0.57 D x 131 degrees at 6 months after hyperopic PRK and 0.04 +/- 0.63 D x 160 degrees at 3 months and 0.08 +/- 0.58 D x 171 degrees at 6 months after myopic PRK. There was no statistically significant difference between the 2 groups in vectoral axis or magnitude of SIA. CONCLUSION: Surgically induced astigmatism after hyperopic PRK was comparable to astigmatism induced by myopic PRK. A peripheral annular ablation for hyperopic correction, similar to a central ablation in myopic PRK, did not appear to result in uneven corneal healing causing astigmatism.

Hyphema caused by a metallic intraocular foreign body during magnetic resonance imaging.

PURPOSE: To report a 63-year-old man with a retained intraocular foreign body who developed a hyphema during magnetic resonance imaging (MRI) of the brain. METHODS: Case report and review of the current literature on ocular injury caused by intraocular foreign bodies when subjected to an electromagnetic field. RESULTS: Our patient underwent a brain MRI, and the intraocular foreign body caused a hyphema and increased intraocular pressure. The presence and location of the intraocular foreign body were determined by computed tomography (CT). CONCLUSION: Magnetic resonance imaging can cause serious ocular injury in patients with ferromagnetic intraocular foreign bodies. This case demonstrates the importance of obtaining an occupational history, and, when indicated, a skull x-ray or CT to rule out intraocular foreign body before an MRI study.

Excimer laser treatment of spherical hyperopia: PRK or LASIK?

PURPOSE: To compare the efficacy and safety of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in the treatment of spherical hyperopia with use of the VISX STAR S2 excimer laser. METHODS: A review of 15 consecutive patients (22 eyes) receiving PRK and 22 consecutive patients (26 eyes) receiving LASIK (median follow-up, 12 months). RESULTS: Mean age was 52 +/- 7 years for patients receiving PRK and 55 +/- 9 years for patients receiving LASIK. Mean preoperative spherical equivalent was +2.25 +/- 1.16 D for PRK patients and +1.81 +/- 0.92 D for LASIK patients. Mean deviation from intended correction was -0.82 +/- 0.89 D after PRK and +0.19 +/- 0.47 D after LASIK at 1 month (P < .01); +0.16 D +/- 0.37 D after PRK and +0.29 +/- 0.51 D after LASIK at 6 months (P = .906); +0.20 +/- 0.35 D after PRK and +0.37 +/- 0.44 D after LASIK at 1 year (P = .301). At 1 year, 83.3% of PRK eyes and 61.5% of hyperopic LASIK eyes were within +/- 0.50 D of intended correction (P = 1.0). At 1 year, all eyes in both groups had acuity of 20/40 or better uncorrected, and 47.1% of PRK eyes and 54.5% of LASIK eyes had acuity of 20/20 or better uncorrected (P = 1.0). At last follow-up (minimum, 6 months), 2 eyes in each group had lost 2 lines of best spectacle-correct visual acuity, but none had lost more than 2 lines. All PRK patients experienced significant postoperative pain that required systemic medication. LASIK patients had only minor, transient discomfort. CONCLUSION: LASIK and PRK are of comparable efficacy and safety. However, PRK was associated with significant post-operative pain, an initial and temporary myopic overshoot peaking at 1 month, and stability not occurring before 6 months. LASIK was less painful and was associated with more rapid stability (at 1 month) and a trend toward better uncorrected visual acuity, although not statistically significant.

Reliability of intraocular pressure measurements after myopic excimer photorefractive keratectomy.

OBJECTIVE: To determine the reliability of intraocular pressure (IOP) measurements by Goldmann applanation tonometry and pneumotonometry in eyes treated with excimer myopic photorefractive keratectomy (PRK). DESIGN: A prospective case series. PARTICIPANTS: Forty consecutive eyes treated with PRK were evaluated. INTERVENTION AND MAIN OUTCOME MEASURES: Central and peripheral corneal Goldmann tonometry and pneumotonometry measurements were done before surgery, at 1 week, and at 1 and 3 months after surgery. RESULTS: The IOP by Goldmann tonometry from the central cornea was significantly lower than the peripheral IOP; however, there was no difference between IOP measured from central and peripheral corneas by pneumotonometry, which, in turn, correlated with peripheral Goldmann measurements. There was a trend, but not a statistically significant correlation, between the spherical equivalent of the treatment and the amount of decrease in central Goldmann IOP. CONCLUSIONS: Pneumotonometry measures the IOP reliably after PRK from all parts of the cornea, whereas central Goldmann tonometry underestimates the IOP by 2.40+/-1.23 mmHg.

The use of conjunctival flaps in the treatment of herpes keratouveitis.

Conjunctival flaps have been used in the treatment of corneal diseases since the 1800s, although in recent years their use has decreased. In selected cases, however, the placement of a conjunctival flap still may be the treatment of choice. We report our experience with the use of conjunctival flaps in patients with herpes keratouveitis who had persistent corneal epithelial defects. Preoperatively, all patients had chronic or recurrent epithelial defects and intraocular inflammation with or without recurrent live viral infection requiring frequent medicine application and office visits. Postoperatively, all patients had an intact, healthy ocular surface and a noninflamed eye requiring few to no medications and infrequent office visits. No patient has had recurrent live viral activity.

The effect of currently available contact lens disinfection systems on Acanthamoeba castellanii and Acanthamoeba polyphaga.

Contact lens disinfection systems were evaluated for their effectiveness in killing Acanthamoeba castellanii and Acanthamoeba polyphaga trophozoites and cysts. Amoebae were inoculated into commercially available contact lens cleaning and soaking solutions. At intervals varying from 30 minutes to 24 hours, solutions were filtered. The filters were removed and cultured for Acanthamoeba organisms. Striking differences were observed in the abilities of the different disinfecting solutions to kill the organisms. Solutions containing chlorhexidine were effective at very short exposure times. Solutions containing benzalkonium chloride required slightly longer exposure times but were faster than solutions containing only thimerosal. Solutions containing sorbate, polyaminopropyl biguanide, or polyquaternium-1 were not effective at killing Acanthamoeba organisms in the time allotted for the experiment. Solutions containing hydrogen peroxide were quite effective if the agent was not prematurely catalyzed. A. polyphaga generally required longer exposure to disinfectants than did A. castellanii for complete inhibition to occur.

Suprofen treatment of contact lens-associated giant papillary conjunctivitis.

This multicenter study of patients with contact lens-associated giant papillary conjunctivitis (GPC) was a randomized, double-masked comparison of a 1.0% suprofen solution versus the suprofen vehicle solution (placebo). Patients were given two drops of medication four times daily for up to 28 days and were clinically examined on days 0, 2, 7, 14, 21, and 28. The physicians' clinical judgments of the patients' responses to therapy significantly favored suprofen over placebo at day 21 (P = 0.02), while strongly favoring suprofen at day 14 (P = 0.057) and at day 28 (P = 0.067). The patients' opinions of their response to therapy significantly favored suprofen on day 14 (P = 0.03); a trend for suprofen was evident on day 28 (P = 0.1). Treatment with suprofen led to a greater overall reduction in ocular signs and symptoms than with placebo. Strong trends approaching statistically significant levels were found for reductions in the principal ocular sign, papillae, at day 28 (P = 0.068) and in mucus strands at days 14 and 28 (P = 0.09), which also favored suprofen.