Ultra-thin double-layered hexagonal CuI: strain tunable properties and robust semiconducting behavior.

In this study, the freestanding form of ultra-thin CuI crystals, which have recently been synthesized experimentally, and their strain-dependent properties are investigated by means of density functional theory calculations. Structural optimizations show that CuI crystallizes in a double-layered hexagonal crystal (DLHC) structure. While phonon calculations predict that DLHC CuI crystals are dynamically stable, subsequent vibrational spectrum analyzes reveal that this structure has four unique Raman-active modes, allowing it to be easily distinguished from similar ultra-thin two-dimensional materials. Electronically, DLHC CuI is found to be a semiconductor with a direct band gap of 3.24 eV which is larger than that of its wurtzite and zincblende phases. Furthermore, it is found that in both armchair (AC) and zigzag (ZZ) orientations the elastic instabilities occur over the high strain strengths indicating the soft nature of CuI layer. In addition, the stress-strain curve along the AC direction reveal that DLHC CuI undergoes a structural phase transition between the 4% and 5% tensile uniaxial strains as indicated by a sudden drop of the stress in the lattice. Moreover, the phonon band dispersions show that the phononic instability occurs at much smaller strain along the ZZ direction than that of along the AC direction. Furthermore, the external strain direction can be deduced from the predicted Raman spectra through the splitting rates of the doubly degenerate in-plane vibrations. The mobility of the hole carriers display highly anisotropic characteristic as the applied strain reaches 5% along the AC direction. Due to its anomalous strain-dependent electronic features and elastically soft nature, DLHC of CuI is a potential candidate for future electro-mechanical applications.

Effect of keratorefractive surgery on choroidal thickness in anisometropic amblyopia.

PURPOSE: To evaluate postoperative change in choroidal thickness (CT) in patients with anisometropic amblyopia undergoing keratorefractive surgery. METHODS: Anisometropic amblyopic patients and nonamblyopic patients who underwent keratorefractive surgery were included in the study. The eyes were divided into three groups. Group 1 consisted of eyes with anisometropic amblyopia, group 2 were the nonamblyopic fellow eyes, and group 3 (control group) were nonamblyopic eyes which had undergone keratorefractive surgery. At the third postoperative month, the CT of these eyes were measured by Enhanced Depth Imaging OCT (EDI-OCT). The choroidal thickness (CT) was measured in the subfoveal area and at 500 micron intervals nasally and temporally. RESULTS: Twenty-three anisometropic amblyopia patients with amblyopic and fellow eyes and 23 control eyes were enrolled. The mean subfoveal choroidal thickness (CT) was 387.3±168.8µm in group 1, 412.2±88.8µm in group 2 and 337.3±99µm in group 3 (P: 0.019). Group 1 and group 2 showed higher choroidal thickness (CT) in the nasal and temporal quadrants than group 3 (P: 0.03, P: 0.04). At the third postoperative month, central foveal choroidal thickness was 356.6±115.5µm in group 1, 375.1±112.5µm in group 2 and 284.4±98.9µm in group 3 (P: 0.071). Choroidal thickness (CT) in the nasal and temporal quadrants at the third postoperative month was also similar (P: 0.210, P: 0.103). CONCLUSIONS: The macular choroid is thicker in amblyopic eyes and non-amblyopic fellow eyes than in the nonamblyopic controls. Improved fixation after refractive surgery may normalize CT.

Long-term assessment of visual and refractive outcomes of laser in situ keratomileusis for hyperopia using the AMARIS® 750S Excimer laser.

PURPOSE: To evaluate the long-term efficacy and safety of hyperopic laser in situ keratomileusis (LASIK) using the AMARIS® 750S (Schwind, Eye-tech-solutions, GmbH) excimer laser. METHODS: The medical records of one hundred eleven eyes of 62 patients who underwent LASIK for hyperopia using the AMARIS® 750S excimer laser were reviewed retrospectively. Patients were divided into three groups based on preoperative spherical equivalent (SE) refraction: low hyperopia (less than +2.50 diopters [D]), moderate hyperopia (+2.75D to +4.00D), and high hyperopia (over +4.00D). Uncorrected and best corrected visual acuity (BCVA), long-term stability of refraction, and complications were evaluated. RESULTS: Of the entire sample, the mean preoperative SE was +3.64D±1.22D. The mean age was 37.4±11.2 years (20-59). The mean follow-up for all eyes was 51 months. At the last visit, the mean SE was +0.85D±0.34D (SD) in the low hyperopia group, +1.09D±0.43D in the moderate hyperopia group, and +1.63D±0.47D in the high hyperopia group. (+1.15D±0.49D overall). Preoperative uncorrected visual acuity (UCVA) was 0.52±0.34 logMAR and increased to 0.18±0.15 logMAR at 4 years follow-up (P<0.01). There was no statistically significant difference between preoperative and postoperative BCVA. The UCVA was 0.30 logMAR or better in 100% of eyes in the low hyperopia group, 93.7% in the moderate hyperopia group, and 69.9% in the high hyperopia group (%89.2 overall). CONCLUSIONS: LASIK is safe and effective for correcting hyperopia in the short term; however, the efficacy of the procedure is limited in the patients with high hyperopia and longer follow-up.

Comparison of botulinum toxin-A injection in lacrimal gland and conjunctivodacryocystorhinostomy for treatment of epiphora due to proximal lacrimal system obstruction.

PurposeTo investigate and compare the efficacy of botulinum toxin-A injection in the lacrimal gland and conjunctivodacryocystorhinostomy surgery for the treatment of epiphora caused by proximal lacrimal system obstruction.MethodsCharts of the patients with proximal canalicular obstruction who had undergone conjunctivodacryocystorhinostomy with permanent tube insertion (18 patients, group 1) or 4 units of botulinum toxin-A injection in the palpebral lobe of the lacrimal gland (20 patients, group 2) were reviewed retrospectively. The upper lacrimal system obstruction was diagnosed by lacrimal system irrigation. Schirmer-1 test and Munk epiphora grading for evaluation of epiphora were performed before the interventions and on tenth day, first, third, and sixth months after the interventions.ResultsImprovement of epiphora was statistically significant at all visits when compared with values before injection (P<0.001) in both of groups. When two techniques were compared, difference in degree of epiphora before and after intervention was not statistically significant (P<0.05). In group 2, none of the patients had punctate epitheliopathy, although there was a significant decrease in Schirmer test results (P<0.001, paired t-test). In group 1, 9 cases (50%) had tube dislocation, 4 cases (22.2%) had obstruction, and granuloma formation. Five cases (25%) had ptosis in group 2.Conclusion Conjunctivodacryocystorhinostomy requires surgical experience, special postoperative care, and multiple revisions. As botulinum toxin-A injection in the lacrimal gland is technically easy, less-invasive, safe, with reversible effects, it can be considered as an alternative treatment in patients with proximal lacrimal system obstruction.

Photoreceptor outer segment layer thickness measured manually on images from spectral domain optical coherence tomography in healthy volunteers.

BACKGROUND AND OBJECTIVE: To investigate photoreceptor outer segment layer thickness measured with a manual technique on images from spectral domain optical coherence tomography (OCT) in healthy volunteers. MATERIALS AND METHODS: In 60 eyes of 30 healthy volunteers, a spectral domain OCT device (Spectralis, Heidelberg Engineering) was used to obtain cross-sectional images of the retina. For each volunteer, two images of each eye were obtained in one sitting. Images were digitally enlarged and the manual calipers feature of the device's software was used to measure, at the lowest point in the fovea, the thickness of the photoreceptor outer segment layer. All measurements were performed by the same investigator. Repeatability was evaluated with the Bland-Altman repeatability coefficient, and intersubject variability with Pearson's coefficient of variation. RESULTS: The mean values of measurements across all the volunteers were as follows: right eye first image 38.1 micrometers, right eye second image 37.9 micrometers, left eye first image 37.9 micrometers, left eye second image 37.9 micrometers. The repeatability coefficient, i.e. the difference between repeated measurements which would be exceeded in only 5% of cases, was 1.6 micrometers. Coefficients of variation for the right eye were 3.4% for the first images and 3.4% for the second images, and for the left eye they were 3.2 and 4.0% respectively. CONCLUSION: With a manual method based on spectral domain OCT, the thickness of the photoreceptor outer segment layer at the central fovea can be measured within a useful range of repeatability and appears to be relatively constant across healthy volunteers.

Intravitreal ranibizumab for neovascular age-related macular degeneration patients with good baseline visual acuity and the predictive factors for visual outcomes.

PURPOSE: To evaluate the efficacy of intravitreal ranibizumab for the treatment of neovascular age-related macular degeneration (nAMD) patients with a visual acuity (VA) of ≥ 20/40 and to investigate the predictive factors for visual outcomes. METHODS: The present study is a retrospective analysis of patients with VA ≥ 20/40. Injections were given monthly for the first 3 months and thereafter as needed. The patients were divided into two groups; group 1, patients not receiving further injections beyond the 3 loading doses, and group 2, those who received further injections. Next, group 2 was divided into two subgroups; group 2A, patients who did not experience VA loss, and group 2B, those who experienced VA loss. Data collected for each patient included VA and central retinal thickness (CRT) measured at baseline, months 3, 6, 9, and 12. RESULTS: The study included 96 eyes of 96 patients. Change in VA showed a significant inverse correlation with total number of injections at month 12 (r=-0.34, P=0.001), and the presence of pigment epithelial detachment (PED) at baseline (r=-0.35, P<0.01). VA outcomes were better in group 1 than group 2 at all time points (P<0.001 for all). Change in VA at month 3 was not significantly different between groups 2A and 2B (P=0.26); however, change in VA at month 6, 9, and 12 were statistically different between the two groups (P<0.001 for all). CONCLUSION: Intravitreal ranibizumab is an effective treatment for nAMD patients with good VA. The presence of PED, need for reinjection, and VA loss were unfavorable prognostic factors.

Remove, rotate, and reimplant: a novel technique for the management of exposed porous anophthalmic implants in eviscerated patients.

PURPOSE: To describe and to evaluate a new and relatively easy technique for porous implant exposure repair. METHODS: Eleven patients with exposed porous orbital implants after evisceration were included in this study. Five patients with large exposures (diameter >7 mm) and six patients with small exposures of orbital implants (diameter <7 mm) that persisted despite posterior vaulting of the prosthesis and usage of antibiotics and steroids for more than 6 weeks, underwent revision surgery with the remove-rotate-reimplant technique (3R technique). Negative microbiological culture taken from the exposed socket surface before surgery was the major inclusion criterion. Five patients with insufficient conjunctival tissue also underwent additional mucosa or hard palate grafting of the defect in addition to the remove-rotate-reimplant procedure. RESULTS: Patients have been followed up for more than 18 months (ranging from 18-30 months). None of them received motility peg insertion after repair. Implant reexposure was detected in one patient during the follow-up period, which was managed by dermis fat grafting with implant removal. CONCLUSION: The remove-rotate-reimplant technique is an effective surgical method for repairing exposed porous anophthalmic implants after evisceration with a 90% success in this study. It avoids the removal of the implant from the sclera, which is a traumatic procedure that may lead to the tearing and loss of scleral tissue covering the implant. Saving the porous implant and scleral cover reduces the surgical time and cost.

Ocular imaging findings of bilateral optic disc pit in a child.

BACKGROUND: To report a rare condition of bilateral optic disc pit in a child. CASE DESCRIPTION: A ten-year-old female was admitted with a complaint of headache. Visual acuity was 20/20 in both eyes (OU). Anterior segment examination was normal in OU. Fundus examination revealed optic disc pit (ODP) located temporally with a diameter of 1/5 disc diameter in OU. Intraocular pressure was within normal limits in both eyes. Macular optical coherence tomography (OCT) showed a loss of retinal tissue at the site corresponding to the ODP in both eyes. Retinal nerve fiber OCT revealed decreased RNFL thickness at the temporal side of the optic nerve, corresponding to the ODP in both eyes. The patient and patient's parents were informed about the disease and called for follow-up examinations every 6 months. In addition, the family was informed about optic pit maculopathy (OPM) and, they were told to return immediately if the patient ever complained of decreased vision in either of her eyes. After a follow-up period of 12 months, visual acuity remained stable, and no complications secondary to ODP were detected. CONCLUSION: Optic disc pit is diagnosed incidentally unless it is complicated with OPM. The retinal nerve fiber layer thickness is decreased at the side of the optic nerve corresponding to the ODP.

Vertical muscle transposition augmented with lateral fixation (Foster) suture for Duane syndrome and sixth nerve palsy.

PURPOSE: To report the postoperative results of full-tendon vertical rectus transposition (VRT) augmented with lateral fixation suture for the treatment of type 1 Duane syndrome and sixth nerve palsy and to determine whether there was a decrease in the effect of the Foster suture over time. METHODS: This retrospective, consecutive case series included patients who underwent a full-tendon VRT transposition with lateral fixation for type 1 Duane syndrome or sixth nerve palsy. The primary outcome measures included deviation, abnormal head posture(AHP), abduction deficiency, and postoperative binocular single visual field (BSVF). RESULTS: Eighty-seven patients (87 eyes: 40 eyes with Duane syndrome and 47 eyes with sixth nerve palsy) were included in this study. In Duane syndrome patients, the deviation was reduced by a mean of 95%, the AHP was eliminated in 86% of patients, the abduction was improved by 42%, and a useful BSVF of ≈ 67% of normal was achieved at 1 year post operation. In sixth nerve palsy patients, the deviation was reduced by 99%, the abduction was improved by 59%, and a useful BSVF of ≈ 71% of normal was achieved at 1 year post operation. In both groups, the improvements in deviation angle and abduction were stable postoperatively. Sixteen patients needed reoperation for undercorrection. CONCLUSION: VRT surgery with posterior fixation is an effective treatment method for complete sixth nerve palsy and Duane syndrome with esotropia, AHP, and abduction deficiency. The procedure carries a small risk of reoperation for undercorrection. The effect of the Foster suture did not decline over time.

Changes in choroidal thickness, axial length, and ocular perfusion pressure accompanying successful glaucoma filtration surgery.

PURPOSE: To investigate the changes in choroidal thickness (CT), axial length (AL), and ocular perfusion pressure (OPP) accompanying intraocular pressure (IOP) reduction after trabeculectomy. methods: Thirty-nine eyes of 39 patients with primary open-angle glaucoma uncontrolled by medical therapy were included in this prospective and interventional study. All patients underwent a fornix-based trabeculectomy. The CT was measured by enhanced depth imaging-optical coherence tomography. IOP, AL, and systolic/diastolic blood pressure were also measured, and OPP was calculated. All measurements were performed at baseline and 1 month after surgery. RESULTS: The mean IOP was 25.0 ± 5.8 mm Hg at baseline and 11.7 ± 2.6 mm Hg after trabeculectomy (P<0.001), and the mean subfoveal CT was 295 ± 84 mm Hg at baseline and 331 ± 82 mm Hg after trabeculectomy (P<0.001). The mean AL was 23.64 ± 0.98 mm at baseline and 23.54 ± 0.96 mm after trabeculectomy (P<0.001), whereas the mean OPP was 38.8 ± 6.2 mm Hg preoperatively, and 51.1 ± 7.3 mm Hg postoperatively (P<0.001). The change in CT negatively correlated with the change in IOP (r=-0.785, P<0.001) and AL (r=-0.693, P<0.001), whereas it positively correlated with the change in OPP (r=0.418, P=0.008). CONCLUSION: These results suggest that the large IOP decrease following trabeculectomy causes choroidal thickening. In addition, CT changes are associated with IOP and AL reduction as well as OPP increase.

Long-term results of half-dose photodynamic therapy for chronic central serous chorioretinopathy with contrast sensitivity changes.

PURPOSE: To evaluate the efficacy and safety of photodynamic therapy (PDT) with half-dose verteporfin in patients with chronic central serous chorioretinopathy (CCSC) and retinal functional changes, by functional acuity contrast test (FACT). METHODS: In this study, 27 eyes of 24 patients with CCSC were treated with PDT with half-dose verteporfin. Best-corrected visual acuity (BCVA), central foveal thickness (CFT) and resolution of subretinal fluid on optical coherence tomography (OCT), and leakage on fluorescein angiography (FA) and indocyanine green angiography (ICGA) were assessed. Contrast sensitivity test was performed at baseline and at 12th month for investigating retinal functional changes. RESULTS: The mean follow-up period was 25.33 ± 11.08 months. The mean age was 43.7 ± 8.6 years. Seventeen patients were male (70.8%) and seven patients were female (29.2%). Post PDT at 1st, 3rd, 6th, 12th month and at last follow-up, BCVA were significantly improved compared with the baseline BCVA (P<0.001), and CFT post PDT were significantly thinner than the baseline measurement (P<0.001). There was significant difference between pre- and post-PDT 12th month contrast sensitivities at all five different spatial frequency channels (P<0.01). CONCLUSIONS: Half-dose PDT is an effective and safe method in the treatment of CCSC with anatomical and functional success. The measurement of contrast sensitivity by FACT can be useful for evaluating the functional effectiveness of half-dose PDT for CCSC.

The biomechanical properties of the cornea in patients with systemic lupus erythematosus.

UNLABELLED: PUPOSE: The purpose of this study was to compare the biomechanical properties of the cornea and intraocular pressure (IOP) between patients with systemic lupus erythematosis (SLE) and age-matched controls. PATIENTS AND METHODS: In this prospective study, 30 healthy individuals (control group) and 30 patients with SLE (study group) underwent Reichert ocular response analyzer (ORA) measurements. In the right eye of each participant, the corneal hysteresis (CH), corneal resistance factor (CRF), and Goldman-related IOP (IOPg) were recorded using the ORA. RESULTS: Mean CH, CRF, IOPg were significantly different between groups. Mean CH was 10.2 ± 0.6 mm Hg in the study group and 11.3 ± 1.3 in the control group (P=0.02); mean CRF was 9.7 ± 1.1 mm Hg and 11.9 ± 1.5 mm Hg, respectively (P=0.001). Mean IOP(g) was 13.9 ± 2.9 mm Hg in the study group and 16.9 ± 2.6 mm Hg in the control group (P=0.001). CONCLUSION: The biomechanical properties of the cornea are altered in patients with SLE compared with normal controls. These findings should be taken into account when measuring IOP values in patients with SLE as IOP readings may be underestimated in SLE eyes.

A Turkish case of subcortical/subependymal heterotopia associated with corpus callosum dysgenesis, craniofacial dysmorphism, severe eye abnormalities, and growth-mental retardation.

The patient is a 12-year-old boy with a history of learning disability, growth retardation, and strabismus. Weight, height and head circumference were below the 3rd percentile. A café-au-lait spot, 1x1 cm a diameter, on the back region and pectus excavatum deformity were diagnosed. He had facial asymmetry, a broad nose, sparse eyebrows and eyelashes, a rudimentary frontal sinus, deviation of the nasal septum, and bilateral small maxillary bones. The left orbital fossa was also mildly rudimentary. On eye examination the movements of the left globe to the upward and lateral side were limited and internal strabismus was noted at this side. Visual acuity was 1/10, bilaterally. Bilateral choroid coloboma, glaucoma, vertical and horizontal nystagmus were diagnosed. Fundoscopic examination revealed bilateral optic atrophy and macular and paramacular granulation tissues on the left side. Intelligence quotient was 46. Electroencephalography revealed bilateral frontal slow-wave activity. Visual evoked potential revealed prolonged p100 wave latencies bilaterally. Magnetic resonance imaging of the brain demonstrated corpus callosum dysgenesis, bilateral subcortical heterotopia in the frontal lobes and subependymal heterotopia in the posterior horn of the left ventricle. Chromosomal analysis revealed a normal male karyotype, 46, XY. Although several cases of heterotopia in association with mental retardation, craniofacial dysmorphism, cerebral, and eye abnormalities have been described the combination of abnormalities diagnosed in our case has not previously been reported. We hypothesize that the combination of subcortical/subependymal heterotopia, corpus callosum dysgenesis, craniofacial dysmorphism, severe eye abnormalities, and growth-mental retardation may be a new syndrome.

Effects of fibrovascular traction and pooling of tears on corneal topographic changes induced by pterygium.

AIM: To investigate the effects of fibrovascular traction and the pooling of tears at the pterygium apex on the corneal topographic changes induced by pterygium. METHODS: A total of 16 eyes of 14 cases with primary pterygium were included in the study. A computerized corneal topography system was used for corneal topography examinations. Baseline keratographs were taken two times at straight gaze. A repeat corneoscope photograph was immediately obtained in temporal gaze. Then the tears at the pterygium apex were dried with a cellulose sponge, and a new corneoscope photograph was immediately obtained without allowing one to blink. Corneal topographic maps (numeric maps) were divided into 301 fields in 24 meridians. One colour was allocated to each field, representing its mean refractive power for all groups. In all eyes, keratometric astigmatism at the 3 mm central cornea and total mean corneal refractive power were found. Data were compared using paired-samples two-tailed t-tests. RESULTS: Keratometric astigmatism at the 3 mm central cornea was significantly reduced at the temporal gaze (3.10+/-2.34 D, t=3.40, P=0.027) and dried eyes (2.12+/-1.01 D, t=4.74, P=0.001) according to the first baseline measurement (4.31+/-1.91 D) of the total mean corneal refractive power was found to be 43.45+/-1.28 D (39.29-45.87) at the first baseline measurement. There was no change at the temporal gaze (43.54+/-1.06 D, P>0.05). However, the total corneal refractive power was significantly higher in dried eyes (44.26+/-0.93 D, t=34.92, P<0.001). The steepest region of corneal topography was a superior quadrant, and the flattest area was a nasal quadrant at the baseline. At the temporal gaze, the cornea was significantly flatter in the superior and inferior sides of the pterygium meridian. After dried pooling of tears, topographic abnormalities returned, and the cornea became more uniform and symmetric. CONCLUSION: We conclude that the pooling of tears at the pterygium apex plays an important role, but fibrovascular traction has no effect on the corneal topographical changes induced by pterygium.

The effect of pterygium surgery on corneal topography.

OBJECTIVE: The aim of this prospective randomized clinical study was to evaluate the effect of pterygium surgery on the corneal topography using a computerized corneal topography system. PATIENTS AND METHODS: Computerized corneal topography was performed on 27 patients with primary pterygium before and after pterygium excision surgery. The topographical changes that occurred following surgery were evaluated using paired and unpaired two-tailed t-test and Pearson coefficient of correlation analyses. Simulated keratometric astigmatism at the central 3 mm and the total mean refractive powers of the whole cornea were measured before and after surgery. Following surgery, flattened or steepened corneal areas were determined. RESULTS: Simulated keratometric astigmatism at 3 mm was found to be 2.30 +/- 2.08 D (0.2 - 7.63) preoperatively and 0.82 +/- 0.74 D (0.06 - 2.79) postoperatively. The difference between these two values was statistically significant (t = -3.46, P = 0.002). Total mean refractive power of the whole cornea was found to be 42.26 +/- 0.63 (40.80 - 43.64) preoperatively and 43.69 +/- 0.88 (41.50 - 44.90) postoperatively and the difference was 1.42 +/- 0.87. There was a statistically significant high difference (t = 28.36, P < 0.001). When preoperative and postoperative corneal topographies were compared, the whole cornea was found steeper at the postoperative period except a little region in the superior nasal quadrant. CONCLUSION: We believe that corneal topographical changes caused by the pterygium are almost reversible after surgical treatment, and postoperatively the cornea becomes steeper.

Changes in anterior chamber depth and axial length measurements after radial keratotomy.

PURPOSE: To evaluate the changes that occur in anterior chamber depth and globe axial length after radial keratotomy (RK) surgery in cases with different degrees of myopia. METHODS: One hundred and twelve eyes that underwent RK were studied. The eyes were divided into two groups: 70 eyes with a correction of myopia of 4.00 D and under after RK (group 1) and 42 eyes with a correction of myopia of more than 4.00 D (group 2). Routine examinations were done in all cases. Ultrasonic biometry and central anterior chamber depth and axial length were measured pre-operatively and on the third day, second week, third month and sixth month post-operatively. RESULTS: Pre-operatively the average globe axial length was longer in group 2 than group 1. When all post-operative measurements were compared with pre-operative measurements in group 1, there was a decrease in anterior chamber depth and globe axial length, but no significant difference was found except on the third day (t = 3.15, p = 0.003). In group 2 there was an insignificant decrease in axial length but the decrease in anterior chamber depth was significant at all measurement times except for the sixth month. CONCLUSIONS: Refractive changes related to biometric changes after RK are not important compared with the total refractive corrections of RK. These changes should be considered, however, when planning RK procedures.

A comparative study on the effect of radial keratotomy in patients who live at sea level and high altitude.

PURPOSE: To compare the refractive and keratometric results of matched pairs of patients who underwent radial keratotomy (RK) at sea level and high altitude. METHODS: The results of 30 eyes that underwent RK procedures in two clinical centres at different altitude were analysed. One centre was at sea level (Istanbul) and the other at an altitude of 1720 m (Van). The patients in the two centres were matched regarding gender, age, degree of myopia, number of incisions and optic zone size. There were 15 eyes in each group. All operations were performed with a diamond blade using a Russian technique by the same surgeon. RESULTS: The mean pre-operative spherical equivalent cycloplegic refractions (SECR) were -6.33 +/- 1.15 D and -6.32 +/- 1.01 D in the Istanbul and Van groups, respectively (p = 0.96). The mean post-operative SECRs were -1.93 +/- 1.03 D and -0.28 +/- 0.57 D in the Istanbul and Van groups, respectively (p < 0.001). The mean SECR changes were 4.40 +/- 0.92 D and 6.03 +/- 1.13 D in subjects who had undergone RK at sea level and at 1720 m, respectively (p < 0.001). CONCLUSION: These results show that a higher myopic correction can be provided in patients who undergo RK at high altitude compared with those operated on at sea level. The RK nomograms used by refractive surgeons performing RK surgery at high altitude may need to be redesigned in the light of future studies with long-term follow-up.

The effect of 0.25% apraclonidine in preventing intraocular pressure elevation after Nd:YAG laser posterior capsulotomy.

PURPOSE: The efficacy and adverse effects of 0.25% apraclonidine on intraocular pressure (IOP) after Nd:YAG laser posterior capsulotomy were investigated, and the results were compared with placebo, 0.50% timolol maleate and 1% apraclonidine. METHODS: Eighty eyes were randomly assigned to four groups of 20 eyes. In a double-masked design, the groups were treated with placebo (group 1), 0.50% timolol maleate (group 2), 1% apraclonidine (group 3), 0.25% apraclonidine (group 4) one hour before and five minutes after Nd:YAG laser posterior capsulotomy. IOP was measured by applanation tonometry 1 hour before (baseline IOP) and 1, 3, 24 hours after capsulotomy. RESULTS: The average baseline IOP increased respectively 3.90 +/- 5.35, 5.95 +/- 5.32, 1.15 +/- 3.20 mmHg in the first group 1, 3 and 24 hours post-treatment. There were significant differences between baseline IOP and 1 and 3 hours but not at 24 hours (p = 0.004, p = 0.001, p = 0.13). IOP increased 0.40 +/- 4.08, 0.75 +/- 5.33, 0.80 +/- 6.03 mmHg in the second group at the same times. The differences between the average baseline IOP and the 1, 3 and 24 h measurement were not significant (p = 0.83, p = 0.65, p = 0.93). In the third group, IOP decreased 3.70 +/- 2.40, 3.30 +/- 2.47, 2.65 +/- 1.56 mmHg at the measurement times, with significant differences between the average baseline IOP and the 1, 3 and 24 hour measurements (p = 0.001, p = 0.0001, p = 0.01). In the fourth group IOP increased 0.35 +/- 3.32 mmHg at 1 hour, but decreased 1.25 +/- 3.41, 0.90 +/- 2.07 mmHg at 3 and 24 hours. The differences were not significant (p = 0.94, p = 0.16, p = 0.08). When the 0.25% and 1% apraclonidine groups were compared, there were significant differences between the average IOP at 1 hour in both groups but not at 3 and 24 hours (p = 0.01, p = 0.17, p = 0.21). Similarly, there were no significant differences between the average IOP at the same times when the 0.25% apraclonidine group was compared with the timolol group (p = 0.30, p = 0.08, p = 0.16). Some systemic and local side effects were seen in the timolol and 1% apraclonidine groups, but none with 0.25% apraclonidine. CONCLUSIONS: It was concluded that 0.25% apraclonidine is effective in preventing the early elevation of IOP after Nd:YAG laser posterior capsulotomy and may offer an alternative to 0.50% timolol maleate and 1% apraclonidine.