Outcome of cataract surgery in Nigeria: visual acuity, autorefraction, and optimal intraocular lens powers--results from the Nigeria national survey.

OBJECTIVE: To describe presenting and corrected visual acuities after cataract surgery in a nationally representative sample of adults. Another objective was to describe refractive errors in operated eyes and to determine the optimal range of intraocular lens (IOL) powers for this population. DESIGN: Cross-sectional, population-based survey. PARTICIPANTS: Adults aged 40 years and more were selected using multistage stratified sampling and proportional to size procedures. A sample size of 15027 was calculated, and clusters were selected from all states. METHODS: Individuals who had undergone cataract surgery were identified from interview and examination. All had their presenting visual acuity (VA) measured using a reduced logarithm of the minimum angle of resolution chart and underwent autorefraction. Corrected VAs were assessed using the autorefraction results in a trial set. An ophthalmologist conducted all examinations, including slit-lamp and dilated fundus examination. Causes of visual loss were determined for all eyes with a presenting VA <6/12 using the World Health Organization recommendations. Biometry data were derived from 20449 phakic eyes using the SRK-T formula after excluding those with poor VA or corneal opacities. MAIN OUTCOME MEASURES: Presenting and corrected visual acuities in pseudo/aphakic individuals and autorefraction findings; biometry profile of Nigerian adults. RESULTS: Data from 288 eyes of 217 participants were analyzed. Only 39.5% of eyes had undergone IOL implantation at surgery. Only 29.9% of eyes had a good outcome (i.e., ≥6/18) at presentation, increasing to 55.9% with correction. Use of an IOL was the only factor associated with a good outcome at presentation (odds ratio 9.0; 95% confidence interval, 4.3-18.9; P=0.001). Eyes undergoing cataract surgery had a higher prevalence and degree of astigmatism than phakic eyes. Biometry data reveal that posterior chamber IOL powers of 20, 21, and 22 diopters (D) (A constant 118.0) will give a postoperative refraction range of -2.0 D to emmetropia in 71.4% of eyes, which increases to 82.6% if 19 D is also included. CONCLUSIONS: Postoperative astigmatism needs to be reduced through better surgical techniques and training, and use of biometry should be standard of care

Prevalence and risk factors for hypertension and association with ethnicity in Nigeria: results from a national survey.

OBJECTIVE: Non-communicable diseases are now a global priority. We report on the prevalence of hypertension and its risk factors, including ethnicity, in a nationally representative sample of Nigerian adults recruited to a survey of visual impairment. METHODS: multi-stage, stratified, cluster random sample with probability proportional to size procedures was used to obtain a nationally representative sample of 13 591 subjects aged ≥ 40 years. Of these, 13 504 (99.4%) had a blood pressure measurement. RESULTS: The prevalence of hypertension was 44.9% [95% confidence interval (CI): 43.5-46.3% ]. Increasing age, gender, urban residence and body mass index were independent risk factors (p < 0.001). The Kanuri ethnic group had the highest prevalence of hypertension (77.5%, 95% CI: 71.0-84.0%). CONCLUSIONS: The high prevalence of hypertension in Nigeria is a cause for concern and suggests that it is inevitable that the impact of hypertension-related ill health is imminent, with the accompanying financial and societal costs to families and the state of Nigeria

Coverage of hospital-based cataract surgery and barriers to the uptake of surgery among cataract blind persons in nigeria: the Nigeria National Blindness and Visual Impairment Survey.

PURPOSE: To determine cataract surgical coverage, and barriers to modern cataract surgery in Nigeria. METHODS: Multistage stratified cluster random sampling was used to identify a nationally representative sample of 15,027 persons aged 40+ years. All underwent visual acuity testing, frequency doubling technology visual field testing, autorefraction, and measurement of best corrected vision if <6/12 in one or both eyes. An ophthalmologist examined the anterior segment and fundus through an undilated pupil for all participants. Participants were examined by a second ophthalmologist using a slit lamp and dilated fundus examination using a 90 diopter condensing lens if vision was <6/12 in one or both eyes, there were optic disc changes suggestive of glaucoma, and 1 in 7 participants regardless of findings. All those who had undergone cataract surgery were asked where and when this had taken place. Individuals who were severely visually impaired or blind from unoperated cataract were asked to explain why they had not undergone surgery. RESULTS: A total of 13,591 participants were examined (response rate 89.9%). Prevalence of cataract surgery was 1.6% (95% confidence interval 1.4-1.8), significantly higher among those aged ≥70 years. Cataract surgical coverage (persons) in Nigeria was 38.3%. Coverage was 1.7 times higher among males than females. Coverage was only 9.1% among women in the South-South geopolitical zone. Over one third of those who were cataract blind said they could not afford surgery (36%). CONCLUSIONS: Cataract surgical coverage in Nigeria was among the lowest in the world. Urgent initiatives are necessary to improve surgical output and access to surgery

Diamagnetic Persistent Currents and Spontaneous Time-Reversal Symmetry Breaking in Mesoscopic Structures

Recently, new strongly interacting phases have been uncovered in mesoscopic systems with chaotic scattering at the boundaries by two of the present authors and R. Shankar. This analysis is reliable when the dimensionless conductance of the system is large, and is nonperturbative in both disorder and interactions. The new phases are the mesoscopic analogue of spontaneous distortions of the Fermi surface induced by interactions in bulk systems and can occur in any Fermi liquid channel with angular momentum $m$. Here we show that the phase with $m$ even has a diamagnetic persistent current (seen experimentally but mysterious theoretically), while that with $m$ odd can be driven through a transition which spontaneously breaks time-reversal symmetry by increasing the coupling to dissipative leads.Comment: 4 pages, three eps figure

STM conductance of Kondo impurities on open and structured surfaces

We study the scanning tunneling microscopy response for magnetic atoms on open and structured surfaces using Wilson's renormalization group. We observe Fano resonances associated with Kondo resonances and interference effects. For a magnetic atom in a quantum corral coupled to the confined surface states, and experimentally relevant parameters, we observe a large confinement induced effect not present in the experiments. These results suggest that the Kondo screening is dominated by the bulk electrons rather than the surface ones.Comment: 6 pages, 6 figure

Edge reconstructions in fractional quantum Hall systems

Two dimensional electron systems exhibiting the fractional quantum Hall effects are characterized by a quantized Hall conductance and a dissipationless bulk. The transport in these systems occurs only at the edges where gapless excitations are present. We present a {\it microscopic} calculation of the edge states in the fractional quantum Hall systems at various filling factors using the extended Hamiltonian theory of the fractional quantum Hall effect. We find that at $\nu=1/3$ the quantum Hall edge undergoes a reconstruction as the background potential softens, whereas quantum Hall edges at higher filling factors, such as $\nu=2/5, 3/7$, are robust against reconstruction. We present the results for the dependence of the edge states on various system parameters such as temperature, functional form and range of electron-electron interactions, and the confining potential. Our results have implications for the tunneling experiments into the edge of a fractional quantum Hall system.Comment: 11 pages, 9 figures; minor typos corrected; added 2 reference

Exact solution of Calogero model with competing long-range interactions

An integrable extension of the Calogero model is proposed to study the competing effect of momentum dependent long-range interaction over the original {1 \ov r^2} interaction. The eigenvalue problem is exactly solved and the consequences on the generalized exclusion statistics, which appears to differ from the exchange statistics, are analyzed. Family of dual models with different coupling constants is shown to exist with same exclusion statistics.Comment: Revtex, 6 pages, 1 figure, hermitian variant of the model included, final version to appear in Phys. Rev.

Quantum Dots with Disorder and Interactions: A Solvable Large-g Limit

We show that problem of interacting electrons in a quantum dot with chaotic boundary conditions is solvable in the large-g limit, where g is the dimensionless conductance of the dot. The critical point of the $g=\infty$ theory (whose location and exponent are known exactly) that separates strong and weak-coupling phases also controls a wider fan-shaped region in the coupling-1/g plane, just as a quantum critical point controls the fan in at T>0. The weak-coupling phase is governed by the Universal Hamiltonian and the strong-coupling phase is a disordered version of the Pomeranchuk transition in a clean Fermi liquid. Predictions are made in the various regimes for the Coulomb Blockade peak spacing distributions and Fock-space delocalization (reflected in the quasiparticle width and ground state wavefunction).Comment: 4 pages, 2 figure

A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade

We provide a framework for analyzing the problem of interacting electrons in a ballistic quantum dot with chaotic boundary conditions within an energy $E_T$ (the Thouless energy) of the Fermi energy. Within this window we show that the interactions can be characterized by Landau Fermi liquid parameters. When $g$, the dimensionless conductance of the dot, is large, we find that the disordered interacting problem can be solved in a saddle-point approximation which becomes exact as $g\to\infty$ (as in a large-N theory). The infinite $g$ theory shows a transition to a strong-coupling phase characterized by the same order parameter as in the Pomeranchuk transition in clean systems (a spontaneous interaction-induced Fermi surface distortion), but smeared and pinned by disorder. At finite $g$, the two phases and critical point evolve into three regimes in the $u_m-1/g$ plane -- weak- and strong-coupling regimes separated by crossover lines from a quantum-critical regime controlled by the quantum critical point. In the strong-coupling and quantum-critical regions, the quasiparticle acquires a width of the same order as the level spacing $\Delta$ within a few $\Delta$'s of the Fermi energy due to coupling to collective excitations. In the strong coupling regime if $m$ is odd, the dot will (if isolated) cross over from the orthogonal to unitary ensemble for an exponentially small external flux, or will (if strongly coupled to leads) break time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we are treating charge-channel instabilities in spinful systems, leaving spin-channel instabilities for future work. No substantive results are change