We can't afford to turn a blind eye to myopia.

BACKGROUND: Myopia is becoming increasingly prevalent throughout the world. It is an overlooked but leading cause of blindness, particularly among the working aged population. Myopia is often considered benign because it is easily corrected with glasses, contact lenses or refractive surgery. Traditionally myopia has been classified into physiological and pathological subtypes based on the degree of myopia present. Higher levels of myopia are associated with increased risk of pathological complications but it is important to note that there is no safe level of myopia. Even low levels of myopia increase the risk of retinal detachment and other ocular comorbidities which will be discussed in detail later. The most serious complication, myopic maculopathy, is the only leading cause of blindness without an established treatment and therefore leads to inevitable loss of vision in some myopes, even at a young age. AIM: To highlight the current myopia epidemic and the sight threatening complications associated with it. DESIGN: This is a commissioned review article. Data were gathered by performing a literature review, searching the PubMed database for recent articles regarding myopia. CONCLUSIONS: Myopia is a potentially blinding disease. By identifying at risk individuals and intervening before they become myopic, eye care practitioners can prevent or delay spectacle use, reduce the risk of the myriad of myopic complications, thereby improve the patient's quality of life and positively impact its socio-economic effects.

Psychophysical impact and optical and morphological characteristics of symptomatic non-advanced cataract.

PURPOSE: To investigate whether psychophysical, morphological, and/or optical characteristics of symptomatic non-advanced cataract are complementary to, or more appropriate than, visual acuity (VA) for the purposes of recording visual data that reflect subjective visual difficulty in patients with cataract that exhibit relative sparing of high contrast acuity (0.4 logarithm of minimal angle of resolution (logMAR) scale or better). METHODS: Eighty-two patients with symptomatic non-advanced cataract and no other ocular pathology were asked to complete a validated questionnaire, and to perform a series of visual function assessments including: corrected distance VA (CDVA); photopic and mesopic contrast sensitivity; photopic and mesopic glare disability (GD); reading acuity and reading speed; stereoacuity; and retinal sensitivity. Optical and morphological characteristics of the cataract were evaluated by lens optical density and by the Lens Opacities Classification System III, respectively. Correlations between questionnaire score and each of these measures were calculated. RESULTS: Statistically significant negative correlations were observed between the Rasch-scaled questionnaire score and mesopic GD (at 3 and 6 cycles per degree (cpd); r=-0.396 (P<0.01) and -0.451 (P<0.05), respectively) and between the Rasch-scaled questionnaire score and photopic GD (at 3 and 6 cpd; r=-0.328 (P<0.01) and -0.440 (P<0.01), respectively). CONCLUSION: Symptomatic non-advanced cataract, in the presence of good CDVA, is associated with measurable subjective visual difficulty, best reflected in a decrease in mesopic and photopic GD (at medium spatial frequencies). CDVA does not reflect the patient's visual dissatisfaction in such cases.

Changes in intraocular pressure and anterior segment morphometry after uneventful phacoemulsification cataract surgery.

PURPOSE: To study changes in anterior segment morphometry after uneventful phacoemulsification cataract surgery, and to investigate whether there is a relationship between any observed changes and intraocular pressure (IOP) reduction after the procedure. METHODS: The anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA), central corneal thickness (CCT), and IOP were measured in 101 non-glaucomatous eyes before and after uneventful phacoemulsification cataract surgery. RESULTS: After cataract surgery, the mean ACD, ACV, and ACA values increased by 1.08 mm, 54.4 mm(3), and 13.1 degrees , respectively, and the mean IOP (corrected for CCT) decreased by 3.2 mm Hg. The predictive value of a previously described index (preoperative ACD/preoperative IOP (corrected for CCT) or CPD ratio) for IOP (corrected for CCT) reduction after cataract surgery was confirmed, reflected in an r(2) value of 23.3% between these two parameters (P<0.001). Other indices predictive of IOP reduction after cataract surgery were also identified, including preoperative IOP/preoperative ACV and preoperative IOP/preoperative ACA, reflected in r(2) values of 13.7 and 13.7%, respectively (P<0.001 and P<0.001, respectively). CONCLUSIONS: Our study confirms the predictive value of the CPD ratio for IOP reduction after cataract surgery, and may contribute to the decision-making process in patients with glaucoma or ocular hypertension. Furthermore, two novel indices of preoperative parameters that are predictive for IOP reduction after cataract surgery were identified, and enhance our understanding of the mechanisms underlying IOP changes after this procedure.

Four genes are required for the system II cytochrome c biogenesis pathway in Bordetella pertussis, a unique bacterial model.

Unlike other cytochromes, c-type cytochromes have two covalent bonds formed between the two vinyl groups of haem and two cysteines of the protein. This haem ligation requires specific assembly proteins in prokaryotes or eukaryotic mitochondria and chloroplasts. Here, it is shown that Bordetella pertussis is an excellent bacterial model for the widespread system II cytochrome c synthesis pathway. Mutations in four different genes (ccsA, ccsB, ccsX and dipZ) result in B. pertussis strains unable to synthesize any of at least seven c-type cytochromes. Using a cytochrome c4:alkaline phosphatase fusion protein as a bifunctional reporter, it was demonstrated that the B. pertussis wild-type and mutant strains secrete an active alkaline phosphatase fusion protein. However, unlike the wild type, all four mutants are unable to attach haem covalently, resulting in a degraded N-terminal apocytochrome c4 component. Thus, apocytochrome c secretion is normal in each of the four mutants, but all are defective in a periplasmic assembly step (or export of haem). CcsX is related to thioredoxins, which possess a conserved CysXxxXxxCys motif. Using phoA gene fusions as reporters, CcsX was proven to be a periplasmic thioredoxin-like protein. Both the B. pertussis dipZ (i. e. dsbD) and ccsX mutants are corrected for their assembly defects by the thiol-reducing compounds, dithiothreitol and 2-mercaptoethanesulphonic acid. These results indicate that DipZ and CcsX are required for the periplasmic reduction of the cysteines of apocytochromes c before ligation. In contrast, the ccsA and ccsB mutants are not corrected by exogenous reducing agents, suggesting that CcsA and CcsB are required for the haem ligation step itself in the periplasm (or export of haem to the periplasm). Related to this suggestion, the topology of CcsB was determined experimentally, demonstrating that CcsB has four transmembrane domains and a large 435-amino-acid periplasmic region.

The surgical diathermy: principles of operation and safe use.

An understanding of the principles of operation and hazards of the surgical diathermy is necessary for the safety of the anaesthetized patient. The surgical diathermy performs its function by the application of high density radio frequency current which can be used to cut or coagulate tissue. Its improper use can result in electrical burns and even electrocution. The principles underlying its safe use are outlined, and detailed recommendations are made to ensure the patient's safety.

Measurement errors in pneumotachography due to pressure transducer design.

When pneumotachography is used during intermittent positive pressure ventilation (IPPV), the design of some differential pressure transducers can cause measurement errors. These errors may be avoided by using differential pressure transducers which have small, equal chambers free from temperature sensitive electrical elements. Few of the transducers which are sensitive enough for clinical use fulfil these requirements.

Errors in pneumotachography with intermittent positive pressure ventilation.

Instrument errors that can occur when pneumotachography is used during Intermittedt Positive Pressure Ventilation (IPPV) have been described previously (Kafer 1973). Our efforts to eliminate these errors led to the discovery of further inaccuracies, which appear to be due to the design of the differential pressure transducers used with pneumotachograph head. A system was used in which a sine-wave pump delivered a constant tidal volume to a dummy lung, the tidal volume being measured by means of a pneumotachograph. Using Grass, Statham and Devices differential pressure transducers, the volume recorded as leaving the dummy lung was consistently greater than that recorded as entering, and changing the pneumatic polarity of the differential pressure transducer produced large differences in the recorded volume. In some cases the error was greater than the volume being measured. There would seem to be several causes of such errors. The Sanborn 270 differential pressure transducer and the Greer micromanometer appeared to be free of these artifacts. The results of this study throw into doubt much previously published work using pneumotachography during IPPV.