Shape and radius of posterior corneal surface

BACKGROUND

The posterior corneal surface is often ignored in predictive models concerned with refractive surgery. In previous studies, the radius of this surface has been measured in a variety of ways, primarily over a large chord diameter of the surface, with the common assumption that the surface is spherical. The asphericity of this surface has not been adequately addressed in the past.

METHODS

An algorithm is derived for the calculation of posterior corneal surface apical radius and using characteristics of the anterior corneal surface and topographic corneal thickness variation. Anterior corneal asphericity was measured using a commercially available photoelectric keratoscope. Using a marked soft contact lens, a simple method of locating noncentral corneal sites is described as an aid to ultrasonic pachometry.

RESULTS

In a group of 20 normal subjects ranging in age from 19 to 23 years, the average posterior corneal surface apical radius and asphericity (p) was 5.80 mm (SD = +/- 0.42) and 0.64 (SD = 0.37) for the vertical meridian, and 5.82 mm (SD = +/- 0.40) and 0.52 (SD = 0.30) for the horizontal meridian. Average central corneal thickness was 533 mu (SD = +/- 19).

CONCLUSIONS

The average asphericity values are below 1, hence the posterior corneal surface is described as a flattening ellipse. The rate of flattening of this surface is greater than the rate of flattening along the averaged anterior corneal surface.

Absorbed aluminium is found with two cytosolic protein fractions, other than ferritin, in the rat duodenum

After in vivo perfusion of the upper intestine of the rat with a range of concentrations of aluminium chloride, entry of the metal into the portal system was only detected when the perfusate exceeded 400 mumol/l, suggesting a mucosal block. Using gel filtration of a mucosal cytosol extract, two consistently appearing aluminium peaks were identified which may represent aluminium binding proteins. Both were heat stable at 60 degrees C and had molecular sizes of about 700 (kilo daltons) (kD) and 17 kD respectively. The larger molecule was distinct from ferritin. Neither molecule associated with 59Fe nor 45Ca. It is suggested that the aluminium peaks are relatively specific aluminium binding proteins that have a scavenging role, reducing entry of the metal from the intestinal contents into the portal blood.

Lung liquid production by in vitro lungs from fetal guinea pigs: effects of arginine vasopressin and arginine vasotocin

Lungs from near-term fetal guinea pigs were supported in vitro for 3 h; lung liquid production rates were measured by a dye dilution technique. Seventy preparations were used to study the effects of arginine vasopressin (AVP) placed in the outer saline for the middle hour, at concentrations reported at birth [fetuses 61 +/- 2 days of gestation; 94.7 +/- 16.2 g (SD) body weight]. At 1200 microU/ml, AVP arrested fluid production (rates, successive hours, 3.03 +/- 0.60, 0.50 +/- 0.14 and 0.02 +/- 0.08 ml/kg body weight per h; falls significant, P < 0.01-0.0005). At 600, 300 and 100 microU/ml there were significant but smaller reductions. Reabsorptions were seen in 8 preparations given 600-1200 microU/ml, AVP. Preparations given 10 microU/ml AVP, AVP carrier or control saline showed no significant change. The responses (% reductions during treatment), were linearly related to the log concentration of AVP (r = 0.99); theoretical threshold, 8 microU/ml). Increasing treatment to 2h did not increase final responses. Preparations from 5 fetuses > 120 g body weight showed significantly greater responses (P < 0.025) [fetuses 64 +/- 2 days of gestation; 135.1 +/- 18.6 g (SD) body weight]. 10(-6) M amiloride abolished responses to AVP [fetuses 62 +/- 1 days of gestation; 93.4 +/- 18.5 g (SD) body weight, n = 30; rates, succeeding hours; AVP alone, 1.78 +/- 0.22, 0.48 +/- 0.09, 0.16 +/- 0.99 (P < 0.01-0.0005); AVP with amiloride, 1.15 +/- 0.07, 0.93 +/- 0.10, 0.86 +/- 0.08 (no significant fall) ml/kg body weight per h]. Thirty-six preparations treated with arginine vasotocin (AVT, 10-600 microU/ml) showed closely similar responses to those from AVP. These studies extend results to fetal guinea pigs, and show that AVP, at concentrations reported at delivery, can slow lung liquid production or cause reabsorption by a direct action on the lung. The effect increases close to term, and is due to activation of amiloride-sensitive Na+ channels.

Corneal light scattering and visual performance in myopic individuals with spectacles, contact lenses, or excimer laser photorefractive keratectomy

Corneal transparency and visual performance are currently receiving much attention after excimer laser surgery. To date, emphasis has been on comparison of eyes on which laser surgery has been performed to eyes with emmetropia. A more appropriate comparison should be between eyes on which laser surgery has been performed and eyes with other forms of correction for myopia. Forward-scattered light, back-scattered light, and visual acuity were investigated and data were collected from 35 myopic individuals with various types of correction for myopia (spectacles, hard and soft contact lenses, and excimer laser surgery). Forward-scattered light was measured by using a new computerized technique, back-scattered light was measured with a charge coupled device-camera system, and visual acuity was measured with a computerized system at various levels of contrast. Spectacles, hard contact lenses, and excimer laser surgery are all superior to soft contact lenses in terms of light scatter and low-contrast visual acuity and excimer laser photorefractive keratectomy produces comparable results to spectacles one year postoperatively. At low-contrast visual acuity, mean visual acuity was 2.45 minutes of arc for the spectacle wearers, 3.21 minutes of arc for the hard contact-lens wearers, and 5.04 minutes of arc for the soft contact-lens wearers. Excimer laser patients had a mean visual acuity of 9.04 minutes of arc three months postoperatively, and 2.53 minutes of arc after one year. A mean value of 2.4% contrast for forward light scatter was obtained for spectacle wearers compared with a level of 3.84% contrast for hard contact-lens wearers and 16.1% contrast for soft contact-lens wearers. The mean value for excimer laser patients was 20% contrast three months postoperatively and 2.1% contrast one year postoperatively.

Halos--a problem for all myopes? A comparison between spectacles, contact lenses, and photorefractive keratectomy

After photorefractive keratectomy (PRK) using excimer lasers (193 nm) many patients report the presence of halos around light sources at night. However, halos are not unique to PRK patients, as they are a common observation in myopic contact lens wearers. We present an objective measurement of the halos using a computerized technique. The patient fixated on a red cross within a white circle in the center of a video monitor which served as the halo source. The screen surrounding the circle was not illuminated. The operator controlled the movement of the white spot and moved the spot toward the halo source until the subject indicated when the cursor was at the outer parameter of the halo. Measurements were made at 30 degree intervals around the halo source and expressed as square degrees. The study found that spectacles, soft contact lenses, and excimer laser surgery were superior to hard contact lenses in terms of the size of the halo. A mean value of 2.51 square degrees was obtained for spectacles wearers compared with 3.18 square degrees for soft contact lenses, 3.14 square degrees for excimer laser patients with 4-millimeter ablation zone, 2.76 square degrees for excimer laser patients with a 5-millimeter ablation zone, and 89.5 square degrees for hard contact lenses. It appears that this device is very useful for measuring the halo size after excimer laser PRK. We concluded that halos were not a problem for our patients after excimer laser photorefractive keratectomy.

Assessment during postgraduate training

The author reviews the traditional process of assessing both undergraduates in medical school and physicians in postgraduate training, contending that this traditional, and still dominant, process is inadequate because of its limitations. It focuses narrowly on end-point evaluation, using predominantly multiple-choice questions, rather than on identifying deficiencies during the training period so that trainees are able to correct these deficiencies before their end-point evaluations. An example of a more valid process of assessment is the set of tests employed by the Royal Australian College of General Practitioners to assess the skills of family practice physicians, by using behavioral ratings. The author concludes that where such tests are used, there may be some difficulty in comparing the performances of undergraduates with those of practicing physicians, in view of the different behaviors being assessed. In any follow-up studies of graduates, attention should be paid to the reliability and validity of the assessment procedures, particularly because differences in the assessment tools may account for some discrepancies between training programs.

Case study of a schizophrenic patient during social skills training in a forensic psychiatry ward

A schizophrenic patient's behaviour was monitored over 12 weeks using the Assessment Schedule and Adult Training Instrument, the patient's self-reports of his symptoms of anxiety, scores on the Social Behaviour Schedule, and the frequency of nocturnal enuresis. Contrary to expectations, the patient's functioning deteriorated generally, with the exception that the trend of deteriorating behaviour, as assessed by hospital staff, appeared to have slowed down during a period involving activities out of the ward.

A survey of aphasia services in the United Kingdom

A survey of the service available, in speech and language therapy departments, to adults with aphasia revealed that many districts in the United Kingdom are unable to fulfil the professional recommendations for the care of aphasic clients. Although individual 'good practice' criteria could be satisfied, only a minority of districts were able to provide a comprehensive service. Levels of staffing for the adult neurological caseload are variable and even, at best, hinder therapists in delivering the recommended standard of management to aphasic clients and their carers.

Correlation between lipids extracted from Bruch's membrane and age

BACKGROUND

There is increasing circumstantial evidence that the chemical composition of the deposits in Bruch's membrane influences the clinical outcome in age-related macular disease. In particular, it has been postulated that deposition of neutral lipids in Bruch's membrane may cause hydrophobicity and predispose to detachment of the retinal pigment epithelium and cause functional loss.

METHODS

Analysis of the lipid extracted from Bruch's membrane of eye bank eyes from donors of different ages has been undertaken using thin layer and gas chromatography. No clinical information was available concerning any previous eye disease.

RESULTS

It is shown that the lipid extracted increases with the age of the donor, and that the total quantity and ratio of neutral fats to phospholipids varies widely from one specimen to another from donors older than 60 years of age. The ratios of the different phospholipids imply that they are not derived from blood.

CONCLUSION

The results are compatible with the concept of hydrophobicity developing with age in Bruch's membrane.

Diet in the epidemiology of postmenopausal breast cancer in the New York State Cohort

A number of authors have presented evidence that high dietary fat increases the risk of breast cancer, and a number have presented evidence to the contrary. In this study, dietary histories were obtained in 1980 from 18,586 postmenopausal women in New York State. These women were followed through 1987 to ascertain their incidence of breast cancer and other cancers and deaths from all causes, as registered in the New York State Tumor Registry and Office of Vital Statistics. Survival analysis revealed that the incidence of breast cancer increased with age, was higher among the nulliparous, was higher for those with a late (> 26 years) age at first pregnancy, and increased with increasing socioeconomic status--all risk factors discovered before for breast cancer. No increase in risk was related to the ingested amount of calories, vitamins A, C, or E, dietary fiber, or fat. Although dietary fat has been found to be associated with higher risk of cancer at a number of other sites, e.g., the lung, colon, and rectum, and although some previous writers have suggested an association with risk of breast cancer, the findings in three cohort studies as well as in eight substantial case-control studies are negative and suggest that a relation is far from established.

[Corneal opacity after photorefractive keratectomy with an excimer laser. Cause, objective measurement and functional consequences]

A marginal loss of corneal transparency or 'haze' is a phenomenon commonly experienced after photorefractive keratectomy using excimer lasers (193 nm). The putative causes of this phenomenon are the presence in the surgical site of (1) activated keratocytes, (2) vacuoles and (3) newly synthesized collagen. A CCD camera device was employed in order to measure the corneal transparency. Both scattered and reflected light in the slit image of patients' corneas was measured using polarizing filters and image analysis software. We observed an increase in reflected and scattered light until the second postoperative month, followed by a subsequent decline. However, the combined signal generated by reflected and scattered light showed a second increase at 4 months postoperatively, whereas the signal generated by scattered light alone stayed at lower levels. These objective measures of changes in corneal transparency were correlated with changes in visual performance using psychophysical tests measuring visual acuity at different contrast levels (100%, 20% and 5%). In all patients we observed a good correlation between the signal generated by scattered light alone and the reduction in the 5% contrast visual acuity performance. These disturbances in low contrast visual performance were only significant during the first 3-4 months postoperatively, and thereafter most patients returned to their preoperative value. Eighteen percent of our patients discontinued topical steroids postoperatively. No difference in corneal transparency was observed.

Long-term results of Goode's tympanostomy tubes in children

The results of a retrospective study of the complications of middle ear ventilation by Goode's T-tubes in children are presented. 248 T-tubes were inserted into 119 patients. 16.9% progressed to spontaneous extrusion with a mean period of ventilation approaching 20 months. 54.9% of patients experienced otorrhoea which was found to be significantly more common in those ears with a mucoid effusion at the time of T-tube insertion. 21.1% of ears developed a persistent perforation where spontaneous extrusion had occurred or the T-tubes had been removed. Perforation also occurred more frequently in those with otorrhoea.

Adjunctive thrombolytic therapy for angioplasty in ischemic rest angina: results of a double-blind randomized pilot study

OBJECTIVES

A multicenter pilot study was instituted to assess the role of intracoronary thrombolytic therapy during angioplasty for ischemic rest angina.

BACKGROUND

Acute thrombotic coronary occlusion is increased during angioplasty for unstable angina, and intracoronary thrombolytic agents have been used to maintain patency. Prophylactic use of intracoronary thrombolytic agents has been advocated in certain high risk subgroups, although no studies have randomized therapy.

METHODS

Ninety-three patients with either unstable angina and pain at rest (trial A, 66 patients) or postinfarction pain at rest (trial B, 27 patients) were randomized in double-blind fashion to administration of either intracoronary urokinase, 150,000 U, or saline solution placebo given immediately before angioplasty. Cineangiograms of the culprit lesion were recorded and analyzed in blinded fashion by a core laboratory for definite or possible (haziness) filling defects 15 min after angioplasty or after acute closure.

RESULTS

Urokinase decreased filling defects at 15 min after angioplasty in comparison with placebo (14% vs. 29%, respectively, p = 0.08). Four patients in each treatment group developed acute vessel closure. However, although urokinase significantly reduced the incidence of filling defects in trial A (3% vs. 23%, p = 0.03), the drug had no effect at the selected dose in trial B (42% vs. 43%, respectively). Acute vessel closure occurred significantly more frequently in trial B than in trial A, and urokinase at the selected dose also had no effect. Ischemic events after angioplasty appeared to be related more to dissection than to thrombosis, although redilation, which was more frequent after placebo administration, may have reduced their incidence as well as that of acute closure.

CONCLUSIONS

These data suggest a possible role for intracoronary urokinase during angioplasty for unstable angina. The lack of effect after infarction may represent a greater thrombus burden or degree of plaque disruption. A trial utilizing higher doses of urokinase in a larger patient group is in progress.

Correlation between biochemical composition and fluorescein binding of deposits in Bruch's membrane

PURPOSE

The fluorescence of drusen during fluorescein angiography is believed to have important prognostic and pathogenetic implications in age-related maculopathy. It is believed that deposits containing predominantly neutral lipids would be hydrophobic, resulting in hypofluorescence on fluorescein angiography, while the presence of polar phospholipids would be indicated clinically by hyperfluorescence because of its hydrophilic properties. To identify the potential determinants of fluorescence of drusen and Bruch's membrane, a series of macular specimens from human donors older than 60 years of age was examined. No clinical information was available concerning any previous eye disease.

METHODS

In vitro fluorescein binding was recorded microscopically, and the presence of fibronectin was sought by immunohistochemistry. The results were correlated with the proportions of phospholipids to neutral lipids identified by histochemical and biochemical studies.

RESULTS

It was found that high content of neutral fats was associated with lack of both fluorescein binding and fibronectin, and, conversely, in those specimens with high proportions of phospholipids, fluorescein binding was strong and fibronectin was present.

CONCLUSIONS

These observations support the central hypothesis concerning biophysical changes in Bruch's membrane with age and the potential importance of fluorescein angiography in the characterization of Bruch's membrane deposits.

A comparative analysis of two preparations of human chorionic gonadotrophin

A biophysical analysis of two pharmaceutical preparations of human chorionic gonadotrophin (Endo and Profasi) demonstrated that both contained high hCG specific activity. HCG protein analysis by occlusion HPLC and SDS gel electrophoresis showed similar profiles for both products. Although the purified protein components of both preparations were similar their were differences in the contents of the unpurified preparations. The Endo preparation exhibited greater inter-vial variability and contained an unidentified aromatic substance which interacted with the desalting column.

Expression of the mRNAs for the Kv3.1 potassium channel gene in the adult and developing rat brain

1. The gene for a mammalian Shaw K+ channel has recently been cloned and has been shown, by alternative splicing, to give rise to two different transcripts, Kv3.1 alpha and Kv3.1 beta. To determine whether these channels are associated with specific types of neurons and to determine whether or not the alternately spliced K+ channel variants are differentially expressed, we used ribonuclease (RNase) protection assays and in situ hybridization histochemistry to localize the specific subsets of neurons containing Kv3.1 alpha and Kv3.1 beta mRNAs in the adult and developing rat brain. 2. In situ hybridization histochemistry revealed a heterogeneous expression pattern of Kv3.1 alpha mRNA in the adult rat brain. Highest Kv3.1 alpha mRNA levels were expressed in the cerebellum. High levels of hybridization were also detected in the globus pallidus, subthalamus, and substantia nigra reticulata. Many thalamic nuclei, but in particular the reticular thalamic nucleus, hybridized well to Kv3.1 alpha-specific probes. A subpopulation of cells in the cortex and hippocampus, which by their distribution and number may represent interneurons, were also found to contain high levels of Kv3.1 alpha mRNA. In the brain stem, many nuclei, including the inferior colliculus and the cochlear and vestibular nuclei, also express Kv3.1 alpha mRNA. Low or undetectable levels of Kv3.1 alpha mRNA were found in the caudate-putamen, olfactory tubercle, amygdala, and hypothalamus. 3. Kv3.1 beta mRNA was also detected in the adult rat brain by both RNase protection assays and by in situ hybridization experiments. Although the beta splice variant is expressed at lower levels than the alpha species, the overall expression pattern for both mRNAs is similar, indicating that both splice variants co-expressed in the same neurons. 4. The expression of Kv3.1 alpha and Kv3.1 beta transcripts was examined throughout development. Kv3.1 alpha mRNA is detected as early as embryonic day 17 and then increases gradually until approximately postnatal day 10, when there is a large increase in the amount of Kv3.1 alpha mRNA. Interestingly, the expression of Kv3.1 beta mRNA only increases gradually during the developmental time frame examined. Densitometric measurements indicated that Kv3.1 alpha is the predominant splice variant found in neurons of the adult brain, whereas Kv3.1 beta appears to be the predominant species in embryonic and perinatal neurons. 5. Most of the neurons that express the Kv3.1 transcripts have been characterized electrophysiologically to have narrow action potentials and display high-frequency firing rates with little or no spike adaptation.(ABSTRACT TRUNCATED AT 400 WORDS)

Processing of mutant cystic fibrosis transmembrane conductance regulator is temperature-sensitive

Cystic fibrosis transmembrane conductance regulator (CFTR) is a plasma membrane Cl- channel regulated by cyclic AMP-dependent phosphorylation and by intracellular ATP. Mutations in CFTR cause cystic fibrosis partly through loss of cAMP-regulated Cl- permeability from the plasma membrane of affected epithelia. The most common mutation in cystic fibrosis is deletion of phenylalanine at residue 508 (CFTR delta F508) (ref. 10). Studies on the biosynthesis and localization of CFTR delta F508 indicate that the mutant protein is not processed correctly and, as a result, is not delivered to the plasma membrane. These conclusions are consistent with earlier functional studies which failed to detect cAMP-stimulated Cl- channels in cells expressing CFTR delta F508 (refs 16, 17). Chloride channel activity was detected, however, when CFTR delta F508 was expressed in Xenopus oocytes, Vero cells and Sf9 insect cells. Because oocytes and Sf9 cells are typically maintained at lower temperatures than mammalian cells, and because processing of nascent proteins can be sensitive to temperature, we tested the effect of temperature on the processing of CFTR delta F508. Here we show that the processing of CFTR delta F508 reverts towards that of wild-type as the incubation temperature is reduced. When the processing defect is corrected, cAMP-regulated Cl- channels appear in the plasma membrane. These results reconcile previous contradictory observations and suggest that the mutant most commonly associated with cystic fibrosis is temperature-sensitive.

Confocal imaging of the fundus using a scanning laser ophthalmoscope

A confocal scanning laser ophthalmoscope (cSLO) was used to examine the effects of confocal optics on the image of the human fundus in vivo. Patients from a retinal clinic and a glaucoma clinic were examined using the cSLO in the confocal mode. A degree of optical sectioning could be achieved, and the results agree with a best axial resolution of 300 microns measured in a model eye. The main advantage of using a confocal system was found to be the improved contrast of the images. This improved the resolution of structures such as the lamina cribrosa and optic disc drusen which are seen in low contrast in conventional images. The improved contrast of the confocal images is partly achieved by excluding light which has been scattered within the plane of focus. Structures which multiply scatter light will become less visible with confocal optics and hard exudates were found to be an example of such a structure. The cSLO and the fundus camera are seen as complementary instruments rather than as alternatives for imaging the fundus. It is envisaged that confocal imaging will enable details of the fundus to be revealed which are at present not seen in conventional images.

Excimer laser photorefractive keratectomy. 18-month follow-up

PURPOSE

This study, comprising 120 patients (follow-up, 12 to 22 months; mean, 18 months), was designed to evaluate the efficacy and safety of excimer laser photo-refractive keratectomy.

METHODS

Ablation zone diameter (4 mm), ablation rate (0.22 microns/pulse), fluence (180 mJ/cm2), and frequency (10 Hz) were kept constant, and all patients used a standard topical corticosteroid regimen.

RESULTS

Overcorrection was followed by regression to a stable refraction by 4 months. At 1 year, 95% and 70%, respectively, of patients undergoing - 2.00 diopters (D) and -3.00 D corrections and 40% and 20% of those undergoing -6.00 D and -7.00 D corrections were within +/- 1.00 D of intended refraction. Anterior stromal "haze," maximal at 6 months and diminishing thereafter, was detected in 110 patients (92%). However, best-corrected Snellen visual acuity was reduced in only 22 (18%). Good correlation existed between haze and regression (r = 0.68). Night "halos," due to the relatively small 4-mm diameter ablation zone, were reported by 94 patients (78%) in the early postoperative period, and, at 1 year, 12 (10%) declined treatment of the other eye because of persistence of this problem.

CONCLUSION

Marked individual variation was found after photorefractive keratectomy. However, in low myopia, predictability is "fair," and the procedure is safe. The authors conclude that excimer laser photorefractive keratectomy holds considerable promise for refractive surgery in the future.