Quantifying biomarkers of axonal degeneration in early glaucoma to find the disc at risk

To evaluate regional axonal-related parameters as a function of disease stage in primary open angle glaucoma (POAG) and visual field (VF) sensitivity. Spectral domain optical coherence tomography was used to acquire 20° scans of POAG (n = 117) or healthy control (n = 52) human optic nerve heads (ONHs). Region specific and mean nerve fibre layer (NFL) thicknesses, border NFL and peripapillary NFL, minimum rim width (MRW)/ area (MRA) and prelamina thickness; and volume were compared across POAG disease stages and with visual field sensitivity. Differences identified between early glaucoma (EG), preperimetric glaucoma (PG) and control (C) ONHs included thinner PG prelamina regions than in controls (p < 0.05). Mean border NFL was thinner in EG (p < 0.001) and PG (p = 0.049) compared to control eyes; and EG mean, and inferior and ST, border NFL was thinner than in PG (p < 0.01). Mean, superior and inferior PG peripapillary NFL were thinner than in controls (p < 0.05), and EG ST peripapillary NFL was thinner than in PG (p = 0.023). MRW differences included: PG SN and inferior less than in controls (p < 0.05); thinner EG mean regional, inferior, nasal, and ST MRW versus PG MRW (p < 0.05). Regional border NFL, peripapillary NFL, MRW, MRA, prelamina thickness (except centre, p = 0.127) and prelamina volume (p < 0.05) were significantly associated with VF mean deviation (MD). Novel axon-derived indices hold potential as biomarkers to detect early glaucoma and identify ONHs at risk.

The optical detection of retinal ganglion cell damage

We provide an overview of developments in the use optical coherence tomography (OCT) imaging for the detection of retinal ganglion cell (RGC) damage in vivo that avoid use of any exogenous ligands to label cells. The method employs high-resolution OCT using broad spectral light sources to deliver axial resolution of under 5 μm. The resolution approximates that of cellular organelles, which undergo degenerative changes that progress to apoptosis as a result of axon damage. These degenerative changes are manifest as the loss of RGC dendrites and fragmentation of the subcellular network of organelles, in particular, the mitochondria that support dendritic structure. These changes can alter the light-scattering behavior of degenerating neurons. Using OCT imaging techniques to identify these signals in cultured neurons, we have demonstrated changes in cultured cells and in retinal explants. Pilot studies in human glaucoma suggest that similar changes are detectable in the clinical setting. High-resolution OCT can be used to detect optical scatter signals that derive from the RGC/inner plexiform layer and are associated with neuronal damage. These findings suggest that OCT instruments can be used to derive quantitative measurements of RGC damage. Critically, these signals can be detected at an early stage of RGC degeneration when cells could be protected or remodeled to support visual recovery.

Quantitative analysis of three-dimensional fibrillar collagen microstructure within the normal, aged and glaucomatous human optic nerve head

The aim of this study was to quantify connective tissue fibre orientation and alignment in young, old and glaucomatous human optic nerve heads (ONH) to understand ONH microstructure and predisposition to glaucomatous optic neuropathy. Transverse (seven healthy, three glaucomatous) and longitudinal (14 healthy) human ONH cryosections were imaged by both second harmonic generation microscopy and small angle light scattering (SALS) in order to quantify preferred fibre orientation (PFO) and degree of fibre alignment (DOFA). DOFA was highest within the peripapillary sclera (ppsclera), with relatively low values in the lamina cribrosa (LC). Elderly ppsclera DOFA was higher than that in young ppsclera (p < 0.00007), and generally higher than in glaucoma ppsclera. In all LCs, a majority of fibres had preferential orientation horizontally across the nasal–temporal axis. In all glaucomatous LCs, PFO was significantly different from controls in a minimum of seven out of 12 LC regions (p < 0.05). Additionally, higher fibre alignment was observed in the glaucomatous inferior–temporal LC (p < 0.017). The differences between young and elderly ONH fibre alignment within regions suggest that age-related microstructural changes occur within the structure. The additional differences in fibre alignment observed within the glaucomatous LC may reflect an inherent susceptibility to glaucomatous optic neuropathy, or may be a consequence of ONH remodelling and/or collapse.

Improving accuracy and efficiency of mutual information for multi-modal retinal image registration using adaptive probability density estimation

Mutual information (MI) is a popular similarity measure for performing image registration between different modalities. MI makes a statistical comparison between two images by computing the entropy from the probability distribution of the data. Therefore, to obtain an accurate registration it is important to have an accurate estimation of the true underlying probability distribution. Within the statistics literature, many methods have been proposed for finding the 'optimal' probability density, with the aim of improving the estimation by means of optimal histogram bin size selection. This provokes the common question of how many bins should actually be used when constructing a histogram. There is no definitive answer to this. This question itself has received little attention in the MI literature, and yet this issue is critical to the effectiveness of the algorithm. The purpose of this paper is to highlight this fundamental element of the MI algorithm. We present a comprehensive study that introduces methods from statistics literature and incorporates these for image registration. We demonstrate this work for registration of multi-modal retinal images: colour fundus photographs and scanning laser ophthalmoscope images. The registration of these modalities offers significant enhancement to early glaucoma detection, however traditional registration techniques fail to perform sufficiently well. We find that adaptive probability density estimation heavily impacts on registration accuracy and runtime, improving over traditional binning techniques.

Observation of electron-antineutrino disappearance at Daya Bay

The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle θ(13) with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GWth reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43,000 ton-GWth-day live-time exposure in 55 days, 10,416 (80,376) electron-antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is R=0.940±0.011(stat.)±0.004(syst.). A rate-only analysis finds sin(2)2θ(13)=0.092±0.016(stat.)±0.005(syst.) in a three-neutrino framework.

Muscle histology vs MRI in Duchenne muscular dystrophy

OBJECTIVE

There are currently no effective treatments to halt the muscle breakdown in Duchenne muscular dystrophy (DMD), although genetic-based clinical trials are being piloted. Most of these trials have as an endpoint the restoration of dystrophin in muscle fibers, hence requiring sufficiently well-preserved muscle of recruited patients. The choice of the muscles to be studied and the role of noninvasive methods to assess muscle preservation therefore require further evaluation.

METHODS

We studied the degree of muscle involvement in the lower leg muscles of 34 patients with DMD >8 years, using muscle MRI. In a subgroup of 15 patients we correlated the muscle MRI findings with the histology of open extensor digitorum brevis (EDB) muscle biopsies. Muscle MRI involvement was assigned using a scale 0-4 (normal-severe).

RESULTS

In all patients we documented a gradient of involvement of the lower leg muscles: the posterior compartment (gastrocnemius > soleus) was most severely affected; the anterior compartment (tibialis anterior/posterior, popliteus, extensor digitorum longus) least affected. Muscle MRI showed EDB involvement that correlated with the patient's age (p = 0.055). We show a correlation between the MRI and EDB histopathologic changes, with MRI 3-4 grades associated with a more severe fibro-adipose tissue replacement. The EDB was sufficiently preserved for bulk and signal intensity in 18/22 wheelchair users aged 10-16.6 years.

CONCLUSION

This study provides a detailed correlation between muscle histology and MRI changes in DMD and demonstrates the value of this imaging technique as a reliable tool for the selection of muscles in patients recruited into clinical trials.

Transretinal degeneration in ageing human retina: a multiphoton microscopy analysis

AIM

Retinal cell remodelling has been reported as a consistent feature of ageing. However, the degree to which this results in transretinal degeneration is unclear. To address this, the authors used multiphoton microscopy to quantify retinal degeneration in post-mortem human eyes of two age groups.

METHODS

Retinas from six young subjects (18-33 years old) and six older subjects (74-90 years old) were prepared as wholemount preparations. All retinas were stained with 4,6-diamidino-2-phenylindole and imaged by multiphoton confocal microscopy to quantify neuron densities in the retinal ganglion cell layer (RGCL), inner nuclear layer (INL) and outer nuclear layer (ONL). Neurons were counted using automated cell identification algorithms. All retinas were imaged hydrated to minimise tissue artefacts.

RESULTS

In both groups, 56% of the area within the central 4 mm eccentricity and 27% of the area with eccentricity between 4 mm and 7 mm were imaged. Compared with young subjects, the peak RGCL neuron loss in the aged subjects (25.5%) was at 1 mm eccentricity. INL and ONL neuron densities significantly decreased at 1-2 mm eccentricity (8.7%) and 0.5-4 mm eccentricity (15.6%) respectively (P <0.05). The reduction in neuron density in the INL corresponded, spatially, to the region with the greatest neuron loss in the RGCL and ONL.

CONCLUSIONS

This is the first study to correlate neurodegeneration in different populations of cells in the ageing retinas. These data confirm that the greatest neuronal loss occurs in the RGCL and ONL in human ageing retinas, whereas the INL is relatively preserved.

Mouse models of dominant optic atrophy: what do they tell us about the pathophysiology of visual loss?

Dominant optic atrophy (DOA) is the most common inherited optic neuropathy affecting one in every 12,000 people. It presents with bilateral visual loss, central visual fields defects, colour vision disturbance and optic disc pallor. OPA1 has been identified as the responsible gene and its locus mapped to chromosome 3q28-q29. Mutations in this gene are responsible for the clinical phenotype in over 70% of patients with DOA. Histopathological studies in tissues from patients reveal loss of retinal ganglion cells but the paucity of viable human tissue has raised the importance of an animal model to study the pathophysiology of the disease. In the last decade considerable work has gone into the generation of animal, most notably mouse, models of Opa1 DOA. Two murine models of DOA have been published, designated B6;C3-Opa1(Q285STOP) and B6;C3-Opa1(329-355del) and they provide valuable insights with respect to neurological and visual phenotyping, mitochondrial dysfunction, optic nerve and axonal changes, retinal ganglion cell depletion and dendritic atrophy. Here we summarise the current state of knowledge of the mechanisms of disease based on data from these models of Opa1 DOA.

BMP signalling permits population expansion by preventing premature myogenic differentiation in muscle satellite cells

Satellite cells are the resident stem cells of adult skeletal muscle, supplying myonuclei for homoeostasis, hypertrophy and repair. In this study, we have examined the role of bone morphogenetic protein (BMP) signalling in regulating satellite cell function. Activated satellite cells expressed BMP receptor type 1A (BMPR-1A/Alk-3) and contained phosphorylated Smad proteins, indicating that BMP signalling is operating during proliferation. Indeed, exogenous BMP4 stimulated satellite cell division and inhibited myogenic differentiation. Conversely, interfering with the interactions between BMPs and their receptors by the addition of either the BMP antagonist Noggin or soluble BMPR-1A fragments, induced precocious differentiation. Similarly, blockade of BMP signalling by siRNA-mediated knockdown of BMPR-1A, disruption of the intracellular pathway by either Smad5 or Smad4 knockdown or inhibition of Smad1/5/8 phosphorylation with Dorsomorphin, also caused premature myogenic differentiation. BMP signalling acted to inhibit the upregulation of genes associated with differentiation, in part, through regulating Id1. As satellite cells differentiated, Noggin levels increased to antagonise BMP signalling, since Noggin knockdown enhanced proliferation and impeded myoblast fusion into large multinucleated myotubes. Finally, interference of normal BMP signalling after muscle damage in vivo perturbed the regenerative process, and resulted in smaller regenerated myofibres. In conclusion, BMP signalling operates during routine satellite cell function to help coordinate the balance between proliferation and differentiation, before Noggin is activated to antagonise BMPs and facilitate terminal differentiation.

Topography of neuron loss in the retinal ganglion cell layer in human glaucoma

AIM

To determine if retinal ganglion cell (RGC) loss influences the loss of surrounding RGCs to generate clustered patterns of cell death in human glaucoma. It is hypothesised that retinal ganglion cell loss accelerates the loss of surrounding cells to generate, at a local, cellular scale, clustered patterns of retinal of RGC death. The absence of these interactions would result in a diffuse pattern RGC loss.

METHOD

Six glaucomatous retinas (67-83 years old) and six age-matched control retinas (61-89 years old) were prepared as wholemounts and stained by 4',6-diamidino-2-phenylindole (DAPI) solution (3 microg/ml in PBS). An area corresponding to central 14 degrees of the visual field was imaged. The nearest-neighbour distribution was determined for cells in both normal and glaucomatous RGCL.

RESULTS

Clustered RGC loss in human glaucoma was observed on a background of diffuse loss. The mean nearest-neighbour distance (NND) of the glaucomatous retinas was significantly higher than with controls (p<0.001). The distribution of NND in glaucomatous retinas was skewed to the higher values with a higher positive kurtosis relative to controls. The quantitative analysis of the pattern of cell loss is supported by the visual inspection of the patterns of cell loss.

DISCUSSION

The nearest-neighbour analysis is consistent with the presence of two patterns of cell loss in the RGCL in glaucoma. While the diffuse of cell loss can account for an overall reduction in the RGC population, an additional non-random pattern is consistent with the hypothesis that RGC loss has a local influence on the viability of surrounding cells.

Genetic analysis of milk production and composition in crossbred ewes from different maternal genotypes

Milk production and milk composition were measured in 1056 crossbred ewes managed under pasture grazing in a lamb production system. Most ewes were milked on three occasions at ~3, 4 and 12 weeks of lactation. The ewes were the progeny of mainly Merino dams and 91 sires from several maternal crossing breeds including Border Leicester, East Friesian, Finnsheep and Coopworth. The ewes were born over 3 years and run at three sites where they were joined naturally to meat rams. Most of the ewes were first parity (autumn-joined at 7 months of age and spring-joined at 14–17 months of age), with the remainder second or third parity. The cohorts of ewes and sites were linked genetically by three common maternal sires. The 4-h oxytocin-induced milking procedure was used to estimate daily milk production and milk samples were analysed for composition (fat%, protein% and lactose%). Daily milk yield and milk composition traits were analysed using restricted maximum likelihood mixed models procedures. The sire breed of crossbred ewes was significant for milk yield (P < 0.01), fat% (P < 0.01) and lactose% (P < 0.05). There was a significant (P < 0.01) interaction of sire breed × days of lactation, mainly due to the relatively higher milk yield of the East Friesian and White Suffolk cross ewes compared with the other crosses, at the end of the lactation. The East Friesian cross ewes had lower milk fat% than the other cross ewes. Ewes suckling multiple lambs had 29% higher peak milk yield than those bearing and suckling single lambs (P < 0.001). There was an increase in peak milk yield of the ewes from first to second parity, and third parity ewes had a greater decline to the end of lactation causing a significant interaction (P < 0.001). The overall decline in milk yield from peak to late lactation was –21.2 ± 0.7 g/day. Separate analysis showed a significant increase in milk yield with ewe pre-joining weight (regression 6.1 ± 1.8 g/day.kg). The estimate of heritability for daily milk yield was 0.24 ± 0.04 at 90 days of lactation and 0.10 ± 0.02 at 21 days of lactation. The estimates of heritability for the milk composition traits were generally moderate. Estimates of genetic correlations between measurements early and late in the lactation for milk yield and most composition traits were high. The within ewe by stage variance component estimates of repeatability were moderate to high for milk yield, fat% and protein%, with lactose% being low.

Comparative analysis of antisense oligonucleotide sequences for targeted skipping of exon 51 during dystrophin pre-mRNA splicing in human muscle

Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene that result in the absence of functional protein. In the majority of cases these are out-of-frame deletions that disrupt the reading frame. Several attempts have been made to restore the dystrophin mRNA reading frame by modulation of pre-mRNA splicing with antisense oligonucleotides (AOs), demonstrating success in cultured cells, muscle explants, and animal models. We are preparing for a phase I/IIa clinical trial aimed at assessing the safety and effect of locally administered AOs designed to inhibit inclusion of exon 51 into the mature mRNA by the splicing machinery, a process known as exon skipping. Here, we describe a series of systematic experiments to validate the sequence and chemistry of the exon 51 AO reagent selected to go forward into the clinical trial planned in the United Kingdom. Eight specific AO sequences targeting exon 51 were tested in two different chemical forms and in three different preclinical models: cultured human muscle cells and explants (wild type and DMD), and local in vivo administration in transgenic mice harboring the entire human DMD locus. Data have been validated independently in the different model systems used, and the studies describe a rational collaborative path for the preclinical selection of AOs for evaluation in future clinical trials.

Measurement of intraocular pressure (IOP) in chickens using a rebound tonometer: quantitative evaluation of variance due to position inaccuracies

Intraocular pressure (IOP), an important risk factor for glaucoma, is a continuous trait determined by a complex set of genetic and environmental factors that are largely unknown. Genetic studies in laboratory animals may facilitate the identification of genes that affect IOP. We examined the use of the rebound tonometer for measuring IOP in non-anaesthetised birds, along with the device's robustness to alignment errors. Calibration curves were obtained by measuring the IOP of cannulated chicken eyes with the rebound tonometer over a range of pressures. To simulate different types of alignment errors that might be expected with measurement of IOP in alert chickens, for some calibrations the tonometer was positioned (1) at various distances from the cornea, (2) laterally displaced from the visual axis, or (3) angled away from the visual axis. In vivo measurements were taken on three-week-old alert chickens from a layer line, a broiler line, and a layer-broiler "advanced intercross line" (AIL) designed to facilitate QTL mapping. The rebound tonometer showed excellent linearity (R2=0.95-0.99) during calibration, as well as robustness to variation in the probe-to-cornea distance over the range 3-5mm and to lateral displacement over the range 0-2mm. However, the tonometer appeared less robust to off-axis misalignment over the range 0-20 degrees (P<0.05). Also, the slope of calibration curves sometimes differed between eyes (P<0.001), presumably reflecting differences in ocular structure. The IOP measured in non-anaesthetised three-week-old AIL chickens was 17.51+/-0.13 mmHg (mean+/-S.E.; N=105 birds). IOP was significantly associated with corneal thickness (P<0.05) and body weight (P<0.001) in a regression model. Replicate measurements were necessary in order to gauge IOP accurately in individual birds; a series of seven tonometry sessions over a 12-h period during the light phase of the light/dark cycle permitted IOP to be measured with a 95% CI of +/-0.7 mmHg. IOP did not differ significantly between the broiler and layer chicken lines which served as the progenitor lines for the AIL. In conclusion, the rebound tonometer permits rapid estimation of IOP in chickens and is well tolerated. The small alignment errors that are expected when taking measurements in non-anaesthetised animals are unlikely to affect accuracy. Since high IOP is a major risk factor for glaucoma, identifying QTL controlling IOP may offer future health benefits. However, our preliminary findings highlight several obstacles to mapping such QTL using the chicken advanced intercross line evaluated here.

The relationship of lamb growth from birth to weaning and the milk production of their primiparous crossbred dams

The growth rate of 667 single cross lambs from birth to 4 weeks (Period 1) and 4 weeks to weaning at 12 weeks (Period 2) was measured, along with the milk production of their 520 primiparous crossbred ewe dams over 3 years. The lambs were the progeny of Poll Dorset rams and first cross ewes lambing for the first time at 12 and 19 months of age. The first cross ewes were the progeny of Merino ewes mated to 30 individual sires from several maternal sire breeds, including Border Leicester, East Friesian, Finnsheep and Coopworth. Milk production of the ewes was measured at ~3, 4 and 12 weeks of lactation using a 4-h milk test. The effect of ewe milk production on lamb growth rate in Period 1 included a significant interaction with lamb birth and rearing type (P < 0.001). These regressions were 52 ± 18 g/day per kg/day for single born and reared, 24 ± 17 g/day per kg/day for multiple born and single reared and 18 ± 17 g/day per kg/day multiple born and reared lambs. The regression of ewe milk production in Period 2 on lamb growth rate in Period 2 was also significant (P < 0.001), although milk production in Period 1 accounted for more variation in lamb growth. There were significant interactions of ewe weight gain (from mid pregnancy to lamb weaning) with season in Period 1 (P < 0.01) and year in Period 2 (P < 0.001). There was also a significant interaction (P < 0.001) of year with ewe mid-pregnancy weight for lamb growth in Period 2. Lamb birthweight had a significant effect on lamb growth rate in Period 2 (regression coefficient 6.68 ± 2.57 g/day.kg, P < 0.01).

Milk yield and milk composition from grazing primiparous non-dairy crossbred ewes

Milk production and milk composition were studied in 520 primiparous Merino crossbred ewes that were the progeny of 30 sires from several maternal crossing breeds including Border Leicester, Coopworth, Finnsheep and East Friesian. The ewes were born in 3 years (1997, 1998, and 1999), with 3 sires used in every year to provide genetic links. The crossbred ewe lambs were randomly assigned to autumn or spring joining groups and mated to Poll Dorset rams to lamb at 12 or 19 months of age. Ewes were milked on 3 days during their first lactation at approximately 3, 4, and 12 weeks after lambing. On each milking day, each ewe was initially injected with oxytocin, milked out by machine, and then hand-stripped. This procedure was repeated approximately 4 h later, with the milk weight and time recorded to extrapolate to daily milk yield, and composition of the milk was determined. Daily milk yield was analysed using REML mixed models procedures and 3 measures of milk production were predicted: peak milk yield at 21 days of lactation, total milk yield from 21 to 90 days of lactation, and length of lactation (days for daily yield to decline to 600 g/day). Milk composition traits (%fat, %protein, %lactose) and proportion of machine milk yield were analysed with similar models. Sire breed, number of lambs born and suckled, season, and ewe weight gain from mid-pregnancy until lamb weaning were all significant (P < 0.01) for daily yield, which declined from 2.1 kg/day at 21 days to 0.7 kg/day at 90 days of lactation. The Finnsheep-cross ewes had lower peak milk yield (1.84 ± 0.08 v. 2.09–2.19 ± 0.1 kg/day) and lower total yield of lactation (21–90 days) than all the other breed-cross ewes (78 ± 3 v. 92–107 ± 5 kg). The East Friesian-cross ewes had significantly longer lactations (128.8 ± 10.9 days) than the Border Leicester (98.1 ± 4.4 days) and Coopworth (93.7 ± 4.2 days), with the Finnsheep-cross ewes the shortest (80.1 ± 3.1 days). The East Friesian-cross ewes had the greatest and the Finnsheep-cross ewes the least total yield of lactation (107 ± 5 and 78 ± 3 kg, respectively). There were significant differences in peak milk yield for ewes bearing and suckling single lambs, twin-born and single-raised lambs, and twin-born and raised lambs (1.86 ± 0.04, 2.03 ± 0.09, and 2.37 ± 0.07 kg/day, respectively). There was a significant decline in daily milk yield with increasing ewe weight gain from mid-pregnancy to lamb weaning (–18.1 ± 4.2 g/kg). All the components of milk composition changed from the peak of milk production at 3 weeks to the end of lactation. The East Friesian-cross ewes had significantly lower milk %fat (by approx. 1 percentage point) at both 21 days and 90 days of lactation than ewes by all other sire breeds. The 30 sire progeny mean deviations for daily milk yield ranged from –292 to +276 g/day, with considerable ranges between sires within the sire breeds. The implications for lamb production and breeding programs are discussed.

Stem cells to treat muscular dystrophies

Stem cells, capable of giving rise to both differentiated skeletal muscle and to more stem cells, would be ideal for treating chronic myopathies such as Duchenne Muscular Dystrophy. However, although satellite cells have been shown to be functional muscle stem cells in animal models, other muscle or non-muscle stem cells are far less capable of contributing to skeletal muscle regeneration. This review discusses recent work on stem cell contribution to skeletal muscle regeneration and highlights the problems to be overcome before stem cell treatment of muscle diseases may become a possibility.

Digital imaging of the optic nerve head: monoscopic and stereoscopic analysis

AIMS

To compare monoscopic and stereoscopic assessment of the optic disc using novel software for the digital stereoscopic analysis of optic disc stereopairs.

METHODS

Software was developed for the stereoscopic display of digital optic disc images using an interlaced display method. Neuroretinal rim width was determined at 10 degree intervals around the optic disc using a custom (stereoscopic) cursor whose depth was adjusted to that of Elschnig's rim. Measurements were taken, first viewing the disc monoscopically and at a separate sitting, stereoscopically.

RESULTS

Measurements were made in 35 eyes from 35 patients (1260 estimates for each observer) using three observers. The mean cup to disc ratio (CDR) ranged from 0.57 to 0.66 (SD 0.13-0.14) for monoscopic viewing compared with 0.64 to 0.69 (SD 0.12-0.14) for stereoscopic viewing. Stereoscopic assessments gave higher CDRs in temporal, superior, nasal, and inferior aspects of the optic disc (p<0.001, Mann-Whitney U test). Agreement between observers in estimating CDR was high for monoscopic assessment (intraclass correlation coefficient 0.74 (CI 0.72 to 0.76) increasing to 0.80 (0.78 to 0.82) for stereoscopic assessment.

CONCLUSION

Digital stereoscopic optic disc assessment provides lower estimates of neuroretinal rim width and higher levels of interobserver agreement compared with monoscopic assessments.

Ocular complications of neurological therapy

Treatments used for several neurological conditions may adversely affect the eye. Vigabatrin-related retinal toxicity leads to a visual field defect. Optic neuropathy may result from ethambutol and isoniazid, and from radiation therapy. Posterior subcapsular cataract is associated with systemic corticosteroids. Transient refractive error changes may follow treatment with acetazolamide or topiramate, and corneal deposits and keratitis with amandatine. Intraocular pressure can be elevated in susceptible individuals by anticholinergic drugs, including oxybutynin, tolterodine, benzhexol, propantheline, atropine and amitriptyline, and also by systemic corticosteroids and by topiramate. Nystagmus, diplopia and extraocular muscle palsies can occur with antiepileptic drugs, particularly phenytoin and carbamazepine. Ocular neuromyotonia can follow parasellar radiation. Congenital ocular malformations can result from in utero exposure to maternally prescribed sodium valproate, phenytoin and carbamazepine. Neurologists must be aware of potential ocular toxicity of these drugs, and appropriately monitor for potential adverse events.

Evaluation of the high specificity Screening Program (C-20-1) of the Frequency Doubling Technology (FDT) perimeter in clinical practice

AIMS

To compare the efficacy of the high specificity Frequency Doubling Technology (FDT) Perimeter Screening Program (C-20-1) to standard threshold automated perimetry in the diagnosis of open-angle glaucoma.

METHODS

A total of 100 consecutively presenting patients attending a glaucoma clinic who volunteered for the study (approximately 30% of whom were attending for an initial visit) were examined with the FDT C-20-1 Screening Program and with the Humphrey Field Analyzer (HFA) SITA Fast algorithm and Program 24-2.

RESULTS

Of the patients, 17 were excluded due to unreliable visual field results or non-glaucomatous ocular abnormalities. In all, 10 patients were diagnosed as normal, 54 with open-angle glaucoma, eight with ocular hypertension, and 11 as glaucoma suspects. Of the 54 glaucomatous patients, 45 exhibited high-tension glaucoma and nine normal tension glaucoma. Perimetry with the HFA gave a sensitivity of 81.5% for the combined category of glaucoma and glaucoma suspect and a specificity of 83.3% for the combined category of normal and ocular hypertension. Perimetry with the FDT gave a sensitivity of 74.5% and a specificity of 85.2% compared to that of the HFA.

CONCLUSION

In the detection of glaucoma, Program C-20-1 of the FDT perimeter exhibits high specificity. It exhibits low sensitivity for the detection of mild loss but high sensitivity for advanced field loss relative to Program 24-2 and the SITA Fast algorithm of the HFA.

Discrimination of glaucomatous optic neuropathy by digital stereoscopic analysis

PURPOSE

To evaluate the diagnostic power of a novel digital stereoscopic imaging system in the diagnosis of glaucomatous optic neuropathy.

DESIGN

Prospective cross-sectional analysis of the diagnostic accuracy of digital stereoscopic optic disc analysis in the diagnosis of glaucomatous optic neuropathy exhibiting mild to moderate field loss.

PARTICIPANTS

Fifty-two patients with open-angle glaucoma and 54 normal individuals were recruited. The presence of a reproducible visual field loss characteristic of glaucoma was used as the reference standard for the presence of glaucoma independent of the optic nerve head appearance. Patients were excluded if the optic disc, fundus, or visual field indicated other disease. One eye from each patient and individual was included in the study, the eye with the least field loss and a randomly designated normal eye, respectively.

METHODS

Simultaneous stereoscopic optic disc photography was performed on each specified eye. Three experienced observers viewed the resultant stereoscopic image of each nerve head using a Z screen, recorded a subjective clinical diagnosis, and undertook digital stereoscopic planimetry. Separate linear regression analysis was performed, post hoc, from the planimetric results for each observer of the logarithm of neuroretinal rim (NRR) against optic disc area derived from each normal eye. Eyes with NRR areas below the 95th prediction interval of the normal cohort were then classified as glaucomatous.

MAIN OUTCOME MEASURES

Sensitivity and specificity for the detection of glaucomatous optic neuropathy.

RESULTS

With subjective stereoscopic analysis, sensitivity for glaucoma detection among the 3 observers was 80.8%, 76.9%, and 90.4%, with respective specificities of 94.4%, 79.6%, and 79.6%. Regression analysis of the NRR in 30 degrees segments gave sensitivities between 69.2% and 80.8% and specificities between 83.3% and 90.7%. A combination of the subjective and quantitative analysis did not significantly improve discrimination.

CONCLUSIONS

The subjective analysis of digital stereoscopic images provides a useful method for the discrimination of normal and glaucomatous optic nerves. Planimetric analysis does not significantly improve the diagnostic precision of this technique.

Human muscle precursor cell regeneration in the mouse host is enhanced by growth factors

The aim of this study was to optimize human muscle formation in vivo from implanted human muscle precursor cells. We transplanted donor muscle precursor cells (MPCs) prepared from postnatal or fetal human muscle into immunodeficient host mice and showed that irradiation of host muscle significantly enhanced muscle formation by donor cells. The amount of donor muscle formed in cryodamaged host muscle was increased by exposure of donor cells to growth factors before their implantation into injured host muscle. Insulin-like growth factor type I (IGF-I) significantly increased the amount of muscle formed by postnatal human muscle cells, but not by fetal human MPCs. However, treatment of fetal muscle cells with IGF-I, in combination with basic fibroblast growth factor and plasmin, significantly increased the amount of donor muscle formed. In vivo, human MPCs formed mosaic human-mouse muscle fibers, in which each human myonucleus was associated with a zone of human sarcolemmal protein spectrin.

Circulation and axonal transport in the optic nerve

Retinal ganglion cells are the output cells of the retina whose axons are under considerable metabolic stress in both health and disease states. They are highly polarised to ensure that mitochondria and enzymes involved in the generation of ATP are strategically concentrated to meet the local energy demands of the cell. In passing from the eye to the brain, axons are protected and supported by glial tissues and the blood supply of the optic nerve head is regulated to maintain the supply of oxygen and nutrients to the axons. In spite of this, the optic nerve head remains the point at which retinal ganglion cell axons are most vulnerable to the effects of increased intraocular pressure or ischaemia. Considerable work has been undertaken in this area to advance our understanding on the pathophysiology of axon damage and to develop new strategies for the prevention of retinal ganglion cell death.

Advances in broad bandwidth light sources for ultrahigh resolution optical coherence tomography

Novel ultra-broad bandwidth light sources enabling unprecedented sub-2 microm axial resolution over the 400 nm-1700 nm wavelength range have been developed and evaluated with respect to their feasibility for clinical ultrahigh resolution optical coherence tomography (UHR OCT) applications. The state-of-the-art light sources described here include a compact Kerr lens mode locked Ti:sapphire laser (lambdaC = 785 nm, delta lambda = 260 nm, P(out) = 50 mW) and different nonlinear fibre-based light sources with spectral bandwidths (at full width at half maximum) up to 350 nm at lambdaC = 1130 nm and 470 nm at lambdaC = 1375 nm. In vitro UHR OCT imaging is demonstrated at multiple wavelengths in human cancer cells, animal ganglion cells as well as in neuropathologic and ophthalmic biopsies in order to compare and optimize UHR OCT image contrast, resolution and penetration depth.

Histological measurement of retinal nerve fibre layer thickness

PURPOSE

Accurate assessment of the retinal nerve fibre layer (RNFL) is central to the diagnosis and follow-up of glaucoma. The in vivo measurement of RNFL thickness by a variety of digital imaging technologies is becoming an important measure for early detection, as well as for follow-up, of glaucomatous damage. However, when drawing clinical inference concerning the state of the RNFL, it is important to have valid reference data on RNFL thickness in both healthy and diseased eyes. In this review, we summarize the knowledge currently available about RNFL thickness in human and primate eyes.

METHODS

A review of the literature on histological analysis of RNFL thickness in the context of glaucomatous damage.

CONCLUSIONS

Six studies have so far analysed RNFL thickness. Despite the diverse study methodology taken, a consistent feature of all the data is that the superior and inferior quadrants of the peripapillary retina are thicker than the nasal and temporal quadrants; that the RNFL thickness rapidly diminishes with increasing distance from the disc margin; and that apparently at different locations the ratio of axons to supportive tissue varies significantly. We conclude that limited data are available to describe the normal variation in RNFL thickness in the normal human eye. Further studies may help better characterize the RNFL thickness in health and disease and to facilitate the correlation with clinical methods for nerve fibre layer assessment.

Duchenne's muscular dystrophy: animal models used to investigate pathogenesis and develop therapeutic strategies

Duchenne's muscular dystrophy (DMD) is a lethal childhood disease caused by mutations of the dystrophin gene, the protein product of which, dystrophin, has a vital role in maintaining muscle structure and function. Homologues of DMD have been identified in several animals including dogs, cats, mice, fish and invertebrates. The most notable of these are the extensively studied mdx mouse, a genetic and biochemical model of the human disease, and the muscular dystrophic Golden Retriever dog, which is the nearest pathological counterpart of DMD. These models have been used to explore potential therapeutic approaches along a number of avenues including gene replacement and cell transplantation strategies. High-throughput screening of pharmacological and genetic therapies could potentially be carried out in recently available smaller models such as zebrafish and Caenorhabditis elegans. It is possible that a successful treatment will eventually be identified through the integration of studies in multiple species differentially suited to addressing particular questions.

Comparison of laser interferometry and ultrasound A-scan in the measurement of axial length

AIM

Laser interferometry is a new, non-contact technique for the measurement of axial length. In this study we compared measurements of axial length obtained with this technique with those obtained with ultrasound (A-scan). The reproducibility and examiner-dependency of the two methods were also analysed.

METHODS

Patients presenting at the cataract assessment clinic were invited to participate in the study. Axial length measurements were obtained both by contact ultrasound (A-scan) and by non-contact laser interferometry (IOLMasterTM V1.1, Carl Zeiss, Jena, Germany). Intraocular lens powers were calculated using both sets of measurements. The coefficient of variation served as a measure of reproducibility.

RESULTS

A total of 100 eyes in 100 patients were evaluated after informed consent had been obtained. Although estimates of axial length obtained with the two techniques were highly correlated, axial lengths obtained with the contact method (mean 23.35 mm, SD 1.81 mm) were consistently lower than those obtained with the non-contact method (mean 23.55 mm, SD 1.76 mm) and the difference was statistically significant (p < 0.001). The coefficient of variation was lower with laser interferometry (0.1%) than with the ultrasound technique (0.49%).

CONCLUSIONS

Different estimates of axial length are obtained using contact and non-contact techniques, with the latter producing consistently higher measurements than the former. Laser interferometry provides more reproducible results that should improve the accuracy of measurements of axial length in the clinical setting.

Compact, low-cost Ti:Al2O3 laser for in vivo ultrahigh-resolution optical coherence tomography

A compact, low-cost, prismless Ti:Al2O3 laser with 176-nm bandwidth (FWHM) and 20-mW output power was developed. Ultrahigh-resolution ophthalmic optical coherence tomography (OCT) ex vivo imaging in an animal model with approximately 1.2-microm axial resolution and in vivo imaging in patients with macular pathologies with approximately 3-microm axial resolution were demonstrated. Owing to the pump laser, this light source significantly reduces the cost of broadband OCT systems. Furthermore, the source has great potential for clinical application of spectroscopic and ultrahigh-resolution OCT because of its small footprint (500 mm x 180 mm including the pump laser), user friendliness, stability, and reproducibility.

Acutance, an objective measure of retinal nerve fibre image clarity

BACKGROUND/AIMS

The interpretation of high contrast retinal nerve fibre layer (RNFL) images in glaucoma can be confounded by the presence of image blur; it can be difficult to discern diffuse axon loss in a poor quality image. One solution is to provide an objective measure of the image quality based on features in the image other than the RNFL. In this study the authors have developed an objective method to quantify the clarity of RNFL images, comparing it with a subjective image grading system.

METHODS

Digitally acquired, monochrome retinal images were taken from 58 eyes (one image per eye) with a Topcon 50 IX retinal camera. Image resolution was 1320 x 1032 pixels at 8 bits per pixel. Image sharpness was subjectively graded by two masked experienced observers on a scale 1 to 5 relative to a reference set of RNFL images. Software algorithms were developed using Matlab (5.2) to calculate the acutance, an objective measure of the physical characteristics that underlie the subjective impression of sharpness in an image.

RESULTS

Acutance values could be calculated for all the images. The Pearson correlation coefficients of the log of the acutance for each image and the subjective grades of observer 1 and observer 2 were 0.90 (p<0.001, n=58) and 0.84 (p<0.001, n=58) respectively.

CONCLUSIONS

These data suggest that acutance may provide a useful objective measure of image quality, which correlates well with the subjective impression of the digital retinal image sharpness. Objective measures of image quality should help in the discrimination of diffuse retinal nerve fibre loss from image blur in patients with diffuse glaucomatous damage.

Psychophysical characterisation of early functional loss in glaucoma and ocular hypertension

AIM

The psychophysical evaluation of selective cell loss in early glaucoma and ocular hypertension.

METHODS

Contrast sensitivity was measured for the detection of luminance modulated gratings at a range of spatial (0.5, 2, 8 c/deg) and temporal (0, 16 Hz) frequency combinations in three groups of age matched patients (primary open angle glaucoma, ocular hypertension, normal controls; n=16). Stimuli of 5 degrees were presented foveally and at 15 degrees along the nasal horizontal meridian under photopic conditions.

RESULTS

Fovea: Compared to the normal group, the thresholds for the glaucoma patients were significantly elevated at all spatial and temporal frequencies (p<0.0001), but this reduction was not significantly different at any particular spatial or temporal frequency (p>0.1). There was no difference in contrast sensitivity between the normals and OHTs (p>0.10). Periphery: The thresholds of the glaucoma patients were elevated compared to the normal controls (p<0.01). The loss of sensitivity was slightly greater at the higher spatial frequencies for both stationary and flickering patterns but this did not reach significance (p=0.09). The contrast sensitivity in normal and OHT groups was not significantly different (p>0.10).

CONCLUSIONS

In early glaucoma, the reduction in contrast sensitivity to stimuli which isolate the magnocellular pathway (0.5 c/deg, 16 Hz) was not significantly different compared with the reduction in contrast sensitivity to stimuli that isolate the parvocellular pathway. These findings are not consistent with the hypothesis that the magnocellular pathway is selectively damaged in early glaucoma.

Glaucoma: squaring the psychophysics and neurobiology

Advances in our understanding of the pathophysiology of retinal ganglion cell death in glaucoma are providing important insights into the functional changes occurring in retinal ganglion cells in the early stages of the disease. These exciting new findings may help us develop psychophysical tests to monitor early retinal ganglion cell damage, possibly before neurons are committed to the process of cell death.

Retinal ganglion cell shrinkage in glaucoma

SUMMARY

There has been some debate concerning the selective loss of retinal ganglion cells belonging to the magnocellular pathway in early glaucoma. Although histologic studies of retinal ganglion cells in experimental and human glaucoma have suggested selective loss of the larger cells and, by implication, selective damage to the magnocellular pathway, this has not been confirmed using psychophysical tests. Recent studies of retinal ganglion cell morphology in experimental glaucoma provide evidence that retinal ganglion cells undergo morphologic changes prior to cell death; cell volume is reduced in surviving cells with corresponding reductions in the size of the axon and dendritic tree. The magnitude of these changes is consistent with cell shrinkage as an explanation for the apparent selective damaged reported in earlier studies. It is also likely that widespread changes in the retinal ganglion cell population precede cell death, which will affect the physiologic behavior of these cells.

Remodelling the filtration bleb

AIMS

To report remodelling of enlarged dysmorphic filtration blebs with conjunctival compression sutures and autologous blood injection.

METHODS

A retrospective analysis of consecutively recruited patients with enlarged and dysmorphic filtration blebs who were managed with conjunctival compression sutures and subconjunctival autologous blood injections. Under topical anaesthesia, conjunctival (8.0-9.0 Nylon or 8.0 Vicryl) compression sutures were placed either side of blebs that were not showing signs of spontaneous resolution. In each case up to 0.75 ml of autologous blood was then injected into the areas of the bleb to be flattened. Supplemental injections of autologous blood were given in clinic as required.

RESULTS

In 11 eyes of 11 patients, conjunctival compression sutures were placed and autologous blood was injected, on average, 568 days following filtration surgery (range 41-2023). Supplemental autologous blood injections were required in eight patients, with three injections being given in one patient. In each case, the sutures were well tolerated and satisfactory compression of the conjunctiva was achieved. The highest intraocular pressure following injection was 25 mm Hg (mean 17.3, SD 4.2) and in none of the cases did blood enter the anterior chamber or parts of the filtration bleb bounded by the sutures.

CONCLUSION

Conjunctival compression sutures with autologous blood provide a simple and effective means for remodelling the filtration bleb. The procedure can be performed under topical anaesthesia and does not hinder further bleb surgery, should this be required.

A multicentre evaluation of the diagnostic efficiency of serological investigations for C1 inhibitor deficiency

AIM

To determine the diagnostic efficiency of assays routinely used in the investigation of hereditary angio-oedema.

METHODS

Over a four year period, 1144 samples were received for analysis from 907 patients suspected of C1 inhibitor deficiency. Analyses were performed for C4 and C1 inhibitor (functional and immunochemical). Notes were reviewed retrospectively on patients with low serological indicators to determine diagnosis.

RESULTS

These are the first data to indicate the sensitivity, specificity, and predictive values of the assays most frequently used to screen for C1 inhibitor deficiency. A combination of low C4 and low C1 inhibitor function has 98% specificity for C1 inhibitor deficiency in this population and a 96% negative predictive value, and is thus a very effective screen. All patients with untreated C1 inhibitor deficiency had a low C4 value.

CONCLUSIONS

All patients considered for a diagnosis of C1 inhibitor deficiency should have serum examined to measure both C4 and functional C1 inhibitor. If either is normal at presentation this essentially excludes a diagnosis of C1 inhibitor deficiency. These tests can be performed sequentially. If C4 is normal it is not necessary to proceed to C1 inhibitor analysis. If C1 inhibitor function and C4 are both low then a repeat sample should be obtained to confirm the findings.

Confidential student information in nursing education

Nurse educators frequently know intriguing personal information about students and must decide whether to share such information with colleagues. While sharing with colleagues is sometimes necessary, often it is not. Discussing stories about students may be an effective stress-relieving strategy for faculty, but stress reduction must not be achieved at the expense of ethical behavior. The author explores the fine line between gossip and collegial discourse that focuses on educational goals, considers whether a separate code of ethics for nurse educators is needed, and offers recommendations for action.

The Humphrey optical coherence tomography scanner: quantitative analysis and reproducibility study of the normal human retinal nerve fibre layer

BACKGROUND/AIMS

To determine the reproducibility of the Humphrey optical coherence tomography scanner (OCT), software version 5.0, for measurement of retinal nerve fibre layer (RNFL) thickness in normal subjects and to compare OCT measurements with published histological thickness of the human RNFL.

METHODS

Three independent measurements were obtained at each session for one eye from 15 normal subjects with a mean age of 30.8 (SD 10.9) years. Scans were taken in the peripapillary retina using the default setting (1.74 mm radius from centre of the optic disc) and were repeated 1 week later. Additional scans were obtained at the optic nerve head (ONH) margin overlying the scleral rim, for comparison with available histological data on the human RNFL.

RESULTS

For the 1.74 mm circular scan, the mean coefficient of variation (COV) for the global RNFL thickness measurement was 5% (SD 3%). This increased to 8% (3%) for quadrant measurements and to 9% (3%) with further subdivision into 12 segments. Significant differences (p<0.05) between sessions were only found when the data were divided into segments. The mean RNFL thickness for the 1.74 mm scan was 127.87 (9.81) microm. The RNFL was maximal at the superior disc pole, 161.44 microm (14.8), and minimal at the temporal pole, 83.1 (12.8) microm. Peak thickness values occurred superior temporal and inferior temporal to the vertical axis. RNFL thickness for every sector of the disc was greatest at the margin of the optic disc (mean 185.79 microm; SD 32.61). Although the variation in RNFL thickness around the disc follows published histology data, the OCT underestimates RNFL thickness by an average of 37% (SD 11; range 21-48%).

CONCLUSION

The OCT provides reproducible measurement of the retinal structures that are consistent with the properties of the RNFL. However, comparison with available studies of RNFL thickness in the human suggests that in its present form, the OCT underestimates RNFL thickness. Further refinement of this technology is required to improve the accuracy with which the OCT measures retinal nerve fibre layer thickness.

Role of the PR intermediate in the reaction of cytochrome c oxidase with O2

The first discernible intermediate when fully reduced cytochrome c oxidase reacts with O2 is a dioxygen adduct (compound A) of the binuclear heme iron-copper center. The subsequent decay of compound A is associated with transfer of an electron from the low-spin heme a to this center. This reaction eventually produces the ferryl state (F) of this center, but whether an intermediate state may be observed between A and F has been the subject of some controversy. Here we show, using both optical and EPR spectroscopy, that such an intermediate (P(R)) indeed exists and that it exhibits spectroscopic properties quite distinct from F. The optical spectrum of P(R) is similar or identical to the spectrum of the P(M) intermediate that is formed after compound A when two-electron-reduced enzyme reacts with O2. An unusual EPR spectrum with features of a CuB(II) ion that interacts magnetically with a nearby paramagnet [cf. Hansson, O., Karlsson, B., Aasa, R., Vänngård, T., and Malmström, B.G (1982) EMBO J. 1, 1295-1297; Blair, D. F., Witt, S. N., and Chan, S. I. (1985) J. Am. Chem. Soc. 107, 7389-7399] can be uniquely assigned to the P(R) intermediate, not being found in either the P(M) or F intermediate. The binuclear center in the P(R) state may be assigned as having an Fe(a3)(IV)=O CuB(II) structure, as in both the P(M) and F states. The spectroscopic differences between these three intermediates are evaluated. The P(R) state has a key role as an initiator of proton translocation by the enzyme, and the thermodynamic and electrostatic bases for this are discussed.

Stable strontium accumulation by earthworms: a paradigm for radiostrontium interactions with its cationic analogue, calcium

The accumulation of stable strontium and its chemical analogue calcium by four species of earthworm, representing three distinct ecophysiological groups inhabiting celestite (SrSO4)-rich natural soils, was investigated. An increase in soil strontium concentration over a four-orders-of-magnitude range was accompanied by an increase in earthworm tissue strontium concentration. In contrast, no relationship between soil and tissue calcium concentrations was apparent, indicating that this essential cation is strongly regulated within earthworm tissues but that nonessential strontium burdens are not physiologically regulated. Concentration factors for strontium ranged from 0.1 to 1.42, with an inverse relationship between this parameter and soil strontium concentration. The use of concentration factors and discrimination coefficients lead to the conclusion that earthworms discriminate against strontium accumulation at increased soil calcium concentrations, such that strontium would be predicted to be more efficiently accumulated by worms inhabiting acidic, calcium-poor soils. Although few consistent trends in strontium and calcium concentration were apparent between earthworm species, the species with the highest calcium turnover (i.e., the litter-inhabiting Lumbricus rubellus) typically accumulated higher concentrations of strontium than representatives of contrasting ecophysiological classes. These findings are considered in the context of the distribution, retention, and cycling of radiostrontium in soils.

The effects of astigmatism and working distance on optic nerve head images using a Heidelberg Retina Tomograph scanning laser ophthalmoscope

PURPOSE

To determine effects of astigmatism and working distance on optic nerve head images in normal patients using the Heidelberg Retina Tomograph.

METHODS

The optic disks of 51 normal healthy subjects, aged 19 to 44 years, were imaged through dilated pupils. Subjects with 0.75 DC or less of astigmatism were imaged without correction at a working distance of 15 mm. They were then re-imaged with a cylindrical correction of +3.00 DC at 90 degrees axis (n = 20). Naturally astigmatic subjects with more than 1.00 DC were imaged without correction and then re-imaged once this was neutralized with their appropriate spectacle prescription (n = 15). The effects of working distance were studied using subjects with 0.75 DC or less (n = 16). Two working distances were used, 15 and 25 mm. At each session the means of three topographic images were taken from which standard deviations and parameters were recorded. Parameters analyzed included cup shape measure, rim area, and inferior temporal rim volume. Z-profile full width at half maximum was calculated from one image per subject for each condition.

RESULTS

No significant difference was found in the measured parameters of the optic disk for any astigmatic condition or changes in working distance (P >.05), (paired t test). Both the standard deviation of the mean topographic images and the Z-profile half-maximum width of the axial intensity profile were significantly greater with induced astigmatism of +3.00 DC (P values 0.3 and.00, respectively).

CONCLUSIONS

Optic disk parameters are not significantly affected by uncorrected astigmatism (up to 2.50 DC) or working distance. The algorithm used by the Heidelberg Retina Tomograph to generate topographic maps is sufficiently robust that astigmatism up to 2.50 DC does not require correction.

Electron and proton transfer in the arginine-54-methionine mutant of cytochrome c oxidase from Paracoccus denitrificans

Arginine 54 in subunit I of cytochrome c oxidase from Paracoccus denitrificans interacts with the formyl group of heme a. Mutation of this arginine to methionine (R54M) dramatically changes the spectral properties of heme a and lowers its midpoint redox potential [Kannt et al. (1999) J. Biol. Chem. 274, 37974-37981; Lee et al. (2000) Biochemistry 39, 2989-2996; Riistama et al. (2000) Biochim. Biophys. Acta 1456, 1-4]. During anaerobic reduction of the mutant enzyme, a small fraction of heme a is reduced first along with heme a(3), while most of heme a is reduced later. This suggests that electron transfer is impaired thermodynamically due to the low redox potential of heme a but that it still takes place from Cu(A) via heme a to the binuclear site as in wild-type enzyme, with no detectable bypass from Cu(A) directly to the binuclear site. Consistent with this, the proton translocation efficiency is unaffected at 1 H(+)/e(-) in the mutant enzyme, although turnover is strongly inhibited. Time-resolved electrometry shows that when the fully reduced enzyme reacts with O(2), the fast phase of membrane potential generation during the P(R )()--> F transition is unaffected by the mutation, whereas the slow phase (F --> O transition) is strongly decelerated. In the 3e(-)-reduced mutant enzyme heme a remains oxidized due to its lowered midpoint potential, whereas Cu(A) and the binuclear site are reduced. In this case the reaction with O(2) proceeds via the P(M) state because transfer of the electron from Cu(A) to the binuclear site is delayed. The single phase of membrane potential generation in the 3e(-)-reduced mutant enzyme, which thus corresponds to the P(M)--> F transition, is decelerated, but its amplitude is comparable to that of the P(R)--> F transition. From this we conclude that the completely (4e(-)) reduced enzyme is fully capable of proton translocation.

The pattern electroretinogram (PERG) with contralateral corneal reference

The pattern electroretinogram (PERG) is a sensitive test for investigation of the proximal retina. For monocular recording, the contralateral corneal reference (CCR) electrode position has been suggested as a possible alternative to the conventional ipsilateral temporal reference (ITR). We therefore compared the effect of these electrode positions on 26 subjects (median age 45.5 years, IQR 24.5-61.5). The signals were recorded monocularly with DTL nylon fibre electrodes. The visual stimuli were high contrast 19' black-white checkerboard patterns, reversing 4 times/s. PERG responses obtained from the CCR gave larger amplitudes and the increase in amplitude was statistically significant (P < 0.001). Because the CCR signal is larger, new normative ranges must be established to avoid false negative results.

The s-cone PHNR and pattern ERG in primary open angle glaucoma

PURPOSE

To compare the sensitivity of the photopic negative response (PhNR) from the shortwave (S)-sensitive and the long (L)- and medium (M)-wave-sensitive cone electroretinograms (ERGs), with the pattern electroretinogram (PERG) in the early stages of primary open-angle glaucoma (POAG).

METHODS

Eighteen patients under treatment for diagnosed POAG and 19 normal control subjects were investigated. S-cone ERGs were elicited using adaptation to 650-nm light to suppress L-cone activity, and substitution between 450 nm and 535 nm to silence M-cone response at luminances higher than rod saturation. PhNRs from the L&M-cone pathways were elicited by a 200-msec pulse of red light (650 nm) on a continuous blue (450 nm) background. PERGs were recorded in accordance with the International Society for Clinical Electrophysiology of Vision (ISCEV) standard.

RESULTS

Each method showed a statistically significant difference in the two groups. The S-cone PhNR was the most sensitive test and provided the most statistically significant results, with the largest area enclosed by the receiver operating characteristic (ROC) curve.

CONCLUSIONS

The findings indicate that all three types of ERG may be useful in glaucoma investigation. The L- and M-cone PhNRs may have a role in monitoring established glaucoma. The previously reported high sensitivity of the PERG was confirmed. Extensive diffuse damage to S-cone bipolar and bistratified ganglion cells appears to occur at a very early stage in POAG, owing to a pressure-related mechanism, and the S-cone PhNR was the most sensitive test. It may in future have an important role in diagnosis and monitoring of early glaucoma. Further investigation of this possibility is recommended.