Biological and Cognitive Markers of Presenilin1 E280A Autosomal Dominant Alzheimer's Disease: A Comprehensive Review of the Colombian Kindred

The study of individuals with autosomal dominant Alzheimer's disease affords one of the best opportunities to characterize the biological and cognitive changes of Alzheimer's disease that occur over the course of the preclinical and symptomatic stages. Unifying the knowledge gained from the past three decades of research in the world's largest single-mutation autosomal dominant Alzheimer's disease kindred - a family in Antioquia, Colombia with the E280A mutation in the Presenilin1 gene - will provide new directions for Alzheimer's research and a framework for generalizing the findings from this cohort to the more common sporadic form of Alzheimer's disease. As this specific mutation is virtually 100% penetrant for the development of the disease by midlife, we use a previously defined median age of onset for mild cognitive impairment for this cohort to examine the trajectory of the biological and cognitive markers of the disease as a function of the carriers' estimated years to clinical onset. Studies from this cohort suggest that structural and functional brain abnormalities - such as cortical thinning and hyperactivation in memory networks - as well as differences in biofluid and in vivo measurements of Alzheimer's-related pathological proteins distinguish Presenilin1 E280A mutation carriers from non-carriers as early as childhood, or approximately three decades before the median age of onset of clinical symptoms. We conclude our review with discussion on future directions for Alzheimer's disease research, with specific emphasis on ways to design studies that compare the generalizability of research in autosomal dominant Alzheimer's disease to the larger sporadic Alzheimer's disease population.

Valorisation of biowaste digestate through solid state fermentation to produce biopesticides from Bacillus thuringiensis

The main goal of this work is the production of a biopesticide through solid-state fermentation of biowaste digestate inoculated with Bacillus thuringiensis (Bt) at pilot scale using different configurations of reactors. Fermentations were carried out using insulated and non-insulated, stirred and non-stirred reactors at different scales (10, 22 and 100 L) in order to assess the influence of the reactor configuration on the biopesticide production process. A maximum temperature of 60 °C was reached in 10-L insulated non-stirred reactors where increments of Bt viable cells and spores with respect to initial values of 1.9 and 171.6 respectively, were attained. In contrast, when temperature was regulated by using 22-L non-insulated stirred reactors the increment of viable cells and spores were 0.8 and 1.9, respectively, at a stable temperature of 27 °C. When the non-insulated stirred reactor was scaled up to 100-L, the increase of viable cells and spore counts were 1.2 and 3.8 respectively, with an average temperature of 28 °C. These results demonstrated that the election of a proper reactor configuration is important when considering the development of a new SSF process, especially when dealing with non-conventional substrates as digestate.

Rickettsial keratitis in a Case of Mediterranean spotted fever

The first documented case of infectious keratitis (an ameboid-like corneal ulcer) caused by Rickettsia conorii is described. Corneal infection was probably caused by contamination through the tears during systemic rickettsial dissemination. Topical tetracyclin ointment was effective. Rickettsial keratitis should be considered in the differential diagnosis of ameboid-like corneal ulcers in areas where Mediterranean spotted fever is endemic.

Accuracy of the Potential Acuity Meter in Predicting the Visual Outcome in Cases of Cataract Associated with Macular Degeneration

In order to ascertain the accuracy and specificity of the Potential Acuity Meter (PAM) in the preoperative evaluation of likely postoperative visual acuity in cases of cataract associated with age-related macular degeneration (ARMD), we studied the results in 130 cases, 54 of whom had preoperatively proved or suspected ARMD associated with a cataract. All of them were operated with extracapsular extraction and implantation of an intraocular lens (IOL), and final visual acuity was established when all the patients were visited three months postoperatively. A positive linear correlation was found between normal ocular fundus and PAM prediction (r = 0.77), and in the group of patients with preoperatively confirmed ARMD (r = 0.77). No difference was found between the preoperative PAM estimation and the final visual acuity in both groups. The PAM prediction was less accurate in cases with doubtful preoperative ARMD (r = 0.58) for whom showed PAM the highest score of false negatives in favor of the final visual acuity. Our results show that PAM is a reliable clinical technique for the prediction of visual results after cataract surgery in cases with preoperatively proved or doubtful macular pathology. To the best of our knowledge, this is the first report regarding the sensitivity and specificity of the PAM in diseased or suspicious maculas associated with cataract.

Wear Behaviour of the Pair Ti–6Al–4V–UHMWPE of Acrylic Bone Cements Containing Different Radiopaque Agents

The objective of this study was to improve the wear behaviour of acrylic bone cements by substituting the conventional inorganic radiopaque agents (BaSO4, ZrO2) for different iodinated radiopaque monomers which can co-polymerize with the methyl methacrylate monomer, MMA. To this aim, the wear behaviour of the pair Ti–6Al–4V–UHMWPE (ultra high molecular weight polyethylene) was studied in the absence and in the presence of cement particles (the third body).

The nucleus raphe magnus OFF-cells are involved in diffuse noxious inhibitory controls

Diffuse noxious inhibitory controls (DNIC) are very powerful long-lasting descending inhibitory controls which are pivotal in modulating the activity of spinal and trigeminal nociceptive neurons. DNIC are subserved by a loop involving supraspinal structures such as the lateral parabrachial nucleus and the subnucleus reticularis dorsalis. Surprisingly, though, whether the nucleus raphe magnus (NRM), another supraspinal area which is long known to be important in pain modulation, is involved in DNIC is still a matter of discussion. Here, we reassessed the role of the NRM neurons in DNIC by electrophysiologically recording from wide dynamic range (WDR) neurons in the trigeminal subnucleus oralis and pharmacologically manipulating the NRM OFF- and ON-cells. In control conditions, C-fiber-evoked responses in trigeminal WDR neurons are inhibited by a conditioning noxious heat stimulation applied to the hindpaw. We show that inactivating the NRM by microinjecting the GABAA receptor agonist, muscimol, both facilitates C-fiber-evoked responses of trigeminal WDR neurons and strongly attenuates their inhibition by heat applied to the hindpaw. Interestingly, selective blockade of ON-cells by microinjecting the broad-spectrum excitatory amino acid antagonist, kynurenate, into the NRM neither affects C-fiber-evoked responses nor attenuates DNIC of trigeminal WDR neurons. These results indicate that the NRM tonically inhibits trigeminal nociceptive inputs and is involved in the neuronal network underlying DNIC. Moreover, within NRM, OFF-cells might be more specifically involved in both the tonic and phasic descending inhibitory controls of trigeminal nociception.

Odours and volatile organic compounds emitted from municipal solid waste at different stage of decomposition and relationship with biological stability

Odours (OU(E)) and volatile organic compounds (VOC) emission during biological process used to treat MSW were studied under standardized conditions in order to detect potential risk for workers and population. Results obtained indicated that odours and VOCs emitted depend on the biological stability of waste measured by the dynamic respiration index (DRI) and a very good correlation were found between these parameters (OU(E) vs. DRI, r=0.96, p<0.001, n=6; VOC vs. DRI, r=0.97, p<0.001, n=6). GC-MS study of the VOCs indicated the presence of a group of molecules that were degraded during the process. On the other hand, a second group of molecules, i.e. aromatic and halogenated compounds, and furan persisted in the waste sample, although molecule concentrations were always lower than Threshold Limit Value-Time Weighted Average (TLV-TWA).

Potential odour emission measurement in organic fraction of municipal solid waste during anaerobic digestion: Relationship with process and biological stability parameters

The aim of the present study is to investigate the correlation between microbial activity, i.e., biological stability measured by aerobic (OD(20) test) and anaerobic tests (ABP test), and odour emissions of organic fraction of municipal solid waste during anaerobic digestion in a full-scale treatment plant considering the three stages of the process (input, digested and post-digested waste). The results obtained indicated that the stabilization of the treated material reduces the odour impact measured by the olfactometric approach. Successive application of gas chromatography mass spectrometry (GC-MS) and electronic nose (EN) allowed the characterization of the different groups of volatile organic compounds (VOCs) responsible of odour impacts determining, also, their concentration. Principal component and partial least squares analyses applied to the EN and GC-MS data sets gave good regression for the OD(20) vs the EN and OD(20) vs the GC-MS data. Therefore, OD(20) reduction could be used as an odour depletion indicator.

Potential odour emission measurement in organic fraction of municipal solid waste during anaerobic digestion: relationship with process and biological stability parameters

The aim of the present study is to investigate the correlation between microbial activity, i.e., biological stability measured by aerobic (OD20 test) and anaerobic tests (ABP test), and odour emissions of organic fraction of municipal solid waste during anaerobic digestion in a full-scale treatment plant considering the three stages of the process (input, digested and post-digested waste). The results obtained indicated that the stabilization of the treated material reduces the odour impact measured by the olfactometric approach. Successive application of gas chromatography mass spectrometry (GC-MS) and electronic nose (EN) allowed the characterization of the different groups of volatile organic compounds (VOCs) responsible of odour impacts determining, also, their concentration. Principal component and partial least squares analyses applied to the EN and GC-MS data sets gave good regression for the OD20 vs the EN and OD20 vs the GC-MS data. Therefore, OD20 reduction could be used as an odour depletion indicator.

New frontiers for the perioperative data method for IOL calculation following corneal refractive surgeries

PURPOSE

To evaluate the efficiency of the perioperative data method for intraocular lens (IOL) calculation after correction of myopia and hyperopia with different techniques, including reoperated cases.

METHODS

Thirty-five eyes (26 patients) that developed cataract after corneal refractive procedures were evaluated retrospectively. They were categorized according to initial error of refraction into myopes and hyperopes and according to types of refractive procedures into ablative, incisional, both, or others. Reoperated cases were also considered. Number of refractive procedures was noted. Time interval between the first procedure and cataract extraction was indicated. Perioperative method was used to calculate the K value. SRK/T formula was used to calculate IOL power. Difference between intended and finally achieved manifest refraction was an indicator for efficiency of the calculation.

RESULTS

Postoperatively, 77.2% of cases had manifest refraction +/-1.5 D of intended refraction. There was no difference between myopes and hyperopes in terms of final manifest refraction, best-corrected visual acuity, and difference between intended and finally achieved manifest refraction. Similarly were groups of different types of surgeries. Efficiency of the method decreased with high axial lengths and low IOL powers. Neither the number of refractive surgeries nor time interval between surgeries affected efficiency of the method.

CONCLUSIONS

The perioperative data method is equally effective for myopes and hyperopes. The types, numbers of refractive procedures, as well as the time interval between refractive surgery and cataract extraction do not alter the credibility of the method. In high degrees of myopia, the method gives less accurate results.

Propagation of fatigue cracks in acrylic bone cements containing different radiopaque agents

In this work three iodine-containing monomers were proposed as new radiopaque agents for acrylic bone cements. In previous studies the addition of iodine-containing methacrylate monomers provided a statistically significant increase in tensile stress, fracture toughness and ductility, with respect to the barium sulphate(BaSO4)-containing cement. However, since fatigue resistance is one of the main properties required to ensure a good long-term performance of permanent prostheses, it is important to compare the fatigue properties of these new bone cement formulations with the radiolucent and BaSO4-containing bone cements. Because the acrylic cements have initial cracks, fatigue crack propagation studies were performed. It can be observed that these acrylic cements followed the Paris-Erdogan model. The results showed that the addition of some organic radiopacifiers (DISMA, TIBMA) increased the fatigue crack propagation resistance as compared to the radiolucent cement, being similar to the BaSO4-containing cement. The radiolucent cement showed a low crack propagation resistance.

Diabetes mellitus concomitantly facilitates the induction of long-term depression and inhibits that of long-term potentiation in hippocampus

Memory impairments, which occur regularly across species as a result of ageing, disease (such as diabetes mellitus) and psychological insults, constitute a useful area for investigating the neurobiological basis of learning and memory. Previous studies in rats found that induction of diabetes (with streptozotocin, STZ) impairs long-term potentiation (LTP) but enhances long-term depression (LTD) induced by high- (HFS) and low-frequency stimulations (LFS), respectively. Using a pairing protocol under whole-cell recording conditions to induce synaptic plasticity at Schaffer collateral synapses in hippocampal CA1 slices, we show that LTD and LTP have similar magnitudes in diabetic and age-matched control rats. But, in diabetic animals, LTD is induced at more polarized and LTP more depolarized membrane potentials (V(ms)) compared with controls: diabetes produces a 10 mV leftward shift in the threshold for LTD induction and 10 mV rightward shift in the LTD-LTP crossover point of the voltage-response curve for synaptic plasticity. Prior repeated short-term potentiations or LTP are known to similarly, though reversibly, lower the threshold for LTD induction and raise that for LTP induction. Thus, diabetes- and activity-dependent modulation of synaptic plasticity (referred to as metaplasticity) display similar phenomenologies. In addition, compared with naïve synapses, prior induction of LTP produces a 10 mV leftward shift in Vms for inducing subsequent LTD in control but not in diabetic rats. This could indicate that diabetes acts on synaptic plasticity through mechanisms involved in metaplasticity. Persistent facilitation of LTD and inhibition of LTP may contribute to learning and memory impairments associated with diabetes mellitus.

Elimination of barium sulphate from acrylic bone cements. Use of two iodine-containing monomers

The aim of this work is to present a new approach to joint arthroplasty failure related to bone cement mantle. As barium sulphate is considered one of the main causes of mechanical weakness in the cement, we substituted this inorganic radiopacifier of the solid component for radiopaque monomers in the liquid component. We obtained two different cements, one containing 5 vol% 2-[2',3',5'-triiodobenzoyl] ethyl methacrylate (TIBMA) and the other containing 3,5-diiodine salicylic methacrylate (DISMA). In both cases, the mechanical properties of these new cements were better than those of the barium sulphate-containing cement. The radiopacity obtained was comparable to that of the aforementioned cement and all the samples showed good biocompatibility.

Increased spike broadening and slow afterhyperpolarization in CA1 pyramidal cells of streptozotocin-induced diabetic rats

Diabetes mellitus is associated with impairments of cognitive function both in humans and animal models. In diabetic rats cognitive deficits are related to alterations in activity-dependent synaptic plasticity in the hippocampus. Many similarities with the pathophysiology of normal brain aging have been noted, and the view emerges that the effects of diabetes on the brain are best described as "accelerated brain aging."In the present study we examined whether CA1 pyramidal neurons from streptozotocin-induced diabetic rats display an increased slow afterhyperpolarization, often considered as a hallmark of neuronal aging. We found no differences in resting membrane potential, input resistance, membrane time-constant, and action potential amplitude and duration between CA1 pyramidal neurons from streptozotocin-induced diabetic and age-matched control rats. During a train of action potentials, however, there is an increased broadening of the action potentials in diabetic animals, so-called "spike broadening." The amplitude of the slow afterhyperpolarization elicited by a train of action potentials is indeed increased in diabetic animals. Interestingly, when the slow afterhyperpolarization is elicited by a Ca(2+) spike, there is no difference between control and diabetic rats. This indicates that the increased slow afterhyperpolarization in diabetes is likely to be due to an increased Ca(2+) influx resulting from the increased spike broadening. These data underscore the notion that the diabetic brain at the neuronal level shares properties with brain aging.

A radiopaque polymeric matrix for acrylic bone cements

As part of the search for an alternative to inorganic radiopaque agents, this work studies the possibility of modifying bone cement formulations by incorporating a radiopaque monomer, that is, 4-iodophenol methacrylate (IPMA), in the liquid phase. The monomer was synthesized in the laboratory, and cements were prepared by the standard method. The influence on the different cement characteristics of various monomer concentrations was studied. It was seen that the setting time decreased as the percentage of monomer increased. The radiopacity attained in the 15 vol.% IPMA formulations was about the same as that for a cement containing 10 wt.% barium sulphate. Dynamic and static mechanical properties were measured. The materials did not show significant differences in the glass transition temperature. However, static mechanical properties showed enhanced compressive strength, tensile strength, and elastic modulus with respect to conventional cements formulated with barium sulphate. Histological studies showed a good response of muscular tissue to implanted specimens.

The Involvement of N-Methyl-D-Aspartate Receptors in Induction and Maintenance of Long-Term Potentiation in Rat Visual Cortex

Pyramidal neurons from layers II and III of rat visual cortex slices were studied with intracellular recordings. The involvement of N-methyl-D-aspartate (NMDA) receptors was investigated: (1) in the synaptic response to white matter stimulation; (2) in the induction of long-term potentiation (LTP); and (3) in the maintenance of LTP. Bath application of 25 microM of 2-amino-5-phosphonovalerate (APV), an NMDA receptor antagonist, caused a slight (< 10%) reduction of the amplitude of the synaptic response elicited by white matter stimulation. The APV-sensitive excitatory postsynaptic potential (EPSP) had a longer peak latency and duration than the APV-resistant EPSP. Bath application of 10 microM of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA glutamate receptor antagonist, revealed a CNQX-resistant EPSP in response to white matter stimulation which was APV-sensitive. The time course of the CNQX-resistant EPSP was similar to that of the APV-sensitive EPSP and its onset latency was similar to that of the synaptic response in normal medium. Bath application of the GABA-A antagonist bicuculline (0.1 to 0.5 microM) led to a progressive enhancement of the amplitude of the APV-sensitive EPSP. At bicuculline concentrations above 0.3 microM the amplitude of this EPSP increased with membrane depolarization as was the case for the CNQX-resistant EPSP implying that the NMDA receptors were located on the recorded neuron. The susceptibility of the cells to undergo LTP was tested at various concentrations of bicuculline. The effectiveness of bicuculline treatment was quantified by comparing the amplitudes of the synaptic response to just subthreshold stimuli at two post-stimulus delays: (i) at 22 ms, which corresponds to the time to peak of both the initial inhibitory postsynaptic potential and the APV-sensitive EPSP; and (ii) at 8 - 11 ms post-stimulus, which corresponds to the peak of the postsynaptic potential (PSP) in normal medium. Bath application of APV, 20 min after the conditioning tetanus, allowed the authors to measure the amplitude of the APV-sensitive EPSP in the potentiated response. In normal medium, the ratio of the late over the early PSP amplitude was 33.6 +/- 4.1% and tetanic stimulation failed to induce LTP. The conditions remained the same at bicuculline concentrations of 0.1 to 0.2 microM. At higher concentrations of bicuculline the amplitude ratio of late versus early PSP increased and tetanic stimulation induced LTP. In cells, in which bicuculline had caused small ratio increases, only the APV-sensitive EPSP underwent LTP. In cells in which bicuculline had caused large ratio changes, both the APV-resistant and the APV-sensitive EPSP showed LTP. Together with the previous finding that blockade of NMDA receptors prevents LTP (Artola and Singer, 1987) these results suggest that there is a threshold for LTP induction, which is only reached if NMDA receptor-gated channels are sufficiently activated. The data indicate further that the NMDA receptor-mediated EPSP is itself susceptible to LTP whereby its LTP threshold is lower than that of the APV-resistant EPSP. Given the different LTP thresholds of the APV-resistant and APV-sensitive EPSPs, the possibility is raised that their potentiation depends on different mechanisms.

Haze after laser in situ keratomileusis in eyes with previous photorefractive keratectomy

In cases with previous photorefractive keratectomy (PRK), there is a risk of developing severe haze after laser in situ keratomileusis (LASIK). We report 3 patients (4 eyes) who developed severe haze after LASIK treatment for residual myopia following PRK. Both PRK and LASIK procedures were performed using the VISX 20/20 excimer laser. We report the grade of haze, amount of regression, and visual acuity after the patients were treated with topical steroids. In 2 eyes, the uncorrected visual acuity was 1.0 after 1 year with grade I haze. In the other 2 eyes, there was a residual refractive error, and the best spectacle-corrected visual acuity was 0.7 with grade II haze.

Laser in situ keratomileusis for treatment of residual myopia after photorefractive keratectomy

PURPOSE

To evaluate the results of laser in situ keratomileusis after photorefractive keratectomy.

METHODS

Eighty eyes of 80 patients with residual myopia after photorefractive keratectomy were reoperated with laser in situ keratomileusis. The study was retrospective. Laser in situ keratomileusis was performed using the automated corneal shaper microkeratome and Chiron Technolas 217-C d1 excimer laser. Data measured after laser in situ keratomileusis included uncorrected visual acuity, best-corrected visual acuity, refraction, haze, pachymetry, and keratometry. The follow-up was at least 12 +/- 1.6 months (range, 12 to 15 months).

RESULTS

After laser in situ keratomileusis the mean spherical equivalent was -0.24 diopters +/- 0.78. (range, -3 to +1.5) at 12 months, and the mean uncorrected visual acuity was 0.76 diopters +/- 0.24 (range, 0.1 to 1). Sixty-five eyes (81.3%) had various degrees of haze after laser in situ keratomileusis. One eye (1.2%) lost 2 lines of best-corrected visual acuity.

CONCLUSIONS

Laser in situ keratomileusis enhancement may be a good alternative to correct residual myopia and astigmatism after primary photorefractive keratectomy. Corneal haze is a common problem in these eyes, and the treatment after laser in situ keratomileusis enhancement should be the same as the treatment after primary photorefractive keratectomy.

Laser in situ keratomileusis for undercorrection and overcorrection after radial keratotomy

PURPOSE

To evaluate laser in situ keratomileusis (LASIK) in the management of overcorrection and undercorrection after radial keratotomy (RK).

SETTING

Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

This prospective study comprised 20 eyes of 13 patients. The eyes were divided into 2 groups: 11 eyes that were overcorrected after RK and 9 eyes that were undercorrected after RK. Both groups were treated with LASIK after a mean interval of 22 months +/- 8.4 (SD) (range 12 to 45 months). The follow-up was 6 months.

RESULTS

Six months after LASIK, there was a significant decrease in the spherical equivalent in both groups. Ninety-one percent of eyes in the overcorrected group and 89% in the undercorrected group were within +/-1.0 diopter of the intended correction. There was a significant improvement in the uncorrected visual acuity in both groups. In the overcorrected group, 91% showed no change or improvement in their best corrected visual acuity; in the undercorrected group, 89% showed no change or improvement.

CONCLUSIONS

Laser in situ keratomileusis was relatively safe in treating both overcorrection and undercorrection after RK. With proper intraoperative precautions, LASIK can effectively treat the residual refractive defects after RK.

Laser in situ Keratomileusis to Correct Residual Myopia After Cataract Surgery

PURPOSE

To evaluate the effectiveness, predictability, and safety of laser in situ keratomileusis (LASIK) for correcting residual myopia after cataract surgery with intraocular lens implantation.

METHODS

Twenty-two eyes of 22 patients underwent LASIK for the correction of residual myopia after cataract surgery. LASIK was carried out using the Chiron Automated Corneal Shaper and the NIDEK EC-5000 excimer laser. In all eyes, the follow-up was 12 months.

RESULTS

Before LASIK, 1 eye (4.5%) had an uncorrected visual acuity of 0.5 or better; 12 months after LASIK, 10 eyes (45.4%) achieved this level of visual acuity and 0 eyes achieved 1.00 or better. Before LASIK, mean refraction was -2.90 +/- 1.80 D; 12 months after LASIK it decreased significantly to 0.40 +/- 0.60 D (P < .01). In 18 eyes (81.8%) at 12 months after LASIK, spherical equivalent refraction was within +/-1.00 D of emmetropia; 11 eyes (50%) were within 0.50 D. No vision-threatening complications occurred.

CONCLUSION

LASIK with the Automated Corneal Shaper and Nidek EC-5000 excimer laser was an effective, predictable, stable, and safe procedure for correcting residual myopia after cataract surgery. No intraocular lens or cataract incision related complications occurred when LASIK was performed at least 3 months after phacoemulsification.

Isotherm Model Analysis for the Adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) on Anaerobically Digested Sludge

Adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) from aqueous solutions on anaerobically digested sludge has been investigated. Experimental data has been fit to Langmuir, Freundlich, and Redlich-Peterson isotherms to obtain the characteristic parameters of each model. Based on the maximum adsorption capacity obtained from the Langmuir and the Redlich-Peterson isotherm the affinity of the studied metals for the sludge has been established as Cu (II)>Cd (II)>Zn (II)>Ni (II). Adsorption tests from multimetal systems confirm the affinity order obtained in the individual metal tests. The adsorption capacity for Cu (II) measured in individual tests is not reduced by the presence of the other above referred metals. Desorption of Zn (II) and Cd (II) previously bound to the sludge in front of Cu (II) and HCl solutions is also reported. Copyright 2000 Academic Press.

Choroidal neovascularization in myopic eyes after photorefractive keratectomy

PURPOSE

To evaluate the incidence, characteristics, and results of treatment of choroidal neovascularization (CNV) in myopic eyes corrected by photorefractive keratectomy (PRK).

SETTING

University Miguel Hernández, Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

This study was of the incidence of CNV in 5936 consecutive eyes that had PRK for the correction of myopia. Mean follow-up was 38.5 months +/- 17.4 (SD).

RESULTS

Extrafoveal CNV developed in the right eye of a 44-year-old woman 26 months after PRK for the correction of -12.00 diopters (D) of myopia. The follow-up after PRK was 38 months. Best corrected visual acuity (BCVA) before PRK was 20/40 (spherical equivalent [SE] -12.00 D). After PRK, BCVA was 20/32 SE -1.75 D). The CNV was treated by direct argon-green laser photocoagulation and did not recur in the subsequent 12 months). After CNV treatment, BCVA was 20/32 (SE -2.25 D).

CONCLUSION

The incidence of CNV after PRK for myopia was low. Choroidal neovascularization is a possible complication in myopic eyes, and the risk exists before PRK. After PRK, the risk of CNV in myopic patients did not increase.

Selective zonal ablations with excimer laser for correction of irregular astigmatism induced by refractive surgery

OBJECTIVE

To demonstrate the safety and efficacy of selective zonal ablations with excimer laser for the correction of irregular astigmatism induced by refractive surgery.

DESIGN

Thirty-one eyes of 26 patients. Retrospective and noncomparative case series.

METHODS

The authors reviewed the medical results of the two series of consecutive cases of irregular astigmatism induced by refractive surgery. One group showed a topography map with a defined pattern: decentered ablation, decentered steep central island, central irregularity, and peripheral irregularity. The other group showed an irregular astigmatism without defined pattern. Selective zonal ablation was performed with a broad-beam excimer laser. Laser ablations were adjusted according to the Munnerlyn formula. A phototherapeutic keratectomy (PTK) mode was used in all cases without using viscous masking solution.

MAIN OUTCOME MEASURES

Uncorrected visual acuity, best spectacle-corrected visual acuity (BCVA), and Holladay diagnostic summary (Eye Sys 2.000) were considered before and after surgery to obtain the qualitative and quantitative characteristics of the visual acuity and corneal topography. The corneal uniformity index (CUI) was used to evaluate the corneal surface changes induced by the selective zonal ablations in the correction of irregular astigmatism. It proved to be a useful tool in the understanding of astigmatic changes when it is not possible to apply the vector analysis.

RESULTS

In group 1, the irregular astigmatism was significantly improved in 96.4% of cases. The CUI was improved from 58+/-0.3% to 87+/-0.8%, P < 0.005 (Student's t-test). The improvement of the BCVA was from 20/40+/-20/100 to 20/25+/-20/100, P < 0.005 (Student's t-test). The results obtained in group 2 were not clinically significant in terms of improvement of CUI and BCVA.

CONCLUSIONS

Using the corneal topographic map as a guide, selective zonal ablations with excimer laser can be used to create a more regular corneal surface, when a defined pattern of topographic irregularities can be defined.

Synaptic activity modulates the induction of bidirectional synaptic changes in adult mouse hippocampus

Activity-dependent synaptic plasticity is critical for learning and memory. Considerable attention has been paid to mechanisms that increase or decrease synaptic efficacy, referred to as long-term potentiation (LTP) and long-term depression (LTD), respectively. It is becoming apparent that synaptic activity also modulates the ability to elicit subsequent synaptic changes. We provide direct experimental evidence that this modulation is attributable, at least in part, to variations in the level of postsynaptic depolarization required for inducing plasticity. In slices from adult hippocampal CA1, a brief pairing protocol known to produce LTP can also induce LTD. The voltage-response function for the induction of LTD and LTP in naive synapses exhibits three parts: at a postsynaptic membrane potential during pairing (V(m)) </= -40 mV, no synaptic modification is obtained; at V(m) between -40 and -20 mV, LTD is induced; and, finally, at V(m) > -20 mV, LTP is generated. This function varies with initial synaptic efficacy. In depressed synapses, Theta(-), the V(m) above which LTD is generated, is shifted toward more depolarized V(ms) and Theta(+), the LTD-LTP crossover point or, equivalently, the V(m) above which LTP is induced, toward more polarized V(ms). Conversely in potentiated synapses, Theta(-) is shifted toward more polarized V(ms). Therefore synaptic activity changes synaptic efficacy and accordingly adjusts the voltages for eliciting subsequent synaptic modifications. The concomitant shifts in the voltages for inducing LTD and LTP in opposite directions promote synaptic potentiation and inhibit synaptic depression in depressed synapses and vice versa in potentiated synapses.

Retinal detachment in myopic eyes after photorefractive keratectomy

PURPOSE

To analyze the incidence and characteristics of retinal detachment (RD) in myopic patients who had photorefractive keratectomy (PRK).

SETTING

Universidad Miguel Hernández, Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

The incidence of RD in 5936 consecutive eyes that had PRK to correct myopia was studied. Mean follow-up was 38.5 months +/- 17.4 (SD).

RESULTS

Retinal detachment occurred in 5 eyes (0.08%); 2 in women and 3 in men. The mean interval between PRK and RD was 21. 00 +/- 15.89 months (range 9 to 48 months). The mean best corrected visual acuity (BCVA) after PRK and before RD development was 20/81 (range 20/200 to 20/25). After RD repair, the mean BCVA was 20/460 (range 20/2000 to 20/29). In 4 of the 5 eyes, BCVA after RD was within 1 line of the preoperative value; in 1 eye, it decreased from 20/40 to 20/2000. The mean spherical equivalent (SE) before RD treatment was -1.35 +/- 1.08 diopters (D) (range 0 to -3.00 D) and after RD treatment, -2.95 +/- 0.83 D (range -2.00 to -4.00 D). Differences between SE before and after RD treatment were statistically significant (P =.01, paired Student t test).

CONCLUSIONS

The incidence of RD after PRK to correct myopia was 0.08%. In 4 of 5 eyes, there was little or no visual loss; but in the group as a whole, there was a significant increase in myopic SE.

Photorefractive keratectomy for residual myopia after cataract surgery

PURPOSE

To evaluate the effectiveness, predictability, and safety of photorefractive keratectomy (PRK) for correcting residual myopia and myopic astigmatism after cataract surgery with intraocular lens implantation.

SETTING

Refractive Surgery and Cornea Unit, Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

Thirty consecutive eyes (30 patients) had PRK for residual myopia after cataract surgery. Surface PRK with a VISX Twenty-Twenty excimer laser was used in all patients. Follow-up was 1 year.

RESULTS

Before PRK, no eye had an uncorrected visual acuity (UCVA) of 20/40 or better. Twelve months after PRK, 16 eyes (53.33%) had a UCVA of 20/40 or better. After PRK, best corrected visual acuity (BCVA) improved 1 line or more in 14 eyes (46.66%) over the preoperative values, and 15 eyes (50.00%) had the same BCVA as before PRK. Mean pre-PRK refraction of -5.00 diopters (D) +/- 2.50 (SD) decreased significantly to -0.25 +/- 0.50 D at 12 months (P < .001). At 12 months, the spherical equivalent was within +/- 1.00 D of emmetropia in 27 eyes (90.00%). No vision-threatening complications occurred.

CONCLUSION

Photorefractive keratectomy was an effective, predictable, and safe procedure for correcting residual myopia and myopic astigmatism after cataract surgery.

Induced endothelial cell loss in phacoemulsification using topical anesthesia plus intracameral lidocaine

PURPOSE

To determine whether lidocaine 1% injected into the anterior chamber during phacoemulsification damaged the corneal endothelium.

SETTING

Ophthalmology Service, University Hospital, San Juan de Alicante, Spain.

METHODS

In 19 eyes of 19 patients, small incision phacoemulsification and foldable lens (AcrySof MA60BM) implantation was performed using topical anesthesia supplemented by lidocaine 1% (0.3 mL) in the anterior chamber. All cases were operated by the same surgeon. Specular microscopy was performed before surgery and 1 and 3 months postoperatively.

RESULTS

Mean endothelial cell loss was 5.41% +/- 8.50 (SD) at 1 month and 5.93 +/- 8.50% at 3 months.

CONCLUSIONS

The endothelial damage was similar to that described by other authors, suggesting that phacoemulsification surgery can be performed successfully using topical anesthesia supplemented by lidocaine 1% in the anterior chamber.

Metallic fragment deposits during phacoemulsification

PURPOSE

To describe the nature and origin of foreign metallic intraocular bodies appearing after phacoemulsification.

SETTING

Department of Ophthalmology, University Hospital of San Juan, Alicante, Spain.

METHODS

Two metallic particles, 1 extracted during surgery and the other from a patient in whom surgery had been performed, were studied by scanning electronic microscopy and X-ray dispersive energy spectroscopy. Also evaluated were all metallic elements used in phacoemulsification including phaco tips, Sinskey hooks, and handpieces. A morphologic analysis at various magnifications was performed and the composition of the elements studied.

RESULTS

Scanning electronic microscopy showed irregularities of the phaco tip and Sinskey hook after their use. Spectrographic analysis found that the phaco tip was mainly aluminum and titanium; the Sinskey hook, iron, chromium, cobalt, and nickel; the handpiece, iron, chromium, and nickel; and the 2 metallic particles, iron, chromium, and nickel, the same as the handpiece.

CONCLUSION

The metallic particles extracted corresponded to those of the phaco handpiece. Vibration during prolonged use of the phacoemulsifier probably caused these particles to chip off the handpiece.

Complications of photorefractive keratectomy for myopia: two year follow-up of 3000 cases

PURPOSE

To evaluate the results and complications of photorefractive keratectomy (PRK) for myopia.

SETTING

Alicante Institute of Ophthalmology, University of Alicante, Spain.

METHODS

This prospective study evaluated the results and complications of the first 3000 cases of PRK performed with a VISX Twenty-Twenty excimer laser. Myopia ranged from -1.0 to -14.0 diopters (D) and astigmatism, from -1.0 to -5.0 D. Follow-up was 2 years.

RESULTS

Ten eyes (0.7%) lost two or more lines of best corrected visual acuity 1 year after surgery. Retreatment for undercorrection or regression was done in 7.41% in the low myopia group and 38.69% in the high myopia group. Central islands, which could be detected only on videokeratoscopy, occurred frequently but influenced the refractive and visual outcomes in few cases. Severe haze was present in 17 eyes only after 1 year follow-up. There were no cases of progressive hyperopia. Other complications such as eccentric ablation producing astigmatism (n = 15), delayed re-epithelialization, or recurrent corneal erosion were rare.

CONCLUSION

There were few complications after PRK in 3000 eyes. With proper patient selection, PRK can be considered relatively safe compared with other refractive procedures.

Survey on drugs-of-abuse testing in the European Union

A survey on the quality of drugs-of-abuse testing in European laboratories was performed in 1993 (Part I) and 1994 (Part II). A total of 195 laboratories participated in Part I and 228 in Part II. There were 154 repeater laboratories. In each part of the survey, six urine samples were sent for analysis under routine conditions. A set of reference materials, including deuterated drug-standard solutions, was provided in Part II of the survey for optimization of analytical procedures. Screening for groups of substances was mainly performed by immunological techniques. Rates of false-positive (FP) results were 0 and 0.5%, respectively, in Parts I and II, and rates of false-negative (FN) results were 7.7% in Part I and 3.4% in Part II. Identification and quantitation of specific substances was mainly carried out by chromatographic methods, particularly gas chromatography coupled to mass spectrometry. Application of chromatographic methods showed a lack of sensitivity (14.9% and 16.7% FN in Parts I and II, respectively) and a lack of specificity (0.8% FP in Part I versus 1.1% in Part II). Repeater laboratories improved their results (17.4% FN in Part I versus 14.2% Part II). The improvement of repeater laboratories emphasizes the need of external quality control programs. The experience is being used as a basis for a recommendation on drug-testing guidelines by a group of European toxicologists.

Photorefractive keratectomy for pediatric myopic anisometropia

PURPOSE

To evaluate the visual results of excimer laser photorefractive keratectomy (PRK) to treat pediatric patients with amblyopic myopic anisometropia in whom conventional amblyopia treatments have failed.

SETTING

Instituto Oftalmológico de Alicante, University of Alicante, Spain.

METHODS

Six patients aged 5 to 7 years with amblyopic myopic anisometropia were treated by PRK in the more myopic eye using a VISX Twenty-Twenty excimer laser. Minimum preoperative refraction in the amblyopic eyes ranged from -4.00 to -13.00 diopters and best corrected visual acuity (BCVA), from 20/40 to 20/400. All cases completed a minimum of 2 years follow-up of antiamblyopic treatment.

RESULTS

After PRK, preoperative BCVA was maintained without optical correction and complementary refraction resulted in increased BCVA in every case. One patient with high myopia developed severe haze. There were no other significant complications.

CONCLUSION

Our results indicate that PRK may be an alternative for the correction of pediatric myopic anisometropia and an important aid in treating amblyopia. When other therapies have failed, using PRK in children of the ages in this study must be carefully evaluated; however, our results suggest a beneficial effect.

Relation between dendritic Ca2+ levels and the polarity of synaptic long-term modifications in rat visual cortex neurons

Long-term changes of synaptic efficacy, in particular when they are use-dependent, are candidate mechanisms for the storage of information in the nervous system. In a variety of brain structures, including the neocortex and hippocampus, synapses are susceptible to long-term potentiation (LTP) and long-term depression (LTD). It has been hypothesized that the polarity of the synaptic gain change depends on the amplitude of the postsynaptic [Ca2+]i rise, the threshold for the induction of LTD being lower than that for the induction of LTP. To test this assumption, we characterized Ca2+ signals in layer II/III pyramidal cells of rat visual cortex slices, using the fluorescent Ca2+ indicator fura-2, during application of stimulation protocols that had been adjusted to reliably induce either LTP or LTD in cells not loaded with fura-2. At dendritic sites activated by the stimulated afferents the intracellular [Ca2+] concentration ([Ca2+]i) reached higher amplitudes and decayed more slowly with stimuli inducing LTP than with those inducing LTD. To directly analyse the functional significance of the observed difference in the Ca2+ signal amplitude, we examined whether a tetanization protocol suitable for the induction of LTP can be converted into a protocol inducing LTD by injecting the postsynaptic cells with Ca2+ chelators that reduce the concentration of effective free Ca2+. In the presence of fura-2 or BAPTA [bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetate], the stimulation protocol that would normally produce LTP induced either LTD or failed to induce synaptic modifications altogether. These results support the hypothesis that the amplitude of the postsynaptic rise in [Ca2+]i is a key factor in the determination of the polarity of synaptic gain change.

Correction of Hyperopia Induced by Photorefractive Keratectomy Using Non-contact Ho:YAG Laser Thermal Keratoplasty

PURPOSE

To evaluate the safety and effectiveness of non-contact holmium:YAG laser thermal keratoplasty in correcting hyperopia induced by photorefractive keratectomy (PRK).

METHODS

Non-contact holmium:YAG laser thermal keratoplasty was applied to 14 eyes with significant hyperopia induced by PRK. The mean spherical equivalent refraction before holmium:YAG laser thermal keratoplasty was +4.20 +/- 1.80 diopters (D) (range, +1.75 to +6.25 D). The results were evaluated 12 months after holmium:YAG laser thermal keratoplasty.

RESULTS

No sight-threatening complications occurred. Recovery of spectacle-corrected visual acuity took from 2 to 6 weeks. The immediate significant myopic shift that developed in all eyes gradually receded over 6 to 8 weeks. All eyes were relatively stable after 9 months. At 12 months, there was no statistically significant difference (p < .005) between the mean preoperative spectacle-corrected visual acuity (0.71 +/- 0.12) and the mean postoperative uncorrected visual acuity (0.65 +/- 0.28). At 12 months there was a mean increase of 4.60 +/- 1.20 D in central keratometric power. Total regression did not occur in any eye.

CONCLUSIONS

Non-contact holmium:YAG laser thermal keratoplasty offers a safe and effective alternative to correct PRK-induced hyperopia.

Calcium-induced long-term depression in the visual cortex of the rat in vitro

1. In many brain areas, including neocortex and hippocampus, excitatory synapses can undergo both long-term potentiation (LTP) and long-term depression (LTD). It is established that a change in the postsynaptic calcium concentration ([Ca2+]i) is critical for the induction of both LTP and LTD. Protocols that induce these long-term synaptic modifications typically involve afferent stimulation. But, in hippocampus, LTP can also be induced by a transient increase of the extracellular calcium concentration ([Ca2+]o). The purpose of the present study was to determine whether raising [Ca2+]o also induces long-term modifications of excitatory synaptic transmission in the neocortex. 2. Intracellular recordings were obtained from regular spiking cells in layers II-III of slices of the rat visual cortex. Test stimuli were evoked with stimulation electrodes located in the white matter (w.m.) below the recorded cell and intracortically (i.c.) adjacent to the cell. Both the depolarizing slope and the amplitude of excitatory postsynaptic potentials (EPSPs) were measured. For exposure to elevated [Ca2+]o, the normal medium ([Ca2+]o = 2 mM) was exchanged for a period of 10 min against a medium containing 4 mM [Ca2+]o. 3. Elevated [Ca2+]o leads, after return to normal medium, to a long-lasting decrease of intracellularly recorded synaptic responses to both w.m. and i.c. stimulation even if activation of these two pathways is discontinued or N-methyl-D-aspartate (NMDA) receptors are blocked during elevated [Ca2+]o. This decrease is due to reduced efficacy of excitatory transmission because it is observed in the presence of the gamma-aminobutyric acid-A (GABAA) receptor antagonist, bicuculline. 4. Induction of LTD by raising [Ca2+]o is voltage dependent. First, elevated [Ca2+]o elicits LTD only in cells whose resting membrane potential (Vmr) is less polarized than -79 mV (and more polarized than -70 mV, which is the Vmr of the least polarized cell). Second, hyperpolarizing cells whose Vmr is in this susceptible range by 20 mV below Vmr during exposure to high [Ca2+]o prevents Ca2+-induced LTD. Third, when elevated [Ca2+]o is associated with postsynaptic depolarizing pulses, LTD is readily induced in cells whose Vmr is more polarized than -79 mV. This voltage dependence implies that the depression is induced by a postsynaptic process and hence that it occurs at synapses formed by excitatory terminals on the recorded neuron. 5. Assuming that a transient elevation of [Ca2+]o leads to an increase of [Ca2+]i, the results of this study suggest that a transient increase of [Ca2+]i is sufficient to elicit LTD. This may provide a mechanism for the induction of heterosynaptic LTD, a depression that occurs in afferents that are silent while the postsynaptic neuron is activated by other inputs.

The polysialic acid modification of the neural cell adhesion molecule is involved in spatial learning and hippocampal long-term potentiation

The alpha-2,8-linked polysialic acid (PSA) modification of the neural cell adhesion molecule (NCAM) modulates morphogenetic cell interactions. PSA is strongly expressed during neural development and generally down-regulated in the adult. However, it remains prominent in some areas of the brain, e.g., the hippocampus. We assayed the functional role(s) of PSA in synaptic plasticity in the hippocampus in two experimental paradigms by removing PSA with endo-neuraminidase NE (endo-N) an enzyme which specifically cleaves alpha-2,8-linked polysialic acid. (1) The acquisition and retention of spatial memory of rats in the Morris water maze, critically dependent on the hippocampus, was significantly impaired after a localized injection of endo-N into the hippocampus, whereas visual and motor capacities were unaffected. (2) Tetanic stimulation of the Schaffer collaterals in endo-N-treated hippocampal slices in vitro failed to elicit LTP and yielded only a short post-tetanic potentiation, but the response returned to control levels within 2 minutes, whereas basal synaptic activity and short-term potentiation were not affected. Our findings suggest that the carbohydrate epitope PSA plays an important role in synaptic plasticity.

Different threshold levels of postsynaptic [Ca2+]i have to be reached to induce LTP and LTD in neocortical pyramidal cells

Changes in [Ca2+]i were measured in layer II-III pyramid cells of the rat visual cortex slices during application of either LTP or LTD inducing stimulation protocols. At dendritic sites activated by the stimulated afferents [Ca2+]i reached higher amplitudes and decayed more slowly with LTP than with LTD inducing stimuli. In the presence of Ca2+ chelators, the stimulation protocol that would normally produce LTP induced either LTD or failed to induce a synaptic modifications altogether. These results support the hypothesis that the polarity of synaptic gain changes depends on the magnitude of postsynaptic [Ca2+]i responses, the induction of LTP requiring a more pronounced surge of [Ca2+]i than the induction of LTD.

Correcting simple myopic astigmatism with the excimer laser

For one year we followed 46 eyes that had photoastigmatic refractive keratectomy with an excimer laser to correct simple myopic astigmatism. Mean preoperative cylinder was -2.50 +/- 0.70 diopters (D); mean preoperative best corrected visual acuity was 20/25 +/- 1 Snellen line. Mean postoperative refraction one year after surgery was -0.5 +/- 0.2, and mean uncorrected visual acuity was 20/25 +/- 1 Snellen line. In all eyes, the final axis of the residual cylinder was +/- 5 degrees around the preoperative axis. Uncorrected visual acuity equaled best preoperative acuity in 24 eyes. Eight eyes gained one line of best corrected visual acuity, six gained more than one line, and eight lost one line. No patient lost more than one line of uncorrected visual acuity. No significant complications such as haze, halos, eccentric ablation, or hypercorrection were observed.

All-or-none excitatory postsynaptic potentials in the rat visual cortex

Intracellular recordings were obtained from supragranular neurons in slices of the rat visual cortex. In approximately 25% of the cells large (0.5-1.6 mV) excitatory postsynaptic potentials (EPSPs) of constant amplitude were observed after minimal, presumably single-fibre stimulation. The amplitude variance of these large EPSPs was surprisingly small and within the range of the variance of the noise. These EPSPs could be reduced in amplitude by paired-pulse and low-frequency stimulation or by raising extracellular Mg2+ concentration. Reduced EPSPs could either continue to behave as all-or-none responses, or they could fluctuate between several amplitude levels. Conversely, responses where the amplitude fluctuated from trial to trial under control conditions could be converted into large all-or-none responses by paired-pulse facilitation. This indicates that the large all-or-none EPSPs were composed of several subunits, probably reflecting the action of several different release sites. It is concluded that these release sites are either independent and operate with a probability close to 1 or, if operating with a lower probability, are coordinated by a mechanism which synchronizes release. Several observations suggest that release probabilities can switch from values close to 1 to 0 with repetitive stimulation or high Mg2+ concentration. Thus, a substantial fraction of single-fibre inputs to supragranular cells possess synapses which operate with high synaptic efficiency and extremely low variance under control conditions but can undergo drastic changes in efficacy when release probabilities are interfered with. Such modifications of release probability could serve as an effective mechanism to regulate the gain of synaptic transmission.

Effect of topical antioxidant therapy on experimental infectious keratitis

To test the effect that the treatment with topical antioxidants may have on corneal infection, we have studied the effect of topically applied antioxidants, such as dimethylthiourea 0.5% (DMTU) and dismutase superoxide 0.2% (SOD), on infectious experimental keratitis caused by Staphylococcus aureus. We have quantified the results of the incubated corneas in ex vivo as well as in in vivo treated with antioxidants by using the luminol amplified chemiluminescence technique (LAC). The evaluation of corneal inflammation was performed calculating the average inflammatory index obtained from the clinical observation of the corneal secretion, corneal edema and ciliary injection. The evolution of the corneal infiltration was evaluated by means of computerized planymetry. The antioxidants used in this study demonstrated a significant reduction of the LAC values when compared with a control group both in the in vivo as well as in ex vivo studies. No significant differences in the clinical evaluation of the average inflammatory index were observed between the study and the control groups. However, a significant increase in the corneal infiltration was registered in the antioxidant treated group (p < 0.001) evaluated by computerized planymetry. Our results indicate that the use of antioxidants as antiinflammatory drugs may have a potential negative influence on the course of infectious keratitis.

Antioxidant therapy in the treatment of experimental acute corneal inflammation

To ascertain the effectiveness of topical antioxidant therapy on acute corneal inflammation, we have studied the effectiveness of topical treatment with a saline solution and with antioxidants such as 0.2% superoxide dismutase and 0.5% dimethylthiourea (DMTU) in a controlled experimental study. The evolution of the inflammatory process was evaluated by a multimodel approach, including computer-assisted planimetry of the corneal ulcer and infiltrate, ultrasonic pachymetry, luminol-amplified chemiluminescence and the study of corneal transparency by direct spectral spectrophotometry transmittance. The experimental model was a corneal ulcer created by a 60-second application of 1 N sodium hydroxide. Topical treatment with DMTU was shown to significantly improve all parameters tested, while superoxide dismutase reduced only the corneal ulcers. Antioxidant topical therapy with DMTU was shown to be efficient in reducing the inflammatory reaction that occurs during acute corneal inflammation. This suggests that antioxidant therapy could be considered as a complementary treatment in the pharmacological modulation of acute corneal inflammation.

Topical treatment of experimental acute corneal inflammation by dexamethasone and nonsteroidal drugs

In this study, we have correlated the relative effectiveness of nonsteroidal anti-inflammatory drugs versus corticosteroids in the topical treatment of acute corneal inflammation. The authors have studied the effect of 1 drop every 6 h of flurbiprofen 0.03%, indomethacin 1%, diclofenac 0.1% and dexamethasone 0.1% in an experimental model of corneal alkali burn. The objective parameters used to evaluate the corneal inflammatory response were Luminol-enhanced chemiluminescence, ultrasonic pachymetry and computer-assisted analysis of the area of the corneal ulceration. Indomethacin 1% showed statistically significant effects on the improvement of all the parameters tested in the study. No such effect was demonstrated for flurbiprofen 0.03% or diclofenac 0.1%. We can conclude that indomethacin 1% is an effective drug in the treatment of experimental acute corneal alkali-burn inflammation.

Long-term depression of excitatory synaptic transmission and its relationship to long-term potentiation

In many brain areas, including the cerebellar cortex, neocortex, hippocampus, striatum and nucleus accumbens, brief activation of an excitatory pathway can produce long-term depression (LTD) of synaptic transmission. In most preparations, induction of LTD has been shown to require a minimum level of postsynaptic depolarization and a rise in the intracellular Ca2+ concentration [Ca2+]i in the postsynaptic neurone. Thus, induction conditions resemble those described for the initiation of associative long-term potentiation (LTP). However, data from structures susceptible to both LTD and LTP suggest that a stronger depolarization and a greater increase in [Ca2+]i are required to induce LTP than to initiate LTD. The source of Ca2+ appears to be less critical for the differential induction of LTP and LTD than the amplitude of the Ca2+ surge, since the activation of voltage- and ligand-gated Ca2+ conductances as well as the release from intracellular stores have all been shown to contribute to both LTD and LTP induction. LTD is induceable even at inactive synapses if [Ca2+]i is raised to the appropriate level by antidromic or heterosynaptic activation, or by raising the extracellular Ca2+ concentration [Ca2+]o. These conditions suggest a rule (called here the ABS rule) for activity-dependent synaptic modifications that differs from the classical Hebb rule and that can account for both homosynaptic LTD and LTP as well as for heterosynaptic competition and associativity.

Protective properties of viscoelastic substances (sodium hyaluronate and 2% hydroxymethylcellulose) against experimental free radical damage to the corneal endothelium

Hydrogen peroxide (H2O2) has potent oxidant properties due to the action of free radicals (OH.) induced from its degradation. The free radicals specie derived from H2O2 are extremely toxic to the corneal endothelium and quickly induce corneal edema. In the present work, in order to ascertain the endothelial cell protection from viscoelastic substances, we have studied experimental corneal endothelial cell damage caused in the rabbit eye after intracameral injection of different H2O2 concentrations, with and without previous filling and washing out of two widely used viscoelastic substances from the anterior chamber such as 1% sodium hyaluronate (Healon) and hydroxypropylmethylcellulose (HPMC). We observed a dose-dependent endothelial damage in the controls. The experimental groups protected with Healon or HPMC showed statistically fewer corneal endothelial cell lesions than the control group (p < 0.001) for all of the concentrations used. Healon showed superior protective properties than HPMC at higher H2O2 concentrations (100 mM). However, HPMC was superior with 1 and 10 mM peroxide. From this experimental evidence, we conclude that Healon and HPMC are effective as protectors against the corneal endothelial lesions caused by free radicals. This finding may explain some of the beneficial effects of these viscoelastic substances.

Retinal detachment as a potential hazard in surgical correction of severe myopia with phakic anterior chamber lenses

Phakic anterior chamber lenses have been proposed as an effective refractive surgical procedure for the correction of severe myopias. We managed three cases of retinal detachment that complicated this operation. Two patients had retinal detachment in the immediate postoperative period at the fourth and sixth weeks, respectively. Both patients had preoperative equatorial lattice degeneration, which was prophylactically managed with argon laser in one case. The third patient developed retinal detachment at the eighth postoperative month and was associated with a severe fibrinoid uveitis and a combined exudative and rhegmatogenous retinal detachment. This third patient did not have any previous retinal degenerative lesion. Scleral buckling was successful in two of the patients, whereas the patient with preoperative inflammation required vitreous surgery because of proliferative vitreoretinopathy. The retinas were reattached in all three patients without explanting the phakic anterior chamber lens, but severe loss of visual acuity occurred in one patient. Retinal detachment should be regarded as a potentially important hazard in this type of refractive surgery.

Treatment of experimental acute corneal inflammation with inhibitors of the oxidative metabolism

The authors studied the effect of topical 2% 6-aminonicotinamide and 0.1% adenosine on an experimental model of acute corneal inflammation. Luminol-enhanced chemiluminescence (LAC), as an indirect measurement of free-radical release, and computer-assisted planimetry of the corneal ulcer and its infiltrate were performed both ex vivo and in vivo on the fifth day following the induction of experimental alkali burn keratitis. The authors proved that both drugs significantly inhibited LAC both ex vivo and in vivo and that such treatments had also a significant beneficial effect on the evolution of the corneal ulcer and its infiltrate. To the best of the authors' knowledge, this finding had not been previously reported in experimental corneal inflammation and may indicate that treatment with inhibitors of the oxidative metabolism could offer a new approach in the pharmacological modulation of acute corneal inflammation.

Lipid peroxidation in the iris and its protection by means of viscoelastic substances (sodium hyaluronate and hydroxypropylmethylcellulose)

Free radicals, especially the hydroxyl radical (OH.), are known to be toxic for several ocular structures including the cornea, lens, iris and retina through the initiation of lipid peroxidation of cell membranes. The oxidative damage to the iris epithelial-cell membranes, induced by the injection of hydrogen peroxide (H2O2) at different concentrations into the anterior chamber of the rabbit eye, was studied by means of the measurement of lipid peroxidation products. Thiobarbituric acid reactive (TBAR) products were significantly increased compared with normal control iris after the intracameral injection of H2O2 at concentrations of 0.1 (p < 0.02), 10 and 100 mM (p < 0.001). Viscoelastic substances, widely used in anterior ocular surgery, sodium hyaluronate (Healon) and hydroxypropylmethylcellulose, show a protective effect against rabbit iris lipid peroxidation. A statistically significant (p < 0.001) inhibition of the release of TBAR products occurred in both experimental groups that received an injection of these substances prior to a H2O2 injection. This is the first report of lipid peroxidation of the iris and the 'antioxidant'-protective effect of viscoelastic substances. This new technical approach could be used as a test of efficacy of the protective effect of viscoelastic substances.