Juan Bellot

Laser in situ keratomileusis to correct high myopia

Purpose: To evaluate the effectiveness, predictability, and safety of laser in situ keratomileusis (LASIK) in 143 eyes with myopia from 8.00 to 20.00 diopters (D). Setting: Alicante Institute of Ophthalmology, University of Alicante School of Medicine, Alicante, Spain. Methods: This prospective study comprised 143 eyes (94 patients) that had LASIK with the Chiron Automated Corneal Shaper and the VISX 20/20 excimer laser using a multizone profile and a sutureless hinged corneal flap technique. Results: Uncorrected visual acuity was 20/40 or better in 45.0% of eyes 3 months postoperatively and in 46.4% at 6 months. Best corrected visual acuity (BCVA) improved by 0.07 at 3 and 6 months and was stable after 3 months. Mean spherical equivalent was ‐13.19 diopters (D) ± 2.89 (SD) preoperatively and +0.51 ± 1.63 D at 3 months and +0.18 ± 1.66 D at 6 months postoperatively. At 3 months, spherical equivalent was within 1.00 D of emmetropia in 57.5% of all eyes, 71.0% of eyes with a baseline refraction from ‐8.00 to ‐11.99 D (n = 59), 44.4% with a baseline refraction from ‐12.00 to ‐15.99 D (n = 54), and 53.0% of eyes with a baseline refraction from ‐16.00 to ‐20.00 D (n = 30). The respective 6 month percentages were 60.0, 72.4, 46.0, and 50.0%. The regression of effect was similar in all groups (approximately 0.50 D) between 1 and 3 months, although the high myopia group had further regression. Significant corneal steepening and an increase in corneal thickness occurred between 1 and 3 months. Flap thickness was always less than predicted with both the 130 and 160 &mgr;m plates, and achieved laser ablation was deeper than programmed. The relationships between postoperative refraction and preoperative keratometry and postoperative refraction and the difference in achieved versus programmed ablation were significant. Complications at 6 months included epithelial ingrowth, corneal flap melting, decentered ablation, and irregular astigmatism with loss of BCVA, although none was vision threatening. Conclusion: In this study, LASIK was effective and predictable in the correction of high myopia but was more accurate for myopia up to 12.00 D. Current surgical algorithms must be modified to improve predictability in higher corrections. Longer follow‐up is necessary to evaluate long‐term incidence of vision‐threatening complications.

POTENTIAL FOR USING FACILITATION BY GRASSES TO ESTABLISH SHRUBS ON A SEMIARID DEGRADED STEPPE

In arid and semiarid environments, isolated vegetative patches establish islands of fertility in which facilitation is a dominant interaction between plant species. These patches may provide favorable microsites for revegetation with desirable species in areas where traditional revegetation procedures fail. Alpha grass (Stipa tenacissima) steppes are widely distributed within the semiarid areas of southern Europe and northern Africa and represent a degraded stage of climax vegetation. In this study, we analyzed the effects of S. tenacissima tussocks on the survival, growth, and ecophysiological features of experimentally planted seedlings of Medicago arborea, Quercus coccifera, and Pistacia lentiscus in three sites in a semiarid region in southeastern Spain. Our main objective was to test whether S. tenacissima was able to facilitate shrub establishment in semiarid degraded steppes. Soils under S. tenacissima tussocks had higher organic matter content and water availability than those from open areas. Sti...

Small-scale Environmental Heterogeneity and Spatiotemporal Dynamics of Seedling Establishment in a Semiarid Degraded Ecosystem

In semiarid environments, surface soil properties play a major role in ecosystem dynamics, through their influence on processes such as runoff, infiltration, seed germination, and seedling establishment. Surface soil properties usually show a high degree of spatial heterogeneity in semiarid areas, but direct tests to evaluate the consequences of this heterogeneity on seedling establishment are limited. Using a combination of spatial analysis by distance indices (SADIE) and principal components analysis (PCA) we quantified the spatiotemporal patterns of seedling survival of a Mediterranean native shrub (Pistacia lentiscus) during the first 3 years after planting on a semiarid degraded site in southeastern Spain. We used a variation partitioning method to identify environmental variables associated with seedling survival patterns. Three years after planting, only 36% of the seedlings survived. During the first summer, one-third of the seedlings died, with secondary major mortality in the 3rd summer after planting. The spatial pattern of survival became strongly clumped by the end of the first summer, with clearly defined patches (areas of high survival) and gaps (areas of low survival). The intensity of this pattern increased after subsequent high-mortality periods. Of the 14 variables, the ones most strongly coupled to seedling survival were bare soil cover, sand content, and soil compaction. These findings contribute to our understanding of the linkages between the spatial heterogeneity of abiotic factors and the response of plant populations in semiarid degraded ecosystems and can be used to optimize restoration practices in these areas.

Mulching treatment for postfire soil conservation in a semiarid ecosystem

Fire may generate soil degradation and accelerate erosion processes, depending among other factors, on the regeneration capacity of the ecosystem. Conservation measures will be beneficial in those fragile systems where a high degradation hazard is estimated. Mulching treatment was evaluated in order to establish its efficiency in protecting soil and preventing runoff generation in a semiarid area affected by a wildfire. Straw mulch was applied at 200 g m‐2 in three replicated plots. Paired mulched and control plots were established in a three block experimental design. Runoff, sediment yield, plant cover, and dynamics of soil physical properties were measured in these plots over a 2‐year period. Most of the plant regeneration after the fire resulted from resprouting of the dry grassland species, dominated by Brachypodium retusum. Total plant cover was only 50% two years after passage of the fire. Runoff and sediment yield were significantly greater from control plots. Soil loss from control plots was abou...

Does Pinus halepensis facilitate the establishment of shrubs in Mediterranean semi-arid afforestations?

Aleppo pine (Pinus halepensis) dominates forest ecosystems in dry and semi-arid areas of the Mediterranean Basin. In addition to its natural distribution, this species has been used extensively in afforestation projects during this century. The improvement in soil fertility and microclimate provided by the P. halepensis canopy is known to facilitate the establishment of perennial grasses, but little is known about the interactions of this species with woody species in natural stands and afforestations under semi-arid climate. In this study, we analyze the effects of the P. halepensis canopy on the survival and ecophysiological features of experimentally planted seedlings of several Mediterranean shrub and tree species in two semi-arid afforestations of SE Spain. Soils under P. halepensis (pine microsite) showed small differences in nutrient content relative to those outside the canopy (open microsite). Radiation reaching pine microsites was four times lower than in open microsites. Soil moisture did not show significant differences between both microsites during most of the year. One year after planting, survival of the introduced seedlings was significantly higher in the open microsites than in the pine microsites. Predawn and midday water potentials and chlorophyll fluorescence of seedlings measured before the summer did not show any microsite effect. Our results suggest that the changes in understorey microclimate associated with P. halepensis are not sufficient to facilitate the establishment of shrubs under semi-arid conditions.

Saharan dust and the atmospheric inputs of elements and alkalinity to mediterranean ecosystems

Saharan dust delivered by so-called ‘red rains’ strongly influences precipitation chemistry in the Mediterranean region. We show here that at rural sites in eastern Spain, red rains have much higher ion concentrations than non-red rains, and they account for up to 50% of the mean annual input of dissolved elements in bulk precipitation, though they make up only a minor part of the annual rainfall. The mean annual input of alkalinity in red rains is enough to neutralize the input of free acidity in acidic precipitation. Transport of Saharan dust is thus a major ecological force in Mediterranean ecosystems through its effects on the acid neutralizing capacity of the atmosphere and the atmospheric deposition of elements.

Morphological traits and water use strategies in seedlings of Mediterranean coexisting species

The distribution of plants is associated with their different patterns of response to their environment. Mediterranean plants have evolved a number of morphological and physiological adaptations that determine their ability to survive and grow, being an effective water uptake and use important factors for drought resistance. In this article, we evaluated interspecific differences in morphology, biomass allocation, and architectural traits and their relationship with water use strategies in seedlings of seven co-occurring Mediterranean species (Anthyllis cytisoides L., Genista scorpius L. DC., Myrtus communis L., Pistacia lentiscus L., Rosmarinus officinalis L., Spartium junceum L. and Ulex parviflorus Pourr.). The results showed that morphological root features vary among species and they are significantly correlated with root hydraulic conductance and leaf gas exchange variables. Species with high specific root length (SRL) showed a low hydraulic conductance per root length (KRRL) but high specific hydraulic conductance (KAs). M. communis and P. lentiscus showed the most contrasting water use patterns with respect to the other species studied. The results are not affected when considering phylogenetic relatedness. Thus, the variability observed in root hydraulic properties and leaf gas exchange suggests important mechanisms for understanding species coexistence in water-limited ecosystems.

GOTILWA: An Integrated Model of Water Dynamics and Forest Growth

GOTILWA is a simulation model of forest growth. Its name, GOTILWA, is an acronym for Growth Of Trees Is Limited by WAter. The name itself defines the main characteristic of the model. Water is, very often, the limiting factor for plant growth (Pinol et al. 1991; Sala 1992; Chap. 13) and thus it constitutes a key factor in the model (Tello et al. 1994). In a standard simulation, daily climatic data are analyzed. From the interaction between daily rainfall and the forest structure, the amount of intercepted water by the canopy layer, throughfall and stemflow are estimated. This effective rainfall increases the water stored in the soil which is used by the trees. The proportion of sapwood to heartwood, the leaf area of each tree and, consequently, the leaf area index (LAI) of the forest are all highly dependent on water availability in the model.

Effect of different vegetation type cover on the soil water balance in semi-arid areas of South Eastern Spain

Abstract The simulated soil water balances under five vegetation types, using a developed model for the purpose, shows that the interception by plants represents 22 % to 35 % of annual rainfall (553 mm), in dry grasses and pine with grasses respectively. Eta is the main outflow from the soil; being more than 80 % of net precipitation in pine plus shrub vegetation type. The bare soils and dry grasses show the highest deep drainage values (208 and 142 mm, respectively), however, is difficult to estimate what portion of this infiltrated water results in aquifer recharge. During the studied year one large rainfall event (134.6 mm) produced the main infiltration flow under all vegetation types, with a significant observed change in the aquifer piezometric level. A second simulation without this event, shows that the annual drainage in all types of cover was reduced. The soil water content evolution under each vegetation type, shows that the bare soils and dry grasses present the highest values. The most complex vegetation type, with high shrub biomass and pinus presents the highest consumption. Coefficients of determination for the regression of predicted daily soil water content on observed values were 0.65, 0.87, 0.90 and 0.93 for the pine reforestation with shrub understory; pine reforestation with dry grass understory; shrubland and dry grassland, respectively.

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 (ρ <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.