Lenticular Thickness Research Articles

Long-Term Visual Quality and Pupil Changes after Small-Incision Lenticule Extraction for Eyes without Preoperative Cylinder Refraction.

To investigate the long-term changes in visual quality and pupil size after small incision lenticule extraction (SMILE) for eyes without preoperative cylinder refraction. Thirty-three myopic eyes (33 patients) without preoperative cylinder refraction were corrected using SMILE. Refractive outcomes, corneal curvature, aberrations, contrast sensitivity (CS), and pupil diameter were evaluated preoperatively, and 30 months postoperatively. The 30-month postoperative uncorrected and corrected distance visual acuity (UDVA and CDVA, LogMAR) were -0.10 ± 0.09 and -0.14 ± 0.06, respectively, whereas the preoperative CDVA (LogMAR) was -0.07 ± 0.05. Cylinder refraction of -0.11 ± 0.21 D (ranging from -0.50 to 0.00) was observed at 30 months postoperatively, increasing from the preoperative cylinder refraction of 0.00 ± 0.00 D (P=0.004). Moreover, the centroid coordinates x, y of corneal anterior astigmatic vectors were -0.19 ± 0.22, 0.81 ± 0.33 at 30 months postoperatively, and 0.02 ± 0.28, 0.76 ± 0.51 preoperatively (Px < 0.001 and Py=0.810, respectively). Furthermore, a 15° axis change in the mean anterior corneal astigmatic vector was observed at 30 months postoperatively from the preoperative state, as measured by Pentacam. At 30 months postoperatively, the photopic Log CS reduced significantly with glare at three and six cycles/degrees (P < 0.001 and P=0.015, respectively), a decreased photopic pupil diameter (3.27 ± 0.55 mm vs. 3.10 ± 0.66 mm, P=0.030), and an increased Coma (Z31) and Trefoil (Z3-3) at 4 mm diameter area analysis. However, a significant linear regression relationship was only observed between changes in photopic pupil diameter and changes in photopic Log CS with glare at 12 cycles/degree (P=0.038 and β = 0.282). Slight cylinder regression was observed with thicker corneal lenticular extraction after SMILE correction of nonastigmatic eyes 30 months postoperatively. This regression was mainly because of the axis changes in anterior corneal astigmatism power. Therefore, a cylinder nomogram modification of 0.25 to 0.50 D is considerable for correcting nonastigmatic myopic eyes with a predicted spherical lenticular thickness over 100 µm.

Commentary: Reliability, repeatability, and accuracy of Sirius topographer in assessing anterior segment morphology following laser peripheral iridotomy in primary angle-closure disease.

Commentary: Reliability, repeatability, and accuracy of Sirius topographer in assessing anterior segment morphology following laser peripheral iridotomy in primary angle-closure disease.

Morphological, Immunohistochemical, and Ultrastructural Studies of the Donkey's Eye with Special Reference to the AFGF and ACE Expression.

The donkey is mainly used as a working animal for riding and pack transport, as well as for dairy and meat production. Eye afflictions are common in donkeys, thus requiring a detailed study. A few studies had focused on the donkey's eye, and most of them had considered it, merely, a horse's eye. This study aimed to investigate the anatomy, histology, ultrastructure, and immunohistochemical features of the donkey's eye. The results were recorded and compared to those of horses in certain dimensions. Unlike horses, the donkey's eye is more circular in the contour of the cornea, has smaller lenticular thickness, and has longer anterior and vitreous chambers. Positive immunoreactivity to acidic fibroblast growth factor in the basal cell layers of the cornea was observed, indicating their role in cell differentiation and the renewal of the epithelium. Moreover, the corneal keratocytes expressed angiotensin-converting enzyme, which plays a role in corneal homeostasis and wound healing. Additionally, telocytes, hyalocytes, and other immune cells were observed within the iris and ciliary processes. Hence, this work is an updated detailed study of the morphology and ultrastructure of the donkey's eye and reveals some similarities and dissimilarities to the horse's eyes, which should be considered in clinical practice.

Differences in corneal and anterior segment morphology between diabetic vs. healthy children and adolescents: a systematic review and meta-analysis.

To compare corneal and anterior segment morphology among children and adolescents with and without diabetes. PubMed, Embase and Scopus databases were systematically searched. Studies that were observational in design were considered. Included studies should have been done in young children and/or adolescents and compared relevant outcomes of interest based on the diabetic status. The outcomes of interest were related to corneal morphology, morphology of lens, as well as important characteristics of anterior segment such as depth, pupillary diameter, intra-ocular pressure and axial length. The pooled effect sizes were reported as weighted mean difference (WMD). STATA software was used for statistical analysis. The meta-analysis included 17 studies. Diabetic children had lower corneal endothelial cell density (cells/mm2) (WMD -215.7, 95% CI: -406.5, -24.9), higher central corneal thickness (µm) (WMD 12.66, 95% CI: 5.47, 19.84), higher lenticular thickness (mm) (WMD 0.25, 95% CI: 0.13, 0.36) and density (WMD 3.02, 95% CI: 2.23, 3.81) than non-diabetic children. The anterior chamber depth (mm) (WMD -0.17, 95% CI: -0.24, -0.09) and pupillary diameter (mm) (WMD -0.61, 95% CI: -1.12, -0.10) was significantly reduced in diabetic children, compared to non-diabetic children. No differences in the corneal curvature, corneal diameter, spherical equivalent, intra-ocular pressure, axial length, tear film breakup time and Schirmer test were noted among diabetic and non-diabetic children. Significant structural changes in cornea and lens along with reduction in anterior chamber depth and pupillary diameter were found. These morphological changes may be indication for early and prompt management and underscore the need for more advanced ophthalmological evaluation techniques, in addition to routine examination.

Nomogram for single-pass automated microkeratome graft preparation for ultrathin Descemet stripping automated endothelial keratoplasty.

To create a nomogram including the translational speed of the microkeratome blade, microkeratome head size and precut tissue thickness to predict the postcut thickness for Descemet stripping automated endothelial keratoplasty to obtain the thinnest possible graft. This prospective study incorporated 48 grafts for DSAEK from March 2017 to June 2020. Corneal tissue for DSAEK was prepared by 3 experienced physicians using the Moria Evolution 3E (Moria Inc, Antony, France) microkeratome with 400, 450 and 500μm head sizes. Precut central corneal thickness was measured with a DGH 550 handheld pachymeter (Pachette 2), taking an average of 3 readings. The microkeratome head was selected according to precut tissue thickness. The selected microkeratome head size was 150μm less than the donor cornea thickness. Two translational speeds were used for the microkeratome cuts. One month after surgery, the central lenticular thickness was measured with a Visante® Optical Coherence Tomography caliper (Carl Zeiss Meditec Inc, Germany). A descriptive analysis was performed. Forty-eight donor grafts were prepared. Mean graft thickness was 97.58 ± 29.84μm (range 39-176μm). Of the 48 samples, central graft thickness was < 120µm (81.3%) in 39, < 100µm (58.3%) in 28 and < 80µm (37.5%) in 18 at 1-month follow-up. There were no statically significant differences between translational speeds. A nomogram with an automated microkeratome to obtain thin grafts for DSAEK provided good graft thickness results without donor waste.

Comparison of the Effects of Temperature and Dehydration Mode on Glycerin-Based Approaches to SMILE-Derived Lenticule Preservation

The aim of this study was to explore the optimal method of small-incision lenticule extraction (SMILE)-derived lenticules, subjected to long-term preservation using glycerol, under a range of temperatures, and using an array of dehydration agents. In total, 108 myopic lenticules were collected from patients undergoing the SMILE procedure. Fresh lenticules served as a control group for this study, whereas all other lenticules were separated into 8 groups, which were preserved at 4 different temperatures (room temperature [RT], 4, -20, and -80°C) with or without silica gel in anhydrous glycerol. Evaluated parameters included thickness, transmittance, hematoxylin and eosin staining, transmission electron microscopy, and immunohistochemistry analyses. After a 3-month preservation period, lenticular thickness in these different groups was significantly increased, particularly for samples stored at RT. The mean percentage transmittance of lenticules stored at -80°C with or without silica gel was closest to that of fresh lenticules. Hematoxylin and eosin staining revealed sparsely arranged collagen fibers that were more scattered in preserved lenticules relative to fresh lenticules, particularly in RT samples. Transmission electron microscopy revealed that the fibril bundles densities in lenticules stored at RT were significantly less than those stored at other temperatures. Immunohistochemistry analyses revealed reductions in or loss of CD45 and human leukocyte antigens in all preserved lenticules relative to control samples. Of the tested approaches, the preservation of SMILE-derived lenticules over a 3-month period was optimal at -80°C with or without silica gel in anhydrous glycerol.

Analysis of factors associated with unintended initial dissection of the posterior plane during small incision lenticule extraction.

BackgroundTo investigate potential risk factors for unintended initial dissection of the posterior plane in the initial learning curve of small incision lenticule extraction (SMILE).MethodsData were derived from consecutive 263 eyes of 136 patients who underwent SMILE at the beginning of the surgeon’s learning curve. Probabilities of unintended initial dissection of the posterior plane in left and right eyes were analyzed. Preoperative sphere, cylinder, spherical equivalent (SE), J0, J45, lenticular diameter, lenticular thickness, corneal thickness, and axial length were assessed between eyes in which posterior plane dissection was unintended and those in which it was not.ResultsUnintended initial dissection of the posterior plane occurred in 29 eyes, corresponding to an incidence rate of 11.03%. The probability of difficulty in plane dissection in the left eye was significantly higher than that in the right eye (P=0.003). Significant differences were found in sphere (T =2.8, P=0.006), SE (T =2.37, P=0.019), J0 (T =2.05, P=0.043) and axial length (T =−2.79, P=0.006) between eyes with and without unintended initial dissection of the posterior plane.ConclusionsIn the present study, difficulty in plane dissection during SMILE was encountered significantly more often in left eyes for a right-hand doctor, and in eyes with low SE or high J0 values. Special attention should be paid to prevent unintended initial dissection of the posterior plane in such situations.

Quantitative analysis of internal components of the human crystalline lens during accommodation in adults

To quantitatively analyze changes in the inner components of the human crystalline lens during accommodation in adults. Eyes of 23 subjects were sequentially examined using CASIA2 Optical Coherence Tomography under 0D, − 3D and − 6D accommodation states. The anterior chamber depth (ACD), anterior and posterior crystalline lens radius of the curvature (ALRC and PLRC) were obtained using built-in software. The lens thickness (LT), lenticular nucleus thickness (NT), anterior cortex thickness (ACT), posterior cortex thickness (PCT), anterior and posterior lenticular nucleus radius of the curvature (ANRC and PNRC), anterior and posterior lenticular nucleus vertex (ANV and PNV) were quantified manually with the Image-pro plus software. During accommodation, the ACD became significantly shallower and LT significantly increased. For changes in the lens, the ALRC decreased by an average magnitude (related to accommodative stimuli) 0.44 mm/D, and PLRC decreased 0.09 mm/D. There was no difference for the ACT and PCT in different accommodation states. For lenticular nucleus response, NT increased on average by 30 μm/D. Both the ANRC and PNRC decreased on average by 212 μm/D and 115 μm/D respectively. The ANV moved forward on average by 0.07 mm under − 3D accommodative stimuli and 0.16 mm for − 6D. However, there was no statistically significant difference between different accommodation states in the PNV movement. Under accommodation stimulation, lens thickness changed mainly due to the lenticular nucleus, but not the cortex. For the lenticular nucleus, both the ANRC and PNRC decreased and ANRC changed the most. The anterior surface of the nucleus moved forward while the posterior surface of the nucleus moved backward but only slightly.

Ocular Biometry and its Relationship with Body Size and Head in French Bulldog Dogs

Background: Ocular biometrics is an easy to perform, safe, non-invasive and low-cost exam that provides immediate results with excellent definition. Brachycephalic dogs have a high risk of developing eye problems, and the early appearance is frequent due to factors linked to anatomical conformation. The aim of the present study was to perform eye biometrics in French Bulldog dogs through ultrasound, correlating with body and head size.Materials, Methods &amp; Results: Clinical examination, ophthalmic examination and ocular biometrics were performed using B-mode ultrasonography, using a 10 megahertz frequency transducer in 30 French Bulldog dogs, aged 1-6 years old, male and females from the Br Lord's Staff kennel and the Radiovet - Rio de Janeiro veterinary clinic. A drop of anesthetic eye drops containing 1% tetracaine hydrochloride and 0.1% phenylephrine hydrochloride was instilled and the direct contact technique was performed with the cornea with the help of sterile water-soluble lubricating acoustic gel between the transducer and the examined eye. These measurements were correlated with cephalic measurements (frontal-occipital distance, skull circumference, distance between the zygomatic arches and frontal-nasal distance) and with body measurements (length of the dog from the cranial end of the sternum to the ischial tuberosity and height of the withers from the cranial angle of the scapula to the ground). No chemical restraint was necessary. Dogs were positioned seated or in sternal decubitus, with slight physical restraint. All measurements were performed by the same examiner. There was no significant difference between the parameters of male and female eye biometrics and there was no difference between the measurements of the right and left eyes. The mean value of axial bulb length was 19.51 ± 0.58 mm, for the thickness of the lens, 6.71 ± 0.66 mm, for depth of the anterior chamber, 2.36 ± 0.89 mm and for the depth of the vitreous chamber, 10.44 ± 1.32 mm, showing the same pattern as other studies with brachycephalic dogs. The size of the dog or skull did not interfere with the measurements of eye biometrics.Discussion: The French Bulldog breed was selected for this study due to the scarcity of publications on ocular biometrics in brachycephalic breeds.The knowledge of ocular biometrics is extremely important for the understanding and early diagnosis of some anomalies related to the growth of ocular structures. It is an essential method of exploration and diagnosis of diseases of the eye bulb and orbit, being indicated to evaluate variations in size, shape and position of the eye bulb. The casuistry of these dogs with eye diseases in the ophthalmological clinical routine is large, since they have a high risk of developing eye problems. Ultrasonography is an easy to access and safe, non-invasive exam and the direct corneal contact technique allows clearer images. As there was no significant difference in measurements of intraocular structures between the right and left eyes, the normal eye can be a reliable parameter to establish the prosthetic eye bulb for the injured or enucleated eye. In the present study, there were 21 females and 9 males, which may have generated interference in these values since there was no sex ratio. The measurements of axial length, lenticular thickness, depth of the anterior chamber and the vitreous chamber had values similar to other studies with brachycephalic dogs.

Ocular echobiometry and head measurements in Jersey cattle from different age groups.

A longitudinal study was conducted to identify the morphological development of eyes and head of Jersey cattle at different ages. A total of 48 healthy Jersey cattle, 1 to 58months of age, were included in the study. Ophthalmologic examinations were performed to identify healthy cattle to form the age groups: GI (1- to 11-month-old), GII (16- to 24-month-old) and GIII (25- to 58-month-old). The animals were physically restrained and examined by transcorneal ultrasound of both eyes; the axial length (AxL), corneal thickness (CO), lenticular thickness (L), depth of the anterior (AC) and vitreous (VC) chambers were evaluated. The cranial measurements obtained included the total, cranial, and nasal lengths and widths. Subsequently, the cephalic index (CI) was calculated. The AxL (GI: 2.83cm; GII: 3.16cm; GIII: 3.24cm), AC (GI: 0.44cm; GII: 0.53cm; GIII: 0.53cm), L (GI: 0.88cm; GII: 1.01cm; GIII: 1.04cm) and VC (GI: 1.44cm; GII: 1.55cm; GIII: 1.59cm) increased (p≤.001) according to age, but the CO (GI: 0.07cm; GII: 0.08cm; GIII: 0.08cm) (p>.05) did not. The total length (GI: 30.83cm; GII: 43.29cm; GIII: 44.15cm), cranial length (GI: 18.11cm; GII: 23.82cm; GIII: 22.69cm), nasal length (GI: 12.72cm; GII: 19.47cm; GIII: 21.46cm) and nasal width (GI: 26.22cm; GII: 33.82cm; GIII: 34.00cm) increased (p<.001), and the CI (GI: 85.66cm; GII: 78.15cm; GIII: 77.02cm) decreased (p<.001). The AxL correlated positively (p<.001) with the cranial length and width and negatively with the CI (p>.05). The ocular biometry of Jersey cattle correlates with their cranial measurements at different ages. With increasing age, the eyes and the head grow, establishing growth curves similar to those of other mammals.

Risk Factors for Opaque Bubble Layer in Small Incision Lenticule Extraction (SMILE).

To assess the independent effect of myopia and astigmatism on the risk of the occurrence of opaque bubble layer (OBL) in small incision lenticule extraction (SMILE) and further investigate the relationship between scanning depth and OBL. Twenty-two cases and 317 controls were included in a case-control study from the database of Tianjin Eye Hospital from April 2015 to July 2016. Baseline characteristics were recorded and all of the eyes were manually reviewed by two different observers masked to preoperative refractive status. Multiple regression analysis was used to assess the independent relationship between the attempted correction in diopters and the risk of OBL and to further analyze the association between scanning depth and the risk. The risk of OBL significantly decreased with increasing myopia (diopters) (odds ratio [OR] = 0.44; 95% confidence interval [CI]: 0.30 to 0.64; P < .0001). The risk of OBL also significantly decreased with increasing astigmatism (diopters) (OR = 0.10; 95% CI: 0.02 to 0.42; P = .0017). Lenticular thickness changed by 14.86 μm per diopter for myopia (β =14.86; 95% CI = 14.56 to 15.15; P < .0001) and 15.10 μm per diopter for astigmatism (β = 15.10; 95% CI = 13.96 to 16.24; P < .0001), respectively. A low correction was a significant independent risk factor for OBL during SMILE and the effect of astigmatism on OBL was greater than that of myopia. Deepening the photodisruption plane appropriately may reduce the risk of OBL. [J Refract Surg. 2017;33(11):759-764.].

Cap Lenticular Adhesion During Small Incision Lenticular Extraction Surgery: Causative Factors and Outcomes.

To study the factors causing cap lenticular adhesion (CLA), a rare complication of small incision lenticule extraction (SMILE) surgery, and its effect on surgical outcomes. A prospective, observational, cross-sectional study involving 550 eyes of 285 subjects. SMILE was performed using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) with a minimum of 3 months follow-up. Preoperative visual quality assessment, measurement of corneal biomechanics, and Bowman membrane imaging were performed. Based on the mean refractive spherical equivalent (MRSE), subjects were classified into mild, moderate, and high myopes. Causes of CLA and postoperative outcomes were evaluated. CLA was seen in 1.8% of patients, in whom the median preoperative MRSE was -1.5 (-2.75 to -1.38), deformation amplitude was 1.13 (1.10 to 1.21), and lenticular thickness was 46.2 (39.9 to 54.31). They had microdistortions in the Bowman layer and poor quality of vision. A median Strehl ratio of 0.08 (0.07 to 0.11) and modulation transfer function of 9.88 (8.98 to 13.34) were noted on the first day after surgery, which gradually improved to 0.17 (0.15 to 0.18) and 33.90 (27.27 to 38.94), respectively. On observing the surgical videos, a distinct shining reflection, "the shimmer sign," was seen around the dissector in patients with CLA when the posterior plane was dissected before the anterior. Cap lenticular adhesion was associated with a low preoperative MRSE and thin lenticules. The shimmer sign serves as an indicator for identification of the correct plane of dissection.

Severe ocular side effects with acetazolamide: Case report

Abstract Clinical case A 44-year-old woman arrived in the emergency department complaining of decreased visual acuity (VA) in oculus uterque (OU) of 4 h onset. Signs of myopia, increased intraocular pressure (IOP) in OU, and a narrow grade II anterior chamber (AC) were observed. In the posterior segment ultrasound scan, a choroidal peripheral detachment is evident, and a lenticular thickness of 4.05 mm is measured in the anterior segment of the right eye (OD) and 4.00 mm in the left eye (OS). On treatment with oral with naproxen (non-steroidal anti-inflammatory drug), and acetazolamide for migraine. The acetazolamide is suspended and topical treatment is started with timolol and brimonidine every 12 h, with prednisolone and ayclopentolate every 8 h. In the follow-up, a gradual reduction of myopia and lens thickness is observed, as well as anterior chamber expansion. In the last control, the patient had a sphere of −0.75 diopters (D) in OD and −0.25 D in OS. IOP was 15 mmHg in OU and AC was grade III . The ultrasound showed a lens thickness of 3.59 mm in OD and 3.61 mm in OS. Conclusion This was an iatrogenic case of acute angle closure induced by an anterior displacement of the irido-lenticular complex, secondary to the use of acetazolamide. The treatment of this condition involves suspending the drug responsible and applying topical corticosteroids, hypotensive and cycloplegic eye drops, with the aim of lowering the eye pressure and the degree of myopia due to the re-positioning of the irido-lenticular complex.

Reacción ocular adversa a la acetazolamida: a propósito de un caso

Clinical caseA 44-year-old woman arrived in the emergency department complaining of decreased visual acuity (VA) in oculus uterque (OU) of 4hours onset. Signs of myopia, increased intraocular pressure (IOP) in OU, and a narrow grade II anterior chamber (AC) were observed. In the posterior segment ultrasound scan, a choroidal peripheral detachment is evident, and a lenticular thickness of 4.05mm is measured in the anterior segment of the right eye (OD) and 4.00mm in the left eye (OS). On treatment with oral with naproxen (non-steroidal anti-inflammatory drug), and acetazolamide for migraine. The acetazolamide is suspended and topical treatment is started with timolol and brimonidine every 12hours, with prednisolone and ayclopentolate every 8hours. In the follow-up, a gradual reduction of myopia and lens thickness is observed, as well as anterior chamber expansion. In the last control, the patient had a sphere of −0.75 diopters (D) in OD and −0.25 D in OS. IOP was 15mmHg in OU and AC was grade III. The ultrasound showed a lens thickness of 3.59mm in OD and 3.61mm in OS. ConclusionThis was an iatrogenic case of acute angle closure induced by an anterior displacement of the irido-lenticular complex, secondary to the use of acetazolamide. The treatment of this condition involves suspending the drug responsible and applying topical corticosteroids, hypotensive and cycloplegic eye drops, with the aim of lowering the eye pressure and the degree of myopia due to the re-positioning of the irido-lenticular complex.

The Influence of Diabetes Mellitus on Lenticular Thickness

The prevalence of diabetes is increasing exponentially often causing an enormous public health burden. A hospital based observational study was undertaken and 144 type I diabetic subjects with equal number of non-diabetic controls were enrolled. The mean lens thickness, duration, fasting blood sugar, post prandial blood sugar and glycated hemoglobin were assessed. The crystalline lens was thicker in the diabetic group (4.33±0.38 mm vs 4.05±0.55 mm) which was statistically significant (p<0.001). There was a significant correlation between lens thickness and age (p<0.001, r=0.651) and between lens thickness and duration of diabetes (p<0.001, r=0.468). However, HBA1c and blood sugar levels had no significant influence on lenticular thickness.

Changes in ultrastructure and cytochemistry of the agarophyte Gracilaria domingensis (Rhodophyta, Gracilariales) treated with cadmium

The agarophyte macroalgae Gracilaria domingensis (Kützing) Sonder ex Dickie is widely distributed along the Brazilian coast. While this species produces agarana, it is more important in the human diet. Therefore, the present study aimed to evaluate the biological effects of cadmium on its morphology and cellular organization. To accomplish this, the effects of cadmium in apical segments of G. domingensis were examined in vitro. Over a period of 16 days, the segments were cultivated and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m(-2) s(-1), with cadmium treatments in doses of 100, 200 and 300 μM. The samples were processed for light, transmission and scanning electron microscopy. Histochemical analyses included Toluidine Blue for acidic polysaccharides, Coomassie Brilliant Blue for total protein, and Periodic Acidic Schiff for neutral polysaccharides. In all cadmium treatments, cytochemical analysis showed 1) metachromatic granulation in vacuole and lenticular thickness of the cell wall, 2) a higher concentration of cytoplasmic organelles, and 3) an increase in the number of floridean starch grains. Cadmium also caused changes in the ultrastructure of cortical and subcortical cells, including increased cell wall thickness and vacuole volume, as well as the destruction of chloroplast internal organization and increased number of plastoglobuli. In addition, treated plants showed a gradual increase in surface roughness, apparently the result of cadmium absorption. Taken together, these findings strongly suggested that cadmium negatively affects the agarophyte G. domingensis, posing a threat to the vitality of this plant species as a supplement in the human diet.

Nearwork-induced changes in lenticular thickness in different refractive groups

Purpose The aim of this study was to directly measure lenticular thickness and its additivity after 1 and 2 hours of continuous reading at near in myopic and emmetropic young adults. Methods Thirty-five subjects consisting of 12 early-onset myopes, 11 late-onset myopes, and 12 emmetropes were tested. Axial lenticular thickness was measured in the right eye using A-scan ultrasonography before and immediately after 1 and 2 hours of continuous reading at near (35 to 40 cm). Results Group mean (±SD) changes in lenticular thickness from baseline values after the first and second hours of reading were 0.025 ± 0.011 and 0.035 ± 0.017 mm, respectively. The group mean increase in lenticular thickness after the second hour was significantly larger than after the first hour, with subsequent subgroup analysis indicating that this was found in the myopes only. Conclusion The lenticular increase was additive in nature, but only in the late-onset and early-onset myopes. This confirmed and extended objectively earlier studies that suggested increased nearwork accommodative susceptibility of a primarily lenticular nature in myopes.

Effects of UVB radiation on the agarophyte Gracilaria domingensis (Rhodophyta, Gracilariales): Changes in cell organization, growth and photosynthetic performance

The effects of ultraviolet radiation-B (UVBR) in apical segments of the red macroalgae Gracilaria domingensis (Kützing) Sonder ex Dickie were examined in vitro. Over a period of 21 days, the segments were cultivated and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m −2 s −1 and PAR + UVBR at 1.6 W m −2 for 3 h per day. The samples were processed for electron microscopy, as well as histochemical analysis, and growth rate, photosynthetic pigment contents and photosynthetic performance were measured. Toluidine Blue reaction showed metachromatic granulations in vacuole and lenticular thickness, while Coomassie Brilliant Blue showed a higher concentration of cytoplasmic organelles, and Periodic Acid Schiff stain showed an increase in the number of floridean starch grains. UVBR also caused changes in the ultrastructure of cortical and subcortical cells, which included an increased number of plastoglobuli, changes in mitochondrial organization, destruction of chloroplast internal organization, and the disappearance of phycobilisomes. The algae cultivated under PAR-only showed growth rates of 6.0% day −1, while algae exposed to PAR + UVBR grew only 2.8% day −1. Compared with algae cultivated with PAR-only, the contents of photosynthetic pigments, including chlorophyll a, phycoerythrin, phycocyanin and allophycocyanin, decreased after exposure to PAR + UVBR, and significant differences were observed. Finally, analysis of these four photosynthetic parameters also showed reduction after exposure to PAR + UVBR: maximum photosynthetic rate, photosynthetic efficiency, photoinhibition and relative electron transport rate. Taken together, these findings strongly suggested that UVBR negatively affects the agarophyte G. domingensis.

Ultrasound biomicroscopy of the anterior segment of the enucleated chicken eye during accommodation.

Ultrasound biomicroscopy produces real-time two-dimensional images of ocular structures measured non-invasively. Given recent work which shows that lenses from myopic eyes show shorter focal lengths and reduced accommodative amplitudes compared with controls, this study was undertaken to determine the structural characteristics of the anterior segment of chicken eyes during accommodation using the ultrasound biomicroscope (UBM). Form-deprivation myopia and hyperopia were induced in hatching chicks by the application of either translucent or +15 D defocus goggles. After 7 days, eyes were enucleated and ultrasound biomicrographs of the eye, at rest and during ciliary nerve-stimulated accommodation, were collected. For all eyes, accommodation was associated with a decrease in anterior chamber depth, an increase in lenticular thickness and a steepening of the front lenticular surface curvature. Changes related to refractive error were more difficult to detect. Myopic eyes showed deeper anterior chamber depths and differences in lenticular thicknesses just above the resolution limit for detection. In +15 D lens-treated eyes, anterior chamber differences were opposite but smaller, just at the limit of resolution, while differences in mean lenticular thickness were not resolvable at a pixel or above. The UBM is a good tool for measuring robust changes during accommodation, but is limited in its ability to detect subtle changes associated with experimentally induced ametropias.

Reservoir Geometry and Trapping Mechanisms, Lindsey Slough Gas Field, Southern Sacramento Basin: ABSTRACT

Multiple reservoir units, numerous unconformities and stratigraphic pinch-outs, and extensive faulting make the Lindsey Slough field area (T5N, R2E, MDBM) geologically intriguing and economically attractive. The petroleum geology class of California State University, Northridge, undertook a group mapping project in November 1985, to delineate producing pools, determine reservoir geometries and trapping mechanisms, and identify potential exploration and development locations. More than 12 separate pools, producing from at least one of the 13 reservoir zones, are present. Reservoirs are of two main types: (1) extensive sheet sandstones deposited in delta-front and shelf(.) environments, and (2) lenticular channel sandstones deposited in submarine canyon, slope, and submarine fan environments. Among the sheet sandstones, the upper and lower Petersen members of the Upper Cretaceous Starkey formation are especially productive, with pay zones exceeding 100 ft. Both members pinch out to the southwest, along the paleoshelf edge. Of the lenticular sandstones, reservoir quality and thickness appear to be greatest in delta-mouth slope channels that fed sand basinward to submarine fans. Net pay in the K-1 and related upper Cretaceous channels exceeds 200 ft in some wells. Middle-fan channels of the Upper Cretaceous channels exceeds 200 ft in some wells. Middle-fan channels of the Upper Cretaceousmore » Winters Fan are locally productive, and a small amount of gas has been produced from thin, poorly sorted sandstones within the Paleocene Martinez Submarine Canyon.« less