Maculas, monkeys, models, AMD and aging

Age related macular degeneration (AMD) signs may be found reliably in monkeys (Macaca mulatta) bred selectively in Florida after 14 generations of inbreeding in a closed colony at the University of Puerto Rico. Progression, ultrastructure and functional losses are parallel to those found in humans.     

Fluoroperm extended wear RGP contact lenses for myopia, hyperopia, aphakia, astigmatism, and keratoconus

One hundred fifteen eyes of 62 patients were fit with paflufocon-A (Fluoroperm) rigid gas permeable (RGP) contact lenses. Patients included myopes, hyperopes, aphakes, and keratoconic and astigmatic patients; the latter patients were fit with bitoric designs for large amounts of corneal astigmatism or front toric designs for residual astigmatism. Thirty of the 52 patients (58%) who completed the study were able to wear the lenses continuously without complications; six (12%) were able to achieve extended wear for up to one month. The average visual acuity across the study was 20/20. Three complications were observed, resulting in a complication rate of 6%.     

Combined retinal vascular occlusion: Demography,clinical features,visual outcome,systemic co-morbidities,and literature review

Purpose:To document the clinical features, systemic association, and treatment outcome of patients with a combined retinal vein and artery occlusion (CRVAO) and review of literature.Methods:A retrospective chart review of patients diagnosed with CRVAO at a tertiary eye care center. Patient''s demographic details and associated ocular and systemic factors were recorded. Treatment included laser photocoagulation, anti-vascular endothelial growth factor (VEGF) intravitreal injection or transscleral cyclophotocoagulation (TSCPC), alone or in combination. At last, follow- up treatment response was measured in visual acuity status, regression of neovascularization, and control of intraocular pressure (IOP). All cases reported in the current decade were analyzed and compared with this study.Results:Seventeen eyes with CRVAO accounted for 0.3% of total vascular occlusion (total 5151 patients were seen in this period). The mean age was 48.12 ± 17.5 years (range: 12-87 years) and there were 9 females. Nine eyes had CRVO + CRAO; 6 eyes had BRVO + BRAO, and one patient each had CRVO + BRAO and CRAO + BRVO. Fluorescein angiography (FA) showed delayed ''arm to retina'' time (>20 seconds) in all 10 eyes and delayed arteriovenous transit time in 9 out of 10 eyes. Optical coherence tomography (OCT) showed hypereflective inner retinal layers (16 eyes) and neurosensory detachment (7 eyes). The most common systemic associations were hypertension and dyslipidemia (n = 7 people; 41.18%) each. Four patients (23.5%) had a plaque in carotid arteries with normal 2D echocardiography. Ten (59%) eyes were treated with intravitreal bevacizumab + laser; four (23.5%) eyes were treated with laser only, and three (17.6%) eyes were treated with laser + anti-VEGF + TSCPC. At last follow up, vision improved in 9 (52.9%) eyes; stable in 3 (17.7%) eyes, and reduced to perception of light in 5 (29.4%) eyes.Conclusion:Combined CRVAO is a rare emergency leading to acute vision loss. Early diagnosis and treatment for ocular complications and systemic evaluation for cardiovascular risk factors are needed.     

Intraocular pressure, Goldmann applanation tension, corneal thickness, and corneal curvature in Caucasians, Asians, Hispanics, and African Americans

PURPOSE: This is to investigate whether there are differences in Goldmann applanation tonometry (GAT), central corneal thickness, and corneal curvature among four racial groups. If differences are present, they may alter GAT reading, diagnosis, and management of glaucoma in the population. DESIGN: Observational retrospective cross-sectional study. METHODS: Charts of patients who have had keratorefractive surgery were examined. Central corneal thickness, corneal curvature, refractive power, and GAT were measured in 1482 Caucasian, 172 Asian, 204 Hispanic, and 118 African-American eyes (total 1976 eyes). Refractive components and GAT were compared. We compared intraocular pressure (IOP) adjusted by GAT, central corneal thickness, and corneal curvature among the four groups. RESULTS: There was a statistically significant difference between the mean (+/- standard deviation) central corneal thickness of African American (535.46 +/- 33.39) and Caucasian (552.59 +/- 34.48) eyes. Mean central corneal thickness was near 550 microm in Caucasians, Asians, and Hispanics. No significant difference was noted in corneal curvature in the four groups. There was a significant correlation between central corneal thickness and corneal curvature, and GAT was similar among the four groups. When IOP was adjusted for central corneal thickness, it was significantly greater in African Americans (16.12 +/- 3.27) than in Caucasians (14.32 +/- 2.93). Corneas of women were significantly thinner than corneas of men. CONCLUSIONS: African Americans had significantly thinner central corneal thickness than Caucasians, Asians, or Hispanics, causing the underreading of true IOP. Significant correlation between central corneal thickness and corneal curvature was demonstrated. Uncorrected GAT underreading of African Americans may lead to delay in diagnosis, inadequate treatment target setting, and higher morbidity. Goldmann applanation tonometry needs to be corrected by central corneal thickness and corneal curvature for proper diagnosis and management of glaucoma.     

Retinal ganglion cells: Energetics,compartmentation, axonal transport,cytoskeletons and vulnerability

Retinal ganglion cells (RGCs) are specialized projection neurons that relay an immense amount of visual information from the retina to the brain. RGC signal inputs are collected by dendrites and output is distributed from the cell body via very thin (0.5–1 μm) and long (∼50 mm) axons. The RGC cell body is larger than other retinal neurons, but is still only a very small fraction (one ten thousandths) of the length and total surface area of the axon. The total distance traversed by RGCs extends from the retina, starting from synapses with bipolar and amacrine cells, to the brain, to synapses with neurons in the lateral geniculate nucleus.This review will focus on the energy demands of RGCs and the relevant tissues that surround them. RGC survival and function unexceptionally depends upon free energy, predominantly adenosine triphosphate (ATP). RGC energy metabolism is vastly different when compared to that of the photoreceptors.Each subcellular component of the RGC is remarkably different in terms of structure, function and extracellular environment. The energy demands and distribution of each component are also distinct as evidenced by the uneven distribution of mitochondria and ATP within the RGC – signifying the presence of intracellular energy gradients. In this review we will describe RGCs as having four subcellular components, (1) Dendrites, (2) Cell body, (3) Non-myelinated axon, including intraocular and optic nerve head portions, and (4) Myelinated axon, including the intra-orbital and intracranial portions.We will also describe how RGCs integrate information from each subcellular component in order achieve intracellular homeostatic stability as well as respond to perturbations in the extracellular environment. The possible cellular mechanisms such as axonal transport and axonal cytoskeleton proteins that are involved in maintaining RGC energy homeostasis during normal and disease conditions will also be discussed in depth. The emphasis of this review will be on energetic mechanisms within RGC components that have the most relevance to clinical ophthalmology.     

Effects of aniseikonia, anisometropia, accommodation, retinal illuminance, and pupil size on stereopsis

The sensitivity of clinical measures of stereoacuity in the detection of interocular differences in retinal images was examined in 50 adults with normal binocularity. Interocular differences in retinal image size (aniseikonia), clarity (anisometropia) and brightness, as well as differences in absolute and relative pupil size (anisocoria) were created in small steps over a large range to determine their effect on threshold levels of stereopsis. Their effect on stereoacuity was measured in both contour (Titmus test) and random dot (Randot test) stereograms. Stereoacuity measured by both types of stereograms decreased in a curvilinear manner for aniseikonic and anisometropic test conditions. Monocular blur caused a more rapid decrease in stereoacuity than induced aniseikonia. Stereoacuity measured by the contour stereogram decreased about 1.8 times faster than that measured by the random dot stereogram during induced aniseikonia and anisometropia. This differential sensitivity suggests that the Titmus test would detect small interocular differences in retinal images more effectively than the Randot test in clinical screening procedures for vision abnormalities. However, both tests can miss clinically significant amounts of aniseikonia and anisometropia, and fail to differentiate the cause of reduced stereopsis. Interocular differences in retinal image brightness and pupil size within a normal physiologic range did not reduce stereopsis to clinically unacceptable levels.     

GABA,experimental myopia,and ocular growth in chick

PURPOSE: To learn whether gamma-aminobutyric acid (GABA) participates in retinal mechanisms that influence refractive development. METHODS: White leghorn chicks, some of which wore a unilateral goggle to induce myopia, received daily intravitreal injections of agonists or antagonists to the major GABA receptor subtypes. Eyes were studied with refractometry, ultrasound, and calipers. Retinas of other chicks wearing unilateral goggles were assayed for GABA content. RESULTS: Antagonists to GABA(A) or GABA(A0r) (formerly known as GABA(C)) receptors inhibited form-deprivation myopia. GABA(A) antagonists showed greater inhibition of myopic growth in the equatorial than the axial dimension. A GABA(A0r) antagonist displayed parallel inhibition in the axial and equatorial dimensions. A GABA(A0r) agonist but not GABA(A) agonists altered the myopic refraction of goggled eyes. GABA(B) receptor antagonists, more so than an agonist, also slowed development of myopia, inhibiting axial growth more effectively than equatorial expansion of goggled eyes. When administered to nongoggled eyes, GABA(A) or GABA(A0r) agonists or antagonists also altered eye growth, chiefly stimulating it. Only a GABA(A) agonist induced a myopic refraction. Several of these agents stimulated eye growth in the axial, but not the equatorial, dimension. Retinal GABA content was slightly reduced in goggled eyes. CONCLUSIONS: GABA(A), GABA(A0r), and GABA(B) receptors modulate eye growth and refractive development. The anatomic effects of these drugs reinforce the notion that eye shape and not just eye size is regulated. A retinal site of action is consistent with the known ocular localizations of GABA and its receptors and with the altered retinal biochemistry in form-deprived eyes.     

Schizophrenia, psychotropic medication, and cataract

OBJECTIVE: To compare the distribution of cataract types between psychiatric patients diagnosed with schizophrenia and the general population not exposed to psychotropic medication, and to compare cataract prevalence between users and nonusers of various psychotropic medications in the general community. DESIGN: Case-control. PARTICIPANTS: A total of 151 (93%) eligible patients from a community mental health service and 3271 (83%) eligible residents from the Melbourne Visual Impairment Project (VIP) were examined. MAIN OUTCOME MEASURES: All patients 40 years of age and older from a community mental health service and residents of nine randomly selected areas of Melbourne were eligible. Best-corrected distance visual acuity was determined using a 4-m logarithm of the minimum angle of resolution (LogMAR) chart. The presence of cataract was determined by photographs or slit-lamp examination using direct and indirect retroillumination. Anterior, cortical, nuclear, and posterior subcapsular cataracts were measured. Participants from the Melbourne VIP were classified as to whether they had taken benzodiazepams, phenothiazines, thioxanthenes, butyrophenols, tricyclic antidepressants, or monoamine oxidase inhibitors for at least 12 months during their lifetime. RESULTS: The distribution of cataract type varied between persons with and without schizophrenia. Anterior subcapsular (ASC) cataract was significantly more prevalent (26%) in participants with schizophrenia from the community mental health service than Melbourne VIP participants (0.2%) not exposed to psychotropic medication (chi-square, 1 degree of freedom = 605.5, P = 0.001). This remained significant after controlling for age (odds ratios = 250, 95% confidence interval = 83.3, 1000). The distribution of the age-related cataract was similar across all groups of psychotropic medication users with the exception of the phenothiazine users. They had less of all types of the age-related cataracts, despite being slightly older than the control group (mean age, 60.0 vs. 58.4, t test = 0.85, P = 0.40). However, only cortical cataract in the phenothiazine group was statistically lower (chi-square, 1 degree of freedom = 3.96, P = 0.047). CONCLUSION: This study has identified the need to investigate whether other newer agents, especially high-potency medications, cause ASC opacities if a certain threshold of exposure to psychotropic medications must be attained to develop cataract, or if schizophrenia itself is associated with cataract formation.     

Suprachoroidal haemorrhage complicating cataract surgery in the UK: epidemiology, clinical features, management, and outcomes

AIMS: To study the incidence, management, and outcomes of suprachoroidal haemorrhage (SCH) complicating cataract surgery in the United Kingdom. METHODS: Cases were prospectively collected by active surveillance through the British Ophthalmological Surveillance Unit. Details were obtained using an incident questionnaire with follow up at 6 months. RESULTS: 118 cases were reported in 1 year. The estimated incidence of SCH was 0.04% (95% confidence interval 0.034% to 0.050%). Cataract extractions were by phacoemulsification in 76.2%, extracapsular cataract extraction (ECCE) in 11.0%, and phacoemulsification conversion in 12.8%. SCH was "limited" (1 to 2 quadrants) in 48.7%, "full blown" (3 to 4 quadrants) in 43.1%. SCH in phacoemulsification was more likely to be limited (63.2%), compared with ECCE (11.1%) and phacoemulsification conversion (23.1%) (p<0.001, chi(2) test). Visual acuity (VA) was better than 6/60 in 57 of 95 (60%) cases after a median follow up interval of 185 days. 33 of 34 cases (97.1%) with secondary anterior segment revision had VA better than 6/60. VA was worse than 6/60 in 7 of 8 (87.5%) cases that had intraoperative sclerostomy, and in all 6 (100%) cases that had secondary posterior segment intervention. CONCLUSION: SCH is a rare but serious complication of cataract surgery. Poor prognostic factors included full blown SCH, ECCE, phacoemulsification conversion, retinal apposition, and retinal detachment.     

Diffuse lamellar keratitis: incidence, associations, outcomes, and a new classification system.

PURPOSE: To evaluate the incidence, associations, and visual outcomes in patients with diffuse lamellar keratitis (DLK) after laser in situ keratomileusis (LASIK). SETTING: University-based refractive surgery center, Boston, Massachusetts, USA. METHODS: This retrospective review comprised 2711 eyes that had LASIK between September 1996 and September 1999. All eyes that developed DLK after LASIK were included. They were divided into type I DLK (center sparing) or type II DLK (center involved) and then subdivided into A (sporadic-DLK not diagnosed in other patients treated on the same day) or B (cluster-other patients identified with DLK). Type IA corresponded to center sparing, sporadic; type IB, center sparing, cluster; type IIA, center involved, sporadic; and type IIB, center involved, cluster. The main outcome measures were incidence of DLK after LASIK, time to diagnosis, time to resolution, and changes in best spectacle-corrected visual acuity (BSCVA). Unpaired t tests were used for statistical analyses. RESULTS: Thirty-six eyes (1.3%) developed DLK. Type I occurred in 58.3% of cases (type IA, n = 18; type IB, n = 3) and type II, in 41.7% (type IIA, n = 10; type IIB, n = 5). The mean time to diagnosis was not statistically significantly different between type I (1.8 days) and type II (1.1 days). Fourteen eyes (38.9%) developed DLK after an epithelial defect, representing an odds ratio of 13 times. The association with an epithelial defect was statistically significantly greater with type I (11/21 eyes, 52.4%) than with type II (3/15 eyes, 20.0%; P =.05). The mean time to resolution was 3.5 days in type I (type IA = 3.6 days; type IB = 2.7 days). This was significantly shorter than in type II, which had a mean time to resolution of 12.1 days (type IIA = 9.3 days; type IIB = 10.2 days) (P =.001). Loss of 2 or more lines of BSCVA occurred in 2 of 5 patients with type IIB and in no patients with types IA, IB, or IIA. CONCLUSIONS: Epithelial defects after LASIK increased the risk of DLK occurrence, especially type I. Type II DLK was associated with a prolonged time to resolution and carried a significantly higher risk of BSCVA loss than type I.     

Early postoperative trabeculectomy leakage: incidence, time course, severity, and impact on surgical outcome

AIM: To establish the incidence, time course, and severity of conjunctival wound leakage following trabeculectomy, and also to establish whether early wound leakage adversely affects the ultimate outcome of the surgery. METHOD: A prospective, observational case series of sequential trabeculectomies performed in a single institution over a 12 month period. Datasets on 286 operations were analysed. A fornix based conjunctival flap was used in 254 cases and a limbus based conjunctival flap in 41 cases. At every postoperative visit trabeculectomies were assessed for four grades of leakage (none; mild; moderate; severe), and for success or failure at the 6 month follow up post surgery. Pressure was applied to the trabeculectomy bleb to record the maximum rates of leakage and improve kappa statistics. Study clinicians were validated with respect to their scoring of leaks before starting the study. RESULTS: 169 of the 286 trabeculectomies (59%) showed leakage at some stage postoperatively. 159 of 245 fornix based flaps (65%) leaked compared with 10 of 41 limbus based flaps (24%). Median time to leak was 3.5 (range 0-408) days. Median duration of leakage was 14 (range 2-457) days. 14 (5%) of trabeculectomies failed completely. A further 40 (14%) were a partial failure. In total, 23 of 117 (20%) without postoperative leaks partially or completely failed compared with 31 of 169 (18%) with leaks. Cross tabulation of partial and complete failure by leak shows no evidence of an adverse effect of leaking on the outcome (chi(2) = 1.81, p = 0.4). CONCLUSIONS: There is no evidence to support the hypothesis that early postoperative leakage of fornix based conjunctival flaps affects the outcome of trabeculectomy.     

Abstracts of the 189th Meeting of the Dutch Ophthalmological Society,Groningen, 15–17 March, 1995 Groningen, 15–17 March, 1995

Purpose. To investigate the macular choriocapillary circulation (MCC) in eyes with age-related macular degeneration (ARMD) and to correlate these findings with the associated clinical and angiographic drusen characteristics. Methods. Scanning laser ophthalmoscope fluorescein videoangiography was performed on 34 eyes with age-related macular degeneration and eight age-matched normal volunteers. Drusen characteristics were assessed using the Wisconsin age-related maculopathy grading scale. Results. A delayed macular choriocapillary circulation (DMCC) was defined as a macular choriocapillary filling time greater than 3 standard deviations from the normal mean (greater than 5 seconds). Nine (26%) of the 34 eyes with ARMD were found to have a DMCC. After age adjustment, eyes with DMCC were more likely to have geographic atrophy of the retinal pigment epithelium (p = 0.003) or choroidal neovascularization (p = 0.07) than were eyes with a normal MCC. Regional differences in choriocapillary filling times were present in the eyes with a DMCC, including nasal-to-temporal, central-to-peripheral, and inferior-to-superior gradients of progressively less choriocapillary filling delay. The DMCC correlated with the location, number, size, confluence, and fluorescein staining characteristics of the associated drusen. Conclusion. DMCC occurs in some eyes with ARMD. This finding may not only assist in defining eyes at risk for progressive disease but may also help to elucidate the pathogenesis of age-related macular degeneration.     

Retinal vascular caliber, diabetes, and retinopathy

PURPOSE: To assess the relationship of retinal vessel caliber with diabetes and diabetic retinopathy (DR). DESIGN: Population-based cross-sectional analysis of the Blue Mountains Eye Study, Australia (n = 3,654, age >or=49 years). METHODS: Diabetes was defined as physician-diagnosed or fasting blood glucose >or= 7.0 mmol/l; impaired fasting glucose as fasting glucose 6.1 to 6.9 mmol/l. DR was graded from retinal photographs. Retinal vessel caliber was measured from digitized images. RESULTS: After controlling for age, gender, blood pressure, and other factors, mean retinal venular caliber was significantly wider in participants with moderate-severe nonproliferative DR (severe 262.7 microm; moderate 236.7 microm) than in nondiabetic participants (221.9 microm) or participants with diabetes but no DR (221.2 microm) (P < .0001). Mean retinal arteriolar caliber was significantly wider in participants with diabetes (193.5 microm) than in nondiabetic participants (190.2 microm) (P < .01). CONCLUSIONS: Increasing severity of DR in persons with diabetes is associated with widening of retinal venular caliber.     

Depression, visual acuity, comorbidity, and disability associated with age-related macular degeneration

OBJECTIVE: To examine (1) the prevalence of depressive disorders in community-dwelling adults with advanced age-related macular degeneration (AMD) and (2) the relationship in this population between depression, visual acuity, the number of comorbid medical conditions, disability caused by vision loss as measured by the National Eye Institute-Vision Function Questionnaire (NEI-VFQ) and the vision-specific Sickness Impact Profile (SIPV), and disability caused by overall health status as measured by the Sickness Impact Profile-68 (SIP). DESIGN: Analysis of cross-sectional baseline data from a randomized clinical trial. PARTICIPANTS: Participants were 151 adults aged 60 and older (mean age, 80 years) with advanced macular degeneration whose vision was 20/60 or worse in their better eye. METHODS: Subjects were interviewed using measures of depression, disability, and chronic medical conditions. Visual acuity was obtained. Nonparametric correlation analyses and linear regression analyses were performed. MAIN OUTCOME MEASURES: Structured Clinical Interview for DSM-IV (SCID-IV), Geriatric Depression Scale (GDS), NEI-VFQ, SIPV, and SIP. RESULTS: Of the participants, 32.5% (n = 49) met SCID-IV criteria for depressive disorder, twice the rate observed in previous studies of community-dwelling elderly. Over and above depression (GDS), visual acuity aided in prediction of the level of vision-specific disability (NEI-VFQ and SIPV). CONCLUSIONS: Depressive disorder is a significant problem for the elderly afflicted with advanced macular degeneration. Further research on psychopharmacologic and psychotherapeutic interventions for depressed AMD patients is warranted to improve depression and enhance functioning. Over and above depression, visual acuity aided in predicting vision-specific disability. Treatment strategies that teach patients to cope with vision loss should be developed and evaluated.     

Natural outcomes of stage 1, 2, 3, and 4 idiopathic macular holes.

AIMS--A study was carried out to ascertain the natural outcome of each stage of idiopathic macular hole. METHODS--One hundred and fifty four eyes with different stages of idiopathic macular holes were retrospectively studied: stage 1 (40 eyes), 2 (25 eyes), 3 (58 eyes), and 4 (31 eyes). RESULTS--Of 27 of 40 eyes with a stage 1 lesion with posterior vitreous attachment to the macula initially, nine (33%) eyes developed a full thickness macular hole. No stage 1 lesions with posterior vitreous separation from the macula initially progressed to full thickness holes. Twenty one (84%) of 25 eyes with a stage 2 lesion, 32 (55%) of 58 eyes with a stage 3 lesion, and five (16%) of 31 eyes with a stage 4 lesion underwent macular hole enlargement during the median follow up period of 3 years. Visual acuity decreased two or more lines of Snellen equivalent during the follow up period in 12 (30%) eyes with a stage 1 lesion, 17 (68%) eyes with a stage 2 lesion, 17 (29%) eyes with a stage 3 lesion, and four (13%) eyes with a stage 4 lesion. The percentage was significantly higher in eyes with stage 2 lesions than the other stages (p < 0.01). CONCLUSION--The results suggest that the different stages of idiopathic macular holes have different natural outcomes, and the management depends on the stage at presentation.     

The relationship among race, iris color, central corneal thickness, and intraocular pressure.

PURPOSE: Central corneal thickness (CCT) influences applanation intraocular pressure (IOP) measurement. The present study sought to determine whether iris color might represent a qualitative surrogate for CCT or race, and therefore differential risk for elevated IOP and, consequently, developing glaucoma. METHODS: Eligible patients included those with best-corrected visual acuity (BCVA) better than 20/40 and who had not worn contact lenses within 24 hours. Exclusion criteria were prior ophthalmic surgery, topical ocular or systemic medication that would influence IOP, previous ocular inflammatory conditions, or current treatment for ophthalmic treatment. Data collection included demographic (name, date of birth, race), BCVA, and iris color. Iris color was judged according to a purpose-developed chart (white: blue, green, brown or black: brown) and patients were assigned to one of four groups. Goldmann applanation tonometry and pachymetry measurements were performed consecutively. To attain a power of 90% to find a difference of 40 microm with alpha < 0.05, we examined at least 14 subjects (28 eyes) for each group. RESULTS: Comparing pachymetry measurements among iris colors revealed no statistically significant difference among the three groups of whites: blue (552 microm), green (552 microm), and brown (562 microm). The same held true when comparing IOP and CCT-adjusted IOP with iris color: blue-15.2, 15.1, green-15.4, 15.2, and brown-14.7, 14.0. When comparing CCT between whites and blacks, CCT was significantly thinner in blacks (533 microm), whether evaluating all whites (555 microm, p = 0.03) or comparing only the brown-iris white group with the black group (562 microm vs. 533 microm, p = 0.03). Mean CCT-adjusted IOP was barely significantly different between whites (14.8) and blacks (16.7) (p = 0.04). CONCLUSION: These results suggest that iris color is not associated with CCT and apparently iris color does not influence measured IOP. We were able to establish a relationship between race and IOP when adjusting IOP for CCT. Our data show a significantly higher CCT-adjusted IOP for blacks than whites demonstrating a racial difference in CCT-corrected IOP.     

Occlusion, transparency, and lightness

The lightness of a visual surface is its perceived achromatic reflectance [Adelson, E. H., (2000). Lightness perception and lightness illusions. In M. Gazzaniga (Ed.), The new cognitive neuroscience (2nd ed.) (pp. 339-351) Berlin: Springer; Gilchrist, A. (1999). Lightness perception. In R. W. F. Keil (Ed.), MIT encyclopedia of cognitive science (pp. 471-472). Cambridge: MIT press]. Lightness ranges from black, through various shades of grey, up to white. Anderson and Winawer [Anderson, B., Winawer, J. (2005). Image segmentation and lightness perception. Nature, 434, 79-83] suggested that perceptual decomposition of image luminance into multiple sources in different layers (e.g., perceptual transparency) is critical to the their lightness illusions. However, I show that simple perceptual occlusion evoked by T-junctions will work as well, suggesting that perceptual scission of luminance into multiple layers is unnecessary for such effects. I argue that the lightness illusions presented by Anderson and Winawer involve fundamentally different mechanisms than previously studied lightness illusions, including those involving perceptual transparency.     

Human trabecular meshwork cell responses induced by bimatoprost,travoprost, unoprostone,and other FP prostaglandin receptor agonist analogues

PURPOSE: To determine the functional agonist potencies of the intraocular pressure (IOP)-lowering prostaglandin F (FP)-class prostaglandin (PG) analogues (e.g., travoprost, latanoprost, bimatoprost, and unoprostone isopropyl ester) in human trabecular meshwork (h-TM) cells, by using phosphoinositide (PI) turnover and intracellular Ca(2+) ([Ca(2+)](i)) mobilization, and to confirm the FP nature of these receptors by using an FP receptor antagonist, 11beta-fluoro-15-epi-15-indanyl-PGF(2alpha) (AL-8810). METHODS: FP-receptor-mediated PI turnover and [Ca(2+)](i) mobilization were measured in h-TM cells by determining the accumulation of [(3)H]-inositol phosphates ([(3)H]-IPs) by anion-exchange chromatography and real-time fluorescence imaging, respectively. RESULTS: Various PG analogues concentration-dependently stimulated production of [(3)H]-IPs in h-TM cells with the following agonist potencies (median effective concentration; EC(50)): travoprost acid (EC(50) = 2.4 nM) > cloprostenol (EC(50) = 4.5 nM) > (+/-)-fluprostenol (EC(50) = 10.8 nM) > latanoprost acid (EC(50) = 34.7 nM) > bimatoprost acid (EC(50) = 112 nM) > PGF(2alpha) (EC(50) = 120 nM) > unoprostone (UF-021; EC(50) = 3280 nM) > S-1033 (EC(50) = 4570 nM; all n = 3-9). Prodrug derivatives of these compounds exhibited the following potencies: travoprost (isopropyl ester; EC(50) = 89.1 nM) > latanoprost (isopropyl ester; EC(50) = 778 nM) > bimatoprost (amide; EC(50) = 1410-6940 nM). Travoprost acid, PGF(2alpha,) unoprostone, and S-1033 were tested in addition for [Ca(2+)](i) mobilization and found to have rapid and dose-dependent effects. The FP receptor-selective antagonist AL-8810 antagonized the (+/-)-fluprostenol-induced PI turnover in these cells (K(i) = 2.56 +/- 0.62 micro M) as well as that induced by bimatoprost and acids of latanoprost and travoprost. The agonist and antagonist potencies of the PG analogues from the PI turnover assays in h-TM cells correlated well with PI turnover data obtained from the cloned human ciliary body FP receptor (r = 0.92; P < 0.0001). CONCLUSIONS: The pharmacology of the h-TM cell FP-receptor-mediated PI turnover and [Ca(2+)](i) mobilization was defined using numerous synthetic (FP-selective) PG agonist analogues and an FP receptor antagonist, AL-8810. Bimatoprost, travoprost, latanoprost, unoprostone isopropyl ester, and their respective free acids were shown to be FP agonists in the h-TM cells.     

Asthenopia,Associated Phoria,and Self-Selected Prism

Abstract

Purpose: The vergence position of rest (phoria) has been found to vary over time. We asked whether the vergence position of rest is correlated with discomfort on reading.

Methods: We examined 20 subjects who reported strain on prolonged reading (“asthenopes”) and 20 subjects who did not (“non-asthenopes”). The eyes were normal in all subjects. Associated phoria (AP) was determined by asking the subjects to align monocular markers in the Mallett Near Vision Unit. In addition, subjects were asked to adjust Risley prisms so that viewing appeared most relaxing while they were looking at fully fusionable pictures (self-selected prism?=?SSP). Both AP and SSP were determined at near. Each subject participated in 6 sessions. Before each session, the subjects read a text for 30 minutes. Immediately afterwards they indicated on a visual analogue scale the discomfort they had experienced during the 30 minutes.

Results: In asthenopic individuals, AP fluctuated up to 19Δ, SSP up to 20Δ. In non-asthenopic individuals, AP fluctuated up to 17Δ, SSP up to 20Δ. The correlation between AP and SSP was r?=?0.73 (p?<?0.001) in the non-asthenopes and r?=?0.81 (p?<?0.001) in the asthenopes. Neither AP nor SSP were significantly larger in the asthenopes than in the non-asthenopes. Intra-individually, among the 6 sessions, the magnitude of discomfort was not significantly correlated to AP or SSP, neither in the asthenopes nor in the non-asthenopes. Asthenopes who rated their discomfort higher did not have a larger heterophoria.

Conclusion: The lack of a significant correlation between discomfort and (horizontal) heterophoria (determined as AP or SSP), especially intra-individually among repeated measurements, does not support a causal relationship.