Oxyopia, the Greek word meaning "acute vision," is the title of the weekly vision science seminars presented at the Indiana University School of Optometry in conjunction with graduate course V765. The seminars serve a twofold purpose in that they: stimulate intellectual activity among the faculty, and provide a learning environment for graduate students. Oxyopia presenters are IU School of Optometry faculty members and graduate students as well as visiting lecturers from other departments, universities, research facilities, private practices, industry, etc.

Oxyopia Fall 2009 Schedule

All seminars are held on Friday from 12:00 noon to 1:00 p.m. in Room 105 of the Optometry Building on the IU Bloomington campus unless otherwise stated. Seminar coordinator is Dr. Suresh Viswanathan.

Shining Light on Retinal Ganglion Cell Photoreception

Andrew Hartwick, OD, PhD
Assistant Professor
College of Optometry
The Ohio State University

In addition to its well-recognized role in vision, the retina provides the brain with a measure of the quantity of light (irradiance) in the environment.  This information serves to synchronize internal physiological rhythms to the external day/night cycle and to regulate the size of the pupil.  The neurons responsible for transmitting irradiance information to the mammalian brain include a small group of RGCs that express the photopigment melanopsin and are intrinsically light-sensitive.  In my research, I have been characterizing the light responsiveness of rodent melanopsin RGCs using both in vitro (recordings from wholemount retinas and isolated neurons) and in vivo (pupillary reflexes and circadian rhythm monitoring) methodologies.  A long-term objective of my research is to develop novel clinical tests that assess the functional capacity of retinal ganglion cell photoreception in patients with optic nerve disease.

Central and Peripheral Optics of the Eye: What do we know about their role in visual performance and ocular refractive status?

Larry Thibos, PhD
Professor
School of Optometry
Indiana University

Current theories about the cause of myopia progression include optical blurring of the retinal image of the peripheral visual field as a critical factor. The amount of optical blur present at any given point on the retina depends on four factors: stimulus vergence, accommodation, refractive error, and ocular aberrations.   Although correcting lenses are routinely prescribed to optimize the clarity of the foveal retinal image, the peripheral retinal image is also subject to numerous optical flaws such as curvature of field (i.e. defocus), off-axis astigmatism, the chromatic aberrations, and higher-order aberrations such as coma, spherical aberration, etc.  Characterization of these ocular flaws is necessary, but not sufficient, to determine the extent of degradation of the retinal image at each point in the visual field. We also require knowledge of how aberrations change with accommodation and how object vergence varies across the field.  The outcome of this interaction between the stimulus and the eye's optical system also depends on the optical characteristics across the visual field of contact lenses, spectacles, or other form of treatment.  Summarizing all relevant factors in a quantitative model of the eye at risk of myopia progression will enable the design of contact lenses with compensating aberrations that mitigate the critical features of retinal blur associated with myopia progression.

Neural basis of social cognition

Aina Puce, PhD
Professor
Psychological and Brain Sciences
Indiana University

Social cognition is the study of how individuals interpret the actions and intentions of others. By using functional magnetic resonance imaging and recordings of the electrical activity of the human brain (event-related potentials), it is possible to identify brain regions that are active in these processes, as well as examining the timing of this activity. I will present studies that we have performed in the lab over the last decade the deal with non-verbal communication, an area that is becoming a focus of study in this area. Our studies have identified specific neural signatures that are associated with processing of facial movements and also non-verbal vocalizations.  In future, these specialized brain responses might be used as a basis  for study social interactions in more naturalistic settings – allowing neuropsychiatric disorders with social cognition impairments to be studied more effectively.

On the Nature of Age-Related Changes in Visual Temporal Order Judgment Performance

Tom Busey, PhD
Professor
Psychological and Brain Sciences
Indiana University

In this talk I will describe the results of a large-scale multimodal study of temporal processing in 150 healthy Elder, 20 Middle Aged and 40 Young participants. I will focus on visual temporal order judgments and address the degree to which performance on these tasks is related to perceptual measures such as temporal contrast sensitivity, as well as cognitive measures such as the WAIS III set of measures. We find significant differences between young and elder participants in virtually all measures, and correcting for letter discriminability reduces but does not eliminate group differences. Thus there seems to be an age-related effect that is specific to temporal processing. We use factor analyses to look for common latent factors across tasks, and regression analyses to look for predictors from other tasks.

Outer segment renewal in living human cone photoreceptors

Ravi Jonnal, BS
Graduate Student - Miller lab
School of Optometry
Indiana University

In vertebrate eyes, the outer segment of the photoreceptor is the locus of the first stage of the visual process, phototransduction, which subjects it to the destructive effects of light exposure and oxidative stress.  To combat these effects, the outer segment undergoes a daily cycle of renewal, a process that has been studied for four decades using autoradiography and histology. While successful ex vivo, these approaches are fundamentally invasive and cannot be used to study the living eye. Here we show for the first time that renewal can be directly observed in the living human retina. Using a camera equipped with adaptive optics, which permits the resolution of individual cones, and temporally coherent illumination, which transforms the outer segment into a “biological interferometer,” we successfully measured the elongation rate of the outer segment of the photoreceptors in two volunteers. We determined that the interferometer is sensitive to changes in the outer segment length of 139 nm, twentyfold smaller than the axial resolution of ultra-high resolution optical coherence tomography, the best existing method for depth imaging of the living retina. Elongation of the outer segment causes the reflectance of the cone to oscillate at a Doppler frequency determined by the velocity of its receding tip.  This frequency was used to calculate the elongation rate, which ranged from 93 to 112 nm/hour.  Disc renewal is required for normal functioning of photoreceptors and studies have linked renewal abnormalities with leading causes of blindness. The method presented here is a new tool for studying the process of renewal and its role in disease in the living eye.

A meta-analysis on optical theories of the development of myopia

Christopher Clark, OD
Graduate Student - Thibos lab
School of Optometry
Indiana University

Animal models of refractive development suggest that the retina, independent of cortical feedback, responds to optical blur.  This response follows the sign of the defocus.  In addition, myopia development has been heavily associated with near work and/or lack of far work.  With this in mind, multiple optical theories of myopia development have been proposed including peripheral refraction, accommodative lag and near work induced transient myopia.  Unfortunately, most studies testing these models have disagreed with one another, lacked the sample size necessary to test the hypothesis and/or used questionable methods.  Meta-analysis provides a statistically valid method to compare between and across studies to determine the true effect.  It also gives estimates of the true population variance and between study differences such as study design, age effects and ethnic differences.  In this talk, seventy eight studies will be examined with a population pool of over 8000 subjects.  This method also has applications in study design, creating population based models, and Bayesian statistics.      

The development of Accommodation and vergence coupling

Danielle Warren Teel, OD
Graduate Student - Candy lab
School of Optometry
Indiana University

Neural coupling between accommodation and vergence (AC/A & CA/C ratios) is believed to assist coordination of clear and single binocular vision. Infants have narrow IPDs and typically hyperopic refractions, therefore requiring smaller vergence responses [in angular units of degrees or prism diopters (∆)] and larger accommodative responses (in diopters) than adults to binocularly fixate and focus on stimuli. The relative demands would also change with the growth of eye (decreasing hyperopia) and head (widening of IPD). The vergence demand in meter angles (m-1) would however be similar across all ages. Adult-like coupling between accommodation and vergence might therefore not be optimal during development and might lead to binocular abnormalities, like refractive esotropia that commonly manifests between 2 and 4 years of age. This study was designed to determine whether the couplings are optimized to avoid over-convergence with hyperopia in infants and young children.  Data will be presented that suggests that beneficial recalibration of neural coupling occurs in typically developing children, raising the question of what is different about refractive esotropes? 

Inflammation-Induced Pathologic Keratinization of the Ocular Surface

Shimin Li, PhD
Postdoctoral Fellow - Bonanno lab
School of Optometry
Indiana University

Squamous metaplasia occurs in ocular surface diseases like Sjögren’s syndrome (SS). It is a phenotypic change whereby epithelial cells initiate synthesis of squamous cell-specific proteins such as small proline-rich protein 1B (SPRR1B) that result in pathologic keratin formation on the ocular surface. Our hypothesis is that inflammation is a key inducer of pathologic keratinization and that SPRR1B represents an analytic biomarker for the study of the molecular mechanism. Real-time quantitative RT-PCR and immunohistochemistry were used to examine SPRR1B mRNA and protein in mouse model of dry eye and patients with SS. We found that the SPRR1B gene was induced in the mouse corneas and in ocular impressions of SS patients. This induction was mediated by two inflammatory cytokines, IL1β and IFNg. Two transcription factors, ZEB1 and CREB, were involved in the signaling pathways respectively. Our findings provide a definitive link between inflammation and squamous metaplasia in autoimmune-mediated dry eye disease.

What color naming can tell us about color vision

Delwin Lindsey, PhD
Professor
Department of Psychology
The Ohio State University

We review three interrelated lines of our research that involve the naming of colors. The first explores an analysis of color names used by speakers of the 110 unwritten world languages of the World Color Survey.  The second examines the role of color appearance in visual search.  The third concerns the perceptual scaling of colors.  Taken together, these results provide important insights into the interactions between chromatic processes that mediate color detection and appearance, and high-level cognitive processes that mediate category formation and the lexical partition of color space

Infant visual performance is limited by “mid-level” critical immaturities

Angela Brown, PhD
Professor
College of Optometry
The Ohio State University

We review our work for the last 25 years, which, as a whole, suggests that infants’ visual performance is critically limited by their poor sensitivity to contrast.  For example, infant Vernier acuity and stereopsis are critically limited by the difficulty infants have in seeing the contrast of the stimulus itself, rather than by higher-order difficulties in spatial or binocular vision.  Furthermore, infant luminance increment threshold functions and infant contrast discrimination functions place the contrast sensitivity limitation after the site of light adaptation, but before the site of contrast adaptation.  Thus, psychophysical performance of human infants is not limited by immaturities in high-level processes, such as inattention to the psychophysical task.

Axes and cardinal structures in astigmatic and heterocentric systems

William F. Harris
Department of Optometry
University of Johannesburg, South Africa

Optical, visual and other axes, and cardinal points, are all defined for stigmatic homocentric systems.   What happens in the case of the eye which is typically astigmatic and heterocentric?   Usually it is asserted that the eye has no true optical axis and the best one can have is an approximate axis.  As in the case of focal points one does not expect the eye to have true nodal or principal points in which case the eye has no true visual axis either.  However if the usual definitions are modified suitably it becomes possible to generalize all these concepts to allow for astigmatism and heterocentrism.  Cardinal points usually do not exist as points but become fuzzy yet well-defined structures.  It turns out that the typical eye does have a unique well-defined optical axis.  It also has a unique pair of visual axes, external and internal.  Nodal points expand into structures similar to Sturm's well-known focal interval with a pair of orthogonal focal lines, but nodal lines are not generally orthogonal.  Other structures are also possible in more extreme cases: there may be an isolated nodal line or no nodal line at all.  The same is true of principal points.  Nodal, principal and focal points turn out to be special cases of a general special structure.  Linear optics provides formulae for characterizing and locating special structures and optical and visual axes in an arbitrary eye of known structure.  [Background reading: Harris WF.  Optical axes of eyes and other optical systems.  Optometry and Vision Science 2009 86 537-541.]

Night Blindness and Skin Cancer: Insights Into The Enigma of Melanoma-Associated Retinopathy

Kenneth Alexander, PhD
Professor
Ophthalmology and Visual Sciences
University of Illinois at Chicago

A small percentage of patients with a malignant cutaneous melanoma develop night blindness, as well as other visual symptoms. This form of paraneoplastic visual disorder, termed “melanoma-associated retinopathy,” appears to involve a disturbance in signal transmission specifically within the retinal ON pathway. This presentation will discuss the use of electrophysiological, psychophysical, and immunolabeling techniques to provide new insights into the pathophysiology of this unusual visual disorder.

Two Controversies in Clinical Perimetry: Age Norms & the Role of the Magnocellular Pathway

William Swanson, PhD
Professor and Associate Dean
School of Optometry
Indiana University

Clinical Perimetry is in a time of transition: the FDA is re-evaluating the models for age norms used in different devices, and numerous studies have challenged the idea that early glaucomatous damage can be more readily detected by using frequency-doubling stimuli to target the magnocellular (M-) ganglion cells rather than the parvocellular (P-) ganglion cells.  This talk will address these two topics by presenting analyses of psychophysical age effects and of spike trains from M and P ganglion cells in response to conventional and frequency-doubling stimuli.