Biomedical subjects

Kenneth J Ciuffreda

Publications and source records attributed to Kenneth J Ciuffreda.

At least 19 recordsLinked to original sources

PubMed2007

Conceptual model of human blur perception.

An empirically based, conceptual model of human blur perception is presented. It incorporates the concepts of blur detection and blur discrimination in depth, and across the central and peripheral retina, in two- and three-dimensional visual space. Key aspects of the model are its dynamic nature, predictability regarding the blur-based depth-ordering of objects, patterns of retinal defocus with far and near viewing, and interactions related to retinal defocus between the central and peripheral retina. Furthermore, a two-dimensional schematic representation of the blur-free region during near viewing is depicted in dioptric space. This model has implications with respect to accommodative control, depth perception, and refractive error development and progression.

Accommodation, Ocular↗

PubMed2006

Incremental retinal-defocus theory of myopia development--schematic analysis and computer simulation.

Previous theories of myopia development involved subtle and complex processes such as the sensing and analyzing of chromatic aberration, spherical aberration, spatial gradient of blur, or spatial frequency content of the retinal image, but they have not been able to explain satisfactorily the diverse experimental results reported in the literature. On the other hand, our newly proposed incremental retinal-defocus theory (IRDT) has been able to explain all of these results. This theory is based on a relatively simple and direct mechanism for the regulation of ocular growth. It states that a time-averaged decrease in retinal-image defocus area decreases the rate of release of retinal neuromodulators, which decreases the rate of retinal proteoglycan synthesis with an associated decrease in scleral structural integrity. This increases the rate of scleral growth, and in turn the eye's axial length, which leads to myopia. Our schematic analysis has provided a clear explanation for the eye's ability to grow in the appropriate direction under a wide range of experimental conditions. In addition, the theory has been able to explain how repeated cycles of nearwork-induced transient myopia leads to repeated periods of decreased retinal-image defocus, whose cumulative effect over an extended period of time results in an increase in axial growth that leads to permanent myopia. Thus, this unifying theory forms the basis for understanding the underlying retinal and scleral mechanisms of myopia development.

Animals↗

PubMed2006

Depth-of-focus: control system implications.

The depth-of-focus (DOF) plays a major role in accommodative control. It provides a neurological tolerance for retinal defocus and the perception of blur. Hence, the DOF has been an important component in bioengineering models of the accommodative system, but with its model-based control function limited to the fovea. However, new studies have demonstrated the influence of the near retinal periphery on the DOF: with increased target extent, the DOF increases. Thus, the blur control derived from the combined fovea and near retinal periphery should be incorporated into future models of accommodation.

Accommodation, Ocular↗

PubMed2006

Equiblur zones at the fovea and near retinal periphery.

Knowledge regarding successive blur discrimination thresholds (i.e., equiblur zones) in depth and across the near retinal periphery, and their relation to blur detection (i.e., depth-of-focus), remains unknown. The blur detection threshold and four successive blur discrimination thresholds were measured psychophysically at the fovea, as well as at retinal eccentricities of 0.25 degrees , 2 degrees , 4 degrees , and 8 degrees . A Badal optometer system was used to assess blur sensitivity monocularly in five visually normal young adults with cycloplegia. The foveal test stimulus consisted of a small irregularly shaped black form, and the peripheral test stimulus consisted of high contrast circular apertures of different radii. Both the group mean blur detection and successive blur discrimination thresholds progressively increased with retinal eccentricity. At retinal eccentricities of 0 degrees , 0.25 degrees , 2 degrees , 4 degrees , and 8 degrees , the group mean blur detection thresholds were 0.53+/-0.06 D, 0.59+/-0.10 D, 0.93+/-0.11 D, 0.98+/-0.16D, and 1.25+/-0.25 D, while the average values of the group mean blur discrimination thresholds across the steps were 0.29+/-0.01 D, 0.37+/-0.01 D, 0.48+/-0.00 D, 0.51+/-0.01 D, and 0.72+/-0.02 D, respectively. At each retinal eccentricity, the blur discrimination thresholds were similar to each other, and they were approximately 60% of the blur detection threshold magnitude. These findings provide a conceptual representation of blur perception throughout the central visual field. Possible mechanisms are proposed for the decreased blur sensitivity in the near retinal periphery, as well as for the difference between the blur detection and blur discrimination thresholds.

Adult↗

PubMed2006

Effect of blur adaptation on blur sensitivity in myopes.

Although blur adaptation in myopia has been investigated, knowledge regarding its effect on blur sensitivity remains unknown. In the present study, changes in three blur thresholds (i.e., noticeable, bothersome, and non-resolvable blur) were assessed monocularly after 1h of blur adaptation in myopes. A Badal optical system was used to present either an isolated 20/50 Snellen E or 20/50 lines of text, with the full text field used in the latter condition for all blur judgments. Eight visually normal adult myopes were tested with paralyzed accommodation. All subjects exhibited blur adaptation, with a significant improvement in group mean visual acuity of -0.16 LogMAR. There was a consistent and concurrent significant decrease of 0.15-0.19 D in all blur thresholds for the isolated 20/50 E. However, there was no significant effect of blur adaptation on blur thresholds for the 20/50 text, with large intersubject variability evident. The enhanced blur sensitivity for the isolated E target may in part be attributed to the increased visual resolution following blur adaptation. Differences found in the blur thresholds for the two targets may be related to a variety of neuroperceptual phenomena, in particular lateral masking.

Accommodation, Ocular↗

PubMed2006

Occurrence of ocular disease in traumatic brain injury in a selected sample: a retrospective analysis.

PRIMARY OBJECTIVE: To determine retrospectively the relative risk of ocular disease in a selected, visually-symptomatic sample of clinic patients having traumatic brain injury (TBI; n=160) vs. cerebrovascular accident (CVA; n=60), with all initially presenting at the clinic with symptoms and/or signs of vision dysfunction. METHODS AND PROCEDURES: To review retrospectively 220 medical records of individuals with TBI (n=160) vs. CVA (n=60), as determined by a computer-based query spanning the years 2000-2003, to ascertain the frequency of occurrence of ocular disease in the two major sub-groups of acquired brain injury. MAIN OUTCOMES AND RESULTS: Conditions with high relative risk unique to TBI included corneal abrasion, blepharitis, chalazion/hordeolum, dry eye, traumatic cataract, vitreal prolapse and optic atrophy. This is distinct from those ophthalmic conditions unique to CVA, which included sub-conjunctival haemorrhage and ptosis. CONCLUSION: These new findings should alert clinicians to the potential increased frequency of occurrence of specific ocular diseases in a selected, visually-symptomatic population with TBI and their associated rehabilitative and quality-of-life implications.

Adolescent↗

PubMed2006

Objective blur thresholds in free space for different refractive groups.

The aim of the current study was to measure the objective depth-of-focus (DOF) of myopes (MYO) in free space and compare them with emmetropic (EMM) and hyperopic (HYP) cohorts. The objective DOF was measured in 35 visually normal, young adults including 16 MYO, 13 EMM, and 6 HYP using the Power Refractor (PR II). The DOF was larger in the MYO and HYP than in the EMM. The larger objective DOF found in the MYO subgroup is in agreement with previous studies assessing the DOF subjectively. This finding is consistent with current thinking that increased amounts of retinal-defocus integrated over extended time may be myopiogenic. In agreement with earlier clinical and computer simulation studies, hyperopes demonstrate a relative resistance to increased retinal defocus.

Accommodation, Ocular↗

PubMed2006

Short-term adaptation to vertical yoked prisms.

PURPOSE: The purpose of this study was to investigate short-term adaptation to vertical yoked prisms in visually normal subjects as well as to develop normative data for future comparative purposes in patients with acquired brain injury. METHODS: A full-body enclosure containing a calibrated laser pointer was used to assess egocentric localization (i.e., one's perceived sense of "straight ahead") in total darkness. Fourteen visually normal subjects were tested in a counterbalanced manner under both experimental (20 pd base-down) and control (plano or zero power) test conditions with each test condition lasting 1 hour. A rating scale questionnaire was also administered to assess quantitatively subjective adaptation to the yoked prisms. RESULTS: Group mean egocentric localization showed approximately 50% adaptation during the 1-hour test period. Subjective adaptation results were similar. CONCLUSION: The findings suggest that rapid perceptually driven, sensorimotor adaptation occurred as assessed both objectively and subjectively in response to vertical yoked prisms. These results are similar to those found in other experiments involving short-term adaptation to optical rearrangements.

Adaptation, Ocular↗

PubMed2006

Oculomotor rehabilitation for reading in acquired brain injury.

The purpose of this study was to assess reading-related oculomotor rehabilitation in individuals with acquired brain injury. Adults with either stroke (n=5) or traumatic brain injury (n=9) participated. Training paradigms included single-line and multiple-line simulated reading, as well as basic versional tracking (fixation, saccade, and pursuit), twice per week over an 8 week period. Training modes included normal internal oculomotor visual feedback either in isolation (4 weeks) or concurrent with external oculomotor auditory feedback (4 weeks). Training effects were assessed objectively using infrared eye movement recording technology for simulated and actual reading, with the assessments occurring before, midway, and after training. In addition, the individuals were assessed subjectively using a reading rating-scale questionnaire. All reported considerably improved reading ability, and this was confirmed by several of the objective oculomotor measures. There was a trend for improvement to be better with the combined visual and auditory oculomotor feedback. Reading-related oculomotor rehabilitation produced significant gains in both the subjective and objective domains. It is believed that rapid saccadic oculomotor adaptation, as well as the training of rhythmicity and automaticity, were involved in modifying eye movement behavior to produce a more systematic approach and resultant improved reading profile.

Acoustic Stimulation↗

PubMed2005

An objective technique to measure the depth-of-focus in free space.

BACKGROUND: Determining the depth-of-focus (DOF) objectively in free space is important, as this provides information regarding the range of clear vision under more natural viewing conditions in which target blur, size, and proximal information, as well as other monocular depth cues, are present. METHODS: The DOF was assessed objectively in free space in young adults [n=20, ages 24.9+/-3.1years: myopes (n=14), emmetropes (n=5), hyperope (n=1)] by monitoring accommodation continuously using the commercially available Power Refractor II (PR II) under monocular viewing conditions. A high-contrast target ( approximately 83%) subtending a mean visual angle of 2.3 deg was placed on an optical bench at 25 cm (4 D) along the line-of-sight of the viewing right eye and was displaced slowly ( approximately 0.1-0.15 D/s) proximally and distally. This target provided blur, size, and proximal information, and other depth cues, as normally found in free space. The first consistent change in steady-state accommodative baseline level reflected one edge of the DOF. The mean dioptric difference between these distal and proximal endpoints was averaged, and this represented the total objective DOF. RESULTS: The group mean total objective DOF (n=20) was +/-0.61+/-0.09 D, with a range from +/-0.46 D to +/-0.81 D. Repeatability was excellent. CONCLUSION: A technique was developed and tested to measure the DOF in free space objectively. Further development of this technique will allow the assessment of blur perception under more complex natural viewing conditions simulating the everyday environment.

Accommodation, Ocular↗

PubMed2005

"Bothersome blur": a functional unit of blur perception.

Knowledge regarding the amount of blur perceived to be "bothersome" to an individual, namely that which is assumed to be annoying and to adversely affect task performance, remains limited. A Badal optical system was used to measure the blur detection, bothersome blur, and non-resolvable blur dioptric thresholds monocularly either to an isolated 20/50 or 20/200 Snellen E, or to three 20/50 lines of text. Subjects were comprised of 13 visually normal young adults and 3 absolute presbyopes. Cycloplegia was used to paralyze accommodation in the young adults. Within each target type for the young adults, the mean bothersome blur threshold was always significantly larger than that found for blur detection and significantly smaller than that found for non-resolvable blur. Across target types and blur criteria, the bothersome blur thresholds for the isolated 20/50 E (1.02 D) and the 20/50 text (1.34 D) were not significantly different, although in 12 of the 13 subjects the latter were larger (p<0.002, sign test). However, both were significantly smaller than for the isolated 20/200 E (1.80 D). In a subset of young adult subjects, bothersome blur was found to be repeatable over time. The results were similar in the absolute presbyopes. The bothersome blur threshold was primarily influenced by target detail and secondarily by target extent. These findings have important implications with respect to tolerances for optical lens design and refractive surgery outcomes, as well as provide insight into basic aspects of human blur perception.

Accommodation, Ocular↗

PubMed2005

Central and near peripheral retinal contributions to the depth-of-focus using naturalistic stimulation.

Although the depth-of-focus (DOF) has been investigated separately in the central retina and in the near retinal periphery, knowledge about their combined relative contribution to overall blur perception has remained unknown. In the present study, the DOF was measured psychophysically with a naturalistic pictorial stimulus as a function of spatial extent across the near retinal periphery under monocular Badal viewing conditions with accommodation paralyzed. The group mean total DOF progressively increased linearly with target size. Based on the individual DOF responses, the group was categorized into two subgroups: a predominantly centrally-driven and a centrally plus peripherally-driven subgroup. The results implicated partial cone pooling of blur information, as well as influence from perceptual, attentional, and optical aspects. However, the subgroup response profiles suggested individual differences in the weighting of the near peripheral blur information at the retinal level, and perhaps at higher-level areas of the visual system, involving spatial integration and global attentional processing.

Accommodation, Ocular↗

PubMed2005

Non-ptotic ocular myasthenia gravis: a common presentation of an uncommon disease.

BACKGROUND: Myasthenia gravis (MG) is an acquired autoimmune disease of the neuromuscular junction which causes rapid muscle fatigue and weakness. Two thirds of all cases of myasthenia gravis (MG) initially manifest ptosis. In the absence of the characteristic variable ptosis, MG can present a challenge to the clinician. This article will review the current diagnostic and management strategies for MG. CASE REPORTS: Five cases will be presented that did not initially present with ptosis. Each of these cases was previously misdiagnosed as a result of presentation of atypical myasthenia gravis signs and symptoms. The first two cases had signs and symptoms of a typical accommodative/vergence anomaly. The others manifested diplopia not normally associated with MG: one had a noncomitant vertical deviation; another had a stable 6(th) nerve palsy; and the third had a basic esotropia. CONCLUSION: Although the hallmark findings of MG are ptosis and eye muscle palsy with variability, MG may present without ptosis, affect nonstriated muscles, and/or manifest either as a nonstrabismic vergence anomaly or as comitant nonvariable strabismic deviation.

Adult↗

PubMed2005

Foveal blur discrimination of the human eye.

Although the effect of retinal defocus on the foveal blur detection threshold has been well investigated, knowledge regarding the foveal blur discrimination threshold is limited. In the present study, both thresholds were assessed psychophysically using the ascending method of limits at the fovea with accommodation paralyzed. The unidirectional blur detection threshold was 0.87+/-0.18 D (+/-1 S.E.M.). The subsequent blur discrimination thresholds were relatively constant and significantly smaller than the blur detection threshold, with an average value of 0.48+/-0.006 D (+/-1 S.E.M.). We speculate that the difference in magnitude between these two thresholds may be attributed to the defocus-related change in the ocular modulation transfer function (MTF) and its interaction with contrast discrimination ability, as well as to the presence of a neuroperceptual blur buffering mechanism.

Accommodation, Ocular↗

PubMed2005

The effect of apparent depth in pictorial images on accommodation.

The purpose of this study was to investigate the effect of the apparent depth of pictorial images on accommodation. Steady-state accommodation was assessed objectively while viewing eight pictorial stimuli containing varying degrees of monocular cues to depth. Sixteen young adult subjects were tested monocularly with accommodation either in the closed-loop or open-loop mode. Pictorial depth cues significantly influenced the mean level of accommodation under some of the open-loop conditions in which blur feedback was rendered ineffective. For nearly all stimuli and viewing modes, the mean accommodative responses were biased in the perceptually-appropriate direction, but they were larger in the open-loop condition. Apparent depth cues did not significantly affect accommodation under closed-loop viewing conditions, presumably because blur feedback markedly dampened any perceptually-driven influences. Consistent with current models of accommodation, and several earlier studies, perceptually-based accommodation had only a secondary effect on the overall accommodative response level under naturalistic viewing conditions, with blur dominating.

Accommodation, Ocular↗

PubMed2005

Blur discrimination of the human eye in the near retinal periphery.

BACKGROUND: Although blur discrimination in the foveal region has been investigated, knowledge regarding the effect of retinal eccentricity is limited. METHODS: The initial blur discrimination threshold and the blur detection threshold were assessed psychophysically and compared at the fovea and in the near retinal periphery (up to 8 degrees) with accommodation paralyzed. RESULTS: The blur discrimination and blur detection thresholds increased progressively with retinal eccentricity, with the latter being about twice as large and increasing twice as fast as the former. However, the group mean blur ratio between these two parameters remained relatively constant (0.56) with retinal eccentricity. CONCLUSIONS: The more sensitive blur discrimination vs. blur detection findings may be attributed to variation in the optical modulation transfer function with retinal defocus and to a perceptually based blur-buffering mechanism. The reduced blur sensitivity found with increased retinal eccentricity might be attributed to cone photoreceptor/ganglion cell sampling limitations, sharpness overconstancy, reduced visual attention, and slightly degraded visual optics.

Adult↗

PubMed2004

Oculomotor rehabilitation in acquired brain injury: a case series.

OBJECTIVE: To investigate the effects of systematic, oculomotor rehabilitation on basic versional ocular motility, as well as reading eye movements, in subjects with acquired brain injury, using objective eye movement recording and subjective rating of reading ability. DESIGN: Case series. SETTING: Clinical research laboratory. PARTICIPANTS: Two men with acquired brain injury: one with traumatic brain injury and one with stroke. INTERVENTIONS: Versional oculomotor training was performed for 1 hour, twice weekly for 8 weeks. There were 2 feedback modes of training: normal internal oculomotor visual feedback alone (4wk), or that feedback in conjunction with external oculomotor auditory feedback (4wk). Testing was conducted before and after training. Main outcome measures Objective outcome measures included both basic eye movement parameters (fixational accuracy, saccadic gain and latency, pursuit gain, mean saccade frequency ratio for simulated reading), and reading eye movement parameters (words per minute, grade level equivalent, fixations per 100 words, regressions per 100 words, percentage of reading comprehension, duration of fixation in seconds). Subjective outcome measures included the subject's ability to read based on the responses to the reading rating-scale questionnaire. RESULTS: Both subjects improved objectively in terms of basic versional oculomotor accuracy and reading ability. These findings concurred with their subjective impressions. CONCLUSIONS: This case series provides objective documentation of the positive effects of oculomotor rehabilitation on basic ocular motility and reading ability in selected cases with acquired brain injury, thus suggesting the need for a larger clinical trial in this area.

Adult↗

PubMed2004

Reading-related oculomotor testing and training protocols for acquired brain injury in humans.

Many individuals with acquired brain injury (ABI) report reading problems of oculomotor origin. These may include frequent loss of place, skipping of lines and difficulty shifting to the next line of print. We describe two protocols for the testing and training of reading-related eye movements in adult individuals with ABI (traumatic brain injury [TBI] and stroke with hemianopia), who experience oculomotor-based symptoms when reading. These protocols use objective eye movement recording techniques and computer-based stimulus presentation and analysis. One protocol tests and the other trains basic horizontal and vertical versional eye movements (fixation, saccades and pursuit), as well as reading eye movements using simulated single and multiple line dynamic arrays. In addition, a reading rating-scale questionnaire is administered before and after completion of training to assess subjective reading improvement. In all paradigms, the target consists of a 0.5 degrees luminous square, which is displayed on a computer monitor positioned 40 cm from the subject along the midline. All testing and training are conducted under binocular viewing conditions with optical correction in place. There are two modes of training: normal internal oculomotor visual feedback either alone (4 weeks) or in conjunction with external oculomotor auditory feedback (4 weeks) administered in a counterbalanced manner within each diagnostic group. Training is performed 1 h, twice weekly for the 8 weeks. Oculomotor testing is conducted before, midway and after training. Following training, reading-related eye movements and reading ability improved as assessed both subjectively and objectively. These protocols provide a systematic approach to the quantitative and comprehensive testing and training of reading-related eye movement skills and behaviors in the ABI population manifesting oculomotor-based reading dysfunctions. Furthermore, the training protocol results in the rapid remediation of the eye movement deficits, which appear to transfer to activities of daily living.

Brain Injuries↗