Biomedical subjects

Kenneth J Ciuffreda

Publications and source records attributed to Kenneth J Ciuffreda.

29 records · Page 2Linked to original sources

PubMed2004

Dynamic aspects of accommodation: age and presbyopia.

There has been no comprehensive study involving each of the primary dynamic components of accommodation in the same cohort as related to age and presbyopic onset; furthermore, the current findings are equivocal. Dynamic monocular components of accommodation (latency, time constant, peak velocity/amplitude relationship, and microfluctuations) were assessed objectively using an infrared optometer within the linear region of accommodation in 30 visually-normal human subjects aged 21-50 years. The time constant and the peak velocity/amplitude relationship did not change with age. However, latency progressively increased, and microfluctuation amplitude and frequency progressively decreased, with increasing age. The invariance in time constant suggests that the gross biomechanical aspects of the lens and related structures in the remaining linear region are relatively unaffected by age. In contrast, the decrease in microfluctuation activity with age suggests more subtle alterations in the biomechanical aspects of the lens to these very small perturbations, such as a response amplitude non-linearity. With respect to neurologic control, the progressive latency increase suggests a processing delay of the blur input, and this is consistent with age-related changes in reaction time measures. The lack of any age-related changes in the peak velocity/amplitude relationship implies normalcy of central and peripheral neuromotor control, as well as grossly normal first-order lens biomechanics, in this linear response region. The results are consistent with the Hess-Gullstrand theory of presbyopia.

Accommodation, Ocular↗

PubMed2004

Depth-of-focus of the human eye in the near retinal periphery.

Although the depth-of-focus in the foveal region has been well investigated, knowledge regarding the effect of retinal eccentricity on blur detection and sensitivity is limited. In the present study, the depth-of-focus at the fovea and in the near retinal periphery (0 degrees -8 degrees ) was assessed psychophysically in 7 human subjects using a 5 mm artificial pupil with accommodation paralyzed. The group mean total depth-of-focus progressively increased linearly from 0.89 D at the fovea to 3.51 D at a retinal eccentricity of 8 degrees at the rate of 0.29 D/degree, with response variability (S.E.M.) remaining relatively constant (+/-0.17 D). We speculate that the reduced detection and sensitivity to blur in the near periphery may be attributed to retinal topography, sharpness overconstancy, optical aberrations, and visual attention in peripheral vision.

Accommodation, Ocular↗

PubMed2004

A primer for the optometric management of unilateral spatial inattention.

BACKGROUND: Unilateral spatial inattention (USI) (a.k.a. neglect, unilateral neglect, visual neglect) is a common occurrence after stroke. It can also occur subsequent to traumatic brain injury. Insult to the right inferior (posterior) parietal cortex is the structure that is virtually always involved, although other brain areas have been implicated. The major consequence of USI is that the patient is unaware of one side of the body, and/or one side of visual space. Current literature expresses this as USI in the individual's personal, peri-personal, and extra-personal spaces. METHODS: We discuss the condition's natural history, occurrence and behavioral consequences. CONCLUSIONS: We propose a system for the optometric management of USI in extra-personal and peri-personal spaces.

Brain Injuries↗

PubMed2003

Static aspects of eye and head movements during reading in a simulated computer-based environment with single-vision and progressive lenses.

PURPOSE: Reading with two different intermediate progressive lens designs was investigated regarding eye and head movement patterns and compared with movement patterns with a conventional single vision lens in a computer-based work environment. METHODS: Two-dimensional eye (horizontal, vertical) and three-dimensional head (horizontal, vertical, and torsional) movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of moderate contrast (40%) single- and double-page text formats at 60 cm with binocular viewing. In addition, global reading ability was rated subjectively for each lens. Subjects were 11 visually normal, presbyopic individuals aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses: a single-vision lens (SVL; 60 degrees horizontal [H] clear field-of-view [FOV]); a progressive addition lens (PAL) with a relatively wide intermediate zone (PAL-I; 7.85 mm, 18 degrees H clear FOV); and a PAL with a relatively narrow intermediate zone (PAL-II; 5.60 mm, 13 degrees H clear FOV). RESULTS: Many reading-related parameters, as well as eye- and head-movement parameters, were adversely affected by the PALs compared with the SVL. One reading-related parameter (i.e., number of regressions) differentiated between PALs. Subjective rating of global reading ability was highest with the SVL and lowest with the PAL-II. CONCLUSIONS: The optical design of a spectacle lens had significant impact on reading performance and on the combined eye-head movements initiated during reading. Both horizontal eye and head movements discriminated well between PALs and the SVL, but not between PALs, despite subjective preferences. This suggests that nonoculomotor factors contribute to patients' nonacceptance of PALs. Vertical eye and head movements and torsional head movements were not as discriminatory as were their horizontal counterparts.

Aged↗

PubMed2003

Dynamic interactions of eye and head movements when reading with single-vision and progressive lenses in a simulated computer-based environment.

PURPOSE: To assess dynamic interactions of eye and head movements during return-sweep saccades (RSS) when reading with single-vision (SVL) versus progressive-addition (PAL) lenses in a simulated computer-based business environment. METHODS: Horizontal eye and head movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of single-page (SP; 14 degrees horizontal [H]) and double-page (DP; 37 degrees H) formats at 60 cm with binocular viewing. Subjects included 11 individuals with normal presbyopic vision aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses with a different clear near field of view (FOV): a SVL (60 degrees H clear FOV), a PAL-I with a relatively wide intermediate zone (7.85 mm; 18 degrees H clear FOV), and a PAL-II with a relatively narrow intermediate zone (5.60 mm; 13 degrees H clear FOV). RESULTS: Eye movements were initiated before head movements in the SP condition, and the reverse was found in the DP condition, with all three lens types. Duration of eye movements increased as the zone of clear vision decreased in the SP condition, and they were longer with the PALs than with the SVL in the DP condition. Gaze stabilization occurred later with the PALs than with the SVL in both the SP and DP conditions. The duration of head movements was longer with the PAL-II than with the SVL in both the SP and DP conditions. Eye movement peak velocity was greater with the SVL than the PALs in the DP condition. CONCLUSIONS: Eye movement and head movement strategies and timing were contingent on viewing conditions. The longer eye movement duration and gaze-stabilization times suggested that additional eye movements were needed to locate the clear-vision zone and commence reading after the RSS. Head movements with PALs for the SP condition were similarly optically induced. These eye movement and head movement results may contribute to the reduced reading rate and related symptoms reported by some PAL wearers. The dynamic interactions of eye movements and head movements during reading with the PALs appear to be a sensitive indicator of the effect of lens optical design parameters on overall reading performance, because the movements can discriminate between SVL and PAL designs and at times even between PALs.

Aged↗

PubMed2002

Differential refractive susceptibility to sustained nearwork.

PURPOSE: A possible role for nearwork-induced transient myopia (NITM) (i.e. transient myopia at distance following sustained nearwork) in the development and/or progression of permanent myopia has been suggested. If certain refractive groups are more susceptible to NITM than others, then measures may be implemented to prevent or retard the occurrence of myopia in these individuals. In a recent study (Ciuffreda and Wallis, 1998), it was found that young-adult late-onset myopes (LOM) and early-onset myopes (EOM) were highly susceptible to this NITM accommodative after-effect, while emmetropes (EMMs) were only moderately susceptible, and hyperopes (HYP) were particularly insusceptible, following short periods (10 min) of sustained nearwork at a very close distance (20 cm, 5 D). In the current study, this was extended to encompass a much longer period of nearwork under more naturalistic conditions. METHODS: Young-adult subjects (n = 16) performed a reading task for a continuous period of 4 h at their habitual working distance under naturalistic conditions, i.e. binocular viewing with blur-related visual feedback present. Distance refractive state (binocular viewing) was assessed objectively using a Canon R-1 autorefractor immediately before (pre-task), every hour during the task, and immediately after (post-task) to assess NITM and its subsequent decay to pre-task refractive levels. Subjects were divided into the four refractive subgroups as above, which were each of equal size (n = 4). RESULTS: The NITM was induced in all subjects, except for the hyperopes in which there was a hyperopic refractive shift. The LOMs (0.12 D) and EOMs (0.13 D) were highly susceptible, while the HYPs were especially insusceptible (0.44 D hyperopia), and the EMMs were only moderately susceptible (0.09 D). CONCLUSIONS: The present study extended our earlier investigation by demonstrating the differential refractive susceptibility over a longer period of sustained nearwork, which may be the result of reduced sympathetic activation. It has been speculated that NITM may be a factor in myopigenesis, with a possible mechanism being time-integrated increased retinal defocus from NITM at both distance and near, in conjunction with the normal lag of accommodation during sustained nearwork, thereby causing axial elongation. Hence, a future longitudinal investigation specifically targeting this retinal defocus hypothesis is warranted.

Accommodation, Ocular↗

PubMed2002

Assessing visual performance with progressive addition lenses.

PURPOSE: As a result of lens design limitations, progressive addition lenses (PAL's) present a limited field of view for tasks at intermediate distances, such as with computers. To assess whether this limitation results in diminished visual performance, PAL's were compared with single-vision lenses in four different types of reading tasks in a computer workplace environment. METHODS: Adult subjects performed four computer-based reading tasks using both single-vision lenses and PAL's at an intermediate distance of 64 cm. RESULTS: Single-vision lenses performed significantly better than PAL's in one task, with a trend for better performance in another task. There was no difference in performance for the remaining two tasks. CONCLUSIONS: Visual performance tests that involved stimuli subtending the widest visual angles and demanded more fixational shifts were more sensitive in discerning performance differences between the lens designs. In general, PAL's showed marginally diminished performance compared with single-vision lenses, presumably due to their restricted intermediate channel.

Adult↗

PubMed2002

The scientific basis for and efficacy of optometric vision therapy in nonstrabismic accommodative and vergence disorders.

BACKGROUND: For nearly 75 years, optometric vision therapy has been an important mode of therapy for both children and adults who manifested a range of nonstrabismic accommodative and vergence disorders. METHODS: In this article, the scientific basis for, and efficacy of, optometric vision therapy in such patients will be discussed. Using bio-engineering models of the oculomotor system as the conceptual framework, emphasis will be focused on studies that used objective recording techniques to directly assess therapeutically related changes in oculomotor responsivity. RESULTS AND CONCLUSIONS: The findings clearly support the validity of optometric vision therapy. Furthermore, the results are consistent with the tenets of general motor learning.

Accommodation, Ocular↗

PubMed2002

A 13-year followup of a case of Wallenberg's syndrome: first-person account and ocular motor abnormalities.

BACKGROUND: We present a 13-year followup of a case of Wallenberg's syndrome, including a first-person account and ocular motor abnormalities. METHODS: Objective infrared eye-tracking systems were used to record horizontal and vertical eye movements binocularly under a variety of conditions. RESULTS: Fixation in the dark along the midline remained as before, with vestibular jerk nystagmus continuously present. While saccades and pursuit to a visual target also remained the same as found earlier, fixation was somewhat worse, revealing not only saccadic intrusions but also a prominent right-jerk nystagmus. DISCUSSION: The results suggest lack of additional oculomotor neural plasticity after the end of the initial 10-year test period, and furthermore reveal apparent subtle age-related changes in oculomotor responsivity.

Eye Movements↗

PubMedDate not supplied

Depth-of-focus of the human eye: theory and clinical implications.

The depth-of-focus, or the perceptual tolerance of the human eye to retinal defocus, is important to and imbedded in many aspects of clinical refraction and physiological optics. Although the depth-of-focus is a common concept in classical optics, there is relatively little detailed discussion of its implications as related to normal vision function and to vision anomalies. With current advances in refractive surgery and ophthalmic lens design, the demand for knowledge in this topic is both timely and important. This review of our current understanding of the depth-of-focus should prove to be useful to clinicians, researchers, and students as an introduction to the subject. Two areas will be considered: 1) basic definitions of and factors affecting the depth-of-focus, and 2) its contemporary clinical implications.

Accommodation, Ocular↗

PubMedDate not supplied

Complex regional pain syndrome type I: associated visual sensorimotor case findings.

OBJECTIVE: The objective was to present new visual sensorimotor findings in a patient with complex regional pain syndrome type I, formerly known as reflex sympathetic dystrophy. DESIGN: Clinical measurements were compared for the following visual sensorimotor tasks before and after 10 minutes of near visual stimulation: accommodation, vergence, and reading eye movements. PATIENT: The patient was a 19-year-old female university student with complex regional pain syndrome type I. RESULTS: All visual sensorimotor findings worsened dramatically after performance of the brief near visual task. In addition, the patient experienced severe dizziness, nausea, dull eye ache, and general fatigue, which persisted for 30 to 45 minutes following each test period. CONCLUSIONS: The patient manifested signs and symptoms of complex regional pain syndrome type I per the prior neurologic diagnosis, as well as the newly diagnosed accommodative infacility, accommodative insufficiency, convergence insufficiency, and deficits of saccades and pursuits, which were severely debilitating. The findings neither support nor refute the conventional notion of abnormal sympathetic mediation as a mechanism of fatigue and pain. However, the diagnoses of accommodative infacility and insufficiency suggest abnormal parasympathetic activation. Further investigation is needed to characterize the array of visual dysfunctions in a large sample of such patients, which may help elucidate the precise underlying neurologic causes of the sensorimotor deficits in these patients.

Accommodation, Ocular↗