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PubMed1979

Dynamic contributions of the components of binocular vergence.

Experimental results from step stimulation of the two major dynamic components in ocular vergence showed that while fusional covergence dominated a coordinated binocular vergence movement, accomodative convergence always contributes to the dynamic response. A quantitative analysis of component dynamics, both in isolation and during coordinated movements, indicates that these components are additive at least through a portion of the movement. Two alternative hypotheses are presented for the role of accommodative convergence during the period immediately following a binocular vergence movement.

Accommodation, Ocular↗
PubMed1986

Photorefraction with a catadioptric lens. Improvement on the method of Kaakinen.

Kaakinen (1979) presented a method of measuring refractive error and ocular alignment by simultaneous photography of corneal and fundus reflexes. As presented, the technique was unable to detect refractive errors of less than 2-3 diopters (Howland 1980; Kaakinen 1979). We demonstrate that the use of a catadioptric lens and a long working distance can improve sensitivity to less than 1.0 D. Refractions of a model eye, an accommodating eye and ametropic eyes indicate that refractive errors greater than 0.75 D are readily detectable. The improvement in sensitivity achieved by the present system is attributable to a reduction of the angle between the flash source and the entrance pupil of the photorefractor.

Accommodation, Ocular↗
PubMedDate not supplied

Zonular function: a new hypothesis with clinical implications.

A new hypothesis about zonular function is presented that has implications in regard to the cause and treatment of ocular hypertension and open-angle glaucoma. This hypothesis is based on the concept that the lens is under constant tension. The anterior and posterior zonules serve a different function than do the equatorial zonules. The anterior and posterior zonules are passive in terms of structural support of the lens; the equatorial zonules are the active components during accommodation.

Accommodation, Ocular↗
PubMed1994

Changes in ocular and visual variables during the menstrual cycle.

For most women the menstrual cycle is an integral part of a major portion of their lives. There is widespread agreement about the hormonal changes that occur during the menstrual cycle, but studies of physical and psychological changes have been more controversial. The influence of the menstrual cycle on various ocular and visual variables has been investigated. These include the potential protective role of female sex hormones in some ocular conditions, reports of reduced tolerance to contact lens wear, and changes in visual performance during the cycle. This paper critically reviews the literature on visual and ocular changes across the normal human menstrual cycle. Stereotypical views of an impairment of performance premenstrually and during menstruation are challenged. The shortcomings of, and difficulties associated with, much of the research on this topic are highlighted.

Accommodation, Ocular↗
PubMed2005

Esotropia associated with early presbyopia caused by inappropriate muscle length adaptation.

BACKGROUND: The purpose of this study is to investigate the occurrence of esotropia accompanying early presbyopia. The two primary long-term mechanisms for maintenance of ocular alignment are vergence adaptation (neurologic) and muscle length adaptation (anatomic). Both mechanisms depend upon disparity-driven motor fusion for proper operation. A possible cause for an esotropic shift in early presbyopic adults with insufficient or absent disparity-driven motor fusion is inappropriate muscle length adaptation (medial rectus muscle shortening) occurring in response to increased convergence tonus accompanying increased accommodative effort. METHODS: Of 617 patients, age 10 and older who underwent surgery for esotropia during the period of 1980 to 1996, the age when the deviation occurred or worsened could be determined with confidence in 140. A plot was made of the number of these patients versus the age of onset of the deviation. This was compared with a similar plot of patients operated for exotropia. RESULTS: A statistically significant increase (P = 0.017) in the incidence of an esotropic shift in the age range from 30 to 50 years was found when compared with the incidence of an exotropic shift. CONCLUSION: If the postulated mechanism is correct, full correction of any hyperopia as well as prompt prescription of a reading add (or conversion to monovision correction) may help prevent further progression of small esodeviations accompanying early presbyopia.

Accommodation, Ocular↗
PubMed2003

The symptomatic patient with normal phorias at distance and near: what tests detect a binocular vision problem?

PURPOSE: Patients often manifest symptoms that appear to be related to binocular distress. Many of these patients have normal heterophoria at distance and near, making the etiology of such symptoms perplexing. We performed a visual examination of patients having normal heterophoria at distance and near in order to investigate which visual analysis tests differentiate symptomatic from asymptomatic patients. METHODS: Eighty subjects (30 symptomatic, 50 asymptomatic) with ages between 18 to 35 years of either sex and any race were pooled based on vision-symptom level determined by a 9-question standardized visual-symptoms questionnaire scored using a 100-point scale (asymptomatic: score > or = 85; symptomatic: score < or = 75). Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye, normal phorias, no latent cyclovertical heterophoria, and normal ocular health. RESULTS: Of the 30 symptomatic patients, 18 had reduced vergence facility response using 3 pd base-in/12 pd base-out loose prism at distance (n = 10; t-score = 2.41, p < 0.02, d = 76) and near (n = 15; t-score = 3.32, p < 0.01, df = 78) with a significant difference beyond the 0.02 level. No other test including measurement of accommodation, showed a significant between-group difference. However, three patients with normal vergence facility (distance and near) showed a reduced binocular accommodative facility response (+/-2.00 D at 40 cm). CONCLUSION: Given a patent with asthenopia, normal phorias, and visual acuity, a differential diagnosis may be made based primarily on using vergence facility and accommodative facility testing. From a clinical standpoint, the results expedite diagnosis of binocular vision abnormalities and direct treatment.

Accommodation, Ocular↗
PubMed1983

Border enhancement as a function of binocular fixation performance.

Traditionally, fixation disparity is measured by interocular vertical alignment of unfusable monocular targets. The disparity generally increases with forced ocular vergences, producing characteristic individual functions. This study explores a new method of monitoring binocular fixation performance; the method is based on the effect of the distance of the border stimulus from the foveal center on the lateral spread of border enhancement. That is, as this distance increases, the enhancement spread increases. It is found that, as increasing ocular vergence is applied, the enhancement also increases, in a manner resembling conventional fixation disparity measurements. However, some dissimilarities between the border enhancement functions and the conventional functions suggest that the directional values used as a basis for the latter undergo modifications.

Accommodation, Ocular↗
PubMed1993

Timing of amblyopia therapy relative to strabismus surgery.

BACKGROUND: It is taught that amblyopia must be fully reversed before surgery for esotropia is undertaken to achieve the best surgical outcome. In some cases, this means delaying surgery for many months. The alternative of operating early, before the completion of amblyopia therapy, and continuing to treat the amblyopia postoperatively has not been evaluated previously. METHODS: Forty-seven children younger than 8 years of age were identified with a history of both amblyopia and esotropia. They had no other ocular, medical, or neurologic abnormalities. They had no prior strabismus surgery. Of these 47 patients, 26 had their amblyopia fully treated before surgery, and 21 underwent surgery before completing amblyopia therapy. Five of the latter group did not require amblyopia therapy after surgery even though they were still amblyopic before operation. The motor outcome was assessed by comparing the motor alignment at 6 and 0.33 m using accommodative targets in primary position before surgery, at 6 months after surgery, and at the child's most recent visit. Motor success was defined in this study as a postoperative deviation at distance fixation of 8 prism diopters or less. The sensory result was assessed by comparing the frequency of detectable stereoacuity. RESULTS: The treatment groups did not differ significantly in age, depth of amblyopia, refractive error, or preoperative angle. There was no significant difference detected in motor or sensory outcome whether amblyopia was fully or only partially treated before surgery. CONCLUSION: Performing corrective surgery in children with esotropia before full resolution of amblyopia is safe and efficient if the amblyopia therapy is continued after surgery. This strategy permits earlier surgery without postponing the operation until full resolution of amblyopia. The finding that five patients did not require amblyopia therapy after surgery suggests that eye re-alignment itself can help reverse amblyopia in some cases.

Accommodation, Ocular↗
PubMed1978

Evaluation of drugs in ointment for mydriasis and cycloplegia.

Ointment preparations of cyclopentolate hydrochloride and tropicamide were compared with aqueous drops of these medications for the production of mydriasis and/or cycloplegia in clinic patients. Mydriasis and/or cycloplegia could be accomplished by the single application of a minute volume (around 0.005 ml) of ointment containing these drugs. With the use of ointment preparation, ocular irritation was minimal, and there was no interference with subsequent ocular examination. A delivery system was devised with a piece of silicone-rubber tubing that was filled with an ointment preparation. By squeezing the tubing, a minute volume (about 0.005 ml) of ointment preparation was expressed.

Accommodation, Ocular↗
PubMed2001

A comparison of noninvasive objective and subjective measurements of the optical density of human ocular media.

BACKGROUND: It is important for both researchers and clinicians to know the spectral composition of the light that reaches the retina. With this in mind, Johnson et al. developed a quick, objective instrument called the Lens Absorption Monitor (LAM) to measure the attenuation of light by the ocular media. Using a more refined method of measuring and correcting for scatter, we compared the results of the LAM against those with a subjective method utilizing a bipartite scotopic brightness-matching procedure (BIP). METHODS: We tested 41 healthy subjects (mean age, 35.9 years) with the LAM and BIP. RESULTS: Intereye correlation coefficients for the LAM were 0.70 at 410 nm and 0.83 at both 430 and 450 nm; for BIP, intereye correlation coefficients were 0.56 at 410 nm, 0.42 at 430 nm, and 0.38 at 450 nm. For optical density as a function of age, there was no statistically significant difference between the two instruments at 410 nm in either the slope (p > 0.43) or y intercept (p > 0.75). However, at both 430 and 450 nm, there was a significant difference in both slope (p < 0.001) and y intercept (p < 0.05) for the two instruments. CONCLUSIONS: With the latest refinements, LAM density measures correlated well with BIP estimates at 410 nm, but not at 430 or 450 nm. This underscores the fact that the LAM measures the spectral density of the anterior segment, whereas the BIP method is a measure of all the ocular media except for macular pigment. The difference between these two measures is consistent with the existence of a prereceptoral, presumably intraretinal, pigment (or pigments) located outside the anatomic fovea that absorbs light at short wavelengths.

Accommodation, Ocular↗
PubMed1984

Presbyopia and ocular motor balance.

Presbyopic case analysis generally involves determining the need for base-in prism. Common methods for prescribing prism, and components of convergence and the paradoxical lack of symptoms at near in presbyopic patients, and clinical measurement of fixation disparity are discussed in this context. Prism and vision therapy are treatment choices.

Accommodation, Ocular↗
PubMed2006

Low frequency temporal modulation of light promotes a myopic shift in refractive compensation to all spectacle lenses.

Emmetropization, the process by which ocular growth of young animals adapts to ensure focussed retinal images, can be disrupted by high frequency flicker, causing a hypermetropic shift. Emmetropization can also be disrupted differentially, in a sign dependent manner, by pharmacological alteration of the balance of activation of the ON and OFF retinal sub-systems in normal light or by rearing in an environment with a moving spatiotemporally varied diamond pattern (yielding local sawtooth illumination on the retina). Thus the aim of this experiment was to determine whether low frequency temporal modulation alone was sufficient to cause defocus sign-dependent interference with compensation. Chicks were reared for 6 or 7 days with monocular +/-10 D, 0 D, or No Lenses in a 12h light/dark cycle. Luminance of the environment was temporally modulated during the light cycle with a non-square wave profile pulse of 250 msec duration, with the illumination fluctuating between 1.5 and 180 lux at 1 Hz, 2 Hz, 4 Hz or with no flicker (0 Hz-180 lux). Final refractive state and ocular dimensions, measured using retinoscopy and A-scan ultrasonography, demonstrated that in the absence of temporal luminance modulation (0 Hz), chicks compensated to induced defocus in the expected sign-dependent manner. However, under 1, 2 and 4 Hz flickering light conditions, there was an overall myopic offset of approximately 6D across lens groups with refractive compensation to positive lenses more strongly inhibited. This myopic offset was reflected by increases in the depth of both vitreous and anterior chambers. However, luminance modulation had no effect on refraction or ocular parameters in the No Lens conditions. This is a hitherto unreported strong interaction between lens wear and low frequency temporally modulated light, with the refractive compensation mechanism being overridden by a generalized myopic shift.

Accommodation, Ocular↗
PubMed2002

Heart defects and ocular anomalies in children with Down's syndrome.

AIMS: To investigate whether ocular anomalies are associated with congenital heart defects in children with Down's syndrome. METHODS: 58 children with Down's syndrome were entered into a retrospective observational study. Children were assigned to heart defect groups based on medical records. Optometric tests had previously been carried out at the homes of the children. RESULTS: A relation between congenital cardiac defects, myopia, and nystagmus was observed. Heart problems were not related to accommodative insufficiency, hyperopia, or strabismus. CONCLUSION: In children with Down's syndrome heart defects were associated with both myopia and nystagmus.

Accommodation, Ocular↗
PubMed2006

Improvements in performance following optometric vision therapy in a child with dyspraxia.

SS, an 8-year-old boy with dyspraxia, presented for behavioural optometry assessment. He had been diagnosed with a subtle form of dyspraxia by his paediatric occupational therapist, based on poor proprioception, delayed bilateral integration and poor visual perception. A full visual assessment was carried out. SS was given a programme of reflex inhibition exercises for 3 months. Then, a programme of optometric vision therapy (OVT) exercises was prescribed at home and in practice for a period of 8 months. SS was assessed using a battery of occupational therapy Sensory Integration and Praxis Tests (SIPT) before optometric intervention, and after OVT. There were significant improvements in fusional reserves, accommodative facility and oculomotor control of pursuit and saccadic eye movements. His reading level had changed by 4 years in 11 months. The SIPT results showed improvements in the visual and motor/visual perception subtests, confirming the significant changes in visual perceptual performance. Consideration is given to treatment modalities for dyspraxia, and the studies confirming their effectivity of approach. This case study provides evidence supporting the use of OVT eye exercises in dyspraxia, ocular motility, accommodative dysfunction, learning difficulties and sports performance. The need for further research and inter-professional working is discussed.

Apraxias↗
PubMed2005

Study on the effects of monochromatic aberrations in the accommodation response by using adaptive optics.

The effect of asymmetric monochromatic aberrations in the accommodation response was studied by using an adaptive optics (AO) system. This approach permits the precise modification of ocular aberrations during accommodation. The AO system is composed of a real-time Hartmann-Shack wavefront sensor and a membrane deformable mirror with 37 independent actuators. The accommodation response was measured in two subjects with their normal aberrations and with the asymmetric aberrations terms corrected. We found a significant and systematic increase in the response accommodation time, and a reduction in the peak velocity, in both subjects when the aberrations were corrected in real time. However, neither the latency time nor the precision of the accommodation were affected. These results may indicate that the monochromatic aberrations play a role in driving the accommodation response.

Accommodation, Ocular↗
PubMed1977

[Ocular disturbances in asthenic neurosis and their treatment (author's transl)].

The author has studied over 200 cases of asthenic neurosis. The ocular manifestations could be classified into four clinical types according to the dominant ocular symptoms. 58.34% of these patients were female and 41.66% were male. 78% of the patients were between 20 and 40 years. 59% were students. In 75% of these cases a raised retinal blood pressure as an ocular manifestation was discovered. The ocular disturbances in asthenic neurosis are present especially in persons who regularly work more than 8 hours continuously. The treatment consists of physical and intellectual rest periods, sedatives, tonics, and connective tissue therapy with extracts of whole eyeballs. In 80% of cases we had favourable results.

Accommodation, Ocular↗
PubMed1987

Pharmacokinetic-dynamic study on different oral biperiden formulations in volunteers.

The pharmacodynamic and kinetic profiles of two oral biperiden formulations (tablet with instant-release and sugar-coated tablet with slow-release) were studied in a total of 12 healthy subjects after the administration of a 4 mg dose and compared in part to placebo. Biperiden as slow-release formulation showed much slower absorption than the instant-release tablet; whereas plasma levels peaked as early as 1-2 h after administration of the tablet, with the slow-release formulation a first peak was seen approximately 4.5 h after intake in the majority of the subjects. In some subjects this was followed by a trough, in others by formation of a shoulder at around 0.5 ng/ml. In all subjects a peak of about 1.0 ng/ml was reached after 10-12 h. The instant-release tablet and the slow-release formulation showed comparable bioavailability. Plasma concentrations for the slow-release formulation at 24 h were around 0.5 ng/ml, about twice as high as those for the instant-release formulation. The ratio of peak to 24 h values showed the marked reduction which is characteristic for a slow-release formulation compared with the instant-release tablet. The subjective well-being of the volunteers was not influenced by the slow-release formulation, whereas after the instant-release tablet slight CNS effects (dizziness, drowsiness and fatigue) were reported up to 6 h after ingestion. Furthermore, objectively quantifiable pharmacodynamic ocular parameters (near-point accomodation, pupil size) and the secretion of saliva proved to be less affected by the slow-release formulation than by the instant-release tablet, or not affected at all.

Accommodation, Ocular↗