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PubMed1990

Accommodative convergence in hypermetropia.

We compared the clinical characteristics of esotropic, hypermetropic children whose strabismus was fully corrected with spectacles (refractive accommodative esotropia) with those who remained orthotropic (that is, had no manifest strabismus on the cover test) in the presence of uncorrected hypermetropia. In addition to a standard ophthalmologic and orthoptic examination, we determined the stimulus accommodative convergence/accommodation (AC/A) ratio by using the gradient method over a range of 6 diopters, the near point of accommodation, and random dot stereopsis. Hypermetropic patients without esotropia or significant esophoria were found to have a low AC/A ratio in contrast to those patients with refractive accommodative esotropia. This finding explains why esodeviations may be absent in some hypermetropic patients with uncorrected vision. We found a high prevalence of abnormally low near points of accommodation and defective or absent stereopsis in both groups of patients.

Accommodation, Ocular↗
PubMed1988

Accommodation and convergence insufficiency with left middle cerebral artery occlusion.

We studied accommodation and vergence eye movements in a patient with a left middle cerebral artery embolism. Accommodation was monitored by an infrared optometer with the accommodative target being controlled by a microcomputer. Computed tomography showed low-density areas in the left cortex, with intact brainstem. The patient had convergence palsy and accommodation abnormalities. The amplitude of the accommodative responses was reduced and the accommodation velocity was markedly lowered. Our results further substantiate the neurologic relationship between the cerebral cortex and accommodation and convergence.

Accommodation, Ocular↗
PubMed1978

Anticholinesterase-induced cholinergic subsensitivity in primate accommodative mechanism.

I treated cynomolgus monkeys with topical echothiophate iodide twice daily for several months. Accommodative responses to topical or intramuscular pilocarpine were determined after ciliary ganglion or cholinergic nerve blockade. During echothiophate treatment, there was little or no accommodative response to intramuscular pilocarpine doses which were near maximal in nonechothiophate-treated eyes. Similarly, echothiophate-treated eyes demonstrated little or no response to topical pilocarpine doses that were more than 50 times supramaximal in nontreated eye. Within two weeks after stopping echothiophate, accommodative responses to intramuscular pilocarpine had returned noticeably, and by seven weeks after stopping echothiophate, sensitivity to intramuscular pilocarpine had increased to 30 to 50% of control levels. The findings are compatible with acetylcholine-induced cholinergic subsensitivity of the ciliary muscle.

Accommodation, Ocular↗
PubMed1983

Apparent accommodation in pseudophakic eyes after implantation of posterior chamber intraocular lenses.

We measured apparent accommodation in 42 pseudophakic eyes (34 patients) after implantation of posterior chamber intraocular lenses. The mean apparent accommodation was 2.03 +/- 1.03 diopters. The mean accommodative power of 16 phakic eyes used as controls was 2.91 +/- 1.29 diopters. The diameter of the pupil appeared to be the most important factor in apparent accommodation--the smaller the pupil, the greater the apparent accommodation. Apparent accommodation was inversely proportional to the pupillary diameter. There was no correlation, however, between apparent accommodation and corrected visual acuity, refractive error, corneal astigmatism, or axial length. There was a negative correlation between apparent accommodation and anterior chamber depth.

Accommodation, Ocular↗
PubMed1978

Efficacy of bifocals in the treatment of accommodative esotropia.

We treated 84 patients with a partially refractive accommodative esotropia with bifocals. Twelve patients were able to fuse without bifocals at the end of therapy; in 19, the bifocal power could be reduced and further improvement can be expected in the future. Thirty-nine remained dependent on bifocals; and in 14, fusion had deteriorated in spite of therapy. Patients with a high AC/A ratio and those receiving supportive orthoptic treatment seemed to fare best with bifocals. In those with a low AC/A ratio, fusion tended to deteriorate because of a slowly increasing esodeviation at near fixation.

Accommodation, Ocular↗
PubMed1999

Adie syndrome: evidence for refractive error and accomodative asymmetry as the cause of amblyopia.

PURPOSE: To report objective changes in accommodation in a child with Adie syndrome. METHODS: A child aged 2 years 10 months when initially examined was found to have good visual acuity in both eyes, a low degree of hypermetropia (isometropic), and Adie pupil presumed to be caused by chicken pox that had occurred 2 months earlier. Amblyopia developed but responded well to treatment, which involved correction of the refractive error and occlusion therapy. Objective changes in the refraction of the eye were measured on the Canon R1 autorefractor at 3.8 m and 33 cm. RESULT: The degree of accommodation in the affected eye when both eyes were open was markedly reduced. CONCLUSION: The presence of isometropic hypermetropia, which remains uncorrected when Adie syndrome is present, can lead to the development of amblyopia in a child.

Accommodation, Ocular↗
PubMed1999

Industrial inspection performance depends on both viewing distance and oculomotor characteristics.

The influence of viewing distance and individual differences in the oculomotor resting states (dark vergence and dark focus) on both inspection performance and visual fatigue was investigated by asking 24 college students to perform a visual inspection task for 40 min twice, once with a 20 cm viewing distance and once with a 60 cm viewing distance. During the task participants visually searched enlarged images of contact lenses for six different types of defects. Lens images were presented at a constant visual angle (17.5 degrees) on a CRT. Inspection performance varied significantly across the two viewing distances: participants spent on average more than twice as much time inspecting individual lenses in the near condition (mean = 18.32 s lens(-1)) than in the far condition (mean = 7.25 s lens(-1)). Participants also reported greater visual fatigue in the near condition than in the far condition. At both viewing distances, participants who experienced relatively large inward shifts in dark vergence also tended to be slow inspectors. Neither inspection performance nor measures of fatigue were related to dark focus. These results support existing evidence against the use of near viewing distances and suggest that an oculomotor mechanism links inspection performance and visual fatigue to viewing distance.

Accommodation, Ocular↗
PubMed1999

Developing visual systems and exposure to virtual reality and stereo displays: some concerns and speculations about the demands on accommodation and vergence.

Little is known about the developmental plasticity of the vergence and accommodative systems, an important issue since abnormalities can lead to visual problems, e.g. strabismus. One way of artificially altering the links between accommodation and vergence is to vary the stimulus to vergence while fixing the accommodative stimulus, as is found in virtual reality displays. While it would be of interest to study developmental plasticity in this situation, since many children are exposed to games machines which use this arrangement, no studies to date have tackled this issue. There is, however, some indication that long-term VR viewing in adults can lead to visual problems. It seems important to determine the safety of these systems for the developing human visual system before they come into common use. In this paper, adaptation of the accommodation and vergence systems and the effect of VR viewing in adults is discussed. The sparse literature on adaptation in children is then reviewed, and suggestions made for approaches that would enhance our knowledge of plasticity of accommodation and vergence in children.

Accommodation, Ocular↗
PubMed2003

Presbyopia complicating pre-existing strabismus.

BACKGROUND: Presbyopia may affect pre-existing sensory adaptations or aggravate previously asymptomatic heterophoria. We describe the presentation, underlying problem and management of 11 patients with pre-existing strabismus or heterophoria who presented with new symptoms of double vision attributable to presbyopic change, an association not previously reported. METHODS: Patients with new strabismic symptoms attributable to presbyopia were recruited prospectively over a 1-year period. RESULTS: The 11 patients had had a recent decrease of accommodative amplitude that resulted in blurred vision at near with a breakdown of pre-existing heterophoria (2 patients), alteration of fixation pattern (6 patients), symptomatic alternating fixation (2 patients) or intolerance to correction owing to restrictive strabismus (1 patient). INTERPRETATION: At the onset of presbyopia, symptoms may be varied and subtle. Ophthalmologists and orthoptists should carefully determine the exact nature of the symptoms. Any pre-existing fixation pattern should then be established from the history, old photographs or suppression characteristics. Refractive or surgical management should be aimed at returning the patient to his or her long-standing sensory adaptation. Other important issues, such as incomplete correction of hypermetropia by refractive surgery and problems using bifocals with vertical restrictive strabismus, should be noted.

Accommodation, Ocular↗
PubMed1995

Age-related response of human lenses to stretching forces.

Five human lenses of varying ages were subjected to radial stretching forces which mimic the action of the ciliary muscle in vivo. Although the number of lenses was small, it was found that the human lens becomes more resistant, with age, to radial stretching forces and that lenses over the age of 50 years showed very little response to stretch. In prepresbyopic lenses, stretching has a greater effect on the shape of the anterior surface than it does on the shape of the posterior surface. The five lenses studied showed individual variations in lens size and shape and a trend to increased curvature with age, particularly marked for the anterior surface.

Accommodation, Ocular↗
PubMed1987

Slit-lamp studies of the rhesus monkey eye: II. Changes in crystalline lens shape, thickness and position during accommodation and aging.

Changes in crystalline lens shape and axial thickness, anterior chamber depth and anterior cornea-posterior lens distance during accommodation induced by corneal iontophoresis of carbachol or electrical stimulation of the Edinger-Westphal nucleus were studied in 25 living, surgically aniridic rhesus monkey eyes, aged 1-25 years. Intraocular distances and anterior and posterior lens surface curvatures were evaluated from slit-lamp Scheimpflug photographs; distances were also determined by A-scan ultrasonography. With increasing accommodation, both lens surfaces become more sharply curved, the lens thickens and the anterior chamber shallows, while the posterior lens surface remains fixed relative to the cornea. Within statistical limits, the respective curvature and distance changes are the same for a given dioptric accommodation induced by either stimulation technique. The respective intraocular distance-accommodation relationships are identical whether derived from photographic or ultrasonographic measurements. Temporal and contralateral reproducibility of all measurements is excellent. Each parameter-accommodation relationship is strikingly linear in all eyes, although above 20 D the slopes of the lens surface curvature-accommodation relationships may have decreased. The curvature change per D of accommodation averages approximately 20% more for the posterior than for the anterior lens surface. There is relatively little interindividual variation in the slope of each relationship despite the significant interindividual differences in age and accommodative amplitude, indicating that the relationships are independent of age. However, when extrapolated back to the non-accommodated resting state, the data indicate that the lens thickens, both its surfaces become more sharply curved, and the anterior chamber shallows with age in adult greater than 5 years, while opposite trends are seen in younger animals.

Accommodation, Ocular↗
PubMed1988

Slit-lamp studies of the rhesus monkey eye: III. The zones of discontinuity.

The rhesus monkey lens exhibits two zones of discontinuity, one anteriorly and one posteriorly. They are first discernible by slit-lamp photography as performed in this study at around age 7 years in iridectomized eyes, and become more distinct with increasing age. Their thickness and distance from each other along the polar axis are independent of lens age, but their distance from the lens surface increases with increasing age. Upon accommodation, the distance between the two zones increases while all other distances along the polar axis remain unchanged, indicating that, as in the human, overall alterations in rhesus lenticular shape and thickness with accommodation primarily reflect changes in the shape of the central region. The curvature of each zone becomes sharper in a linear fashion with accommodation, with the slope of the relationship being similar to those for lens surfaces.

Accommodation, Ocular↗
PubMedDate not supplied

Dynamic asymmetries in convergence eye movements under natural viewing conditions.

PURPOSE: To clarify differences in the dynamics of convergence eye movements in response to symmetrical stimuli between the dominant eye and the nondominant eye under natural viewing conditions. METHODS: This study was conducted in 11 normal volunteers (age range, 22-30 years). The subject was seated on a chair, and the head was fixed using a bite-block. The dominant eye was determined with the "hole-in-the-card" test. Horizontal positions of the eyes were recorded using an infrared reflection device. Recordings of right eye movements were subtracted from left eye movements to obtain the vergence response. The fixation target was moved toward the center of both eyes from 50 to 20 cm in front of the face at a constant velocity in five steps (20, 30, 40, 50, and 60 cm/s). The target was moved by a pulse motor controlled by a microcomputer. The dynamic properties of each eye movement and the vergence components were analyzed. RESULTS: At velocities < or =40 cm/s, convergence responses consisted of two components: the fusion-initiating component and the fusion-sustaining component. The fusion-initiating component drove the initial faster dynamic portion of the response, and the fusion-sustaining component maintained the latter slower dynamic portion of the response. The mean peak velocity of the fusion-initiating component was significantly greater in the dominant eye than in the nondominant eye. The mean peak latency of the catch-up component was significantly shorter in the dominant eye than in the nondominant eye. CONCLUSIONS: The present study indicated that the trajectory of convergence eye movement under natural viewing conditions consists of two components, the fusion-initiating component and the fusion-sustaining component, and that the convergence response to symmetric stimuli was asymmetric between the dominant eye and the nondominant eye during the fusion-initiating phase. The neural control system of convergence eye movements preferentially drives the dominant eye during the fusion-initiating phase of the response.

Accommodation, Ocular↗
PubMedDate not supplied

Accommodation and pupilloconstriction areas in the cat midbrain.

The results of our previous studies suggest that the rostral superior colliculus (SC) is involved in the control of accommodation in the cat. The accommodation-related area in the rostral SC projects into the pretectum and the mesencephalic reticular formation (MRF), indicating that these areas may also be involved in the control of accommodation. In this study, we tried to identify cat midbrain areas of accommodation and pupilloconstriction control by systematically mapping microstimulation responses. Three regions were found to evoke the accommodation response: the posterolateral pretectum, including the nucleus of the optic tract and the posterior pretectal nucleus; the posteromedial pretectum, including the nucleus of the posterior commissure (NPC) and adjacent commissural fibers; and the MRF area dorsolateral to the oculomotor nucleus. Pupilloconstriction was evoked by microstimulation of the posteromedial pretectum around the NPC and the anterior pretectum around the olivary pretectal nucleus.

Accommodation, Ocular↗
PubMedDate not supplied

Adrenoceptors affect accommodation by modulating cholinergic activity.

In an attempt to clarify the functional role of adrenoceptors in accommodation, the effects of various adrenergic agents on the state of accommodation were studied. Fifty-two emmetropic, visually normal subjects (24.6 +/- 0.42 years old) participated in this study. Using an infrared optometer, the far and near points of accommodation were measured by a quasistatic method. Tonic accommodation and accommodative adaptation were also investigated. All these parameters were measured before and after topical application of various adrenergic agents. Both bunazosin hydrochloride (0.1%) and phenylephrine hydrochloride (5%) had no effect on tonic accommodation and accommodative adaptation. However, bunazosin hydrochloride increased the near point of accommodation. Timolol maleate (0.5%) and isoproterenol hydrochloride (3.0%) did not affect tonic accommodation. Isoproterenol hydrochloride evoked a hyperopic shift of the far point of accommodation by 0.23 +/- 0.42 diopters (D). Additionally, accommodative adaptation was increased by timolol maleate (0.36 +/- 0.62 D) and decreased by isoproterenol hydrochloride (0.18 +/- 0.48 D). These results indicate that both alpha and beta adrenoceptors affect accommodation. Activation of alpha adrenoceptors increased the near point of accommodation and activation of beta adrenoceptors decreased accommodative adaptation, which suggests that activation of adrenoceptors may modify parasympathetic activity; hence, affecting the state of accommodation.

Accommodation, Ocular↗
PubMedDate not supplied

Voluntary nystagmus associated with accommodation spasms.

BACKGROUND: Voluntary nystagmus has been recognized as a pendular, rapid, conjugate, primarily horizontal, benign eye movement initiated and maintained by voluntary effort. CASE: A 10-year-old Japanese girl presented with voluntary nystagmus associated with accommodation spasms. Her chief complaints, intermittent blurred vision, headache, and soreness of the eyes, were thought to be related to the voluntary nystagmus and accommodation spasms. FINDINGS: The waveform of the nystagmus appeared pendular, the frequency was 13-15 Hz, and the amplitude was 3-5 degrees. Scanning laser ophthalmoscopic video images clearly demonstrated vertical and torsional components in addition to the horizontal eye movements. Her refraction was unstable, varying between -0.5 diopters (D) and -5.5 D, and the recording of the accommodometer increased to -12.0 D when nystagmus was initiated. CONCLUSIONS: This may be a unique form of voluntary nystagmus that consists of horizontal, vertical, and rotational components associated with accommodation spasms. Observation of this patient continues, without any further treatment or examination.

Accommodation, Ocular↗