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PubMed1987

Treatment of partly accommodative esotropia with a high accommodative convergence-accommodation ratio.

We conducted a prospective, randomized, masked comparison of two treatments for the nonaccommodative element in esotropic patients with a high accommodative convergence-accommodation ratio. One group received symmetric medial rectus recessions with posterior fixation sutures; the other received symmetric medial rectus recessions without posterior fixation sutures but augmented according to formula taking into account the near deviation. Previous experience had suggested that our surgical formula based solely on the distance deviation would lead to excessive undercorrections. A higher percentage of the augmented recession group achieved satisfactory alignment and were able to discontinue wearing bifocals postoperatively than the posterior fixation group. The data also showed a trend (though not statistically significant) suggesting that more members of the augmented recession group were able to discontinue wearing spectacles entirely. We concluded that the posterior fixation suture technique is not as effective as the augmented recession technique for the treatment of partly accommodative esotropia with a high accommodative convergence-accommodation ratio.

Accommodation, Ocular↗
PubMed1989

Should recessions of the medial recti be graded from the limbus or the insertion?

In a series of 27 patients who were operated on for esotropia, we compared patient response to surgery and the distance the medial recti were recessed from the insertion and corneoscleral limbus. We found a much more significant correlation between the response and the amount the muscles were recessed from the insertion than from the corneoscleral limbus. Using partial correlation coefficients, we found that when we corrected for the amount of recession from the insertion, there was not a significant correlation between the response to surgery and the amount the muscles were recessed from the corneoscleral limbus. This suggests that the apparent correlation between the response to surgery and the amount of recession from the corneoscleral limbus simply reflects that the greater the recession from the corneoscleral limbus, the farther the muscle is likely to end up posterior to the insertion.

Accommodation, Ocular↗
PubMed1990

In vivo videography of the rhesus monkey accommodative apparatus. Age-related loss of ciliary muscle response to central stimulation.

Fourteen rhesus monkeys, aged 1 to 24 years, underwent permanent implantation of a bipolar stimulating electrode into the Edinger-Westphal nucleus and complete unilateral or bilateral iridectomy. Slit-lamp Scheimpflug videography of the lens and slit-lamp goniovideography of the lens equator, zonule, and ciliary body allowed direct real-time observation and video recording of the movements of these structures during centrally stimulated accommodation and during disaccommodation. Scalloping of the lens capsule at the zonular insertion sites was clearly visible during disaccommodation and even during accommodation when the zonules were folded. During accommodation, the lens became axially thicker, the ciliary ring narrowed, and, at high levels of accommodation, the zonular fibers slackened and even folded and the lens moved downward. With increasing age and concomitantly decreasing accommodative amplitude, these excursions all diminished, so that in the oldest animals, they were very minimal or absent. Maximum centrally stimulated accommodative amplitude declined with age on a time scale similar to that for cholinomimetic drug-induced accommodation in the rhesus monkey and voluntary accommodation in the human.

Accommodation, Ocular↗
PubMed1991

Outflow facility and its response to pilocarpine decline in aging rhesus monkeys.

Refractive error and total outflow facility were determined by Hartinger coincidence refractometry and two-level constant-pressure perfusion, respectively, in 17 rhesus monkeys, aged 5 to 29 years. Maximum accommodative response to corneal (iontophoretic) carbachol hydrochloride, baseline outflow facility, and the facility response to strong but submaximal intracameral doses of pilocarpine hydrochloride all declined with age. The correlation between accommodative response to carbachol and facility response to pilocarpine was slightly stronger than that between age and facility response. Since the ciliary muscle plays a major role in controlling both outflow facility and accommodation, and since histologic and videographic techniques demonstrate an age-related decline in rhesus ciliary muscle excursion induced by topical pilocarpine or electrical stimulation of the Edinger-Westphal nucleus, the present data support the hypothesis that an age-related decline in ciliary muscle mobility is associated, perhaps causally, with an age-related decline in facility and facility responsiveness to cholinergic drugs.

Accommodation, Ocular↗
PubMed1995

Partly accommodative esotropia. Should you overcorrect and cut the plus?

OBJECTIVES: To investigate the long-term motor stability and sensory outcome of patients with partly accommodative esotropia who were overcorrected surgically and in whom the hyperopic correction was reduced postoperatively, and to determine if those results depended on the amount of hyperopia present. DESIGN: A 15-year prospective study that analyzed 5-year outcome. Patients whose esotropia was not initially overcorrected were used as controls. PATIENTS: Of 382 patients who underwent surgery for partly accommodative esotropia, 22 were surgically overcorrected and were followed up for 5 years. RESULTS: Of the eight patients in the study group with 2.5 diopters or less of hyperopia in their fixing eye, seven had good motor alignment compared with four of 14 patients who had more than 2.5 diopters of hyperopia. Ninety-one percent (148/163) of the control patients who had greater than 2.5 diopters of hyperopia maintained good motor alignment 5 years after surgery compared with 29% of the study group patients. This difference was statistically significant. Of the eight study patients with less than 2.5 diopters of hyperopia, five developed good stereopsis compared with one of 14 patients with greater hyperopia. CONCLUSIONS: Surgical overcorrection in patients with partly accommodative esotropia with greater than 2.5 diopters of hyperopia may not be reversible by postoperative reduction in the hyperopic correction. It often is reversible, however, in patients with 2.5 diopters or less of hyperopia.

Accommodation, Ocular↗
PubMed1996

Aging effects on accommodation and outflow facility responses to pilocarpine in humans.

OBJECTIVE: To determine the relationships among age, outflow facility, and refractive and facility responses to pilocarpine in humans. METHODS: Refraction, intraocular pressure, and outflow facility were determined in 30 normal volunteers aged 20 to 75 years, by coincidence refractometry, applanation tonometry, and Schiøtz tonography, respectively, before and 1 hour after a 30-microL drop of 2% or 6% pilocarpine. Simple regression of baseline facility, postpilocarpine facility, and facility change, on age and refractive change singly and jointly, was performed. Stepwise regression models and graphic conditioning plots were used to determine, for each facility variable, its relationship to age or refractive change specifically. RESULTS: Baseline outflow facility and maximum pilocarpine-induced refractive change (ie, accommodation) declined with age, but the decrease in intraocular pressure and the facility response to pilocarpine did not. After adjusting for age, for baseline facility, there was no further relationship to 6% pilocarpine-induced accommodation, and a slight residual relationship to 2% pilocarpine-induced accommodation. After adjusting for both 2% or 6% pilocarpine-induced accommodation, the relationship to age was still significant. The facility increase after 2% or 6% pilocarpine did not depend on age and/or accommodative amplitude. CONCLUSIONS: In humans, as previously described in rhesus monkeys, an age-related loss of ciliary muscle mobility may compromise the basal function of the trabecular meshwork. However, unlike monkeys, humans exhibit no loss of the intraocular pressure or outflow facility response to pilocarpine with age.

Accommodation, Ocular↗
PubMed1997

Controlling the capsular shape in lens refilling.

OBJECTIVES: To investigate control of the capsular shape by determining the ability of the lens capsule to mold injected silicone and to evaluate the relationship among the volume of silicone injected, refraction, and the amplitude of accommodation. METHODS: After endocapsular phacoemulsification following an upper, minicircular capsulorhexis, the lens capsule of a pig eye was refilled with a silicone mixture that polymerizes in vitro in 2 hours. The minicircular capsulorhexis opening was sealed by a small silicone plug to prevent leakage. The anterior capsule curvature and refraction of the lens were measured by a Scheimpflug camera and lensometer, respectively, with and without zonular tension. Zonular tension was created using a ciliary ring sutured to the ciliary bodies and expanded. RESULTS: The mean (+/- SD) anterior curvature of the lenses without zonular tension was 6.50 +/- 0.07 mm after 17 hours and 6.54 +/- 0.04 mm after 42 hours; with zonular tension it was 7.01 +/- 0.11 mm and 7.23 +/- 0.24 mm, respectively. The curvature became flatter when zonular tension was applied or steeper when zonular tension was abolished momentarily during measurements after 17 hours, but after 42 hours the curvature was unaffected by the application or removal of zonular pressure. The mean (+/- SD) amplitude of accommodation (the difference between refraction without zonular tension and that with it) was 3.2 +/- 0.5 diopters (D), 6.1 +/- 1.8 D, 4.8 +/- 0.8 D, and 2.8 +/- 1.3 D, when the lens was refilled with a silicone volume corresponding to 45%, 55%, 75%, and 95%, respectively, of the mean normal lens volume. CONCLUSIONS: The lens capsule possesses some ability to mold the injected silicone during its polymerization. When the eye is atropinized, the lens capsule may conform to its nonaccommodated state. Accommodation could be obtained by various degrees of refilling. Moderate refilling yields a greater amplitude of accommodation than does more complete refilling. Using a silicone plug to seal the capsular opening facilitates lens refilling with excellent reproducibility and seems to be useful in research.

Accommodation, Ocular↗
PubMed1996

Projection from the accommodation-related area in the superior colliculus of the cat.

Our previous study has indicated that accommodative responses can be evoked with weak currents applied to a circumscribed area of the superior colliculus in the cat. We investigated efferent projections from this area with biocytin in the present study. The accommodation area in the superior colliculus was identified by systematic microstimulation in each of five anesthetized cats. Accommodative responses were detected by an infrared optometer. After mapping the superior colliculus, biocytin was injected through a glass micropipette into the accommodation area, where accommodative responses were elicited with low-intensity microstimulation. In addition, accommodative responses to stimulation of the superior colliculus were compared before and after an injection of muscimol, an agonist of inhibitory neurotransmitter, into the pretectum. Following the injection of biocytin, in the ascending projections, labeled terminals were seen mainly in the caudal portion of the nucleus of the optic tract, the nucleus of the posterior commissure, the posterior pretectal nucleus, the olivary pretectal nucleus, the mesencephalic reticular formation at the level of the oculomotor nucleus, and the lateral posterior nucleus of the thalamus on the ipsilateral side. Less dense terminals were seen in the anterior pretectal nucleus, the zona incerta, and the centromedian nucleus of the thalamus. In the descending projections, labeled terminals were observed mainly in the paramedian pontine reticular formation, the nucleus raphe interpositus, and the dorsomedial portion of the nucleus reticularis tegmenti pontis on the contralateral side. Less dense terminals were also seen in the nucleus of the brachium of the inferior colliculus, the cuneiform nucleus, the medial part of the paralemniscal tegmental field, and the dorsolateral division of the pontine nuclei on the ipsilateral side. Following the injection of muscimol into the pretectum, including the nucleus of the optic tract, the posterior pretectal nucleus, and the nucleus of the posterior commissure, accommodative responses evoked by microstimulation of the superior colliculus were reduced to 33-55% of the value before the injections. These findings suggest that the accommodation area in the superior colliculus projects to the oculomotor nucleus through the ipsilateral pretectal area, especially the nucleus of the optic tract, the nucleus of posterior commissure, and the posterior pretectal nucleus, and also projects to the pupilloconstriction area (the olivary pretectal nucleus), the vergence-related area (the mesencephalic reticular formation), and the active visual fixation-related area (the nucleus raphe interpositus).

Accommodation, Ocular↗
PubMed1999

Divergent axon collaterals from the rostral superior colliculus to the pretectal accommodation-related areas and the omnipause neuron area in the cat.

Results of previous studies have suggested that the rostral superior colliculus (SC), which corresponds to the representation of the central visual field, is involved in the control of accommodation and active fixation. To clarify the functional interaction between accommodation and active fixation in the rostral SC, this study was performed to investigate the axon collaterals diverging from the rostral SC to the pretectal accommodation-related areas and the omnipause neuron area in the raphe interpositus (RIP) of the cat by using a fluorescent double-labeling technique. This study was conducted on four cats, weighing 2.5-3.5 kg. Retrogradely labeled neurons in the SC were examined following injections of Fast Blue into the RIP and Diamidino Yellow into the pretectal accommodation-related areas, which were identified with microstimulation techniques. Neurons projecting to the RIP were located mainly in the intermediate layers in the rostral SC, whereas neurons projecting to the pretectal accommodation-related areas were scattered in the superficial and intermediate layers of the rostral SC. The population of double-labeled neurons was highest in the rostral SC, which corresponds to the representation of the central visual field. The presence of double-labeled cells indicated that the accommodation-related area in the rostral SC contains neurons whose axons collateralize to project to both the pretectal accommodation-related areas and the ominipause neuron area in the RIP. Neurons in the rostral SC may be involved in the interaction between accommodation and active fixation.

Accommodation, Ocular↗
PubMed1990

Optical causes of experimental myopia.

Experiments in which chicks are reared wearing a translucent goggle, or some similar device designed to degrade the retinal image, usually result in the induction of a significant degree of myopia. The induced myopia is due to enlargement of the vitreous chamber of the eye. Despite extensive change in the size, shape and refractive index distribution of the crystalline lens, its refractive power is static in the embryonic and early chick eye. The contribution to myopia of the cornea is uncertain; some studies have indicated either an increase or a decrease in corneal radius of curvature while others found no change. The fact that experimental myopia can be produced in chicks even when the optic nerve has been cut or when the degraded retinal image is restricted to one sector of the eye suggests that accommodation is not involved. Nevertheless, when the retinal image is degraded by being defocused with convex or concave lenses, myopia (concave lenses) or hyperopia (convex lenses) results. Chicks wearing concave or convex soft contact lenses from the day of hatching develop refractive states equal to the lens power (+8 and -10 diopters) within one week. The ability of the eye to vary its refractive development according to the sign of defocus suggests a role for accommodation. However, study of the ciliary muscle and accommodative apparatus of myopic and emmetropic chick eyes does not reveal any morphological differences that might indicate that the myopic eye had experienced an increased level of accommodation.

Accommodation, Ocular↗
PubMed1990

Neural control of eye growth and experimental myopia in primates.

Macaque monkeys become myopic when raised with fused lids to expose the retina to formless shadows during the period of postnatal eye development. The effect of the abnormal visual input is an excessive expansion of the posterior segment of the eye, a process that seems to be controlled by the nervous system. The mechanism by which the nervous system influences eye growth appears to be different in the stumptailed macaque (Macaca arctoides) and the rhesus macaque (M. mulatta). Lid-fused arctoides monkeys do not develop myopia when the ciliary muscle is paralysed or the optic nerve is cut, suggesting that the abnormal growth is caused by excessive accommodation. In contrast, paralysis of the ciliary muscle or optic nerve section does not prevent the development of myopia in the rhesus macaque, suggesting that in this species the axial growth is controlled by the retina. In both species neonatal lid fusion causes a marked increase in retinal vasoactive intestinal polypeptide (VIP). VIP is contained in a single type of amacrine cell whose dendrites spread in the middle of the inner plexiform layer. It remains to be determined whether the increase in the level of VIP is related to the abnormal axial elongation caused by lid fusion. At present we are also exploring the effects of accommodation on the growth of the eye by training juvenile arctoides monkeys to work on complex visual discrimination paradigms. Preliminary results show that performing a visual task at close range may influence the axial length and refraction in this macaque species.

Accommodation, Ocular↗
PubMed1990

Teleost vision: seeing while growing.

Teleost fish eyes grow throughout life without compromising visual performance of the animal. This is made possible by a set of novel adaptations in the growth and development of the eye. Increased retinal area is achieved both by stretching the existing retina and by generation of new tissue at the retinal germinal zone at the margin of the eye. Rods are added in a fundamentally different fashion than are all other retinal cell types: they appear last as new retina is produced at the margin and they are inserted throughout the functional retina as it stretches. In this way, the animal maintains a constant rod density to preserve vision in low light level. Because the larger eye produces a larger image, visual acuity improves slightly as the animal grows. Adaptations responsible for regulation of retinal growth are analyzed and discussed.

Accommodation, Ocular↗