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PubMed1995

Neuronal circuitry controlling the near response.

Experiments in primates have contributed greatly to our understanding of the neural mechanisms involved in the eye movements required to view objects at different distances. Early work focused on the circuitry for generating horizontal vergence eye movements alone. However, vergence eye movements are associated with lens accommodation and are usually accompanied by saccadic eye movements, so more recent work has been directed at understanding the interactions between vergence and accommodation, and between vergence and saccades. A new model explains the neural basis for interactions between vergence and accommodation by a neural network in which pre-motor elements are shared by these two systems. The effects of saccades on vergence eye movements appear to be the result of shared pre-motor circuits as well. Current evidence suggests that pontine omnipause neurons, known to be crucial for the generation of saccades, play an important role in the vergence pre-motor circuitry.

Accommodation, Ocular↗
PubMed2004

Medial rectus pulley posterior fixation is as effective as scleral posterior fixation for acquired esotropia with a high AC/A ratio.

PURPOSE: To compare traditional medial rectus (MR) scleral posterior fixation versus MR pulley posterior fixation without scleral sutures for the treatment of acquired esotropia (ET) with a high accommodative convergence over accommodation (AC/A) ratio. DESIGN: Nonrandomized interventional case series. METHODS: Medical records were retrospectively reviewed for twenty-two patients who underwent bilateral MR posterior fixation for acquired ET with a high AC/A ratio, with or without associated MR recessions. The main outcome measure was the reduction in distance-near disparity created by MR scleral posterior fixation compared with MR pulley posterior fixation. RESULTS: Nine patients underwent MR scleral posterior fixation surgery, seven in combination with MR recessions for distance ET. Postoperatively, the distance-near disparity decreased an average of 11.8 prism diopters, stereoacuity improved in six patients, and eight patients no longer needed bifocals. Thirteen patients underwent MR pulley posterior fixation surgery, 10 in combination with MR recessions for distance ET. Postoperatively the distance-near disparity decreased an average of 14.4 prism diopters, stereoacuity improved in eight patients, and 12 patients no longer required bifocals. Statistically, the two procedures were equivalent. One patient in each group was undercorrected at near only, with the residual near ET controlled with bifocals. One patient who underwent MR pulley posterior fixation combined with large MR recessions was overcorrected at distance only. CONCLUSION: Traditional MR scleral posterior fixation and MR pulley posterior fixation are equally effective in treating acquired ET with a high AC/A ratio.

Accommodation, Ocular↗
PubMed2004

Ultrasound biomicroscopic analysis of iris profile changes with accommodation in pigmentary glaucoma and relationship to age.

PURPOSE: To examine the effect of accommodation on iris profile in pigmentary glaucoma and its relationship to age. DESIGN: Interventional case series. METHODS: We measured change in iris profile with accommodation in 92 eyes of 92 patients with pigmentary glaucoma. RESULTS: Mean age was 42 years. Mean change in posterior iris excursion from nonaccommodated to accommodated state was 144.5 microm. (P < .001). Age was plotted against iris excursion with an estimated least-squares regression line. The estimated Pearson correlation coefficient was -0.60, (P < .001). Patients younger than 42 years of age had a mean change in excursion of 209.2 microm compared with 79.8 microm for those patients older than 42 years. (P < .001) CONCLUSION: This study found that there is a significant increase in posterior iris bowing in the accommodated state. Increasing age is associated with decreased posterior iris deviation. These findings add evidence to the theory of accommodation-induced reverse pupillary block in pigmentary glaucoma.

Accommodation, Ocular↗
PubMed2005

Fellow eye comparison between the 1CU accommodative intraocular lens and the Acrysof MA30 monofocal intraocular lens.

PURPOSE: To examine the near visual clinical performance of an accommodative intraocular lens (IOL) when compared with a standard monofocal IOL in a fellow eye comparison. DESIGN: Prospective, randomized fellow eye comparison. METHODS: Thirty patients (60 eyes) with bilateral cataracts but otherwise normal eyes were recruited from a single university hospital cataract waiting list. Patients were randomized to receive either the 1CU accommodative IOL in their first eye or the Acrysof MA30 monofocal IOL. The alternative lens was then implanted in the second eye 4 to 6 weeks later. At all follow-up visits, a full assessment was made of distance, near and reading visual performance, and accommodative amplitude. RESULTS: Data are available for all patients at 6 months and 20 patients at 1 year. At 6 months, no difference was found in distance-corrected visual acuity between the two IOLs. Of the 1CU eyes, nine patients (30%) could read J6 or better at a reading speed of 80 words/min or better. In these nine patients, the mean difference in the amplitude of accommodation between the two eyes was 0.71 diopters. CONCLUSIONS: No measurable variable distinguished eyes that developed functional reading vision from those that did not. The accommodative IOL appears to produce improved near vision in some eyes, but it does not work in all eyes, and in eyes where there is apparent accommodation, there is a discrepancy between subjective reading performance and the modest measured increase of accommodative amplitude.

Accommodation, Ocular↗
PubMed2006

Higher-order aberrations in children.

PURPOSE: To quantify and characterize higher order aberrations in children and to investigate the influence of refractive error and cycloplegia. DESIGN: Observational cross-sectional study. METHODS: setting: Clinical practice. patients: One hundred sixty-two eyes of 82 children were examined. The mean age of the children was 6.7 years (range, 4 to 14 years), and the mean manifest refractive spherical equivalent was 2.39 +/- 3.35 diopters (range, -8.98 to +8.45 diopters). Aberrometry was performed with a wavefront analyzer (after cycloplegia and mydriasis with cyclopentolate 1%). Aberrometry was also conducted on a subgroup of 52 eyes of 27 children, both before and 30 minutes after the instillation of cyclopentolate 1% to investigate the effect of paralysis of accommodation. RESULTS: Mean root mean square values of total-, third-, fourth-, and fifth-order aberrations were 0.37 +/- 0.13 microm, 0.23 +/- 0.12 microm, 0.16 +/- 0.11 microm, and 0.08 +/- 0.12 microm, respectively. Mean root mean square values of total coma (Z(3)(-1), Z(3)(1), Z(5)(-1), Z(5)(1)) and total trefoil (Z(3)(-3), Z(3)(3), Z(5)(-3), Z(5)(3)) were 0.27 +/- 0.31 microm and 0.21 +/- 0.29 microm, respectively. Myopes had statistically significant greater levels of total (P = .005) and fourth order (P = .002) aberrations and Zernicke terms (Z(3)(-3), Z(3)(-1), Z(3)(3), Z(4)(-4), and Z(4)(2)) compared with hyperopes. Cycloplegia had minimal influence on higher-order aberrations. CONCLUSION: Significant levels of higher-order aberrations were found in these children. They were influenced by refractive error, because myopes had significantly greater levels compared with hyperopes. Paralysis of accommodation with cyclopentolate appeared to have little effect on higher-order aberrations.

Accommodation, Ocular↗
PubMed2006

The accommodative element in accommodative esotropia.

PURPOSE: To evaluate the effect of reducing the hyperopic correction on the state of binocular accommodative response in fully accommodative esotropia and to determine the "comfortable" amount of reduction in hyperopic correction. DESIGN: A cohort study. METHODS: Hyperopic corrections of children with a baseline refractive error of +1.50 to +5.0 diopters were gradually reduced in 0.50-diopter increments. Binocular accommodative ability was assessed by dynamic retinoscopy (monocular estimate method). Similar binocular accommodative responses were ascertained among patients with a baseline hyperopic correction of < or =3.0 of hyperopia and >3.0 of hyperopia, and patients were divided into two groups, group 1 (13 patients) and group 2 (18 patients), accordingly. RESULTS: After a reduction of 2.0 diopters in group 1 and 1.0 diopter in group 2, there was a decrease in accommodative response initially in the nondominant eye, accompanied by the dominant eye with a further reduction of 0.50 diopter. To overcome the bilateral accommodative lag, a reinstatement of a 0.50-diopter stronger hyperopic correction was required. Patients in group 1 tolerated a mean undercorrection of 2.37 diopters, and 77% were weaned from their spectacles. All of the children in group 2 were dependent upon spectacles at the completion of the study period. The final spectacle worn was a median of -1.67 diopters less than their full cycloplegic refraction. CONCLUSIONS: A complete binocular accommodative ability seems to be a prerequisite for the establishment of "comfortable" hyperopic undercorrections. It does not seem to be a reasonable approach to consider further reductions in hyperopic correction in the presence of a bilateral decreased accommodative performance.

Accommodation, Ocular↗
PubMed2006

Accommodative spasm after laser-assisted in situ keratomileusis (LASIK).

PURPOSE: To report a case of accommodative spasm following laser-assisted in situ keratomileusis (LASIK). DESIGN: Observational case report. METHODS: Ophthalmic examination including manifest and cycloplegic refraction to assist in diagnosis. RESULTS: Two months following LASIK surgery, a 41-year-old healthy woman complained of intolerable headaches that had interfered with her daily activities. The patient sought medical consultation, and an MRI of the brain was normal. Best-corrected visual acuity (BCVA) was 20/20 and 20/25 with manifest refraction of -2.25 -0.50 x 170 and plano in the right and the left eye, respectively. Cycloplegic refraction was plano in the right and +0.75 sphere in the left eye, and she was corrected to 20/20 bilaterally. After being treated with cyclopentolate 1% one drop at bedtime to each eye for approximately six weeks, the headache completely resolved. CONCLUSIONS: Accommodative spasm should be considered in patients undergoing LASIK surgery complicated with fluctuating refraction of uncertain causes.

Accommodation, Ocular↗
PubMed2006

Strabismus surgery for elimination of bifocals in accommodative esotropia.

PURPOSE: This study reports the outcomes of strabismus surgery to eliminate bifocals in patients with accommodative esotropia with a high accommodative convergence to accommodation (AC:A) ratio. DESIGN: Retrospective interventional case series. METHODS: Sixteen patients who wore bifocals for treatment of accommodative esotropia with a high AC:A ratio underwent strabismus surgery following prism adaptation testing (PAT) for the near angle of esotropia without bifocals. Outcomes were considered successful if patients had microtropias and maintained fusion without bifocals. RESULTS: All patients had successful outcomes after one or two surgeries. Three of 13 (23%) patients with positive PATs required two surgeries. Two of three (67%) patients with negative PATs required two surgeries. Binocularity remained the same in 13 patients and improved in three patients. Glasses were eliminated entirely in eight of 16 (50%) patients. CONCLUSIONS: Strabismus surgery may eliminate the need for bifocal glasses in patients with accommodative esotropia with a high AC:A ratio, with many patients able to discontinue glasses entirely. Preoperative PAT may help predict the risk of requiring more than one surgery.

Accommodation, Ocular↗
PubMed2006

Sensitivity study of human crystalline lens accommodation.

A nonlinear axisymmetric finite element method (FEM) analysis was employed to determine the critical geometric and material properties that affect human accommodation. In this model, commencing at zero, zonular traction on all lens profiles resulted in central lenticular surface steepening and peripheral surface flattening, with a simultaneous increase in central lens thickness and central optical power. An age-related decline in maximum zonular tension appears to be the most likely etiology for the decrease in accommodative amplitude with age.

Accommodation, Ocular↗
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

A study for accommodating the human crystalline lens by finite element simulation.

This paper constructs two finite element models of human crystalline lens and zonules based on published clinical data. Displacement and pressure were applied to study the mechanism of vision accommodation. The simulation results show that, in Model A, under the pull of the zonules, the thickness of the lens decreased linearly, and the lens diameter increased linearly. The optical power of the lens increased as the zonules displacement increased. Furthermore, the pressure had a remarkable influence on the shape of the lens and the optical power. The lens also became thinner and flatter as the pressure increased. The optical power increased when the pressure increased. In Model B, the lens became thicker and optical power increased as the equatorial zonules stretched. It is basically consistent with Schachar's hypothesis. The outcome of this paper proved that the analytical model presented in this paper can be used in the theoretical study of the accommodation mechanism of the lens.

Accommodation, Ocular↗
PubMed2005

Comparison of pilocarpine-induced and stimulus-driven accommodation in phakic eyes.

With the recent introduction of potentially accommodative intraocular lenses (IOL), there is a need for methods to evaluate their accommodative potential. In most studies assessing IOL movement, pilocarpine is used to stimulate contraction of the ciliary muscle. The aim of this study is to determine if pilocarpine-induced ciliary muscle contraction is comparable to physiological stimulus-driven accommodation in young and presbyopic subjects. Ten emmetropic young subjects (23-25 years) and 11 emmetropic presbyopic subjects (51-62 years) were included in this study. Anterior chamber depth (ACD) and lens thickness (LT) were assessed with partial coherence interferometry (PCI). A moveable stimulus was coupled to the PCI equipment for measurement of biometric lens changes. ACD was measured with the stimulus at infinity and then at the subjects individual nearpoint, and after application of two drops of 2% pilocarpine. In young subjects, there was no significant difference in lens change between nearpoint and pilocarpine stimulation. Presbyopic subjects showed no relevant lens change when accommodating at the nearpoint, however, under pharmacologically induced ciliary muscle contraction with pilocarpine, there was a significant forward shift of the anterior and posterior lens pole, leading to a translational forward lens shift of about 150 microm. This study demonstrates that pilocarpine acts "physiologically" in young phakic subjects, but is a "superstimulus" in presbyopic phakic subjects. Therefore, IOL movement may be overestimated when using pilocarpine to stimulate accommodation.

Accommodation, Ocular↗
PubMed2005

Choroidal innervation in primate eyes.

Arteries and arterioles of the choroid are surrounded by numerous nerve fibers staining for nitric oxide synthase (NOS) and vasoactive intestinal peptide (VIP). In most mammalian eyes these nerve fibers derive from the pterygopalatine ganglion via the facial nerve. Stimulation of the facial nerve causes vasodilation of the choroidal vasculature. In primates with a well developed fovea centralis there are ganglion cells in the choroidal stroma which in human eyes amount to around 2000. The postganglionic nerve fibers of these choroidal ganglion cells (CGC) join the perivascular nerve fiber plexus. The CGC stain for NOS and VIP like the nerve cells within the pterygopalatine ganglion. There are, however, differences between the two cell populations. Immunohistochemical and ultrastructural classification of the CGC show that in addition to NOS and VIP almost half of the cells stain for calretinin, single ones for neuropeptide Y (NPY) and galanin. A number of cells is in close contact with numerous boutons staining for nNOS, VIP, NPY, tyrosine hydroxylase (TH), vesicular monoaminergic transporter (VMAT)2, vesicular acetylcholine transporter (VACHT), calretinin, and NPY. These data indicate a more complex integrative function of CGCs e.g. volume regulation in parallel with ciliary muscle contraction during accommodation. Ultrastructural and immunohistochemical studies indicate, that CGCs in addition may have mechanosensory properties. Whether they are involved in volume-regulatory functions independent of accommodation is not yet known. In glaucoma disease the number of CGCs is significantly reduced. This holds true for eyes with primary open angle glaucoma, pseudoexfoliation glaucoma and experimentally induced monkey glaucoma indicating that elevated IOP is involved in the pathogenesis of glaucomatous CGC-degeneration.

Accommodation, Ocular↗
PubMed2006

Edinger-Westphal and pharmacologically stimulated accommodative refractive changes and lens and ciliary process movements in rhesus monkeys.

During accommodation, the refractive changes occur when the ciliary muscle contracts, releasing resting zonular tension and allowing the lens capsule to mold the lens into an accommodated form. This results in centripetal movement of the ciliary processes and lens edge. The goal of this study was to understand the relationship between accommodative refractive changes, ciliary process movements and lens edge movements during Edinger-Westphal (EW) and pharmacologically stimulated accommodation in adolescent rhesus monkeys. Experiments were performed on one eye each of three rhesus monkeys with permanent indwelling electrodes in the EW nucleus of the midbrain. EW stimulated accommodative refractive changes were measured with infrared photorefraction, and ciliary process and lens edge movements were measured with slit-lamp goniovideography on the temporal aspect of the eye. Images were recorded on the nasal aspect for one eye during EW stimulation. Image analysis was performed off-line at 30 Hz to determine refractive changes and ciliary body and lens edge movements during EW stimulated accommodation and after carbachol iontophoresis to determine drug induced accommodative movements. Maximum EW stimulated accommodation was 7.36+/-0.49 D and pharmacologically stimulated accommodation was 14.44+/-1.21 D. During EW stimulated accommodation, the ciliary processes and lens edge moved centripetally linearly by 0.030+/-0.001 mm/D and 0.027+/-0.001 mm/D, with a total movement of 0.219+/-0.034 mm and 0.189+/-0.023 mm, respectively. There was no significant nasal/temporal difference in ciliary process or lens edge movements. 30-40 min after pharmacologically stimulated accommodation, the ciliary processes moved centripetally a total of 0.411+/-0.048 mm, or 0.030+/-0.005 mm/D, and the lens edge moved centripetally 0.258+/-0.014 mm, or 0.019+/-0.003 mm/D. The peaks and valleys of the ciliary processes moved by similar amounts during both supramaximal EW and pharmacologically stimulated accommodation. In conclusion, this study shows, for the first time, that the ciliary processes and lens edge move centripetally, linearly with refraction during EW stimulated accommodation. During pharmacological stimulation, the ciliary processes move to a greater extent than the lens edge, confirming that in adolescent monkeys, lens movement limits the accommodative optical change in the eye.

Accommodation, Ocular↗
PubMed2003

Marshall Parks lecture. Binocular sensory outcomes in accommodative ET.

PURPOSE: To review what is known about the normal maturational sequence for fusion and stereopsis and the binocular sensory deficits associated with accommodative esotropia (ET) and to explore the clues that accommodative ET provides about critical periods for binocular sensory function. METHODS: Studies of binocular sensory function during infancy and early childhood are presented. RESULTS: Most of the maturation of binocular sensory function occurs during the first year of life, yet a later abnormal visual experience-such as the onset of accommodative ET--can profoundly and permanently disrupt fusion and stereopsis. CONCLUSIONS: Some binocular sensory deficits may exist before the onset of accommodative ET, but others may result directly from abnormal binocular experience. The functional organization of the maturing visual system appears to be maximally sensitive to disruption by abnormal visual experience during the first months of life, but susceptibility continues until at least 4 years of age.

Accommodation, Ocular↗
PubMed2004

Stereopsis and long-term stability of alignment in esotropia.

PURPOSE: Recent studies of infantile and accommodative esotropia (ET) have focused on stereoacuity as a final outcome measurement for judging the success or failure of treatment. The purpose of the present study was to extend this approach by evaluating whether the presence of stereopsis developing immediately after surgical alignment or optical correction plays a role in maintenance of long-term alignment. METHODS: Random-dot stereoacuity was assessed within 3 months of initial surgical alignment in 70 children with infantile ET and within 3 months of initial optical correction in 66 children with accommodative ET. At > or = 5 years of age, adverse outcomes were assessed including loss of alignment, amblyopia, and nil stereopsis. Risk-factor analysis was used to evaluate whether early nil stereopsis increased the risk for subsequent adverse outcomes. RESULTS: In the infantile ET cohort, early nil stereopsis was associated with a 3.6 times (95% confidence interval [CI] 2.4 to 4.1) greater risk of surgery for recurrent ET or consecutive exotropia and a 4.2 times (95% CI 3.3 to 4.4) greater risk for nil stereopsis at > or = 5 years of age. In the accommodative ET cohort, early nil stereopsis was associated with a 17.4 times (95% CI 3.3 to 32.2) greater risk of surgery for ET and a 32.2 times (95% CI 15.8 to 35.6) greater risk for nil stereopsis at > or = 5 years of age. CONCLUSION: Treatment protocols designed to optimize stereoacuity outcomes promote long-term stability of alignment.

Accommodation, Ocular↗
PubMed2004

Treatment outcomes in refractive accommodative esotropia.

PURPOSE: To document and compare the clinical features and functional outcomes in patients with accommodative esotropia. To assess the efficacy of conventional management of accommodative esotropia, to determine functional outcomes of amblyopia and binocular vision, and to analyze possible risk factors involving the development of amblyopia. METHODS: We retrospectively reviewed the charts of 147 patients whose esotropia was corrected to within 10 prism diopters of orthotropia at both distance and near with use of full cycloplegic hyperopic correction. Multiple parameters were reviewed, including initial and final cycloplegic refraction, distance, and near deviation with and without glasses, stereoacuity, age of onset, and initiation of treatment, presence of anisometropia, and change in hyperopia. RESULTS: At presentation, 87 (59.2%) of the 147 patients were amblyopic, and anisometropia was found to be the only statistically significant risk factor for this (P = .001). Only 24.2% of these patients have stereo acuity between 40 and 100 sec/arc, 20.96% of patients have 200 to 800 sec/arc, and 22.58% of patients have 1980 to 3000 sec/arc; the remaining 32.26% had no stereo acuity. Fusion was achieved in 73.5% of the patients and later presentation (> 24 months) of esodeviation significantly determined their fusional ability (P = .031). Consecutive exotropia developed in 5.4 % of the patients an average of 5.5 years after institution of full optical correction. For clinical and functional outcomes we did not find any statistically significant difference between early onset (before 1 year old) and typical onset (2 to 3 years) age groups. The trend towards decreasing hyperopia was apparent, averaging -0.16 +/- 0.20 diopters annually in 80.5% of the patients with at least 5 years follow-up, although 23% of patients still had 20/40 or worse visual acuity in the amblyopic eye. CONCLUSIONS: Amblyopia is a commonly associated finding at presentation for patients with accommodative esotropia. Most of the patients developed good fusion but poor stereopsis at the end of treatment.

Accommodation, Ocular↗