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Results for “Optics and Refraction”

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At least 523 records · Page 29Linked to original sources
PubMed1987

Visual deprivation causes myopia in chicks with optic nerve section.

Deprivation of form vision restricted to a region of the retina produces myopia and axial elongation only in that region. We asked whether this control of eye growth by the presence or absence of visual stimuli might take place entirely within the eye. Chicks with neonatal optic nerve section, wearing an occluder that deprived one half of the retina of form vision, had vitreous chamber elongation and myopia both restricted to the deprived region. Chicks with optic nerve section but without occluders had eyes smaller than normal with severe hyperopia. These results suggest that two different mechanisms may control eye growth, one within the eye and the other in the brain.

Animals↗
PubMedDate not supplied

Optic nerve hypoplasia.

Optic nerve hypoplasia is rarely met in otherwise normal eyes. Three unilateral cases of patients with small optic disks, reduced visual acuity, and convergent squint on the affected eye are presented. The anomaly is probably caused by failure of development of the ganglion cell layer of the retina causing a small optic nerve head with normal central vessels. Inheritance or induction by drugs could not be found in our cases.

Child↗
PubMedDate not supplied

The management of esotropia with high AC/A ratio (convergence excess).

This paper reviews the long-term follow-up of esotropia with a high AC/A ratio defined as an increase of 20 delta or more of the esotropia at near compared with distance with the full optical correction of any refractive error in place. Ninety-nine patients were studied for an average follow-up of eight years. Eighty-six achieved fusion but only five achieved central fusion. Forty-five were treated with bifocals. No significant difference in the sensory results were recorded in those patients wearing bifocals compared with those who did not wear bifocals. No patient had miotic therapy for more than a few months. The suppression characteristic of this condition is reviewed.

Child, Preschool↗
PubMedDate not supplied

Clinical experience with the Tscherning aberrometer.

PURPOSE: With the aberrometer based on Tscherning's principle, measurements of wavefront aberrations of human eyes with high accuracy and reproducibility are available for standard diagnostic investigations. METHODS: During investigational and clinical trials, wavefront-aberrations of about 300 human eyes were measured and evaluated within the last few years. RESULTS: measurements are presented in terms of Zernike coefficients and as height maps that can be converted directly to ablation profiles for wavefront-guided laser treatments. CONCLUSION: The Tscherning aberrometer is a simple optical device with high accuracy appropriate for routine clinical investigations on optical aberrations of the human eye.

Adolescent↗
PubMedDate not supplied

Reduction of spherical aberration with the nidek NAVEX customized ablation system.

PURPOSE: Spherical aberration is the most frequent optical aberration induced by refractive surgery, reducing visual acuity and causing halos. We present preliminary results of Custom Ablation Transition Zone (CATz), which we developed for Nidek's Final Fit software, part of the Nidek NAVEX customized ablation system. METHODS: We studied 55 eyes of 51 patients (31 males, 20 females) who underwent refractive surgery. Mean preoperative spherical equivalent refraction was -5.50 +/- 3.30 D (range -12.00 to +4.50 D). Mean age was 35 years (range 23 to 47 yr). All patients underwent complete preoperative ophthalmologic examination, including aberrometry and topography, then surgery with laser epithelial keratomileusis, and OPD-based refractive treatment with the Nidek EC-5000 excimer laser. The Nidek Final Fit software with the CATz feature was always used. Postoperatively, all patients repeated the ophthalmologic examination inclusive of aberrometry at day 30, 60, and 90. RESULTS: The 3-month follow-up rate was 21.8%. Mean postoperative spherical equivalent refraction was -0.33 +/- 0.91 D (range -0.75 to +0.75 D), with a mean sphere of -0.23 +/- 0.78 D (range -2.50 to +0.75 D) and a mean cylinder of -0.21 +/- 0.33 (range -1.00 to 0 D). At 3 months, 43% of eyes achieved 20/15 or better UCVA, and 43% achieved 20/20 or better UCVA; 63% achieved 20/15 or better BSCVA and 25% achieved 20/20 or better BSCVA. Postoperative spherical aberration was unchanged for a 3-mm pupil. CONCLUSION: Customized ablation with the Nidek NAVEX system provided excellent refractive results. The CATz algorithm of the Nidek Final Fit software appeared to prevent induction of spherical aberration.

Adult↗
PubMed2000

Bilateral papillomacular retinal folds and posterior microphthalmus: new features of a recently established disease.

Clinical findings of a 2.5-year-old girl presenting with barely detectable horizontal nystagmus and high hypermetropia are described. Despite the normal appearing anterior segments, the child had posterior microphthalmus and bilateral papillomacular retinal folds, conforming to a recently described, rare congenital disease. The patient also had significant posterior pole excyclorotation and avascular zones at the extreme temporal periphery without ridge formation or neovascularization. These findings were not reported previously. Other remarkable features include mildly depressed photopic and scotopic electroretinogram amplitudes and a short axial length of the vitreous cavity compared to age-matched normals, measured by ultrasonography. The present case adds new elements to this relatively rare ocular developmental abnormality.

Child, Preschool↗
PubMed1975

Optical and neural resolution in peripheral vision.

Visual acuity along the horizontal meridian in the peripheral field of vision was determined at a photopic level in two normal subjects. Two types of sinusoidally modulated, monochromatic test patterns of high contrast were used. One was produced directly on the retina by an interferometric technique. The other type was imaged on the retina by the dioptric apparatus of the eye; the resulting image suffered ordinary optical image degradation. The results from the interferometric acuity determinations represent maximal neural discrimination across the visual field. Acuity decreases monotonically toward the periphery, from about 45 cycles per degree in the fovea, to about 0.8 at 80 degrees of eccentricity in the temporal field. The decline is well described by a second-degree polynomial. Acuity for test patterns imaged by the optics of the eye was consistently lower than interferometric acuity. The difference increases toward the periphery. It is attributable to effects of optical aberrations. The discrepancy between optical and neural resolving power on oblique incidence needs to be taken into account whenever results obtained with external, extra-axial stimuli are to be analyzed in terms of retinal architecture.

Adult↗
PubMed1975

[Ocular symptoms in Rubinstein-Taybi-syndrome (author's transl)].

Report of 2 cases of Rubinstein-Taybi-syndrome. Description of the well known symptoms: Mental and somatic retardation, broad thumbs and toes, highly arched palate, retarded bone age, fine hair on limbs. Besides that there were eye abnormalities: Antimongoloid slant, strabismus, ametropia, monolateral ptosis, papillatrophia, latent nystagmus. Discussion of the differential diagnosis.

Abnormalities, Multiple↗
PubMed1992

Programmed cell death in heterokaryons. A study of the transfer of apoptosis between nuclei.

Thymocytes undergoing apoptosis induced by dexamethasone showed nuclear refractivity changes under Nomarski optics that correlated precisely with internucleosomal DNA degradation and was prevented by cycloheximide. When heterokaryons between thymocytes and 9L or NIH3T3 cells were examined, 99.75% of the nuclei in heterokaryons followed the original and distinct fate characteristic of the parental cells. Thymocyte nuclei proceeded to undergo apoptotic cell death, whereas the 9L and NIH3T3 nuclei in the heterokaryons did not show the morphologic changes of apoptosis or any DNA cleavage on gels, and remained viable and mitotic. Cycloheximide prevented the induction of apoptosis in thymocyte nuclei in the heterokaryons. An excess of up to seven thymocyte nuclei undergoing programmed cell death in a heterokaryon did not detectably damage the 9L nucleus, and an excess of six 9L nuclei did not protect the thymocyte nucleus from apoptosis. The proposed model stating that programmed cell death results from de novo synthesis of death-causing gene products is difficult to reconcile with these findings. A cell-type-specific activity, present in thymocyte nuclei before induction of apoptosis with corticosteroids and unable to diffuse between nuclei, appears to be responsible for DNA fragmentation. These results also show that nuclear disintegration is the trigger of thymocyte death and not a consequence of cell death due to another mechanism.

Animals↗
PubMed1996

[Clinical observation of the pathological changes of axial length, corneal curvature and posterior segment wall of eyeball in eyes with high myopia].

PURPOSE: To study the correlation between the characteristics of the morphologic changes in the wall of eyeball with high myopia and the visual function. METHODS: The axial length, corneal curvature, etc., of 280 eyes in 140 cases (the diopter was from -6.25D to approximately -30.00D) were examined and the data were settled statistically. RESULTS: (1) The corrected visual acuity in the patents with high myopia decreased apparently with the increase of diopter. The difference was significant (P < 0.001). (2) The axial length of anteroposterior diameter in 96.1% eyes increased, with which the diopter also increased. (3) 27.1% exophthalmos were forward. (4) There was no significant difference when compared the anterior surface corneal curvature with emmetropic eyes. (5) Posterior scleral staphyloma occurred in 80.7% eyes. (6) Optic nerve atrophy and optic disk atrophic arc spot occurred in 82.3% eyes. (7) The intraocular pressure increases in 5.3% eyes. CONCLUSION: The severe damage to the visual function because of the pathological changes on the wall of eyeball is the main cause that vision can not be corrected in clinics.

Adolescent↗
PubMedDate not supplied

A new high-power biconcave contact lens for observation and coagulation of the posterior segment.

A wide-angle, high-power negative contact lens was designed for observation and coagulation of the retina and choroid. The new contact lens has a lateral magnification of 0.44 and a field of view of 64 degrees. Due to the prismatic of its biconcave structure, the field of view may be shifted by tilting the lens, induced eye movements beyond the equator of the retina, or both. Because only a negative refractive surface is required, optical aberrations are significantly reduced. Safety during laser irradiation tasks is increased compared with the use of positive wide-angle contact lenses because the irradiance of the crystalline lens is significantly reduced.

Choroid↗
PubMed1990

Ophthalmologic complications of meningomyelocele: a longitudinal study.

Patients with spina bifida have multiple ophthalmologic problems, many of which are preventable. Most of the problems are related to the hydrocephalus, which is caused by the coexisting Arnold-Chiari malformation. When patients are treated for hydrocephalus, and comprehensive eye care is available, 94% of the patients will have 6/12 visual acuity or better. Strabismus is common but it responds well to medical and surgical treatment. Children with spina bifida should have frequent examinations by an ophthalmologist who is familiar with the diagnosis and management of the defects recorded in this study.

Adolescent↗
PubMed1986

Roman ophthalmic science (743 B.C.--A.D. 476).

Literary and archeological evidence for the achievements and progress of Roman ophthalmic science is reviewed. It appears that, by the end of the period under consideration, significant advances had been made in the diagnosis and treatment of a variety of ocular disorders, and in knowledge of ocular anatomy. However, in spite of their possession of skills of a high order in some aspects of glass technology and their familiarity with various aspects of geometrical optics, the Romans never developed optical aids to overcome refractive defects.

Archaeology↗