Home  About us  Contact
 

Mesopic Conditions (mesopic + condition)

Distribution by Scientific Domains
Medical Sciences80%

Selected Abstracts

Visual neurophysiological dysfunction in infants exposed to hydroxychloroquine in utero

ACTA PAEDIATRICA, Issue 9 2009
F Renault
Abstract Aim:, Hydroxychloroquine therapy during pregnancy is thought to be safe for foetuses. Normal visual function has been showed on clinical grounds in infants exposed in utero to hydroxychloroquine, but there are few visual neurophysiological data. Our study was designed to assess retina and visual pathways using electroretinogram and visual evoked potentials in a series of infants born to mothers treated by hydroxychloroquine for connective tissue diseases. Methods:, Twenty-one infants (3,7 months of age) were consecutively examined between June 2002 and May 2007. Full-field electroretinogram was recorded by contact lens electrodes and visual evoked potentials were recorded by occipital surface electrodes using flash stimulation in mesopic condition. Analysis was focused on the amplitudes and latencies of the a - and b -waves of electroretinogram and the latency of the P100 component of visual evoked potentials. Results:, Electroretinogram abnormalities were detected in six infants, associated with delayed visual evoked potentials in four of them. Conclusion:, Early electroretinogram and visual evoked potentials testing evidenced neurophysiological visual disturbances in a subset of infants born to mothers treated by hydroxychloroquine. Systematic clinical and neurophysiological vision testing during childhood is needed to detect possible consequences of antenatal exposure to hydroxychloroquine. [source]

Normal values and standard deviations for pupil diameter and interpupillary distance in subjects aged 1 month to 19 years

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2002
Colleen MacLachlan
Normal values of pupil diameters and interpupillary distances (PDs) were measured in a population of 1311 subjects (in 4294 visits) ranging from 1 month of age to slightly over 19 years of age. Subjects in this study were recruited from birth announcements in a local newspaper for a developmental vision project. Pupil sizes were measured photographically when the corneas were illuminated by 15.9 ± 0.5 lux ambient illumination (i.e. under mesopic conditions). Interpupillary distance was measured with an interocular distance rule while the subject fixated an object at 0.66 m distance. These PD measurements were corrected for systematic measurement errors and to an infinite viewing distance using radii of ocular rotation based on age-dependent axial lengths. Means and S.D. were calculated for age, pupil diameter and PD for each 1-year group of male and female subjects. The second order regression equation for average pupil size as a function of age was determined: [males pupil diameter (in mm)=5.83 + 0.181*age in years , 0053*age in years2, r2=0.897; female pupil diameter=5.40 + 0.285*age in years , 0.0109*age in years2, r2=0.945]. The difference between male and female pupil sizes (mean male , female=0.13 mm) was marginally not significant (p < 0.054). The average corrected PDs as a function of age were found to approximate another second-order regression equation: (males PD=43.36 + 1.663*age in years , 0.034*age in years2, r2=0.986; females PD=41.76 + 1.891*age in years , 0.052*age in years2, r2=0.986). Male PD was wider than female PD by an average of 1.58 mm (p < 0.0003). As expected, the results of this study were similar to a preliminary investigation conducted by Thunyalukul et al. [Invest. Ophthalmol. Vis. Sci.37 (1996) S731] on a portion of the present data set, and also very similar to data from another study of comparable racial composition using a different measurement method [Pryor, Pediatrics44 (1969) 973]. It was concluded that pupil diameter and PD increase more gradually than axial length of the eye in the first few years of life. The normal values and S.D. for both pupil size and PD determined in this study have important clinical implications as well as applications in the optical industry. [source]

Contribution of voltage-gated sodium channels to the b-wave of the mammalian flash electroretinogram

THE JOURNAL OF PHYSIOLOGY, Issue 10 2008
Deb Kumar Mojumder
Voltage-gated sodium channels (Nav channels) in retinal neurons are known to contribute to the mammalian flash electroretinogram (ERG) via activity of third-order retinal neurons, i.e. amacrine and ganglion cells. This study investigated the effects of tetrodotoxin (TTX) blockade of Nav channels on the b-wave, an ERG wave that originates mainly from activity of second-order retinal neurons. ERGs were recorded from anaesthetized Brown Norway rats in response to brief full-field flashes presented over a range of stimulus energies, under dark-adapted conditions and in the presence of steady mesopic and photopic backgrounds. Recordings were made before and after intravitreal injection of TTX (,3 ,m) alone, 3,6 weeks after optic nerve transection (ONTx) to induce ganglion cell degeneration, or in combination with an ionotropic glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 200 ,m) to block light-evoked activity of inner retinal, horizontal and OFF bipolar cells, or with the glutamate agonist N -methyl- d -aspartate (NMDA, 100,200 ,m) to reduce light-evoked inner retinal activity. TTX reduced ERG amplitudes measured at fixed times corresponding to b-wave time to peak. Effects of TTX were seen under all background conditions, but were greatest for mesopic backgrounds. In dark-adapted retina, b-wave amplitudes were reduced only when very low stimulus energies affecting the inner retina, or very high stimulus energies were used. Loss of ganglion cells following ONTx did not affect b-wave amplitudes, and injection of TTX in eyes with ONTx reduced b-wave amplitudes by the same amount for each background condition as occurred when ganglion cells were intact, thereby eliminating a ganglion cell role in the TTX effects. Isolation of cone-driven responses by presenting test flashes after cessation of a rod-saturating conditioning flash indicated that the TTX effects were primarily on cone circuits contributing to the mixed rod,cone ERG. NMDA significantly reduced only the additional effects of TTX on the mixed rod,cone ERG observed under mesopic conditions, implicating inner retinal involvement in those effects. After pharmacological blockade with CNQX, TTX still reduced b-wave amplitudes in cone-isolated ERGs indicating Nav channels in ON cone bipolar cells themselves augment b-wave amplitude and sensitivity. This augmentation was largest under dark-adapted conditions, and decreased with increasing background illumination, indicating effects of background illumination on Nav channel function. These findings indicate that activation of Nav channels in ON cone bipolar cells affects the b-wave of the rat ERG and must be considered when analysing results of ERG studies of retinal function. [source]

4423: The limits of manifest refraction: visual performance under low light conditions

ACTA OPHTHALMOLOGICA, Issue 2010
J CABEZA
Purpose To present a method to optimize the prescription values of ophthalmic lenses based on ocular wavefront information. Those lenses provide improved vision under low light conditions to the patient. Methods We will show first the influence of ocular aberrations on visual performance, and how do they change with pupil size. We will also show the way higher order aberrations affect the manifest refraction procedure. Finally, we will present a method to optimize the prescription values of ophthalmic lenses based on ocular wavefront information. Results Independent studies have shown that such optimized ophthalmic lenses provide on average an improvement in visual acuity of almost one line under mesopic conditions, when compared to conventional opththalmic lenses. Conclusion Visual performance under low light conditions can be improved by ophthalmic lenses whose prescription was optimized taking into account ocular wavefront information. Commercial interest [source]

Ocular wavefront analysis and contrast sensitivity in eyes implanted with AcrySof IQ or AcrySof Natural intraocular lenses

ACTA OPHTHALMOLOGICA, Issue 7 2009
Tamer Takmaz
Abstract. Purpose:, This study aimed to compare ocular wavefront aberrations for pupil diameters of 4 mm and 6 mm, and contrast sensitivity, in eyes with AcrySof IQ and AcrySof Natural intraocular lenses (IOLs). Methods:, Sixty eyes of 60 patients were enrolled in this prospective randomized study. After phacoemulsification the eyes received either AcrySof IQ SN60WF or AcrySof Natural SN60AT IOLs. One month after surgery, all patients underwent complete ophthalmological examination including corneal topography, wavefront analysis for pupil diameters of 4 mm and 6 mm, and contrast sensitivity measurements with the CSV 1000E instrument under photopic and mesopic conditions with and without glare. Results:, There was no statistically significant difference between groups in age, sex or other preoperative ocular characteristics (p > 0.05). Patients with AcrySof IQ IOLs had higher contrast sensitivity at 6 c.p.d. under photopic conditions, at 6 c.p.d. and 18 c.p.d. under mesopic conditions, and at 6 c.p.d., 12 c.p.d. and 18 c.p.d. under mesopic conditions with glare (p < 0.05). Corneal spherical aberration was 0.273 ± 0.074 ,m in the AcrySof Natural group and 0.294 ± 0.086 ,m in the AcrySof IQ group (p = 0489). Ocular spherical aberration was 0.362 ± 0.141 ,m and 0.069 ± 0.043 ,m (p < 0.001) for 6-mm diameter pupils and 0.143 ± 0.091 ,m and 0.017 ± 0.016 ,m (p < 0.001) for 4-mm diameter pupils, with AcrySof Natural and AcrySof IQ IOLs, respectively. There were no significant differences in other higher-order aberrations between the groups (p > 0.05). Conclusions:, Aspherical AcrySof IQ IOLs significantly reduced spherical aberration for pupil diameters of both 4 mm and 6 mm and also improved contrast sensitivity more than spherical AcrySof Natural IOLs, especially in mesopic conditions. [source]