Visual acuity measures do not reliably detect childhood refractive error - an epidemiological study

Purpose To investigate the utility of uncorrected visual acuity measures in screening for refractive error in white school children aged 6-7-years and 12-13-years. Methods The Northern Ireland Childhood Errors of Refraction (NICER) study used a stratified random cluster design to recruit children from schools in Northern Ireland. Detailed eye examinations included assessment of logMAR visual acuity and cycloplegic autorefraction. Spherical equivalent refractive data from the right eye were used to classify significant refractive error as myopia of at least 1DS, hyperopia as greater than +3.50DS and astigmatism as greater than 1.50DC, whether it occurred in isolation or in association with myopia or hyperopia. Results Results are presented from 661 white 12-13-year-old and 392 white 6-7-year-old school-children. Using a cut-off of uncorrected visual acuity poorer than 0.20 logMAR to detect significant refractive error gave a sensitivity of 50% and specificity of 92% in 6-7-year-olds and 73% and 93% respectively in 12-13-year-olds. In 12-13-year-old children a cut-off of poorer than 0.20 logMAR had a sensitivity of 92% and a specificity of 91% in detecting myopia and a sensitivity of 41% and a specificity of 84% in detecting hyperopia. Conclusions Vision screening using logMAR acuity can reliably detect myopia, but not hyperopia or astigmatism in school-age children. Providers of vision screening programs should be cognisant that where detection of uncorrected hyperopic and/or astigmatic refractive error is an aspiration, current UK protocols will not effectively deliver.

Visual comparison of multifocal contact lens to monovision

Purpose. To compare visual function with the Bausch & Lomb PureVision multifocal contact lens to monovision with PureVision single vision contact lenses. Methods. Twenty presbyopic subjects were fitted with either the PureVision multifocal contact lens or monovision with PureVision singlevision lenses. Aftera 1-month trial, the following assessments of visual function were made: (a) distance, intermediate, and near visual acuity (VA); (b) reading ability; (c) distance and near contrast sensitivity function (CSF); (d) near range of clear vision; (e) stereoacuity; and (f) subjective evaluation of near vision ability with a standardized questionnaire. Subjects were then refitted with the alternative correction and the procedure was repeated. All measurements were compared between the two corrections, whereas the ``low addition'' multifocal lens was also compared with the ``high addition'' alternative. Results. Distance and near VA were significantly better with monovision than with the multifocal option (p < 0.05). Intermediate VA (p = 0.13) was similar with both corrections, whereas there was also no significant difference in distance and near CSF (p = 0.29 on both occasions). Reading speeds (p = 0.48) and the critical print size (p = 0.90) were not significantly different between the two contact lens corrections, but stereoacuity (p < 0.01) and the near range of clear vision (p < 0.05) were significantly better with the multifocal option than with monovision. Subjective assessment of near ability was similar for both types of contact lens (p = 0.52). The high addition multifocal lens produced significantly poorer distance and near CSF, near VA, and critical print size compared with the low addition alternative. Conclusions. Monovision performed better than a center-near aspheric simultaneous vision multifocal contact lens of the same material for distance and near VA only. The multifocal option provides better stereoacuity and near range of clear vision, with little differences in CSF, so a better balance of real-world visual function may be achieved due to minimal binocular disruption. (Optom Vis Sci 2009;86:98-105)

Probabilistic methods for drug discovery

This thesis introduces a flexible visual data exploration framework which combines advanced projection algorithms from the machine learning domain with visual representation techniques developed in the information visualisation domain to help a user to explore and understand effectively large multi-dimensional datasets. The advantage of such a framework to other techniques currently available to the domain experts is that the user is directly involved in the data mining process and advanced machine learning algorithms are employed for better projection. A hierarchical visualisation model guided by a domain expert allows them to obtain an informed segmentation of the input space. Two other components of this thesis exploit properties of these principled probabilistic projection algorithms to develop a guided mixture of local experts algorithm which provides robust prediction and a model to estimate feature saliency simultaneously with the training of a projection algorithm.Local models are useful since a single global model cannot capture the full variability of a heterogeneous data space such as the chemical space. Probabilistic hierarchical visualisation techniques provide an effective soft segmentation of an input space by a visualisation hierarchy whose leaf nodes represent different regions of the input space. We use this soft segmentation to develop a guided mixture of local experts (GME) algorithm which is appropriate for the heterogeneous datasets found in chemoinformatics problems. Moreover, in this approach the domain experts are more involved in the model development process which is suitable for an intuition and domain knowledge driven task such as drug discovery. We also derive a generative topographic mapping (GTM) based data visualisation approach which estimates feature saliency simultaneously with the training of a visualisation model.

Magnetoencephalography:technical improvements in image co-registration and studies of visual cortical oscillations

The work presented in this thesis is divided into two distinct sections. In the first, the functional neuroimaging technique of Magnetoencephalography (MEG) is described and a new technique is introduced for accurate combination of MEG and MRI co-ordinate systems. In the second part of this thesis, MEG and the analysis technique of SAM are used to investigate responses of the visual system in the context of functional specialisation within the visual cortex. In chapter one, the sources of MEG signals are described, followed by a brief description of the necessary instrumentation for accurate MEG recordings. This chapter is concluded by introducing the forward and inverse problems of MEG, techniques to solve the inverse problem, and a comparison of MEG with other neuroimaging techniques. Chapter two provides an important contribution to the field of research with MEG. Firstly, it is described how MEG and MRI co-ordinate systems are combined for localisation and visualisation of activated brain regions. A previously used co-registration methods is then described, and a new technique is introduced. In a series of experiments, it is demonstrated that using fixed fiducial points provides a considerable improvement in the accuracy and reliability of co-registration. Chapter three introduces the visual system starting from the retina and ending with the higher visual rates. The functions of the magnocellular and the parvocellular pathways are described and it is shown how the parallel visual pathways remain segregated throughout the visual system. The structural and functional organisation of the visual cortex is then described. Chapter four presents strong evidence in favour of the link between conscious experience and synchronised brain activity. The spatiotemporal responses of the visual cortex are measured in response to specific gratings. It is shown that stimuli that induce visual discomfort and visual illusions share their physical properties with those that induce highly synchronised gamma frequency oscillations in the primary visual cortex. Finally chapter five is concerned with localization of colour in the visual cortex. In this first ever use of Synthetic Aperture Magnetometry to investigate colour processing in the visual cortex, it is shown that in response to isoluminant chromatic gratings, the highest magnitude of cortical activity arise from area V2.

An investigation of reading ability and visual function with eccentric visual field

This study investigated the detrimental effect of central field loss (CFL) on reading ability and general visual function. The aim was to improve the understanding of reading with eccentric retina in order that reading performances of individuals with CFL may be maximised. To improve visual ability of individuals with CFL, it is important to be able to accurately measure the outcome of any intervention. Various methods for determining visual function were therefore compared with perceived visual performance (as measured with a quality of life questionnaire) before and after surgical removal of choroidal new vessels (CNV) in macular disease patients. The results highlight the importance of low contrast measures (low contrast visual acuity and contrast sensitivity) when investigating perceived reading performance. Reading speed was found to be important for reflecting changes in general visual quality of life. Potential causes for reduced peripheral reading ability were investigated using both normally sighted and CFL subjects. For normally sighted subjects reading eccentrically with rapid serial visual presentation (RSVP) text, the inferior visual field was a better position (in terms of reading speed) for the presentation of the text. The size of the visual span was found to reduce with increasing eccentricity of fixation, providing a potential reason for reduced peripheral reading performances. The investigation of the ability to use context when reading with peripheral retina resulted in conflicting results. Studies in this thesis found both a reduction and no reduction in the ability of the peripheral retina to utilise context compared to the fovea. Individuals with long-term CFL showed no improvement in peripheral reading ability over that found for normally sighted subjects reading at the same eccentricity.

Neuro-electromagnetic imaging of the human visual cortex

Methods of solving the neuro-electromagnetic inverse problem are examined and developed, with specific reference to the human visual cortex. The anatomy, physiology and function of the human visual system are first reviewed. Mechanisms by which the visual cortex gives rise to external electric and magnetic fields are then discussed, and the forward problem is described mathematically for the case of an isotropic, piecewise homogeneous volume conductor, and then for an anisotropic, concentric, spherical volume conductor. Methods of solving the inverse problem are reviewed, before a new technique is presented. This technique combines prior anatomical information gained from stereotaxic studies, with a probabilistic distributed-source algorithm to yield accurate, realistic inverse solutions. The solution accuracy is enhanced by using both visual evoked electric and magnetic responses simultaneously. The numerical algorithm is then modified to perform equivalent current dipole fitting and minimum norm estimation, and these three techniques are implemented on a transputer array for fast computation. Due to the linear nature of the techniques, they can be executed on up to 22 transputers with close to linear speedup. The latter part of the thesis describes the application of the inverse methods to the analysis of visual evoked electric and magnetic responses. The CIIm peak of the pattern onset evoked magnetic response is deduced to be a product of current flowing away from the surface areas 17, 18 and 19, while the pattern reversal P100m response originates in the same areas, but from oppositely directed current. Cortical retinotopy is examined using sectorial stimuli, the CI and CIm ;peaks of the pattern onset electric and magnetic responses are found to originate from areas V1 and V2 simultaneously, and they therefore do not conform to a simple cruciform model of primary visual cortex.

Objective and psychophysical studies of infant visual development

Distortion or deprivation of vision during an early `critical' period of visual development can result in permanent visual impairment which indicates the need to identify and treat visually at-risk individuals early. A significant difficulty in this respect is that conventional, subjective methods of visual acuity determination are ineffective before approximately three years of age. In laboratory studies, infant visual function has been quantified precisely, using objective methods based on visual evoked potentials (VEP), preferential looking (PL) and optokinetic nystagmus (OKN) but clinical assessment of infant vision has presented a particular difficulty. An initial aim of this study was to evaluate the relative clinical merits of the three techniques. Clinical derivatives were devised, the OKN method proved unsuitable but the PL and VEP methods were evaluated in a pilot study. Most infants participating in the study had known ocular and/or neurological abnormalities but a few normals were included for comparison. The study suggested that the PL method was more clinically appropriate for the objective assessment of infant acuity. A study of normal visual development from birth to one year was subsequently conducted. Observations included cycloplegic refraction, ophthalmoscopy and preferential looking visual acuity assessment using horizontally and vertically oriented square wave gratings. The aims of the work were to investigate the efficiency and sensitivity of the technique and to study possible correlates of visual development. The success rate of the PL method varied with age; 87% of newborns and 98% of infants attending follow-up successfully completed at least one acuity test. Below two months monocular acuities were difficult to secure; infants were most testable around six months. The results produced were similar to published data using the acuity card procedure and slightly lower than, but comparable with acuity data derived using extended PL methods. Acuity development was not impaired in infants found to have retinal haemorrhages as newborns. A significant relationship was found between newborn binocular acuity and anisometropia but not with other refractive findings. No strong or consistent correlations between grating acuity and refraction were found for three, six or twelve months olds. Improvements in acuity and decreases in levels of hyperopia over the first week of life were suggestive of recovery from minor birth trauma. The refractive data was analysed separately to investigate the natural history of refraction in normal infants. Most newborns (80%) were hyperopic, significant astigmatism was found in 86% and significant anisometropia in 22%. No significant alteration in spherical equivalent refraction was noted between birth and three months, a significant reduction in hyperopia was evident by six months and this trend continued until one year. Observations on the astigmatic component of the refractive error revealed a rather erratic series of changes which would be worthy of further investigation since a repeat refraction study suggested difficulties in obtaining stable measurements in newborns. Astigmatism tended to decrease between birth and three months, increased significantly from three to six months and decreased significantly from six to twelve months. A constant decrease in the degree of anisometropia was evident throughout the first year. These findings have implications for the correction of infantile refractive error.

Factors affecting the accommodative response to sustained visual tasks

In the absence of adequate visual stimulation accommodation adopts an intermediate resting position, appropriately termed tonic accommodation (TA). A period of sustained fixation can modify the tonic resting position, and indicate the adaptation properties of TA. This thesis investigates various factors contributing to the accommodative response during sustained visual tasks, in particular the adaptation of TA. Objective infra-red optometry was chosen as the most effective method of measurement of accommodation. This technique was compared with other methods of measuring TA and the results found to be well correlated. The inhibitory sympathetic input to the ciliary muscle provides the facility to attenuate the magnitude and duration of adaptive changes in TA. This facility is, however, restricted to those individuals having relatively high levels of pre-task TA. Furthermore, the facility is augmented by substantial levels of concurrent parasympathetic activity. The imposition of mental effort can induce concurrent changes in TA which are predominantly positive and largely the result of an increase in parasympathetic innervation of the ciliary muscle although there is some evidence for sympathetic attentuation at higher levels of TA. In emmetropes sympathetic inhibition can modify the effect of mental effort on the steady-state accommodative response at near. Late-onset myopes (onset after the age of 15 years) have significantlylower values of TA then emmetropes. Similarly, late-onset myopes show lower values of steady-state accommodative response for nearstimuli. The imposition of mental effort induces concurrent increases in TA and steady-state accommodative response in the myopic group which are significantly greater than those for emmetropes. Estimates of TA made under bright empty-field conditions are well correlated with those made under darkroom conditions. The method by which the accommodative loop is opened has no significant effect on the magnitude and duration of post-task shifts in TA induced by a near vision task. Significant differences in the post-task shifts in TA induced by a near vision task exist between emmetropes and late-onset myopes, the post-task shifts being more sustained for the myopic group.

Effect of disability glare on visual performance

The object of the study was to investigate, establish and quantify the relationship between contrast sensitivity, intraocular light scatter and glare. The aim was to establish the effects on vision, in an effort to provide a more comprehensive understanding of the visual world of subjects prone to increased light scatter in the eye. Disability glare refers to the reduction in visual performance produced by a glare source. The reduction in visual performance can be explained by intraocular scattered light producing a veiling luminance which is superimposed upon the retinal image. This veiling luminance lowers contrast thus sensitivity to the stimulus declines. The effect of glare of luminance and colour contrast sensitivity for young and elderly subjects was examined. For both age groups, disability glare was greatest for the red-green stimulus and least for the blue-yellow. The precise effect of a glare source on colour discrimination depends upon the interaction between the chromaticity of the glare source and that of the stimulus. The effect of a long wavelength pass (red) and a short wavelength pass filter (blue) on disability glare was examined. Disability glare was not significantly different with the red and blue filters, even in the presence of wavelength dependent scatter. An equation was derived which allowed an intrinsic Light Scatter Factor (LSF) to be determined for any given glare angle (Paulsson and Sjöstrand, 1980). Corrections to the formula to account for factors such as pupil size changes are unnecessary. The results confirm the suitability of measuring the LSF using contrast threshold with and without glare, provided that appropriate methods are used. Using this formula an investigation into the amount of wavelength dependent scatter indicated that wavelength dependent scatter in normal young, elderly or cataractous eyes is of little or no significance. Finally, it seemed desirable to investigate the effect ultraviolet (UV) radiation has on intraocular light scatter and subsequently visual performance. Overall the results indicated that the presence or absence of UV radiation has relatively little effect on visual function for the young, elderly or cataract patient.

Quantification of visual field loss in age-related macular degeneration

Background - An evaluation of standard automated perimetry (SAP) and short wavelength automated perimetry (SWAP) for the central 10–2 visual field test procedure in patients with age-related macular degeneration (AMD) is presented in order to determine methods of quantifying the central sensitivity loss in patients at various stages of AMD. Methods - 10–2 SAP and SWAP Humphrey visual fields and stereoscopic fundus photographs were collected in 27 eyes of 27 patients with AMD and 22 eyes of 22 normal subjects. Results - Mean Deviation and Pattern Standard Deviation (PSD) varied significantly with stage of disease in SAP (both p<0.001) and SWAP (both p<0.001), but post hoc analysis revealed overlap of functional values among stages. In SWAP, indices of focal loss were more sensitive to detecting differences in AMD from normal. SWAP defects were greater in depth and area than those in SAP. Central sensitivity (within 1°) changed by -3.9 and -4.9 dB per stage in SAP and SWAP, respectively. Based on defect maps, an AMD Severity Index was derived. Conclusions - Global indices of focal loss were more sensitive to detecting early stage AMD from normal. The SWAP sensitivity decline with advancing stage of AMD was greater than in SAP. A new AMD Severity Index quantifies visual field defects on a continuous scale. Although not all patients are suitable for SWAP examinations, it is of value as a tool in research studies of visual loss in AMD.

Quantification of visual field loss in age-related macular degeneration

Presentation Purpose:To determine methods of quantifying the sensitivity loss in the central 10o visual field in a cross section of patients at various stages of age-related macular degeneration (AMD). Methods:Standard and short-wavelength automated perimetry (SAP and SWAP) visual fields were collected using program 10-2 of the Humphrey Field Analyzer, in 44 eyes of 27 patients with AMD and 41 eyes of 22 normal subjects. Stereoscopic fundus photographs were graded by two independent observers and the stage of disease determined. Global indices were compared for their ability to delineate the normal visual field from early stages of AMD and to differentiate between stages. Results:Mean Deviation (MD) and Pattern Standard Deviation (PSD) varied significantly with stage of disease in SAP (both p<0.001) and SWAP (both p<0.001), but post-hoc analysis revealed overlap of functional values between stages. Global indices of focal loss, PSD and local spatial variability (LSV) were the most sensitive to detecting differences between normal subjects and early stage AMD patients, in SAP and SWAP, respectively. Overall, defects were confined to the central 5°. SWAP defects were consistently greater in depth and area than those in SAP. The most vulnerable region of the 10° field to sensitivity loss with increasing stage of AMD was the central 1°, in which the sensitivity decline was -4.8dB per stage in SAP and -4.9dB per stage in SWAP. Based on the pattern deviation defect maps, a severity index of AMD visual field loss was derived. Threshold variability was considerably increased in late stage AMD eyes. Conclusions:Global indices of focal loss were more sensitive to the detection of early stage AMD from normal. The sensitivity decline with advancing stage of AMD was greater in SWAP compared to SAP, however the trend was not strong across all stages of disease. The less commonly used index LSV represents relatively statistically unmanipulated summary measure of focal loss. A new severity index is described which is sensitive to visual field change in AMD, measures visual field defects on a continuous scale and may serve as a useful measure of functional change in AMD in longitudinal studies. Keywords: visual fields • age-related macular degeneration • perimetry

Relationships between fundus image quantification and visual field status in age-related macular degeneration

Presentation Purpose:To relate structural change to functional change in age-related macular degeneration (AMD) in a cross-sectional population using fundus imaging and the visual field status. Methods:10 degree standard and SWAP visual fields and other standard functional clinical measures were acquired in 44 eyes of 27 patients at various stages of AMD, as well as fundus photographs. Retro-mode SLO images were captured in a subset of 29 eyes of 19 of the patients. Drusen area, measured by automated drusen segmentation software (Smith et al. 2005) was correlated with visual field data. Visual field defect position was compared to the position of the imaged drusen and deposits using custom software. Results:The effect of AMD stage on drusen area within the 6000µm was significant (One-way ANOVA: F = 17.231, p < 0.001), however the trend was not strong across all stages. There were significant linear relationships between visual field parameters and drusen area. The mean deviation (MD) declined by 3.00dB and 3.92dB for each log % drusen area for standard perimetry and SWAP, respectively. The visual field parameters of focal loss displayed the strongest correlations with drusen area. The number of pattern deviation (PD) defects increased by 9.30 and 9.68 defects per log % drusen area for standard perimetry and SWAP, respectively. Weaker correlations were found between drusen area and visual acuity, contrast sensitivity, colour vision and reading speed. 72.6% of standard PD defects and 65.2% of SWAP PD defects coincided with retinal signs of AMD on fundus photography. 67.5% of standard PD defects and 69.7% of SWAP PD defects coincided with deposits on retro-mode images. Conclusions:Perimetry exhibited a stronger relationship with drusen area than other measures of visual function. The structure-function relationship between visual field parameters and drusen area was linear. Overall the indices of focal loss had a stronger correlation with drusen area in SWAP than in standard perimetry. Visual field defects had a high coincidence proportion with retinal manifestations of AMD.Smith R.T. et al. (2005) Arch Ophthalmol 123:200-206.

Visual field and structural correlates of progression in age-related macular degeneration

Presentation Purpose:To examine the correlation of central visual field loss and progression of structural changes in the macular area in age-related macular degeneration (AMD). Methods:Central 10° standard and short-wavelength automated perimetry (SWAP) visual fields were acquired in 39 eyes of 24 patients with AMD using a Humphrey Field Analyzer. Stereoscopic fundus photographs were graded1 by two independent observers and the stage of disease determined2. Custom software mapped perimetric data onto fundus images in order to relate structural changes to functional loss. Results:Mean deviation (MD) in standard perimetry changed from 0.04 dB at stage 1 to -12.39 dB at stage 4 (r2=0.48, p<0.001). The group mean SWAP MD was -5.26 dB at stage 1 and increased to -17.08 dB at stage 4 (r2=0.53, p<0.001). Pattern standard deviation (PSD) also increased with advancing stage in standard perimetry; 1.32 dB to 8.67 dB at stage 1 and 4, respectively (r2=0.54, p<0.001). In SWAP, PSD increased from 2.86 dB to 5.63 dB at stage 1 and stage 4 (r2=0.43, p<0.001). Defect frequency was greater in SWAP than standard perimetry. Early stage defects occurred with the greatest frequency at eccentricities of 3.2° and 5.1° in standard perimetry and at 4.2° in SWAP. Late stage defects were most frequent at 1° eccentricity in standard perimetry and at 1° and 9° in SWAP. MD declined with increasing affected retinal area over the central 3000µm; by 0.20 dB (r2=0.67, p<0.001) and 0.18 dB (r2=0.49, p<0.001) per % increase in defect area for standard perimetry and SWAP respectively. 41% of defects were associated with structural changes on the retina in standard perimetry and 43% in SWAP. Conclusions:Sensitivity decreased with advancing stage of AMD, with a greater effect demonstrated in SWAP compared to standard perimetry. The central field became less uniform as stage increased. SWAP defects occurred at similar locations but were deeper and wider than corresponding defects in standard perimetry. Central loss in SWAP is a sensitive marker of functional progression in AMD.1. Bird et al. (1995) Surv Ophthalmol 39:367-3742. van Leeuwen et al. (2003) Arch Ophthalmol 121:519-526

Methodology of photic stimulation revisited:updated European algorithm for visual stimulation in the EEG laboratory

Intermittent photic stimulation (IPS) is a common procedure performed in the electroencephalography (EEG) laboratory in children and adults to detect abnormal epileptogenic sensitivity to flickering light (i.e., photosensitivity). In practice, substantial variability in outcome is anecdotally found due to the many different methods used per laboratory and country. We believe that standardization of procedure, based on scientific and clinical data, should permit reproducible identification and quantification of photosensitivity. We hope that the use of our new algorithm will help in standardizing the IPS procedure, which in turn may more clearly identify and assist monitoring of patients with epilepsy and photosensitivity. Our algorithm goes far beyond that published in 1999 (Epilepsia, 1999a, 40, 75; Neurophysiol Clin, 1999b, 29, 318): it has substantially increased content, detailing technical and logistical aspects of IPS testing and the rationale for many of the steps in the IPS procedure. Furthermore, our latest algorithm incorporates the consensus of repeated scientific meetings of European experts in this field over a period of 6 years with feedback from general neurologists and epileptologists to improve its validity and utility. Accordingly, our European group has provided herein updated algorithms for two different levels of methodology: (1) requirements for defining photosensitivity in patients and in family members of known photosensitive patients and (2) requirements for tailored studies in patients with a clear history of visually induced seizures or complaints, and in those already known to be photosensitive.

Abnormal visual habituation in pediatric photosensitive epilepsy

Objective - To investigate visual habituation – a measure of visual cortical excitability – in photosensitive patients in pediatric age and compare the findings with a matched sample with idiopathic generalized epilepsies without photosensitivity and with normally developing children. Methods - We presented a full-field black-and-white checkerboard pattern, at 3 reversal/s with 100% contrast binocularly for 600 consecutive trials and measured the N75–P100 and P100–N145 pattern-reversal visual evoked potential inter-peak amplitudes and N75, P100, N145 latencies for the six blocks of 100 responses. As a measure of habituation we used the slope of the linear regression line of the N75–P100 and P100–N145 peak-to-peak amplitudes. The slope of the linear regression line of the N75–P100 and P100–N145 latencies was also analyzed. Results - Statistical analysis revealed significant differences between the three groups in the slope index of N75–P100 PR-VEP amplitude, with increased or constant amplitude in the PS group compare to the IGE and ND across the six blocks. Conclusions - Our results support the notion that photosensitivity is associated with altered control of excitatory and inhibitory cortical processes. The causal relationship between habituation deficit and photo-paroxysmal response needs to be further investigated with longitudinal studies. Significance This study supports the hypothesis that suppression of PR-VEP is a sensitive intermediate phenotype, which discriminates patients with photosensitivity from those with generalized epilepsies in pediatric age.