Human Electroretinography Shows Little Polarity Specificity Following Full-Field Ramp Adaptation.

Purpose: The ramp aftereffect, a visual phenomenon in which perception of light changes dynamically after exposure to sawtooth-modulated light, was first described in 1967. Despite decades of psychophysical research, location and mechanisms of its generation remain unknown. In this study, we investigated a potential retinal contribution to effect formation with specific emphasis on on-/off-pathway involvement. Methods: A 100 ms flash electroretinogram (ERG) was employed to probe the adaptive state of retinal neurons after presentation of stimuli that were homogenous in space but modulated in time following a sawtooth pattern (upward or downward ramps at 2 Hz). Additionally, a psychophysical nulling experiment was performed. Results: Psychophysics data confirmed previous findings that the ramp aftereffect opposes the adapting stimuli in ramp direction and is stronger after upward ramps. The ERG study revealed significant changes of activity in every response component in the low-frequency range (a-wave, b-wave, on-PhNR, d-wave and off-PhNR) and high-frequency range (oscillatory potentials) in amplitudes, peak times, or both. The changes are neither specific to the on- or off-response nor antagonistic between ramp directions. With downward ramp adaptation, effects were stronger. Neither amplitudes nor peak times were correlated with perception strength. Amplitudes and peak times were uncorrelated, and the effect diminished over time, ceasing almost completely with three seconds. Conclusions: Despite abundant effects on retinal responses, the pattern of adaptational effects was not specific to the sawtooth nature of adaptation. Although not ruling out retinal contributions the present findings favor post-retinal mechanisms as the primary locus of the ramp aftereffect.

The adaptive global effect: Luminance contrast modulates the global effect zone.

When two peripheral objects are presented in close proximity, saccades towards one of these objects land at a weighted average location between the two objects. This phenomenon, known as the 'global effect' or 'saccade averaging', disappears when the distance between the objects increases. When objects are further apart, outside the averaging zone, saccades land on one of the objects with little or no saccade averaging. Although it is known that the strength of the global effect is dependent on the specific features of the two objects, it is unclear if the size of the zone in which averaging can occur (i.e., the averaging zone) is adaptive. The aim of the current study was to investigate whether the size of the averaging zone adapts to variations in object luminance contrast of the objects. In order to systematically assess changes in the averaging zone, in two experiments, observers made saccadic eye movements while the luminance of the target and the distractor varied. We report three major findings: 1) When a distractor was more luminant relative to the target, the averaging zone increased (Exp. 1). Notably, saccade averaging never entirely ceased to exist, even for remote distractors. 2) When target and distractor were equiluminant, the averaging zone did not change with absolute luminance (Exp. 2). 3) Higher (relative and absolute) luminance increased the averaging zone especially for shorter saccadic response times (SRT). We conclude that the averaging zone is adaptive and becomes larger with increasing relative luminance and especially when SRTs are short.

Adaptative machine vision with microsecond-level accurate perception beyond human retina.

Visual adaptive devices have potential to simplify circuits and algorithms in machine vision systems to adapt and perceive images with varying brightness levels, which is however limited by sluggish adaptation process. Here, the avalanche tuning as feedforward inhibition in bionic two-dimensional (2D) transistor is proposed for fast and high-frequency visual adaptation behavior with microsecond-level accurate perception, the adaptation speed is over 104 times faster than that of human retina and reported bionic sensors. As light intensity changes, the bionic transistor spontaneously switches between avalanche and photoconductive effect, varying responsivity in both magnitude and sign (from 7.6 × 104 to -1 × 103 A/W), thereby achieving ultra-fast scotopic and photopic adaptation process of 108 and 268 µs, respectively. By further combining convolutional neural networks with avalanche-tuned bionic transistor, an adaptative machine vision is achieved with remarkable microsecond-level rapid adaptation capabilities and robust image recognition with over 98% precision in both dim and bright conditions.

Effect of 4-week preoperative prism adaptation in preventing postoperative residual esotropia.

BACKGROUND: Preoperative prism adaptation (PPA) simulates postoperative status and possibly can predict postoperative undercorrection before surgery in esotropia. The present study aimed to assess the effect of 4-week PPA in preventing postoperative residual esotropia. METHODS: Seventy-five (75) esotropes who had undergone surgery at a single strabismus center were retrospectively enrolled. They included 25 basic, 31 acute comitant, 10 partially accommodative, and 9 recurrent esotropia patients. The preoperative deviation angle, which had been determined using the alternating prism and cover test, was fully corrected with press-on prisms 4 weeks before surgery. If there was an increase of 5 PD or more of esodeviation, the prisms were changed accordingly at 2 weeks. The deviation angle measured at 4 weeks was determined as the surgical target angle. Patients were then divided into increase (≥ 5 PD increase of angle during 4-week PPA) and non-increase groups. Success was defined as either esodeviation of 8 PD or under or exodeviation of 5 PD or under at distance at postoperative 6 months. RESULTS: The increase group included 44 patients (58.7%). The mean deviation angle before PPA was 27.4 PD, and after the 4-week PPA, there was an average increase of 9.4 PD. The success rate was 90.9% in the increase group and 96.8% in the non-increase group (p = 0.316). There were no intergroup differences in preoperative clinical characteristics, esotropia types, postoperative deviation angle or postoperative near stereopsis (p > 0.05). CONCLUSIONS: The results of this study indicated a beneficial effect of 4-week PPA in esotropia of various types, specifically by uncovering the hidden esodeviation in the increase group and simulating the postoperative alignment in both the increase and the non-increase groups.

Retinal development and photoreceptor synaptic ultrastructure are altered by abnormal rearing light regimes

The effects of light rearing regimen on distal retinal development and photoreceptor ultrastructure were investigated using light and electron microscopy. Zebrafish larvae were reared in constant light, control/cyclic light (14 hr light/10 hr dark), or constant dark conditions until 4 or 8 days postfertilization (dpf). Gross retinal morphology was not altered by light rearing conditions; however, ultrastructural differences were noted both within and between age groups. Significant differences were seen in photoreceptor outer segments (OS) and synaptic ribbons, the size of cone photoreceptor mitochondria, and postsynaptic horizontal cell spinules. Larvae reared in constant dark displayed reduced pigment dispersion; OS development was delayed and cone mitochondria were smaller at 4dpf, two results that reversed by 8dpf. Photoreceptor terminals of larvae reared in all treatment conditions displayed anchored synaptic ribbons with arciform densities and no significant differences in ribbon number. Ribbons were 30- 40% longer in photoreceptor terminals within the constant light treatment. The number of horizontal cell spinules invaginating into cone terminals varied and the spinule-to-ribbon ratio was higher in control and constant light-reared tissue by more than 2x at 4dpf. By 8dpf, this ratio was significantly highest in retinas reared in control/cyclic light conditions. Taken together, these results show that abnormal light rearing conditions affect synaptic structure in distal retina. These changes suggest a mechanism for the physiological and behavioral deficits reported in zebrafish larvae grown under constant light and/or dark conditions

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Effects of light on the circadian rhythm of diabetic rats under restricted feeding

The aim of this study was to investigate whether the entrainment of light cue is affected or not in diabetic animals. We found that the individual light/dark (LD) reversal showed a tissue- and gene-specific effect on the circadian phases of peripheral clock genes, which was generally similar between the control and diabetic rats. In the liver and heart, the peak phases of examined clock genes (Bmal1, Rev-erb¥á, Per1, and Per2) were slightly shifted by 0¡­4 h in the liver and heart of control and diabetic rats. However, we found that the peak phases of these clock genes were greatly shifted by 8¡­12 h after the LD reversal for 7 days in the pineal gland of both control and diabetic rats. However, the activity rhythm was greatly different between two groups. After the individual LD reversal, the activity rhythm was completely shifted in the control rats but retained in the diabetic rats. These observations suggested that the behavioral rhythm of diabetic rats may be uncoupled from the master clock after the individual LD reversal. Moreover, we also found that the serum glucose levels of diabetic rats kept equally high throughout the whole day without any shift of peak phase after the individual reversal of LD cycle. While the serum glucose levels of control rats were tightly controlled during the normal and LD reversal conditions. Thus, the impaired insulin secretion induced uncontrollable serum glucose level may result in uncoupled activity rhythm in the diabetic rats after the individual LD reversal

Resultados preliminares de um sistema computadorizado e estereoscópico para pupilometria in vivo / Preliminary results of a computerized and stereoscopic system for in vivo pupillometry

OBJETIVOS: Desenvolver um sistema digital, com capacidade de induzir acomodação, para medida do diâmetro e formato da pupila para dez diferentes níveis de iluminação (LUX), variando do nível mesópico ao fotópico. MÉTODOS: Um sistema óptico para conjugar imagens da pupila iluminada por LED infravermelho e branco foi projetado e montado usando um capacete típico de oftalmoscópio e uma máscara típica de mergulhador como suporte e uma câmera CCD de alta resolução e sensibilidade. Algoritmos usando princípios de processamento de imagens foram implementados para leitura do arquivo de vídeo e a detecção automática do centro geométrico e diâmetro da pupila para cada quadro. RESULTADOS: Apresentamos dados preliminares deste sistema para um paciente voluntário. Os dados sobre posição horizontal (x), vertical (y) do centro geométrico e do diâmetro da pupila foram exportados para arquivos texto que podem ser impressos usando um programa convencional de planilha (Excel). O processo de acomodação é garantido por uma mira virtual (LED branco) localizada a 6 metros do olho do paciente e o nível de iluminação é precisamente controlado por uma placa eletrônica que alimenta o LED central que tem sua potência controlada pelo "software". CONCLUSÕES: Com o instrumento desenvolvido dados precisos da posição e tamanhos da pupila podem então ser obtidos estereoscopicamente (para ambas as pupilas e ao mesmo tempo) para qualquer paciente. Acreditamos que tal instrumento possa ser útil em algumas práticas oftálmicas onde as características geométricas da pupila sejam importantes.

PURPOSE: We developed a digital system with accommodation capacities for measurement of the diameter and shape of the in vivo pupil for 10 different levels of illumination intensity, varying from mesopic to photopic. METHODS: An optical system for conjugating images from an infrared and white light illuminated pupil was designed and mounted using an ophthalmoscope helmet and a typical diving mask as support for a high-resolution and sensitivity CCD. Using an IBM compatible computer sequences of video in AVI format were digitized for several seconds at a mean rate of 30 Hz. Algorithms using principles of image processing were implemented for detection of the pupil edges. RESULTS: We present preliminary results of this system for a voluntary patient. Data for the horizontal (x) and vertical (y) central position and for the diameter of the pupil were then exported to files that could be read by typical spread sheet programs (Excel). CONCLUSIONS: In this manner, precise data can be obtained stereoscopically (for both pupils at the same time) for any patient, given that the accommodation process is guaranteed by using a white LED virtual mire located 6 meters from the patient's eye. An electronic board precisely controls the level of illumination. We believe here developed instrument may be useful in certain ophthalmic practices where precise pupil geometric data are needed.

New comparative ultrasound biomicroscopic findings between fellow eyes of acute angle closure and glaucomatous eyes with narrow angle / Novos achados comparativos de biomicroscopia ultra-sônica entre olhos contralaterais com fechamento angular agudo e olhos glaucomatosos com ângulo estreito

PURPOSE: To compare morphometric features between fellow acute primary angle-closure (APAC) eyes and glaucomatous or suspect eyes with narrow angle (NA). METHODS: Fellow eyes of 30 patients with unilateral APAC and 30 with NA were evaluated by ultrasound biomicroscopy (UBM) under light and dark conditions. UBM parameters such as anterior chamber depth (ACD), angle opening distance at 250 µm/500 µm from the scleral spur (AOD250/AOD500), trabecular ciliary process distance (TCPD) and iris-lens contact distance (ILCD) were measured in the superior (SQ) and inferior (IQ) quadrants. RESULTS: Significant differences between APAC fellow and NA eyes were found in ACD, P<0.001; AOD250 at SQ and IQ, P<0.001; AOD500 at SQ and IQ, P<0.001; TCPD light, P=0.010 and TCPD dark at SQ, P=0.031; and TCPD light at IQ, P=0.010. Significant differences between light and dark examinations of APAC fellow eyes were found in ILCD (P=0.009) at SQ and ILCD at IQ (P=0.006), and of NA eyes in ILCD at SQ (P=0.047) and ILCD at IQ (P<0.001). CONCLUSIONS: APAC fellow eyes have a more crowded anterior segment and shallower ACD than NA eyes. ILCD decreases in both groups when the illumination conditions change from light to dark.

OBJETIVO: Comparar características morfométricas entre olhos contralaterais com fechamento angular primário agudo (FAPA) e olhos glaucomatosos ou suspeitos com ângulo estreito (AE). MÉTODOS: Olhos contralaterais de 30 pacientes com FAPA unilateral e olhos de 30 pacientes com AE foram avaliados através da biomicroscopia ultra-sônica (BUS) no claro e escuro. Parâmetros da BUS como a profundidade central de câmara anterior (PCA), distância da abertura angular a 250 µm/500 µm do esporão escleral (AOD250/AOD500), distância entre o processo ciliar e o trabeculado (TCPD) e distância do contato iris-cristalino (ILCD) foram medidos nos quadrantes superior (QS) e inferior (QI). RESULTADOS: Diferenças significativas entre olhos contralaterais de FAPA e olhos com AE foram encontradas na PCA, p<0,001; AOD250 no QS e QI, p<0,001; AOD500 no QS e QI, p<0,001; TCPD no claro, p=0,010 e TCPD no escuro no QS, p=0,031; e TCPD no claro no QI, p=0,010. Diferenças significativas entre exames no claro e escuro realizados em olhos contralaterais com FAPA foram encontradas na ILCD (p=0,009) no QS e ILCD no QI (p=0,006), e em olhos com SE na ILCD no QS (p=0,047) e ILCD no QI (p<0,001). CONCLUSÕES: Olhos contralaterais de FAPA apresentam um segmento anterior mais aglomerado e uma PCA menor que olhos com AE. ILCD diminui em ambos os grupos quando as condições de iluminação mudam do claro para o escuro.

Adaptación de lentes de contacto rígidas permeables al gas en un caso de glaucoma congénito / Rigid gas permeable contact lenses fitted in a case of congenital glaucoma

Caso clínico: Mujer de 27 años tratada de glaucoma congénito con alta miopía, baja AV y nistagmus en ambos ojos, fue referida para adaptar lentes de contacto. Se adaptan lentes de contacto rígidas permeables a los gases (LC RPG) asféricas y de alta transmisibilidad en uso diario. La paciente mejoró la AV con confort durante 10 horas al día de porte. Discusión: La adaptación de lentes de contacto se realizó teniendo en cuenta la topografía corneal de la paciente. Consideramos las lentes de contacto permeables al gas como las lentes de primera elección para estos pacientes, que con una adecuada adaptación y seguimientos pueden utilizar con seguridad lentes de contacto RPG en uso diario

Case report: A 27-year-old woman with congenital glaucoma with high myopia, low visual acuity and nystagmus in both eyes, was referred for contact lens fitting. We fitted her with aspherical rigid gas permeable (RGP) contact lenses with high transmissibility, which she wore on a daily basis. Her visual acuity improved with the wearing of these lenses, which remained comfortable whilst being worn for 10 hours a day. Discussion: Contact lenses were fitted according to her corneal topography. Gas permeable contact lenses were chosen as first choice and with proper fitting and vigilant follow-up they may be worn safely on a daily basis (Arch Soc Esp Oftalmol 2008; 83: 377-380)

Eletrorretinografia focal em adultos jovens normais / Focal electroretinography in normal young adults

OBJETIVO: Estabelecer valores normativos para o exame de eletrorretinograma focal em adultos jovens normais, segundo protocolo recomendado pela sociedade Internacional de Eletrofisiologia Visual Clínica (IsCEV). MÉTODOS: Participaram 33 indivíduos de idades variando entre 14 a 38 anos (média 22,96±5,73), 14 homens e 19 mulheres. O eletrorretinograma focal foi registrado a partir de um eletrodo corneano bipolar, e oftalmoscópio estimulador com luz branca intermitente em freqüências temporais de 42 Hz e 31,25 Hz na mácula. Os parâmetros, amplitude (em nanovolts) e latência (em milissegundos), foram analisados pela transformada de Fourier. Para análise estatística de ambas as freqüências, foram calculados a mediana, mínimo, máximo, percentis e teste t entre as amplitudes e as latências. RESULTADOS: Para 42 Hz. Amplitude: mediana 614nV; 1° quartil 529nV; 3° quartil 650nV; mínimo 370nV; máximo 794nV; percentil 2,5 378,8nV; percentil 97,5 779,6nV. Latência: mediana 26,4ms; 1° quartil 25,4ms; 3° quartil 26,8ms; mínimo 23,4ms; máximo 28,2ms; percentil 2,5 23,8ms; percentil 97,5 27,88ms. Para 31,25Hz. Amplitude: mediana 632nV; 1° quartil 429nV; 3° quartil 750nV; mínimo 364nV; máximo 1036nV; percentil2,5 364,8nV; percentil 97,5 1018,4nV. Latência: mediana 30,1ms; 1° quartil 29,3ms; 3° quartil 31,2ms; mínimo 25,9ms; máximo 33,9ms; percentil 2,5 27,18ms; percentil 97,5 27,88ms. CONCLUSÃO: O presente estudo estabelece limites de normalidade para o exame de eletrorretinografia focal em adultos jovens para freqüências temporais de 42Hz e 31,25 Hz. Os resultados encontrados mostram valores similares de amplitude para ambas as freqüências temporais e latência significantemente mais rápida para a freqüência de 42 Hz.

Wheel-running and rest activity pattern interaction in two octodontids (Octodon degus, Octodon bridgesi)

Wheel-running and other non-photic stimuli influence the rest-activity pattern of diurnal and nocturnal mammals. A day to night inversion of phase preference of activity was described among Octodon degus, when exposed to ad-libitum wheel running. We have studied the rest-activity pattern response in presence of ad libitum wheel-running in wild-captured male individuals from two species of genus Octodon: O. degus (n=9, crepuscular-diurnal) and O. bridgesi (n=3, nocturnal). After two months of habituation to laboratory conditions, recordings were performed in isolation chambers under a 12:12 light-dark schedule with or without access to a running wheel. Actograms were constructed from data obtained by an automated acquisition system. O. bridgesi were also recorded under constant darkness, with or without access to wheel-running. Entrained to the light-dark schedule, a crepuscular pattern of activity was evident for O. degus, whereas O. bridgesi displayed a robust nocturnal chronotype. The activity of O. degus observed during the dark phase was enhanced when wheel-running was allowed. No significant change in phase preference was observed for O. bridgesi when wheel-running was allowed. A lengthening of endogenous period was observed in O. bridgesi after wheel-running exposure under constant darkness. Nocturnal and diurnal octodontids exhibit different masking responses to wheel-running.

Uso da topografia de córnea na adaptação de lente de contato rígida gás-permeável em pacientes portadores de ceratocone: descrição de técnica e resultados preliminares / Use of corneal topography in rigid gas permeable contact lens adaptation in patients with keratoconus: technique description and preliminary results

Objetivo: Apresentar um método prático baseado nos valores topográficos para adaptação de lente de contato rígida gás-permeável (LCRGP) em pacientes com ceratocone. Método: Foram estudados 33 olhos de 17 pacientes consecutivos portadores de ceratocone, no período de julho de 1997 a abril de 1999. O exame inicial consistiu de medida da acuidade visual, refração, biornicroscopia e topografia de córnea com o topógrafo computadorizado Eye Sys. As sessões de adaptação foram feitas com lentes de contato de teste, com curva-base selecionada a partir da topografia de córnea. Foi considerada como referência inicial o valor médio de K 1,5 mm superior ao centro óptico de cada olho a 90 graus. Resultados: A adaptação de lente de contato rígida gás-permeável foi bem sucedida em 30 olhos (91 por cento). Em todos esses casos houve melhora significativa da acuidade visual, que nofinal variou de 20/20 a 20/6¸. Para a adaptação inicial, foram necessárias, em média, 3 ñ 1 tentativas. Foi realizada readaptação com sucesso em 3 casos (10 por cento). Na maioria dos casos (57 por cento), as lentes pedidas possuíam curva-base com valor mais próximo de K 1,5 mm a 90 graus em relação a K. Esse achado foi comprovado por análise estatísticadas medidas individualmente e das médias das diferenças entre as duas medidas topográficas e a curva-base final de lente pedida. Conclusão: A adaptação baseada na topografia de córnea 1,5mm superiormente 90 graus ao centro óptico mostrou-se rápida e eficaz nos casos de ceratocone.

Avaliaçäo do uso de lentes de contato descartáveis em 100 pacientes / Evaluation of the use of disposable contact lenses in 100 patients

Estudou-se o comportamento de 100 pacientes particulares adaptados com lentes de contato dscartáveis. A maioria dos pacientes considerou o conforto ótim, e a aderência ao uso e os exames de controle, foram ao redor de 95 por cento. Ainda em sua maioria, os pacientes (72 por cento) já tinham sofrido complicaçöes com outros tipos de lentes de contato e destes, apenas uma portador de conjuntivite papilar gigante näo se adaptou com as lentes descartávais. Cinco pacientes desistiram e oito näo foram localizados. Dentro das condiçöes deste estudo as LCD foram uma boa alternativa para paciente com prévio insucesso à lente de contato de outro tipo, e representam uma alvissareira possibilidade de aumentar o número de usuários. Como qualquer novo tipo de lente de contato é necessário um acompanhamento a longo prazo quando os pacientes tendem a ser menos cuidadosos e as complicaçöes menos frequentes e de aparecimento tardio säo detectadas.