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Biomedical subjects

Jennifer C Chen

Publications and source records attributed to Jennifer C Chen.

12 recordsLinked to original sources
PubMed2006

Evaluation of inner retinal function in myopia using oscillatory potentials of the multifocal electroretinogram.

PURPOSE: Oscillatory potentials have been suggested to arise from the inner retina at the level of amacrine cells and inner plexiform layer and they are thought to provide a non-invasive assessment of inner retinal function. We sought to investigate the response dynamics of the inner retina of adult emmetropes and myopes by analysing the oscillatory potentials of the multifocal electroretinogram (mfERG) in these groups. METHODS: Eleven emmetropes and 18 myopes underwent mfERG testing using VERIS 5.1.5X. Myopes were further separated based on whether their myopia was stable (n=9) or progressing (n=9). Oscillatory potentials were recorded using a modified mfERG stimulation technique, the slow flash paradigm, and they were extracted using band-pass filtering from 100 to 300 Hz. The slow flash mfERG stimulus array consisted of 103-scaled hexagons and flickered according to a pseudorandom binary m-sequence (2(13)-1). Amplitudes and implicit times of the first-order oscillatory potentials were analysed. RESULTS: There were significant differences in the implicit time of the oscillatory potentials of the emmetropes, stable myopes and progressing myopes (F(2,25)=3.663, p=0.043). Progressing myopes had significantly shorter implicit times compared to emmetropes (p=0.026 by 1.0-4.7 ms) and stable myopes (p=0.043 by 0.8-1.3 ms), whereas implicit times of stable myopes and emmetropes were similar. There were no statistically significant differences in amplitude of the oscillatory potentials between the groups (F(2,25)=0.890, p=0.426). CONCLUSIONS: Significant differences in multifocal oscillatory potentials between stable and progressing myopes were found. This finding is further evidence of an inner retinal involvement in human myopia progression and may suggest an underlying alteration to dopaminergic or GABAergic retinal systems.

Adolescent↗
PubMed2006

Slow flash multifocal electroretinogram in myopia.

PURPOSE: The purpose of this study was to investigate the characteristics of retinal function in myopes using a modified multifocal electroretinogram (mfERG) protocol, the slow flash (sf-mfERG) paradigm, which is thought to primarily reflect responses of ON- and OFF-bipolar cells and emphasize the late response components. METHODS: Twenty-eight subjects (10 emmetropes and 18 myopes) underwent mfERG testing using VERIS 5.1.5X. The sf-mfERG stimulus array consisted of 103-scaled hexagons and flickered according to a pseudorandom binary m-sequence (2(13)-1). The stimulation sequence was slowed by inserting three dark frames such that each step in the m-sequence was four frames long (53.3ms). The amplitude and implicit time of the major sf-mfERG waveform features (N1, P1, and N2) of the first-order kernel were analysed. RESULTS: Myopes had significantly reduced P1 and N2 amplitudes compared to the emmetropes (F(1,25)=8.818, p=0.007; F(1,25)=6.723, p=0.017). There were no significant differences in N1 amplitude or implicit time between the groups (F(1,25)=1.506, p=0.233; F(1,25)=1.291, p=0.269). CONCLUSIONS: Late response components (P1 and N2) of the first-order sf-mfERG responses were preferentially affected in myopia, suggesting possible reduced ON- and OFF-bipolar cell activity. As bipolar cells form the first synapse of the visual system with the photoreceptors to initiate the ON- and OFF-pathways, future investigations of ON- and OFF-systems in myopia are of interest.

Adult↗
PubMed2006

Retinal adaptation responses revealed by global flash multifocal electroretinogram are dependent on the degree of myopic refractive error.

PURPOSE: There is evidence that the inner retina is involved in eye growth control processes and the development of myopia. We sought to investigate the response dynamics of the inner retina of adult emmetropes and myopes using the global flash multifocal electroretinogram (mfERG) paradigm. METHODS: Fourteen myopes and 10 emmetropic subjects (mean age: 21.0+/-2.8 years) underwent mfERG testing using VERIS 5.1.5X. The global flash stimulus array consisted of 103-scaled hexagons which flickered according to a pseudorandom binary m-sequence (2(13)-1). The stimulation sequence was modified by inserting three frames, a dark frame, a global (full screen) flash, and another dark frame. The amplitude and implicit time of the two distinct waveform features, an early direct component (DC) and a later induced component (IC) of the first-order kernel were analyzed. Retinal responses were averaged over rings of increasing eccentricity, or into nasal and temporal hemifields. RESULTS: There was a significant correlation between the DC and IC response amplitude and myopic refractive error, i.e., the greater the myopic error, the greater the response amplitude. However, when comparing between the two refractive error groups, DC and IC response amplitudes of emmetropes and myopes were similar, even after compensating for the effect of axial length. There were no significant differences in implicit times of the DC and IC in emmetropes and myopes. CONCLUSIONS: Global flash mfERG responses of emmetropes and myopes were not found to be significantly different. The measured retinal adaptation response however varied according to the degree of myopia. We hypothesize that dopamine, a neurotransmitter that plays a key role in retinal adaptation and is known to be reduced in myopic eyes, may be involved in the retinal adaptation effect observed.

Adaptation, Ocular↗
PubMed2006

Changes in implicit time of the multifocal electroretinogram response following contrast adaptation.

PURPOSE: Contrast adaptation, produced by prolonged viewing of high contrast gratings, has been suggested to occur at both retinal and cortical locations within the visual pathway. We sought to investigate the characteristics of retinal contrast adaptation using the multifocal electroretinogram (mfERG). METHODS: Twenty subjects, with a mean age of 27.8 +/- 5.3 years, underwent mfERG testing using VERIS I. The mfERG was measured after 10 minutes of adaptation to 94% contrast, 5 cyc/deg, sinusoidal, vertical gratings and to an equi-luminance blank control. The mfERG stimulus array consisted of 61-scaled hexagons and flickered according to a pseudorandom binary m-sequence (213-1). Changes in amplitude and implicit time of the first-order kernel were analyzed to determine the effect of contrast adaptation on retinal responses. RESULTS: Adaptation to the vertical grating pattern produced a 2.5 ms increase in implicit time, and the response delay was greatest in the more peripheral parts of the retina (7.6 degrees to 30 degrees ). Contrast adaptation did not produce statistically significant changes to the amplitude of the mfERG waveform. CONCLUSIONS: Contrast adaptation produced by prolonged viewing of high contrast gratings had a significant effect on retinal responses. It has been suggested that contrast adaptation may play a role in the development of nearwork induced myopia; further work investigating retinal contrast adaptation in myopic individuals may be of interest.

Adaptation, Ocular↗
PubMed2005

Delayed mfERG responses in myopia.

It has been suggested that changes in the multifocal electroretinogram (mfERG) responses in myopes are primarily due to the increased axial length that accompanies myopia development. We investigated the characteristics of mfERG responses between emmetropes and myopes and determined the contribution of axial length to the mfERG data in 30 subjects (10 emmetropes and 20 myopes) using VERIS I. The amplitude and implicit time of the first positive peak (P1) of the first-order kernel were analyzed. We found that P1 implicit time in myopes was significantly longer by 1.3-3.1 ms than that of the emmetropes and this was not explained by the myopes having greater axial lengths than the emmetropes. Axial length contributed to 15% of the implicit time total variance while refractive error accounted for 27%. Delayed mfERG responses observed in myopes were not attributable to the anatomical change that accompanies myopia and may suggest underlying differences in retinal function that result from being myopic.

Adolescent↗
PubMed2005

The effect of a beta-adrenoceptor antagonist on accommodative adaptation in Hong Kong children.

PURPOSE: Increased susceptibility to nearwork-induced accommodative adaptation has been suggested as a risk factor for myopia development. We investigated whether accommodative adaptation may explain in part the high prevalence of myopia in Hong Kong children and examined the effect of beta-antagonism with topical timolol maleate on accommodative adaptation. METHODS: Thirty children (10 emmetropes and 20 myopes) aged between 8 and 12 years were recruited. Tonic accommodation was measured before and after 5 min of video game-playing using an open-field Shin-Nippon autorefractor. Measurements were repeated 30 min after timolol instillation. RESULTS: Children with progressing myopia demonstrated accommodative adaptation following the near task, whereas stable myopes showed counter-adaptive, hyperopic accommodative changes. Timolol increased the magnitude of accommodative adaptation in the stable myopes but had little effect on responses of the progressing myopes or emmetropes. CONCLUSIONS: Neuropharmacological modulation of the accommodative system may have a possible etiological role in the progression of myopia.

Accommodation, Ocular↗
PubMed2005

Central serous chorioretinopathy and bullous retinal detachment: a rare association.

While idiopathic central serous retinopathy (ICSC) is a common ocular condition, bullous exudative retinal detachment associated with ICSC is a relatively rare finding. Bullous retinal detachment has been described as a severe variant of ICSC, characterised by multiple leaking pigment epithelial detachments and the presence of shifting neuro-sensory sub-retinal fluid. The peculiar clinical findings may present a diagnostic dilemma and lead to inappropriate treatment. Here, we describe the atypical presentation of ICSC with bullous retinal detachment and the effect of focal laser treatment on resolution of the retinal detachment. Despite ICSC being a self-limiting condition in the majority of cases, recognition of this atypical form of ICSC is important. Failure to differentiate this condition from inflammatory disease of the retina and choroid may result in inappropriate use of corticosteroids, leading to exacerbation of the condition and permanent visual loss.

Adult↗
PubMed2004

Effect of unilateral forced nostril breathing on tonic accommodation and intraocular pressure.

BACKGROUND: Unilateral forced nostril breathing (UFNB) has specific measurable effects on the autonomic nervous system. Ocular accommodation, which is controlled by the autonomic nervous system, would be expected to be under the influence of UFNB when it is applied. The purpose of this study was to investigate the effect of UFNB on the resting state of the accommodation system, i. e. tonic accommodation (TA), along with measures of intraocular pressure (IOP), blood pressure and heart rate. METHODS: TA levels were measured using the Shin-Nippon autorefractor before and after 20 minutes of UFNB. IOP, blood pressure and heart rate, which are known to be affected by UFNB, were also measured with a non-contact tonometer and an automated blood pressure monitor respectively. RESULTS: Right and left UFNB produced slight, but not significant changes in TA. However, there was a tendency for left UFNB to produce a greater decrease in TA in subjects with higher base-line TA levels. Right UFNB produced a statistically significant decrease in IOP while the effect of left UFNB on IOP was not significant. CONCLUSION: UFNB produced changes in IOP consistent with previous reports. As studied in this trial, UFNB did not have any significant effect on TA. Further studies using a larger sample size are required to investigate the effect of UFNB on the autonomic inputs to the ciliary muscle of the eye and the subsequent measures of tonic accommodation.

Accommodation, Ocular↗
PubMed2004

Solar retinopathy and associated optical coherence tomography findings.

Solar retinopathy is a rare but well-recognised clinical entity of macular damage, caused by viewing a solar eclipse or direct sun-gazing. Visual deterioration from solar retinopathy typically ranges from 6/9 to 6/60 and in most cases the visual loss is reversible. We present a case of solar retinopathy following direct sun-gazing and illustrate the damage within the retinal structure with optical coherence tomographic (OCT) findings. The visual prognosis of solar retinopathy is usually favourable but prevention remains the mainstay of treatment. The optometrist may play an important role in patient education and reassurance, as well as differentiating solar retinopathy from other likely macular abnormalities.

Adult↗
PubMed2003

The autonomic control of accommodation and implications for human myopia development: a review.

Prolonged nearwork has long been associated with myopia development, however, there is no well described linking mechanism. One theory suggests that if accommodation accuracy during nearwork is not maintained, the defocused retinal image leads to myopia development. Here we review the findings of research aimed at determining whether the autonomic inputs to the ciliary smooth muscle are involved in this type of environmental myopia. We examine whether an autonomic imbalance could be a precursor to axial elongation and the resulting myopia. Accommodation responses, such as tonic accommodation and nearwork-induced accommodative adaptation, as a function of refractive error, are described in relation to an autonomic imbalance model. The collective results of this research point to anomalous accommodation responses, possibly as a result of underlying anomalous autonomic input to the ciliary muscle, being involved in myopia development and progression.

Accommodation, Ocular↗
PubMed2003

AC/A ratios in myopic and emmetropic Hong Kong children and the effect of timolol.

PURPOSE: Caucasian children with myopia have elevated response accommodative vergence to accommodation (AC/A) ratios. The purpose of this study was twofold: to determine if response AC/A ratios vary with refractive error and with myopic progression rate in Hong Kong Chinese children, and to determine the effect of beta-adrenergic antagonism with topical timolol application on AC/A ratios. METHODS: Thirty children aged eight to 12 years participated in the study. All refractive errors were corrected with spectacle lenses. Accommodative responses were measured using a Shin-Nippon autorefractor and concurrent changes in vergence were assessed using a vertical prism and a Howell-Dwyer card at three metres and 0.33 metre. Accommodative demand was altered using plus or minus two dioptre lenses and lens- and distance-induced response AC/A ratios were calculated. Measurements were repeated 30 minutes after the instillation of topical timolol maleate (0.5 per cent). RESULTS: AC/A ratios appeared higher in progressing myopic children but the difference was not statistically significant. Timolol application reduced accommodative convergence (AC) in the stable myopes (reduction = -3 +/- 1.14 prism dioptres) but not in the emmetropes (0.69 +/- 0.96 prism dioptres) or progressing myopes (0.16 +/- 0.43 prism dioptres) and this difference between refractive groups was statistically significant (F(2, 27) = 3.766; P = 0.036). However, timolol did not produce a significant change in the accommodative response to positive or negative lenses or response AC/A ratios. CONCLUSIONS: We did not find that AC/A ratios in myopic Chinese children were elevated and therefore, it is unlikely that elevated AC/A ratios are responsible for the high levels of myopia that occur in Hong Kong. The finding that timolol reduced AC in the stable myopes suggests that the autonomic control of accommodative convergence in these children may be different from that in emmetropic children and those with progressing myopia.

Accommodation, Ocular↗