Variation of multifocal electroretinogram with axial length

Effects of Optical Zone Variation of High-Addition Multifocal Contact Lenses on the Global Flash Multifocal Electroretinography

OBJECTIVES

To evaluate the retinal response to myopic defocus after the wear of soft multifocal contact lenses with high addition through electroretinography.

METHODS

Twenty-seven participants meeting inclusion criteria were enrolled. Tropicamide 1% drops (2) were instilled. Participants were then fitted with three different contact lenses: a single-vision spherical lens (SE +3.00 D), L1, serving as a control, and two soft multifocal lens designs (SE +3.00 D/add +10 D), one with a central distance zone of 4.0 mm (L2) and one with a central distance zone of 7.0 mm (L3). A global flash multifocal electroretinography was performed. Direct component (DC) amplitude, DC peak time, induced component (IC) amplitude, and IC peak time were recorded. Waveforms were grouped into five concentric areas, covering from 0° to 24° of retinal eccentricity. Differences of L2/L3 versus L1 were analyzed with t tests. Finally, correlations were calculated between the percentage of defocus in the pupil area versus the electroretinography results.

RESULTS

Results show that the DC amplitude, caused mainly by photoreceptors and bipolar cells, is not influenced by the design of the lenses. The IC amplitude, however, is significantly decreased when the lens with a smaller optical zone (L2) is worn. This significant difference only concerns the ring 5, which corresponds to a retinal eccentricity of 15.7° to 24.0°.

CONCLUSION

Soft multifocal lens designs influence the peripheral retinal reaction to defocus. A larger treatment zone seems to significantly impact the retinal response to defocus between 15.7° and 24.0° of eccentricity from the macula.

Enhancement of the Inner Foveal Response of Young Adults with Extended-Depth-of-Focus Contact Lens for Myopia Management

BACKGROUND

Myopia management contact lenses have been shown to successfully decrease the rate of eye elongation in children by changing the peripheral refractive profile of the retina. Despite the efforts of the scientific community, the retinal response mechanism to defocus is still unknown. The purpose of this study was to evaluate the local electrophysiological response of the retina with a myopia control contact lens (CL) compared to a single-vision CL of the same material.

METHODS

The retinal electrical activity and peripheral refraction of 16 eyes (16 subjects, 27.5 ± 5.7 years, 13 females and 3 males) with myopia between -0.75 D and -6.00 D (astigmatism < 1.00 D) were assessed with two CLs (Filcon 5B): a single-vision (SV) CL and an extended-depth-of-focus (EDOF) CL used for myopia management. The peripheral refraction was assessed with an open-field WAM-5500 auto-refractometer/keratometer in four meridians separated by 45° at 2.50 m distance. The global-flash multifocal electroretinogram (gf-mfERG) was recorded with the Reti-port/scan21 (Roland Consult) using a stimulus of 61 hexagons. The implicit time (in milliseconds) and response density (RD, in nV/deg2) of the direct (DC) and induced (IC) components were used for comparison between lenses in physiological pupil conditions.

RESULTS

Although the EDOF decreased both the HCVA and the LCVA (one and two lines, respectively; p < 0.003), it still allowed a good VA. The EDOF lens induced a myopic shift in most retinal areas, with a higher and statistically significant effect on the nasal retina. No differences in the implicit times of the DC and IC components were observed between SV and EDOF. Compared with the SV, the EDOF lens showed a higher RD in the IC component in the foveal region (p = 0.032). In the remaining retinal areas, the EDOF evoked lower, non-statistically significant RD in both the DC and IC components.

CONCLUSIONS

The EDOF myopia control CL enhanced the response of the inner layers of the fovea. This might suggest that, besides other mechanisms potentially involved, the central foveal retinal activity might be involved in the mechanism of myopia control with these lenses.

Assessment of factors affecting flicker ERGs recorded with RETeval from data obtained from health checkup screening

PURPOSE

To determine the factors significantly associated with the amplitudes and implicit times of the flicker electroretinograms (ERGs) recorded with the RETeval system by analyzing the comprehensive data obtained during a health checkup screening.

METHODS

Flicker ERGs were recorded with the RETeval system from 373 individuals who had a normal fundus and optical coherence tomography images. The sex, age, anthropometric, ophthalmologic, and hematologic data were collected from all participants who were 40- to 89-years-of-age. Univariable and multivariable linear mixed effects regression analyses were performed to identify factors that were significantly associated with the implicit times and amplitudes of the RETeval flicker ERGs.

RESULTS

Univariable linear mixed effects regression analysis showed significant correlations between the implicit times and the best-corrected visual acuity, the age, the axial length, the blood sugar level, and the blood urea nitrogen level. Analyses by multivariable linear mixed effects regression identified that the axial length (β = 0.28), the age (β = 0.24), and the blood sugar level (β = 0.092) were three independent factors that were significantly correlated with the implicit times of the RETeval flicker ERGs. Univariable linear mixed effects regression analysis also showed significant correlations between the amplitudes of the RETeval flicker ERGs and the age, the platelet count, and the creatinine level. Multivariable linear mixed effects regression models identified the age (β = -0.092), the platelet count (β = 0.099), and the creatinine level (β = -0.12) as three independent factors that were significantly correlated with the amplitudes of the RETeval flicker ERGs. However, the smoking habits, body mass index, and the blood pressure were not significantly correlated with either the implicit times or amplitudes of the RETeval flicker ERGs.

CONCLUSIONS

Our results indicate that the age and some ophthalmologic and hematologic findings but not the anthropometric findings were significantly associated with the implicit times and amplitudes of the RETeval flicker ERGs. Thus, clinicians should remember these factors when analyzing the RETeval flicker ERGs.

Experimentally induced myopia and myopic astigmatism alter retinal electrophysiology in chickens

Myopia (or "short-sightedness") and astigmatism are major causes of visual impairment worldwide. Significant amounts of astigmatism are frequently observed in infants and have been associated with myopia development. Although it is well established that both myopia and astigmatism are associated with ocular structural changes from anterior to posterior segments, very little is known on how these refractive errors alter retinal functions. This study investigated the effects of experimentally induced myopia and myopic-astigmatism on retinal electrophysiology by using an image-guided, multifocal global flash stimulation in chickens, a widely used animal model for refractive error development. Myopia and myopic-astigmatism were experimentally induced, respectively, by wearing spherical (- 10 D, n = 12) and sphero-cylindrical lenses (- 6.00 DS/- 8.00 DCx90: Hyperopic With-The Rule, H-WTR, n = 15; - 6.00 DS/- 8.00 DCx180: Hyperopic Against-The-Rule, H-ATR, n = 11) monocularly for a week (post-hatching day 5 to 12). An aged-matched control group without any lens treatment provided normal data (n = 12). Multifocal electrophysiological results revealed significant regional variation in the amplitude of induced component (IC) (central greater than peripheral; both p < 0.05) in the normal and H-ATR groups, but not in the - 10 D and H-WTR groups. Most importantly, for the first time, our results showed that both H-WTR and H-ATR groups exhibited a significantly longer implicit time of the inner retinal response at the central region when compared to the normal and - 10 D groups, highlighting a significant role of astigmatism in retinal physiology.

Are we overlooking the neurodegeneration in the early stage of Type 1 Diabetes Mellitus without Visual Impairment or Diabetic Retinopathy: is it probably occurred before retinal vasculature dysfunction?

PURPOSE

Using electrophysiology (ERG) to investigate the early alterations of retinal function in diabetic children and adolescents without diabetic retinopathy (DR) or visual impairment (VI).

METHODS

We recorded and compared the data of full-field flicker ERGs between 59 normal subjects and 60 children and adolescents with type 1 diabetes mellitus (T1DM) from the Children's Hospital of Fudan University in Shanghai.

RESULTS

In both groups, patients with diabetes and healthy controls were matched for age, gender, weight, height, BMI, intraocular pressure (IOP), and best-corrected visual acuity (BCVA). Among the parameters of the outcomes of ERG, the implicit time in eyes in DM patients was significantly prolonged compared to normal eyes (p = .008, 16 Td-s; p = .000, 32 Td-s). In the case group, we found significantly positive correlation between implicit time and BMI (p < .05), as well as implicit time and axial length (AL).

CONCLUSIONS

The study reveals that the dysfunction of retina in DM children can be detected with ERGs. It also shows that hyperglycemia has an impact on the occurrence of neurodegeneration in the early stage of DM.

Electroretinogram responses in myopia: a review

The stretching of a myopic eye is associated with several structural and functional changes in the retina and posterior segment of the eye. Recent research highlights the role of retinal signaling in ocular growth. Evidence from studies conducted on animal models and humans suggests that visual mechanisms regulating refractive development are primarily localized at the retina and that the visual signals from the retinal periphery are also critical for visually guided eye growth. Therefore, it is important to study the structural and functional changes in the retina in relation to refractive errors. This review will specifically focus on electroretinogram (ERG) changes in myopia and their implications in understanding the nature of retinal functioning in myopic eyes. Based on the available literature, we will discuss the fundamentals of retinal neurophysiology in the regulation of vision-dependent ocular growth, findings from various studies that investigated global and localized retinal functions in myopia using various types of ERGs.

The link between Keratoconus and posterior segment parameters: An updated, comprehensive review

Keratoconus (KCN) has been typically known as a disorder with effects limited to the cornea. Because of this viewpoint, less attention has been devoted to its effects on the posterior segment structures. We aimed to provide a comprehensive review of the literature to understand the potential link between KCN and posterior segment structures and their functions. It is clear from the extensive evidence in the literature that KCN can be associated with morphological and functional changes in different parts of the posterior segment. It is worth noting that anatomical changes have been not only noted in several layers of the retina but also in the optic nerve head and the choroid. Several mechanisms have been proposed to explain this observation, including incidents induced by oxidative stress in keratoconic corneas and retinal adaptions to the distorted image that lands on the retina. Consequently, when KCN has been diagnosed, it seems practical to consider assessing the retinal and choroidal profile using optical coherence tomography and potentially functional abnormalities through electrophysiology procedures.

Detection of glaucomatous damage using multifocal ERG

The first-order kernel analysis in multifocal electroretinogram (mfERG) using low contrast stimulation is suggested as a way to detect the inner retinal responses in animal studies. In this case report, this protocol is applied to human patients with glaucoma to demonstrate the possibility of using mfERG as a tool to detect glaucomatous damage. Two patients with glaucoma were recruited and had mfERG measurements with the 103-scaled hexagonal stimulus pattern at low (50 per cent) contrast. Their responses were analysed and compared with those from normal subjects with the mfERG measured under the same condition. In the normal subjects, there were obvious oscillatory components on the ascending and descending limbs of the first-order kernel response to 50 per cent contrast. In the glaucomatous patients, the oscillatory component on the descending limb was obviously diminished. In addition, this component was significantly diminished in the quadrant with a glaucomatous visual field defect. This suggests that the low-contrast stimulation condition in mfERG measurement may provide a good way to detect glaucomatous damage and this may help in clinical diagnosis of glaucoma.

Retinal Response of Low Myopes during Orthokeratology Treatment

The aim of this study was to evaluate the changes in retinal activity during orthokeratology (OK) treatment in 20 myopic eyes. Pattern electroretinography (PERG) and visual evoked potential (VEP) were assessed with the RETI-port/scan21 (Roland Consult, Wiesbaden, Germany). Measurements were taken at baseline (BL) and 1 night (1N), 15 nights (15N), 30 nights (30N), and 60 nights (60N) of OK lens wear. Repeated measures analysis of variance (ANOVA) and the Friedman test were used. Twenty eyes (23.20 ± 3.46 years, 70% female) with visual acuity ≤ 0.00 logMAR in post-treatment showed that despite a slight increase in retinal and cortical response amplitude, observed with both PERG and VEP, respectively, immediately after the initial treatment, these differences found were not statistically significant during the 60 days of OK treatment, despite a statistically significant increase in N95 response with PERG. This shows that retinal and cortical visual-related electrical activity is maintained or slightly increased during OK treatment.

Comparison of fovea-sparing and non-internal limiting membrane peeling for retinoschisis with foveal detachment in highly myopic eyes

PURPOSE

To compare the visual and anatomical outcomes of two different treatment strategies (non-internal limiting membrane (ILM) peeling and fovea-sparing ILM peeling) for retinoschisis with foveal detachment (FD) in highly myopic eyes.

DESIGN

A retrospective cohort study.

METHODS

Ninety-five eyes from 92 highly myopic patients with retinoschisis with FD were divided into two groups, including 44 eyes from 43 patients who received 23-gauge, 3-port vitrectomy without ILM peeling (group A) and 51 eyes from 49 patients who received vitrectomy with fovea-sparing ILM peeling (group B). All eyes also underwent cataract surgery.

RESULTS

There were no significant differences between the two groups in terms of sex, age, diopters, axial length (AL), or central foveal thickness (CFT) before surgery (P > 0.05). One month after surgery, foveoschisis and FD were resolved in 74.47% of the eyes in group B and in only 12.50% of those in group A. Six months after surgery, foveoschisis and FD were resolved in 96.08% of the eyes in group B and in only 72.73% of those in group A (P < 0.05). There were no significant differences between the two groups in terms of BCVA 6 months after surgery. The postoperative complication was macular holes, which were found in seven eyes (15.90%) in group A and in one eye (1.96%) in group B (P < 0.05).

CONCLUSION

Highly myopic eyes with FD that underwent fovea-sparing ILM peeling appeared to obtain a better anatomical outcome than those that did not undergo non-ILM peeling. The two procedures obtained similar results in terms of visual function.

Changes in fundus reflectivity during myopia development in chickens

Previous studies have shown that changes in functional activity in the retina can be visualized as changes in fundus reflectivity. When the image projected on the retina is low pass filtered or defocused by covering the eye with a frosted diffuser or a negative lens, it starts growing longer and develops myopia. We have tested the hypothesis that the resulting altered retinal activity may show up as changes in fundus reflectivity. Fundus reflectivity was measured in chickens in vivo, both in visible (400-800 nm, white) and near ultraviolet (UV) light (315-380 nm). Two CCD cameras were used; a RGB camera and a camera sensitive in near UV light (peak sensitivity at 360 nm). White and UV LEDs, respectively, placed in the center of the camera lens aperture, served as light sources. Software was written to flash the LEDs and record the average brightness of the pupil that was illuminated by light reflected from the fundus. The average pixel grey level (px) in the pupil was taken as a measure of the amount of reflected light while refractive errors were corrected by trial lenses after pupil brightness was corrected for pupil size. It was found that myopic eyes had brighter pupils in UV light, compared to eyes with normal vision, no matter whether myopia was induced by diffusers or negative lenses (48 ± 9 vs. 28 ± 3, p<0.001 and 47 ± 7 vs. 27 ± 2, respectively). Using SD-OCT in alert chickens it was found that the retinal nerve fiber layer (RNFL) and the retinal ganglion cell layer (RGCL) in the central retina became thinner already at early stages of myopia development, compared to controls (31.2 ± 5.8 µm vs. 43.9 ± 2.6 µm, p<0.001 and 36.9 ± 1.2 µm vs. 44 ± 0.5 µm, respectively). While the decrease in RNFL thickness occurred concomitantly with the increase in UV reflectivity, it remains unclear whether these changes were causally linked. Thinning of the RNFL could be due to reduced neural activity in retinal ganglion cells but also due to metabolic changes in the retina during myopia development.

Effect of axial length on full-field and multifocal electroretinograms

PURPOSE

The aim was to investigate the effect of axial length on full-field electroretinogram (ffERG) and multifocal electroretinogram (mfERG) in young Indian subjects.

METHODS

One hundred subjects (44 male) with refractive errors from +0.50 to -18.00 DS and no myopic retinopathy underwent axial length measurement. ffERG was measured, which included scotopic and photopic responses according to International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines. The mfERG was recorded after correcting for refractive error according to ISCEV standards. The dark-adapted and light-adapted parameters of ffERG and N1, P1 parameters of six rings in mfERG were analysed with axial length, controlled for refractive error. The subjects were divided into seven groups based on axial length. The b/a ratio of dark-adapted and light-adapted 3.0 ffERG and P1/N1 ratio of mfERG amplitudes were analysed for seven groups of axial length.

RESULTS

The axial length ranged from 21.79 to 30.55 mm. Significant negative correlations were noted for ffERG and mfERG amplitudes, whereas implicit times showed minimal delay with increase in axial length. In ffERG, the scotopic responses were more decreased compared to photopic responses. In mfERG, P1 and N1 amplitudes were significantly decreased in all the rings in all groups and more reduction was noted in the central ring compared to peripheral rings. The P1 amplitudes were more affected as compared to N1 amplitudes. The light-adapted and dark-adapted 3.0 ERG b/a ratio and P1/N1 ratio for seven axial length groups did not show statistically significant difference. The ERG parameters were not significant with refractive error.

CONCLUSION

This study quantifies the relationship of axial length with ffERG and mfERG parameters in a young Indian population. Although the amplitudes were reduced significantly, the implicit times were not significantly affected. The ERG parameters were more related to axial length than refractive error. Hence, interpretation of ffERG and mfERG parameters needs careful consideration in subjects with increasing axial length.

A late foveal response component of multifocal electroretinograms in healthy subjects

PURPOSE

To investigate the characteristics of the late foveal response component (lfrc) that presents on the first slice of the second-order kernel (K2.1) in multifocal electroretinograms (mfERGs).

METHODS

mfERGs with 37 hexagonal stimulus elements were obtained from 27 healthy subjects under a stimulus intensity of 2.67 cds/m², base rate of 75 Hz, and a net recording time of 1 min 49.2 s, using bipolar contact lens electrodes. The responses on the centermost hexagon (with a diameter of 4.5°-5.2°) were designated as foveal mfERGs.

RESULTS

The foveal mfERG of the first-order kernel (K1) was shaped similarly to the K1 of the surrounding mfERGs. The foveal mfERG of K2.1 differed from the K2.1s of the surrounding mfERGs. This difference varied among subjects; however, the potential (0.34 ± 0.10 µV: mean ± SD) of the lfrc acutely changed at approximately 50 ms (range 48.56 ± 1.02-56.86 ± 1.99 ms). Whereas the amplitudes of the other major components of K1 and K2.1 significantly decreased with increasing refractive error, the amplitude of lfrc was not significantly correlated with refraction in this cohort.

CONCLUSIONS

The lfrc was obtained only on the centermost hexagon within an appropriate recording time (<2 min). This finding reflects the particular structure and peculiar adaptiveness of the fovea, a specialized area of the human retina, and enables the estimation of foveal function in clinical practice.

Posterior scleral reinforcement and vitrectomy for myopic foveoschisis in extreme myopia

PURPOSE

To evaluate the effect of surgical posterior scleral reinforcement in extremely myopic patients (axial length ≥30 mm) with myopic foveoschisis.

METHODS

The retrospective interventional case series study included patients with an axial length ≥30 mm, posterior scleral staphyloma, and myopic foveoschisis, who were treated either by posterior scleral reinforcement and 23-gauge 3-port pars plana vitrectomy (posterior scleral reinforcement group) or by vitrectomy (vitrectomy group) alone. All eyes additionally underwent cataract surgery.

RESULTS

The study included 28 patients (28 eyes) with no significant (all P > 0.05) difference between the posterior scleral reinforcement group (n = 14) and the vitrectomy group (n = 14) in age, refractive error, axial length, and preoperative best-corrected visual acuity (BCVA). In addition to posterior scleral staphyloma and foveoschisis, a macular hole, a macular hole-associated retinal detachment, and a macular detachment without macular hole were present in three eyes, five eyes, and one eye, respectively in the study group and in three eyes, three eyes, and six eyes, respectively in the control group. In the study group, BCVA was significantly better after surgery than at baseline (P = 0.005) with an improvement in BCVA in 13 eyes, whereas BCVA was unchanged in 1 eye. In the control group, BCVA at baseline and at the end of follow-up did not differ significantly (P = 0.22). Gain in BCVA was marginally significantly higher in the study group than that in the control group (improvement by 0.69 ± 0.76 logMAR vs. 0.19 ± 0.54 logMAR; P = 0.05). The number of eyes with any improvement in BCVA (13 [93%] eyes vs. 11 [79%] eyes; P = 0.289) did not differ between both groups; an improvement in BCVA by more than 2 lines (10 [71%] eyes vs. 3 [21%] eyes; P = 0.009) was significantly higher in the study group than that in the control group. Anatomical success (defined as closure of macular holes and collapse of the foveoschisis) was achieved earlier in the study group (3.7 ± 3.2 months vs. 6.2 ± 3.0 months; P = 0.04).

CONCLUSION

Posterior scleral reinforcement in association with vitrectomy, as compared with vitrectomy alone, was associated with a higher improvement in visual acuity in extremely myopic eyes with foveoschisis.

Correlation of structural and electrophysiological changes in the retina of young high myopes

PURPOSE

Despite a high prevalence of myopia among young East Asian adults, there is a lack of data on the myopic retina structure-function relationship in this group. We examined the association between optical coherence tomography (OCT) and electroretinogram (ERG) measurements in highly myopic young Asian adults to provide this information and also determined if OCT can be used as an alternative screening tool to assess retinal function in young myopic adults.

METHODS

This was a prospective study comprising young adults aged between 18 and 25 years with spherical equivalent refraction of worse than -6.00 D. A comprehensive ophthalmic examination comprising fundus examination and grading, ocular biometry, time-domain OCT (fovea, macular and retinal nerve fibre layer thickness) and ERG (full field and multifocal) were performed for all the eyes.

RESULTS

A total of 32 eyes (mean spherical equivalent ± standard deviation -10.17 ± 1.51 D, mean age 23.8 ± 1.3 years) were included. None of the eyes showed visible myopic retinopathy and the central retina thickness of all eyes was classified as within the normal range. Full-field ERG amplitude and multifocal ERG P1 amplitudes in the outer rings (R3-R5) were, however, inversely associated with axial length. The multifocal ERG P1 amplitudes were also positively correlated with mean retinal nerve fibre layer thickness in R2, 4, 5 rings and outer macular thickness in R 2-5 rings.

CONCLUSION

These findings suggest that full field ERG changes may precede fundus and OCT changes in highly myopic young adults. Although there was some correlation between multifocal ERG amplitudes with OCT outer macular and retinal nerve fibre layer thickness, the OCT may not be useful as a retinal function screening tool, being within normal limits in all eyes. Further longitudinal studies are required to determine how the relationship between ERG and OCT will evolve over time.

Assessment of neuroretinal function in a group of functional amblyopes with documented LGN deficits

PURPOSE

In this study we examine neuroretinal function in five amblyopes, who had been shown in previous functional MRI (fMRI) studies to have compromised function of the lateral geniculate nucleus (LGN), to determine if the fMRI deficit in amblyopia may have its origin at the retinal level.

METHODS

We used slow flash multifocal ERG (mfERG) and compared averaged five ring responses of the amblyopic and fellow eyes across a 35 deg field. Central responses were also assessed over a field which was about 6.3 deg in diameter. We measured central retinal thickness using optical coherence tomography. Central fields were measured using the MP1-Microperimeter which also assesses ocular fixation during perimetry. MfERG data were compared with fMRI results from a previous study.

RESULTS

Amblyopic eyes had reduced response density amplitudes (first major negative to first positive (N1-P1) responses) for the central and paracentral retina (up to 18 deg diameter) but not for the mid-periphery (from 18 to 35 deg). Retinal thickness was within normal limits for all eyes, and not different between amblyopic and fellow eyes. Fixation was maintained within the central 4° more than 80% of the time by four of the five participants; fixation assessed using bivariate contour ellipse areas (BCEA) gave rankings similar to those of the MP-1 system. There was no significant relationship between BCEA and mfERG response for either amblyopic or fellow eye. There was no significant relationship between the central mfERG eye response difference and the selective blood oxygen level dependent (BOLD) LGN eye response difference previously seen in these participants.

CONCLUSIONS

Retinal responses in amblyopes can be reduced within the central field without an obvious anatomical basis. Additionally, this retinal deficit may not be the reason why the LGN BOLD (blood oxygen level dependent) responses are reduced for amblyopic eye stimulation.

Assessment of the Macula in Keratoconus: An Optical Coherence Tomography and Multifocal Electroretinography Study

<b><i>Purpose:</i></b> The purpose of our study was to assess the macular thickness and the electrophysiological changes in keratoconic patients without any systemic or ocular disorders.<b><i> Methods: </i></b>64 eyes of 32 keratoconus patients as well as 60 eyes of 30 controls participated in the study. All participants underwent a complete ophthalmological examination, including best-corrected visual acuity (BCVA) assessment, color vision testing, fundus examination, intraocular pressure measurement, central foveal thickness (CFT) measurement by optical coherence tomography (OCT) scan, and multifocal-electroretinogram (mf-ERG) recording. CFT, retinal response density (RRD) and P₁ latency were measured. <b><i>Results:</i></b> There was no statistically significant difference between the two groups concerning CFT and P₁ latency in mf-ERG. The RRD in mf-ERG differed significantly between keratoconus patients and controls. Of note, BCVA was positively associated with RRD in keratoconus patients. <b><i>Conclusion:</i></b> In some cases of keratoconus, a macular dysfunction not visible ophthalmoscopically may coexist and the low visual acuity could be due not only to the corneal abnormality, but also to the photoreceptor dysfunction. As a result, the preoperative electrophysiological study of patients with keratoconus is crucial to avoid a needless corneal transplantation.

Multifocal electroretinography

Multifocal electroretinography (mfERG) provides functional and objective evidence of retinal dysfunction. We have found mfERG to be especially useful in the management of occult outer retinopathy and Stargardt's disease.

Features of the multifocal electroretinogram may predict the rate of myopia progression in children

OBJECTIVE

To investigate the multifocal electroretinogram (mfERG) in myopic children in relation to the rate of myopia progression.

DESIGN

Observational study.

PARTICIPANTS

Eighty-one school children with myopia.

METHODS

Cycloplegic refraction, ocular biometry, and mfERG recordings were performed in myopic children aged 9 to 11 years in 2002. The refraction and ocular biometry assessments were repeated 2 years later in 2004. The 2-year myopia progression rate was calculated for a randomly selected eye of each individual. The mfERG parameters recorded at the initial visit in 2002 were compared with subsequent progression rates.

MAIN OUTCOME MEASURES

First-order kernel mfERG responses.

RESULTS

Of the 81 eyes, 12 eyes had a high progression rate (defined as a progression rate of >1 diopter [D]/2 years), 44 eyes had a moderate progression rate (progression rate of >0.25 D but < or =1 D/2 years), and 25 eyes showed no progression or a low progression rate (progression rate of < or =0.25 D/2 years). The P1 amplitude of the mfERG in the high progression group was significantly smaller than that in the moderate (P = 0.023) and non/low-progression groups (P = 0.030) but only within the central 5 degrees (ring 1). None of the other mfERG parameters of the central ring were significantly different among the groups. The mfERG parameters of the outer rings were similar in all groups.

CONCLUSIONS

Decreased foveal function as determined by the mfERG is associated with a high rate of myopia progression. Electrophysiologic examination of central retinal function may predict the progression and severity of myopia in school children.

The clinical applications of multifocal electroretinography: a systematic review

Multifocal electroretinography (mfERG) is an investigation that can simultaneously measure multiple electroretinographic responses at different retinal locations by cross-correlation techniques. mfERG therefore allows topographic mapping of retinal function in the central 40-50 degrees of the retina. The strength of mfERG lies in its ability to provide objective assessment of the central retinal function at different retinal areas within a short duration of time. Since the introduction of mfERG in 1992, mfERG has been applied in a large variety of clinical settings. This article reviews the clinical applications of mfERG based on the currently available evidence. mfERG has been found to be useful in the assessment of localized retinal dysfunction caused by various acquired or hereditary retinal disorders. The use of mfERG also enabled clinicians to objectively monitor the treatment outcomes as the changes in visual functions might not be reflected by subjective methods of assessment. By changing the stimulus, recording, and analysis parameters, investigation of specific retinal electrophysiological components can be performed topographically. Further developments and consolidations of these parameters will likely broaden the use of mfERG in the clinical setting.

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.

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.

L:M-cone ratio estimates of the outer and inner retina and its impact on sex differences in ERG amplitudes

The relative number of L- and M-cones varies greatly between individuals. Differences in the relative number of L- and M-cones may also contribute to the sex difference in the ERG response amplitude reported several times. We therefore investigated the relative number of L- and M-cones and its impact on sex differences in ERG amplitudes. Multifocal ERG (mfERG) and multifocal oscillatory potentials (mfOP) combined with a cone silent substitution technique were used to investigate outer and inner retinal signals recorded from 7 female and 7 male trichromats. L:M ratios were estimated from peak amplitude as well as from area under curve (AUC) analysis. For mfERGs the L:M ratios estimates were independent of the method of analysis, while for mfOPs, differences were found which are possibly due to an artefact in the calculation of ratios for small responses. There was a tendency for lower L:M ratios in female than in male subjects for both analysis of mfERG and mfOP responses. The (L+M)-response amplitudes at both sites were slightly higher and the L:M ratios were lower for female than for male observers. Because the magnitude of the ERG amplitude differences is larger than could be explained by L:M-ratio and axial length differences, we conclude that it may be due to a direct effect of sex hormones on ion channel function.

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.

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.

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.

Effect of myopia on visual acuity measured with laser interference fringes

The aim was to determine how visual acuity is affected by myopia when optical factors of the eye are controlled. Grating acuity was measured with interference fringes to avoid the effects of aberrations, and ocular biometry was used to compensate for differences in retinal image size among subjects. Distance spectacle refractions ranged from +2.25 to -14.75 D. The retinal magnification factor (RMF) in mm/deg was computed for each eye from the distance refraction, central corneal power and ultrasound biometry. A forced-choice orientation discrimination method was used to measure acuity for high-contrast 543 nm laser interference fringes in three retinal locations: the fovea, and at 4 deg and 10 deg eccentricity in the temporal retina. Acuity, expressed in c/deg and adjusted for spectacle magnification, was not significantly correlated with refraction at any of the three retinal locations. When acuity was converted to retinal spatial frequency units (c/mm) via the RMF, acuity decreased with increasing myopia at all three retinal locations (significantly at the fovea and at 10 deg eccentricity). Retinal acuity values in highly myopic subjects (>6 D) are consistent with retinal sampling distances that are larger than published values of human cone or ganglion cell spacing. The results imply that a highly myopic eye has retinal neurons that are more widely spaced than normal, but the increased axial length enlarges the retinal image enough to compensate for the retinal stretching. The data are consistent with a retinal stretching model that primarily affects the posterior pole.

Clinical application of mfERG/VEP in assessing superior altitudinal hemifield loss

Multifocal ERG (mfERG) and multifocal VEP (mfVEP) have been used widely in the investigation of pathological changes or functional variations in the visual system. Altitudinal hemifield loss is a visual field defect that is usually found in patients with ischaemic optic neuropathy (ION). Anterior ischaemic optic neuropathy (AION) is a complex multi-factorial disease and it is difficult to diagnose according to clinical symptoms and signs alone. AION is believed to be caused by an infarction of the optic nerve due to the occlusion of the posterior ciliary arteries. The current report presents a patient diagnosed with non-arteritic AION. In this report, the mfERG findings did not match the results of the visual field test but those of the mfVEP did. After consideration of the visual electrophysiological and visual field results, the defect arises from neither the retina nor the visual pathway behind the optic chiasma. Hence, the optic nerve is the most likely location of the lesion, causing the superior altitudinal hemi-field loss. This report shows that the mfERG and mfVEP techniques can be used for objective visual field assessment to supplement the conventional visual field testing.

The detection of small relative simulated field defects using multifocal VEPs

INTRODUCTION

The multifocal visual-evoked potential (mfVEP) has been widely used in the study of diseases of the visual system. However, the sensitivity of the mfVEP in the objective detection of relative field defects has not been determined. This study investigates variations in mfVEP responses while simulating relative field defects by using different luminous transmission masks [neutral density (ND) filters] on the stimulus pattern.

METHODS

Simulated relative field defects with four different luminous transmissions were obtained by using 0.2, 0.4, 0.6, and 0.8 ND filters, 5 degrees in size, at two different retinal eccentricities (10 and 16 degrees) on a standard mfVEP dartboard stimulus. Eleven normal subjects were recruited for mfVEP measurements. The response amplitudes and latencies of the N1 and P1 of the mfVEP, with and without small simulated relative field defects, were compared.

RESULTS

The mfVEP amplitudes of N1 and P1 decreased substantially when 0.6 and 0.8 ND filters were introduced. The effects were similar at both the 10- and 16-degree eccentricities but there was no change in latency with simulated field defects at either location.

CONCLUSIONS

The mfVEP can detect a simulated relative field defect 5 degrees in size starting with 0.6 log unit reduction in luminance at both 10-degree and 16-degree eccentricities. This illustrates that the sensitivity of the mfVEP measurement is nearly comparable with that of the Humphrey Visual Field Analyser.

Multifocal electroretinography in isolated arterially perfused bovine eye

AIM

To develop an isolated arterially perfused bovine eye as an in vitro model for studying retinal electrophysiology using multifocal electroretinography (mfERG).

METHODS

Fresh bovine eyes were cannulated through the ophthalmic artery and perfused with oxygenated Krebs' solution at 37 degrees C within 15 min postmortem. Multifocal ERG was recorded using the veris 1.0 (Visual Evoked Response Imaging System).

RESULTS

The mfERG waveform of in vitro bovine eyes had a typical trough (negative wave, N1) and peak (positive wave, P1) similar to those of human mfERG. The implicit times (peak latencies) for N1 and P1 were 20 and 42 ms respectively, and the average response amplitude (N1P1) was 55 nV. The implicit times of N1 and P1 were maintained for more than 4 h. The mfERG responses were affected proportionately by the stimulus intensity. Without a neutral density filter, the mean response amplitude was about 55 nV, which was diminished to 26, 18 and 10 nV under neutral density filters of 0.4, 1.0 and 1.4, respectively. Partial occlusion of the pupil completely abolished mfERG responses from the corresponding part of the retina.

CONCLUSIONS

Isolated arterially perfused bovine eye may be used as an experimental model to study retinal electrophysiology using mfERG. The in vitro eye may offer a convenient and easily obtainable alternative to live animals, particularly for drug screening and invasive studies.