Electrooculography features of reticular macular disease: A preliminary observation

doi:10.21203/rs.3.rs-5080352/v1

In this single center retrospective study, we aimed to observe the characteristics of resting potentials between RPE and photoreceptors in RMD patients, based on electrooculography. Seven patients with diffuse RMD diagnosed using infrared fundus photography and optical coherence tomography (OCT) were consecutively reviewed. All 7 patients (14 eyes) underwent routine ophthalmic examinations and were examined by OCT and Electrooculography (EOG). The EOG recordings of the 14 eyes revealed that dark adaptation took 7.21 ± 1.75 minutes to achieve dark trough, whereas light adaptation took 15.79 ± 2.70 minutes from light rise to the light peak. Furthermore, the amplitude of dark trough potential was 262.0–962.1 µV, whereas that of light peak potential was between 373.8 µV and 1.8 mV. In addition, the LP:DT ratio of the 14 eyes observed in this preliminary study was 1.63 ± 0.22, ranged between 1.18 and 1.97, which was lower than 2.35, but was not significantly lower than the lower limit of 1.7 (t = -1.12, P = 0.28). In conclusion, Some EOG parameters of RMD patients are different from normal reference ranges, bioelectric activity between RPE and photoreceptors in patients with RMD may be affected by SDD or RPE abnormalities.

Ophthalmology

age-related macular degeneration

reticular macular disease

reticular pseudodrusen

electrooculography

electrophysiology.

Age-related macular degeneration (AMD) is a degenerative retinal disease characterized by disorders of the outer retinal and choroidal microenvironment, which leads to central vision loss through atrophic or neovascular complications in the advanced stage. AMD is one of the leading causes of severe and irreversible visual impairment worldwide. The overall global prevalence of AMD is approximately 8.69% (age range 45–85 years), and the number of patients is expected to grow to 288 million by 2040 [1]. Reticular macular disease (RMD) is currently recognized as a specific phenotype of AMD characterized by reticular pseudodrusen (RPD) with choroidal capillary layer perfusion dysfunction [2–5]. RPD, together with drusen, is considered a pathway to advanced AMD; however, the two differ in appearance, histology and outcome [5–8]. RPD with a low-reflection network distribution is shown on infrared imaging of the retina, and the part that broke through the outer membrane is shown as a high reflection point at the center of the low-reflection spot (Fig. 1). In optical coherence tomography (OCT) images, RPD appears as subretinal drusenoid deposits (SDD) [9] (Fig. 2). Histologically, RPDs are extracellular deposits located in the subretinal space between the neural retina and RPE, which are in piles or clumps adjacent to the outer segment of photoreceptors and divided by the process, isolated or fused at the top of the RPE. After fusion, adjacent lesions can be connected to each other and appear in a reticular form [9]. RPD is often accompanied by the shortening of the outer segments of photoreceptors, and the outer segments of rod cells may also be buried in the sediment, but the outer segments of cone cells have not been found to enter the sediment; RPE has an abnormal size and shape and can migrate around the RPD but not into the RPD [10]. Most components of RPD are close to drusen, such as apoE, complement factor H, vitronectin, etc. However, apoB and apoA-1 levels were lower in RPD. In addition, RPD contains only free cholesterol and no cholesteryl ester. drusen, however, contains both free and esterified cholesterol. The specific formation mechanism of RPD is still unclear, but it is possible that with aging, the RPE transport machinery becomes dysfunctional and loses its polarity, and metabolites are excreted from the apical side, resulting in material deposition on its inner surface to form RPD. Although the mechanism is not clear, it is certain that RPE and rod cell morphology near the RPD are abnormal, and the RPD disrupts the microenvironment of the subretinal space, which may interfere with visual formation and visual signal transmission. Recent studies have found that mesopic visual sensitivity is generally reduced in eyes with large drusen and cospherical RPD compared to eyes without RPD, with greater reductions with an increasing extent of RPD [11]. Therefore, it is important to identify the retinal electrophysiological features, especially RPE electrophysiological features, of RMD-affected eyes.

Electroretinogram (ERG) is a longitudinal current signal recorded in the cornea or even the eyelid of the retina, which mainly reflects the light-induced current of longitudinally arranged neurons such as photoreceptors and bipolar cells. Studies have been conducted on the ERG characteristics of RMD patients, which reported that some ERG parameters decreased to different degrees [12–14]. flash ERG (fERG), as one kind of ERG, can be used to record the comprehensive response of the whole retina to brief flash stimulation in dark and light adaptation environments. Kong et al. conducted an fERG examination in eyes with different degrees of RMD, as well as in healthy eyes, and found that the response of ERG indicators in diffuse RPD was lower [12]. However, fEGR reflects the comprehensive electrical signal characteristics of the entire retina and cannot determine the specific lesion site. Multifocal ERG (mfERG) can detect the local flash ERG response in different parts of the retina and reflect the tiny local signal characteristics. Florian et al. used mfERG to study the visual electrophysiological characteristics of RMD-affected eyes and found that the amplitude of the RPD-affected areas of RMD eyes decreased significantly compared with that of the non–RPD-affected areas, and the visual function decreased with the prolongation of the disease course. However, the amplitude of mfERG did not correlate with the single morphological parameters, such as RPD size and area and foveal choroidal thickness [13]. In addition, Diao et al. used mfERG to measure the visual function of RMD patients using the quartile method and found that the visual function was decreased in the fovea macula, inferior temporal, and superior nasal in these patients compared with that in the normal group [14].

In contrast to ERG, electrooculogram (EOG) detects the continuous resting potential between the RPE and photoreceptors by measuring the corneoretinal standing potential during dark adaptation (DA) and light adaptation (LA). The standing potential, which reflects the voltage differential across the RPE, is positive at the cornea, which is indirectly reflected by the transepithelial potential (TEP). TEP is the membrane voltage of the electrochemically insulated tight junction between the basolateral and apical membranes of the RPE, which reflects the bioelectrical activity of the interaction between the retinal RPE and neuroretina [15]. Although the dark trough potential of the EOG mainly originates from the RPE, the light rise of the electrical potential requires normal functions of the RPE and neural retina, which is closely related to the biological electrical activity of RPE cells. Under bright light, the bestrophin protein of the endoplasmic reticulum (ER) interacts with the L-type calcium channel of the basolateral membrane to regulate calcium release from the ER, leading to an increase in intracellular free calcium. Intracellular calcium, in turn, triggers the opening of calcium-dependent chloride channels in the basolateral membrane, and this increase in chloride conductivity leads to polarization of the basolateral membrane and an increase in TEP. Due to the wide variation of the amplitude range of light peak (LP) and dark trough (DT) [16], light rise and LP:DT ratio (Arden ratio) were mainly used to evaluate the EOG results [17]. The light rise is the period from the dark trough to the light peak. The LP:DT ratio is the main evaluation index of EOG and reflects the ratio of the peak amplitude of TEP in light and dark changes. The normal ratio should be approximately 2:1, and a ratio < 1.7 is considered abnormal [15]. Any disorder of rod photoreceptor function will affect an EOG, and the light rise is typically severely reduced in an EOG of any widespread photoreceptor degeneration, including RP. However, EOG is principally used in clinical practice in the diagnosis of bestrophin mutations and acute zonal occult outer retinopathy.

It should be noted that, anatomically, SDDs preferentially localize with rods, while drusen localize with cones [7]. As RMD is closely related to RPE dysfunction, it is of great significance to study the characteristics of EOG in RMD patients. However, to the best of our knowledge, rare similar studies on EOG features of RMD have been reported in the literature. To explore whether SDD between RPE and photoreceptors affects their function, this study preliminarily evaluated the EOG characteristics of 7 patients (14 eyes) with RMD consecutively to provide ideas for further research on the physiological function of the RPE–photoreceptor complex in RMD patients.

2.1. Clinical data

In this retrospective, single-center study, 7 consecutive RMD patients diagnosed at the Department of Ophthalmology, the First Affiliated Hospital of Guangzhou Medical University, from February to September 2019 were enrolled. Their ages ranged from 57 to 82 (mean, 69.71) years. All 7 participants were female and had bilateral RMD lesions. The basic information of patients, including visual acuity and refractive status, was obtained from their medical records, and all data were verified by 2 investigators (ZC and QR). The binocular visual acuity of each patient was examined using a standard logarithmic visual acuity chart.

As there are no recognized diagnostic criteria for RMD, the diagnosis of RMD in this study was based on the RMD criteria proposed by Smith and Zweifel [2,9]. The main contents are as follows: 1) Infrared imaging of the fundus revealed reticular low-reflection spots on the background with relatively high reflection (Figure 1). 2) Spectral domain-OCT images showed the presence of clusters of granular hyperreflective deposits located above the RPE, which compressed the ellipsoid reflection zone with wavy uplift or interruption of continuity or breached the outer membrane boundary to the outer nuclear layer (Figure 2). The inclusion criteria were that at least one eye met both of the above criteria and the reticular lesions covered more than 1/2 of the retina above the macular area or more than 1/3 of the retinal area and were dispersed in the papillary temporal and nasal retinas [18]. The exclusion criteria were Stargardt disease, Best disease, advanced stage of AMD, and other known RPE–photoreceptor injury diseases.

This study was approved by the ethics committee of the First Affiliated Hospital of Guangzhou Medical University. All subjects were aware of the purpose and methods of this study and voluntarily participated in the study.

2.2. Electrophysiology

The visual electrophysiology instrument RETI-Port/Scan 21 (Roland Consult Stasche & Finger GmbH, Brandenburg), EOG were determined for each patient's eyes. The detection methods were based on the ISCEV Visual Electrodiagnostic Procedures 2017 edition [19,20]. A gold cup was used as the electrode. After acclimatization in natural light for 30 minutes before examination, each participant used compound topical amide eye drops to dilate both eyes to over 6 mm. The 2 recording electrodes of the right eye were connected to Channel 1 of the amplifier. After cleaning the skin with a facial scrub, the electrodes were glued to the skin of the outer and inner canthus of the right eye using a conductive cream. The 2 recording electrodes of the left eye were connected to Channel 2 of the amplifier, and each electrode was symmetrically fixed to the skin of the outer and inner canthus of the left eye using the same method, with the ground electrode fixed above the skin of the forehead. Each channel was tested, and the examination was started after the impedance was <5.0 kΩ. During the examination, the sphere opening surface of the Ganzfeld stimulator maintained a full field of vision and covered both eyes of the subjects. The dark adaptation examination lasted for 15 minutes, recording 10 seconds per minute with a 50-second rest interval, and then the open adaptation examination lasted for 15 minutes, recording 10 seconds per minute with a 50-second rest interval. The results were analyzed after the examination. EOG parameters were recorded for each patient.

2.3. Data acquisition and analysis of EOG

Values of the dark trough, light peak, light rise, and the amplitude ratio of the light peak and dark trough (LP:DT ratio) were determined for each recording. Variables of light rise and LP:DT ratio were compared with the standard normal values [21,22] using one-sample t test. All data analyses were conducted using SPSS statistical software for windows version 28. The significance level was set at P < 0.05.

Details of the EOG indicators are listed in Table 1. In this preliminary study, during the recording process of EOG in the 14 eyes, the resting potential first decreased in the dark phase at 15 minutes and reached the dark trough at 7.21±1.75 minutes (Figure 3), and the resting potential (dark trough amplitude) ranged from 262.0 μV to 962.1 μV (Figure 4). With the appearance of bright light, the transepithelial potential increased, and the light rose to the light peak at 15.79±2.70 minutes (Figure 3). Overall, the light rise was slower than 12 minutes (t = 5.24, P < 0.001). (Figure 3), and the light peak potential ranged from 373.8 μV to 1.8 mV (Figure 4). In addition, the LP:DT ratio is currently the main evaluation index of EOG and reflects the amplitude change in the transepithelial potential in the dark and light. The LP:DT ratio of the 14 eyes observed in this preliminary study was 1.63±0.22, ranged between 1.18 and 1.97, which was lower than 2.35[22], but was not significantly lower than the lower limit of 1.7(t = -1.12, P = 0.28).

Table 1. EOG indicator values.

Patients	1	2	3	4	5	6	7
Age (year)	58	57	72	76	74	82	69
CDVA
OD	0.8	1.0	0.6	0.6	0.4	0.6	0.8
OS	0.8	0.8	0.5	0.5	0.5	0.4	0.8
EOG
Dark trough^a (OD)	435.0/10.5	682.6/7.5	678.4/6.5	921.9/6.0	962.1/7.5	262.0/5.0	840.9/7.5
Dark trough^a (OS)	413.8/8.5	669.1/8.5	707.5/6.5	491.4/5.0	847.3/8.0	602.3/4.5	981.8/9.5
Light peak^b (OD)	778.7/7.5	1200/8.0	1100/6.0	1800/8.5	1400/6.0	373.8/11.5	1400/9.0
Light peak^b (OS)	664.8/7.0	1200/8.0	1200/6.0	969.0/8.5	1000/7.0	927.5/9.5	1400/9.5
LP:DT ratio (OD)	1.79	1.76	1.62	1.95	1.46	1.43	1.66
LP:DT ratio (OS)	1.61	1.79	1.70	1.97	1.18	1.54	1.43

Note: OD for right eye, OS for left eye. a: Amplitude (μV)/peak time (min); b: Amplitude (μV)/light rise time (min).

Abbreviations: CDVA: corrected distance visual acuity, EOG: electrooculography, LP:DT ratio: amplitude ratio of the light peak and dark trough.

In this study, the EOG characteristics of 7 patients (14 eyes) with RMD were initially observed, which revealed that several parameters of the retinal resting potential between the RPE and photoreceptors were different from the normal reference ranges: The current ISCEV standard gives a range of values for the LP: DT ratio between 1.7 and 4.3 [21], a meta-analysis put the mean at 2.35 [22], the LP: DT ratio of the RMD eyes included in this study was less than 2.35, but was not significantly lower than 1.7, suggesting physiological function of the RPE–photoreceptor complex may be abnormal in RMD eyes. Under normal conditions, the light rise reaches its maximum (light peak) at about 7-12 minutes after photoadaptation, but the results in this study are significantly delayed than 12 minutes. The exact mechanism of light rise is not well understood, but it is clear that it requires a normal interface between the rods and the RPE. This suggests that there may be an abnormal interaction between rods and RPE in RMD eyes. It is important to note that, based on previous studies, RMD seems to primarily affect the rod area.

To the best of our knowledge, previous studies on EOG characteristics of RMD are rare, but those with AMD can be used as a reference. According to previous studies, although the development of AMD spreads to the RPE layer, there seems to be no obvious stable abnormality of EOG in AMD eyes, except when geographic atrophy occurs [23]. Normal EOG parameters require the functional integrity between the photoreceptors and the retinal pigment epithelium. Therefore, the observed delay in light rise in RMD-affected eyes implies abnormal cellular functional status of the RPE–photoreceptor complex. The present study prompts us that bioelectric activity between the RPE and photoreceptors may be abnormal in RMD patients even with normal central vision. The RPE-photoreceptor complex is an important structure for visual production, therefore investigation of the RPE–photoreceptor complex function in RMD has important clinical implications. Current research on RPE function of RMD is limited, EOG is one of the most important research methods, and research efforts on it can link abnormalities in RPE photoreceptor interaction mechanisms to the pathophysiology of RMD.There are still limitations to the study. Because RMD is often combined with confounding factors such as drusen and pigment disorders that may affect EOG indicators, it is necessary to expand the sample and set up a control group to control for confounding factors, conduct an analytical study on EOG in RMD patients, and further explore the value of EOG examination in the diagnosis of RMD.

In conclusion, Some EOG parameters of RMD patients are different from normal reference ranges, bioelectric activity between RPE and photoreceptors in patients with RMD may be affected by SDD or RPE abnormalities.

Institutional Review Board Statement: The study was conducted in accordance with the Declaration of Helsinki, and approved by the Ethics Committee of the First Affiliated Hospital of Guangzhou Medical University (ES-2024-157-01).

Data Availability Statement: The raw data supporting the conclusion of this article will be made available by the authors, without undue reservation.

Conflicts of Interest: The authors declare no conflict of interest.

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The authors declare no competing interests.

Electrooculography features of reticular macular disease: A preliminary observation

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and Methods

3. Results

4. Discussion

Declarations

References

Additional Declarations

Status:

Version 1