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  5. FP1460 : Multifocal ERG Assisted Evaluation of Subthreshold Laser in Acute Central Serous Chorioretinopathy

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Dr. Aanchal Mehta, A19864, Dr. Neha Goel

Introduction

Central serous chorioretinopathy (CSC) is an idiopathic disorder characterized by neurosensory detachment (NSD) with or without concomitant pigment epithelial detachment (PED) and decompensated retinal pigment epithelium (RPE) with one or more focal active leakage sites at the level of RPE.1In the acute stage, fluid accumulation under the retina causes damage to the photoreceptors which may persist even after the fluid is reabsorbed. This can result in diminished contrast sensitivity which may be permanent.2

Non thermal subthreshold laser (STL) photocoagulation is effective in treating CSC with point source leakage. It improves metabolism of the RPE cells and thus accelerates resorption of the subretinal fluid (SRF) which limits photoreceptor damage.2Since spontaneous resolution may occur in CSC within a few months, current indications of treatment include non-resolution after ≥ 3 months, primary detachment with visual decline in a patient who has experienced permanent visual loss from an untreated macular detachment in the fellow eye and in severe forms of CSC.However, it may be wise to reduce SRF accumulation during the early stage in order to minimize the irreversible damage to photoreceptors that follows.

While optical coherence tomography (OCT) is a useful, non-invasive imaging modality to diagnose and monitor CSC, multifocal electroretinography (MF-ERG), developed by Sutter and Tran, gives a topographical measure of retinal activity and provides an objective functional assessment of the macular region.3There has been no published study on MF-ERG assisted evaluation of STL versus observation in patients with acute CSC. Thus, the aim of our study was to evaluate STL as a treatment modality for acute CSC and compare this with the standard of care (conservative management) in terms of anatomical (spectral domain OCT) and functional assessment (visual acuity, contrast sensitivity, MF-ERG) of the central retina.

Materials and Methods

This was a prospectiveinterventional comparative study on 30 eyes with acute CSC, conducted fromJanuary 2015 to January 2016 at a tertiary eye care center. Institutional ethical clearance was obtained before commencement of the study. Informed consent was obtained from all the participants.

Patients aged ≥ 18 years with CSC of ≤ 1 month duration and best corrected Snellen visual acuity(BCVA) ≥6/60, willing and able to provide informed consent, were included. Patients with any significant media opacity precluding clinical and other examination, recurrent or chronic CSC, subfoveal leakage point or multifocal leaks, cataract or any intraocular surgery within last 3 months, history of any previous retinal intervention and subjects with any other ocular disease were excluded.

At baseline, all patients underwent complete ophthalmological examination including measurement of BCVA, contrast sensitivity (CS) using Pelli-Robson chart, Amsler grid charting, anterior segment and fundus examination, fundus fluorescein angiography (FFA) using Topcon TRC 50 Dx and Spectral Domain OCT(SD- OCT) using RTVue, Optovue. The first-order kernel MF-ERG responses recorded using RETI Port/Scan 21 (Roland Consult, Germany) and DTL electrodes, according to ISCEV guidelines,4 were analyzed. Individual MF-ERGresponses for the hexagons were grouped into concentricrings centered on the fovea for analysis (2°, 2–5°, 5–10°, 10–15°, > 15°). The summed P1 amplitude (nV/deg2) and implicit time (ms) were recorded in these 5 rings.

30 eyes with acute CSC were randomized to group A (15 eyes, conservative management) or group B (15 eyes, STL). SLT was performed as an outpatient procedure under topical anaesthesia and mydriasis. A slit lamp integrated frequency-doubled Nd: YAG Photocoagulator (Zeiss VISULAS VITE) using 532nm wavelength was used with ocular Mainster (standard) focal/grid contact lens applied to the cornea with methylcellulose fluid. A test spot was applied to the retina nasal to the optic disc using 50 micron spot size and 200 ms duration, and the power increased to produce a mild grey lesion (visible burn) at the level of the outer retina. The energy needed for the visible burn was kept constant but the duration was halved to 100 ms and treatment carried out. Laser was applied to the leakage site with immediate cessation on occurrence of subtle RPE color changes.

Outcome measures included BCVA, CS, Central Foveal Thickness (CFT) and Mean Macular Thickness (MMT) on SD-OCT and P1 amplitude and implicit time (IT) on MF-ERG. All these parameters were recorded at baseline, 1 month, 3 months and 6 months follow up, except MF-ERG which was evaluated at baseline, 3 months and 6 months follow up.

Statistical analysis was done using SPSS (Statistical Package for the Social Sciences, IBM Corporation) Statistical software version 21.0.Quantitative variables were compared using the non-parametric Mann Whitney test between the two groups.A p value of ˂0.05 was considered statistically significant.

Results

30 eyes of 30 patients with acute CSC were evaluated, group A and B each containing 15 eyes. Mean age ± Standard deviation (S.D.) was 40.8 ± 10.61 years in group A and 39 ± 9.52 in group B (p=0.917). Group A had 14 males and 1 female while group B had 12 males and 3 females (p=0.598).

Mean BCVA in group A increased from 0.51 ± 0.3 at baseline to 0.14 ± 0.14 at 1 month, 0.11 ± 0.13 at 3 months follow up and 0.05 ± 0.08 at 6 months follow up. In group B, mean BCVA was 0.44 ± 0.37 at baseline, 0.14 ± 0.17 at 1 month, 0.03 ± 0.09 at 3 months and 0.02 ± 0.08 at 6 months following STL. There was no significant difference between the two groups at any visit (p=0.946, 0.841, 0.057 and 0.189 respectively). In group A, mean CS was 1.09 ± 0.49 at baseline, 1.33 ± 0.14 at 1 month, 1.43 ± 0.11 at 3 months and 1.42 ± 0.14 at 6 months follow up while in group B the corresponding values were 1.03 ± 0.45, 1.4 ± 0.11, 1.48 ± 0.05 and 1.49 ± 0.04. While these values were not significantly different between the groups at baseline, 1 month and 3 months follow up (p=0.4, 0.145 and 0.169 respectively), at 6 months follow up mean CS was significantly higher in group B (p=0.032)

At baseline, the two groups were matched in terms of mean CFT (634 ± 199.33µm in group A, 514.47 ± 140.36µm in group B, p=0.068) and MMT (496.04 ± 142.59 µm in group A, 426.53 ± 95 µm in group B, p=0.127). Mean CFT and MMT were significantly lower in group B as compared to group A at 1 month (p=0.001 and 0.007 respectively). Mean CFT remained significantly lower in group B as compared to group Aat 3 months while MMT was comparable (p=0.049 and 0.663 respectively); however this difference was not maintained at 6 months (p=0.265 and 0.330respectively).

Mean P1 amplitude (nv/deg2) in ring 1 and 2 were significantly decreased as compared to age and sex matched controls in both groups at baseline; however the values between the two groups were comparable.On follow up, P1 amplitude of ring 1 was significantly lower in group A than in group B at 3 months (p=0.036)and 6 months (p=0.022).Mean P1 implicit time (ms) in all 5 rings was comparable between groups A and B at presentation, and remained at 3 and 6 months follow up.

Discussion

In the present study, outcomes of patients with acute CSC managed conservatively or treated with STL were compared in terms of BCVA, CS, CFT and MMT on SD-OCT and MF-ERG. Both the groups of patients were matched in terms of age, sex and all the outcome measures at baseline. Patients in group B, who underwent STL, showed faster improvement in macular thickness on SD-OCT with values significantly lower than patients being managed conservatively at 1 and 3 months follow up. However, this difference was not maintained at 6 months. Mean BCVA were comparable between the two groups at each visit, suggesting that the faster anatomical resolution of fluid did not translate into better visual outcomes at any time. This is in accordance with previous studies that have shown that laser speeds recovery of CSC but does not positively impact final vision.5

CS is a useful psychophysical measure of visual function. A patient can havenormal values of BCVA with high contrast optotypes butsignificantly abnormal with low contrast, thus making CS an important parameter when dealing with macular disorders like CSC.6 Our study showed increase in CS in both groups with achievement of near normal values by 6 months follow up, however mean CS was significantly better in patients that underwent STL.

MF-ERG can be used objectively to assess the macular function and a topographical analysis of the MF-ERG is useful in the clinical observation of CSC. Persistent functional impairment of the retina has been found by MF-ERG in CSC after the resolution of SRF.7However, there is no published study comparing MF-ERG in patients with acute CSC being managed conservatively or being treated with STL. Our study showed that P1 amplitudes are abnormal compared to controls in acute CSC at presentation and thatP1 amplitude in ring 1 remained significantly lesser in the observation group compared to those treated with STL at 3 and 6 months follow up.

It is not clear whether there is a clinically important benefit to treating acute CSC which often resolves spontaneously as part of its natural history. Recently, an evaluation of preferred practice patterns in CSC showed that most physicians (79.1%) preferred to observe the patient with an acute firsttimeepisode for a minimum of 3 months before suggesting anymode of treatment.8The impairment of MF-ERG responses at 3 and 6 months months despite spontaneous resolution of CSC seen in our study in the observation group and not in the treated group and better CS in the treated group at 6 months follow up suggest that STL may be preferable to conservative management in acute CSC. STL improves metabolism of the RPE cells and thus accelerates resorption of the SRF which in turn might limit functional damage to the macula,2 as evidenced by MF-ERG responses.

Our study was limited by a small sample size and short follow up. A better appraisal of this type of study can be done using a larger sample size from the Indian population with a longer study duration to validate our results.

To conclude, STL is a viable therapeutic option in acute CSC. It leads to faster resolution on SD-OCT and better functional outcomes as evidenced by CS and MF-ERG, as compared to observation alone.MF-ERG is a useful modality to evaluate the macula in CSC and should be employed for objective assessment of macular function.

 References

  1. Klais CM, Ober MD, Ciardella AP, Yannuzzi LA. Central Serous Chorioretinopathy. In: Ryan SJ (ed.). Retina Vol. ll Elsevier: Philadelphia, 2006; 2:1135-1161.
  2. Mehdi B, Mehdi K, Soheil A et al. Improvement in visual acuity and contrast sensitivity in patients with central serous chorioretinopathy after macular subthreshold laser therapy. Retina 2013; 33:324-328
  3. Sutter EE, Tran D. The field topography of ERG components in man – I. The photopic luminance response. Vision Res 1992; 32:433-446.
  4. Hood DC, Bach M, Brigell M et al. ISCEV guidelines for clinical multifocal electroretinography (2007 edition). Doc Ophthalmol. Jan 2008; 116:1–11.
  5. Robertson DM, Ilstrup D. Direct, indirect, and sham laser photocoagulation in the management of central serous chorioretinopathy.Am J Ophthalmol 1983;95:457-466.
  6. Sjöstrand J, Frisén L. Contrast sensitivity in macular disease. A preliminary report. Acta Ophthalmol (Copenh) 1977; 55: 507–514.
  7. Suzuki K, Hasegawa S, Usui T, et al.Multifocal electroretinogram in patients with central serous chorioretinopathy.Jpn J Ophthalmol 2002;46:308-314.
  8. Mehta PH, Meyerle C, Sivaprasad S, Boon C, Chhablani J.Preferred practice pattern in central serous chorioretinopathy.Br J Ophthalmol 2016 Aug 18.

 

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