Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes

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Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes Francisco J. Ascaso a,b,c, Roberto Rodriguez-Jimenez d,e,n, Laura Cabezón a, Raúl López-Antón e,f, Javier Santabárbara e,g, Concepción De la Cámara b,e,h,i, Pedro J. Modrego b,j,h, Miguel A. Quintanilla h,i, Alexandra Bagney d,e, Leticia Gutierrez b,e, Nancy Cruz a, José A. Cristóbal a,c, Antonio Lobo b,e,h a

Department of Ophthalmology, Hospital Clínico Universitario “Lozano Blesa”, Zaragoza, Spain Instituto de Investigación Sanitaria de Aragón (IIS Aragón), Spain Department of Surgery, Area of Ophthalmology, University of Zaragoza, Spain d Department of Psychiatry, Instituto de Investigación Hospital 12 de Octubre (i þ12) Madrid, Spain e Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Instituto de Salud Carlos III, Spain f Department of Psychology and Sociology, University of Zaragoza, Spain g Department of Preventive Medicine and Public Health, University of Zaragoza, Spain h Department of Medicine and Psychiatry, University of Zaragoza, Spain i Department of Psychiatry, Hospital Clínico Universitario “Lozano Blesa”, Zaragoza, Spain j Department of Neurology, Hospital Universitario “Miguel Servet”, Zaragoza, Spain b c

art ic l e i nf o

a b s t r a c t

Article history: Received 26 October 2014 Received in revised form 4 June 2015 Accepted 11 July 2015

Optical coherence tomography (OCT) has been recently used to investigate neuropsychiatric disorders. We aimed to study retinal OCT measures of patients with schizophrenia with respect to healthy controls, and to evaluate possible differences between recent illness episode (RIE) and non-recent illness episode (NRIE) patients. Thirty schizophrenia patients were classified as RIE (n ¼10) or NRIE (n ¼ 20), and compared with 30 matched controls. Statistical analyses included linear mixed-effects models to study the association between OCT measures and group membership. Multivariate models were used to control for potential confounders. In the adjusted linear mixed-effects regression model, patients had a significantly thinner retinal nerve fiber layer (RNFL) in overall measurements, and in the nasal, superior and inferior quadrants. Macular inner ring thickness and macular volume were also significantly smaller in patients than controls. Compared with controls, in the adjusted model only NRIE (but not RIE) patients had significantly reduced RNFL overall measures, superior RNFL, nasal RNFL, macular volume, and macular inner ring thickness. No significant correlation was found between illness duration and retinal measurements after controlling for age. In conclusion, retinal parameters observed using OCT in schizophrenia patients could be related to clinical status and merit attention as potential state biomarkers of the disorder. & 2015 Elsevier Ireland Ltd. All rights reserved.

Keywords: Optical coherence tomography OCT Retinal nerve fiber layer RFNL Neuroimaging Schizophrenia Psychotic episode

1. Introduction Schizophrenia is one of the most severe mental disorders and a serious public health problem. The diagnosis of schizophrenia relies primarily on identifying the characteristic symptoms of the disorder through a clinical interview. Nevertheless, in view of the variety of clinical presentations of schizophrenia among different patients, and the symptom overlap with other disorders (Demirci

n Corresponding author at: Department of Psychiatry, Instituto de Investigación Hospital 12 de Octubre (i þ 12) Madrid, Spain. Fax: þ34 93 3908536. E-mail address: [email protected] (R. Rodriguez-Jimenez).

and Calhoun, 2009), objective markers for diagnosing schizophrenia and related conditions are currently being sought (Zarogianni et al., 2013). The interest of biomarkers in schizophrenia has been emphasized in recent reports (Kasper, 2013), especially those based on neuroimaging methods. Neuroimaging techniques have been extensively studied over the past years, and there is now a considerable number of studies including structural and functional magnetic resonance imaging that aim to develop new diagnostic markers for schizophrenia. Relevant findings of neuroimaging studies in patients with schizophrenia include gray (Glahn et al., 2008) and white (Takayanagi et al., 2013; Bracht et al., 2014) matter abnormalities. Nevertheless, at the present moment it is difficult to draw firm conclusions regarding the

http://dx.doi.org/10.1016/j.psychres.2015.07.028 0165-1781/& 2015 Elsevier Ireland Ltd. All rights reserved.

Please cite this article as: Ascaso, F.J., et al., Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes. Psychiatry Research (2015), http://dx.doi.org/10.1016/j.psychres.2015.07.028i

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precise nature of the underlying neuropathology of the disorder (Fornito et al., 2009). In this context, optical coherence tomography (OCT), a non-invasive imaging technique, provides reproducible, high-resolution cross-sectional imaging of the retinal nerve fiber layer (RNFL) and optic nerve head topography, providing an objective tool to diagnose axonal damage and thus constituting a “window into the brain” (London et al., 2013). A significant reduction in peripapillary RNFL thickness has been reported in patients with various neurological disorders such as multiple sclerosis (Sergott et al., 2007; Thrower, 2007), Alzheimer's disease (Parisi et al., 2001; Berisha et al., 2007; Marziani et al., 2013; Larrosa et al., 2014; Ascaso et al., 2014) or Parkinson's disease (Inzelberg et al., 2004; Hajee et al., 2009; Garcia-Martin et al., 2014; Jimenez et al., 2014), suggesting that this technique may also prove to be useful in other neuropsychiatric disorders. Together with these neuroimaging findings, the impaired functioning of the visual system and the retinal alterations found in patients with schizophrenia support the use of OCT to investigate this disorder (Meier et al., 2013). In the first study reported in the literature, our group found a decreased RNFL thickness as measured with OCT in patients with schizophrenia (Ascaso et al., 2010). Similar results have been later reported by Lee et al. (2013), who additionally found a relationship between abnormal OCT parameters and illness duration, but not by Chu et al. (2012), who did not find significant differences in retinal parameters between patients in the early stages of illness and controls. Thus, the goal of our study was to confirm in a larger sample of patients with schizophrenia the findings described in our first report, testing the hypothesis that a significant thinning of peripapillary RNFL and macular thickness would be found in schizophrenia patients when compared with controls. In addition, on the basis of the contradictory findings reported in the literature, we explored the hypothesis that abnormal OCT parameters would be observed in patients with non-recent illness episodes (NRIE) of schizophrenia, but not in patients with a recent illness episode (RIE). Finally, we studied the correlation between abnormal OCT parameters and illness duration.

2. Methods 2.1. Subjects Thirty-seven patients diagnosed with schizophrenia and fulfilling DSM-IV criteria were consecutively recruited among patients presenting to the outpatient clinic of the Department of Psychiatry at Hospital Clínico Universitario of Zaragoza, Spain from May 2010 to January 2011. Five patients refused participation and two were excluded for clinical reasons. Therefore, the final sample included 30 Caucasian patients with schizophrenia (23 males; mean age 45.1 years, SD¼ 10.4; mean illness duration 16.3 years, SD ¼11.2). The control group included 30 Caucasian healthy volunteers (22 males; mean age 44.5 years, SD ¼10.9), who were matched with patients for age (t¼ 0.20, df ¼58, p ¼0.839) and gender (χ2 ¼0.09, df ¼ 1, p ¼0.766). We had estimated that at least 28 pairs of patients and controls would be required to achieve an 80% probability of detecting a mean between-group difference in RNFL thickness of 9 μm with a standard deviation of 712 μm, and a standardized difference of 0.75 at a 5% significance level. The 9 μm difference in RNFL thickness was considered based on the results of Lee et al. (2013). This research followed the tenets of the Declaration of Helsinki, written informed consent was obtained from all subjects prior to their inclusion in the study, and the local ethics committee approved the protocol. Exclusion criteria for all subjects were as follows: (a) previous

or concurrent systemic disease that may affect the eyes, (b) a history of ophthalmological or neurological disease known to affect the visual pathway (e.g. glaucoma, age-related macular degeneration, diabetic retinopathy, degenerative myopia), (c) media opacification such as cataract, corneal leukoma, or vitreous hemorrhage that impede ocular and OCT examination, (d) refractive error of over þ 2 spheric diopters for hyperopic defects or  2 spheric diopters for myopic defects, as this may cause an artefactual reduction in RNFL thickness and difficulty in fixation (Wu et al., 2011; Zhao and Jiang, 2013; Öner et al., 2013a, b), (e) a history of head injury with loss of consciousness, and (f) drug or alcohol dependence. 2.2. Psychiatric assessment Patients were assessed using the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I) (First et al., 2002). For this study, an illness episode of schizophrenia was defined based on the DSM-IV “A” criterion for the disorder: two or more of the characteristic symptoms (delusions, hallucinations, disorganized speech, grossly disorganized or catatonic behavior, negative symptoms), lasting one month or more. To explore the differences between patients with recent versus non-recent episodes of illness, the patient sample was divided into two subgroups: patients who had suffered their last episode in the month preceding assessment (“Recent illness episode”, RIE, n ¼ 10) and those who had been clinically stable and free from psychotic episodes in the previous 6 months (“Non-recent illness episode”, NRIE, n¼ 20). Patients were considered to be clinically stable when the signs of the disturbance were manifested by only negative symptoms, or by two or more symptoms listed in criterion A present in attenuated form. A period of 6 months was chosen following APA guideline recommendations (Lehman et al., 2004). Eight patients in the RIE subgroup had been admitted to the inpatient unit the month prior to their inclusion in the study. Severity of illness was assessed with the Positive and Negative Syndrome Scale (PANSS) (Kay et al., 1987), in its validated Spanish version (Peralta and Cuesta, 1994). The PANSS can be administered using a semi-structured interview lasting 30–40 min, and includes 30 items which are rated on a severity scale ranging from 1 (absence of psychopathology) to 7 (extremely severe). The total PANSS score is obtained by adding the individual item scores, and ranges from 30 to 210. All patients were treated with antipsychotic medication. Antipsychotic doses were converted into chlorpromazine equivalents, following the consensus-based recommendations described by Gardner et al. (2010). 2.3. Optical coherence tomography OCT and neuropsychological examinations were carried out on the same day. OCT was performed by a trained and experienced ophthalmologist using a time-domain OCT (TD-OCT) system (Stratus OCT, Carl Zeiss Meditec Inc., Dublin, CA, USA) following dilation of the pupils with 1% tropicamide. Only high-quality images (signal strength46) were included. All patients underwent scans to measure peripapillary RNFL thickness, macular thickness and macular volume. RNFL images were acquired for each eye by taking three circumpapillary scans of 3.4-mm diameter centered on the optic disc to effectively intercept all nerve fibers converging toward the optic disc (Schuman et al., 1996). The software allows the mapping of the RNFL thickness in all quadrants (temporal, superior, nasal and inferior), which was calculated by the OCT device software and represented by a line graph indicating RNFL thickness at all sections of the scanning circle. We considered the average values of three different measurements per

Please cite this article as: Ascaso, F.J., et al., Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes. Psychiatry Research (2015), http://dx.doi.org/10.1016/j.psychres.2015.07.028i

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Table 1 Comparison of RNFL thickness (mm), macular thickness (mm) and macular volume (mm3), between controls and patients with schizophrenia. OCT measures Overall RNFL Right eye Left eye Superior RNFL Right eye Left eye Inferior RNFL Right eye Left eye Nasal RNFL Right eye Left eye Temporal RNFL Right eye Left eye Macular outer ring thickness Right eye Left eye Macular inner ring thickness Right eye Left eye Foveal thickness Right eye Left eye Macular volume Right eye Left eye

Controls (n¼ 30)

Patients (n¼30)

RIE patient subgroup (n ¼10)

NRIE patient subgroup (n¼ 20)

103.277 8.99 102.54 7 12.76

95.147 13.40** 94.977 16.77**

101.03 7 10.28* 95.917 20.93*

92.057 14.05*** 94.55 7 15.14**

127.337 14.44 124.837 17.07

114.65 7 17.98** 117.447 22.60*

120.707 17.60* 122.777 22.29

111.477 17.80*** 115.05 7 22.90**

129.377 17.38 134.03 7 22.30

120.147 27.70* 121.177 25.34**

126.0 7 15.72* 116.78 7 35.11**

117.05 7 32.26** 123.157 20.34**

83.43 7 13.98 79.03 7 14.62

75.727 19.79* 70.077 23.80*

82.80 7 19.14 76.677 18.86

72.007 19.59** 67.107 25.60**

72.577 10.32 74.23 7 11.23

70.077 11.20* 69.79 7 15.63*

74.60 7 11.20 67.55 7 20.27*

67.687 10.72* 70.807 13.56*

237.93 7 14.33 238.93 7 14.27

236.56 7 20.74 230.737 20.33*

243.307 18.22* 232.69 7 13.99*

233.017 21.40* 229.85 7 22.89**

274.767 16.89 275.03 7 15.43

266.197 22.79* 254.157 31.31***

274.45 7 17.72 257.447 17.58***

262.007 24.38** 252.677 36.15***

204.337 18.26 206.307 23.19

203.89 7 18.71 192.487 21.76**

203.50 7 21.78 190.007 11.43***

204.107 17.54 193.60 7 25.28**

6.98 7 0.45 6.727 0.38**

6.687 0.64** 6.627 0.68**

6.94 7 0.40 6.98 7 0.39

6.78 7 0.59** 6.65 7 0.60**

Note: Two-tailed t-tests or ANOVA were used. Statistically significant differences when compared to control subjects (p-value o 0.05) are in bold text. RIE: Recent illness episode; NRIE: Non-recent illness episode. *

Cohen's d ranging from 0.2 to 0.5. Cohen's d ranging from 0.5 to 0.8. *** Cohen's d ranging from 0.8 to 2.0. **

quadrant, and the overall data obtained in all quadrants were identified as overall RNFL thickness. Macular thickness and volume measurements were obtained in each eye by the fast macular thickness protocol, which consists of six consecutive radial linear scans (each 6 mm) in a spoke-like pattern centered on the fovea, with each radial scan spaced 30° apart. Stratus OCT software considers retinal thickness as the distance between the first signal from the vitreoretinal interface and the signal from the anterior boundary of the retinal pigment epithelium. The map is composed of nine sectorial thickness measurements in three concentric circles with diameters of 1 mm, 3 mm, and 6 mm. The area bounded by the outer (6-mm) and middle (3-mm) circles forms the outer ring, and the area bounded by the middle (3-mm) and inner circles (1-mm) forms the inner ring. The central 1-mm circular region represents the foveal area. Total average macular thickness, average macular thicknesses in the inner (1–3 mm) and outer (3– 6 mm) rings, and the central 1-mm fovea thickness were analyzed in the study. Total macular volume was calculated automatically by the OCT software. 2.4. Statistical analysis Statistical analysis was performed using the ‘R’ program, version 3.0.0, (R Foundation for Statistical Computing, Vienna, Austria). Normality of distribution of peripapillary RNFL thickness, macular thickness and volume, as well as the PANSS scores and the chlorpromazine equivalents of antipsychotics were assessed with the Shapiro-Wilk test for small sample sizes. Student t-tests and Chi-square tests were used to compare groups (schizophrenia vs. control). One-way analysis of variance (ANOVA) with post-hoc pairwise comparisons using the Scheffé procedure was employed to examine differences across controls, RIE and NRIE patients.

Cohen's d (Cohen, 1988) was calculated to document differences between the patient groups and controls. This coefficient measures the effect size, and may be especially relevant in cases of small samples, such as the RIE and NRIE patient subgroups, when the differences found do not reach statistical significance. To assess the association between OCT measures and group membership, linear mixed-effects (or multilevel) models were used which take into account that successive measurements in each subject (e.g. right and left eyes) are related to each other (Pinheiro and Bates, 2009). Multivariate models were used in which potential confounders (age, gender, and eye) were controlled for. To calculate the correlation between OCT measures and illness duration, Pearson’s partial correlation coefficient was used, controlling for the possible confounding effect of age. The level of statistical significance was set at p o0.05.

3. Results In the group of patients with schizophrenia, the mean total PANSS score was 101.47 27.7. Twenty-three patients were treated only with atypical antipsychotics, six patients with both atypical and typical antipsychotics, and one patient was treated exclusively with a typical antipsychotic. The mean antipsychotic dose (in chlorpromazine equivalents) was 711.6 7490.6 mg. Regarding the subgroups, among RIE patients 9 were males, their mean age was 41.5 713.4 years, and mean illness duration was 17.67 12.5 years. Among NRIE patients 14 were males, their mean age was 46.8 710.4 years, and mean illness duration was 13.7 7 8.1 years. No significant differences were observed between RIE and NRIE patients regarding age (p ¼0.194), gender (p ¼0.372) or illness duration (p ¼0.385). Mean total PANSS scores were

Please cite this article as: Ascaso, F.J., et al., Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes. Psychiatry Research (2015), http://dx.doi.org/10.1016/j.psychres.2015.07.028i

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Table 2 Linear mixed-effects models for the differences between controls and schizophrenia patients in RNFL thickness (mm), macular thickness (mm) and macular volume (mm3). OCT measures

Overall RNFL (ref Control) Schizophrenia patients Superior RNFL (ref Control) Schizophrenia patients Inferior RNFL (ref Control) Schizophrenia patients Nasal RNFL (ref Control) Schizophrenia patients Temporal RNFL (ref Control) Schizophrenia patients Macular outer ring thickness (ref Control) Schizophrenia patients Macular inner ring thickness (ref Control) Schizophrenia patients Foveal thickness (ref Control) Schizophrenia patients Macular volume (ref Control) Schizophrenia patients

Unadjusted model

Adjusted model

β

(95% CI)

p-Value

β

(95% CI)

p-Value

 7.99

(  13.71,  2.28)

0.007

 7.88

(  13.48,  2.30)

0.006

 10.14

(  18.35,  1.92)

0.016

 10.02

(  18.28,  1.75)

0.018

 11.35

(  21.29,  1.40)

0.026

 11.10

(  20.86,  1.34)

0.027

 8.63

(  17.11,  0.16)

0.046

 8.45

(  16.81,  0.09)

0.047

 3.41

(  8.64, 1.82)

0.196

 3.51

(  8.72, 1.69)

0.181

 5.05

(  13.45, 3.34)

0.233

 4.83

(  12.95, 8.95)

0.238

 14.75

(  24.91,  4.58)

0.005

 14.67

(  24.50,  4.84)

0.004

 7.37

(  17.09, 2.34)

0.134

 7.70

(  17.34, 1.94)

0.115

 0.24

(  0.48,  0.01)

0.045

 0.24

(  0.47,  0.01)

0.040

Note: All OCT measures were separately analyzed. In the adjusted model, variables were controlled for age, gender, and eye. β: linear regression coefficient. CI: Confidence interval.

significantly higher among RIE patients when compared with NRIE patients (118.90 721.73 vs. 92.70726.56; t¼2.69, df ¼ 28; p ¼0.012). Mean antipsychotic dose was also higher among RIE than NRIE patients, but this difference was not statistically significant (796.0 7666.4 mg vs. 370.97216.6 mg; t¼1.94; df ¼10.47; p ¼0.080). Patients with schizophrenia showed a decreased overall peripapillary RNFL thickness when compared with controls. This difference was observed in all quadrants of both eyes, and was statistically significant for the right eye overall RNFL (95.14 713.40 mm vs. 103.27 78.99 mm in patients vs. controls respectively; p o0.05), right eye superior RNFL (114.65 717.98 mm vs. 127.33714.44 mm; p o0.05), and left eye inferior RNFL (121.17 725.34 mm vs. 134.03722.30 mm; p o0.05). Macular thickness and volume were also decreased in schizophrenia patients when compared to healthy controls for both eyes, reaching significance for left eye macular inner ring thickness (254.15 731.31 mm vs. 275.037 15.43 mm; p o0.05), foveal thickness (192.48 721.76 mm vs. 206.30 723.19 mm), and macular volume (6.65 70.60 mm vs 6.987 0.39 mm; p o0.05) (see Table 1). In the fully adjusted linear mixed-effects regression model (table 2), patients also had significantly thinner RNFL in overall measurements (β ¼  7.88; p ¼0.006) and in the superior (β ¼  10.02; p ¼0.018), inferior (β ¼  11.10; p ¼0.027) and nasal (β ¼  8.45; p ¼0.047) quadrants (see Fig. 1). Furthermore, macular inner ring thickness (β ¼  14.67; p ¼0.004) and macular volume (β ¼  0.24; p ¼0.040) were also significantly smaller in the patient group. When comparing the patient subgroups (RIE and NRIE) with controls, significant differences in measures of RNFL thickness, macular thickness and macular volume were observed mainly for NRIE patients. Furthermore, in several OCT parameters where no significant differences were found, the effect size documented by means of Cohen’s d (Cohen, 1988) ranged from 0.5 to 0.8 (see Table 1). In addition, after adjustment (Table 3), significant differences with controls were not observed for RIE patients, but appeared only for the NRIE subgroup in RNFL overall measures (β ¼ 5.12; p ¼0.210 in RIE and β ¼  9.25; p ¼0.005 in NRIE patients), macular volume (β ¼  0.16; p¼ 0.324 and β ¼  0.28; p ¼0.036), superior RNFL (β ¼  4.68; p ¼0.433 and β ¼  12.63; p ¼0.008), nasal RNFL (β ¼  2.56; p ¼0.669 and β ¼ 11.35; p ¼0.018), and macular inner ring thickness (β ¼  11.22; p ¼ 0.120

Fig. 1. Time-domain optical coherence tomography (OCT). The colors represent normal distribution percentiles, where green¼ 95–5%, yellow¼ 5–1%, red¼1–0%. The black line shows retinal nerve fiber layer (RNFL) measures for each quadrant (TEMP¼ temporal, SUP¼ superior, NAS ¼ nasal, INF ¼inferior): (A) Normal peripapillary RNFL thickness in a control subject; (B) Decreased peripapillary RNFL thickness in the nasal quadrant of a patient diagnosed with schizophrenia (arrow). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

and β ¼  16.34; p¼ 0.004). Finally, after controlling for age effects, no significant correlation was observed between illness duration and peripapillary RNFL thickness, macular thickness or macular volume either for the total sample of patients with schizophrenia or for the patient subgroups.

4. Discussion The findings in this study confirm the results described in our first report (Ascaso et al., 2010) showing that, when compared to matched controls, patients with schizophrenia have a reduced

Please cite this article as: Ascaso, F.J., et al., Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes. Psychiatry Research (2015), http://dx.doi.org/10.1016/j.psychres.2015.07.028i

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Table 3 Linear mixed-effects models for differences between controls and subgroups of patients with schizophrenia (RIE and NRIE) for RNFL thickness (mm), macular thickness (mm) and macular volume (mm3). OCT measures

Overall RNFL (ref Control) RIE patients NRIE patients Superior RNFL (ref Control) RIE patients NRIE patients Inferior RNFL (ref Control) RIE patients NRIE patients Nasal RNFL (ref Control) RIE patients NRIE patients Temporal RNFL (ref Control) RIE patients NRIE patients Macular outer ring thickness (ref Control) RIE patients NRIE patients Macular inner ring thickness (ref Control) RIE patients NRIE patients Foveal thickness (ref Control) RIE patients NRIE patients Macular volume (ref Control) RIE patients NRIE patients

Unadjusted model

Adjusted model

β

(95% CI)

p-Value

β

(95% CI)

p-Value

 4.22  9.85

(  12.33, 3.88) (  16.22,  3.49)

0.301 0.003

 5.12  9.25

(  13.21, 2.97) (  15.53,  2.96)

0.210 0.005

 4.26  13.04

(  15.85, 7.63) (  22.15,  3.92)

0.465 0.006

 4.68  12.63

(  16.54, 7.18) (  21.87,  3.40)

0.433 0.008

 10.07  11.99

(  24.37, 4.21) (  23.20,  0.77)

0.163 0.036

 11.30  11.00

(  25.54, 2.93) (  22.06, 0.05)

0.117 0.051

 1.58  12.11

(  13.45, 10.28) (  21.44,  2.77)

0.790 0.012

 2.56  11.35

(  14.51, 9.39) (  20.66,  2.04)

0.669 0.018

 1.76  4.22

(  9.26, 5.74) (  10.11, 1.67)

0.640 0.165

 2.75  3.88

(  10.34, 4.82) (  9.78, 2.01)

0.569 0.192

 0.73  7.20

(  12.63, 11.17) (  16.58, 2.18)

0.902 0.130

 2.19  6.14

(  13.94, 9.56) (  15.31, 3.03)

0.710 0.185

 8.67  17.74

(  23.08, 5.73) (  29.06,  6.42)

0.233 0.027

 11.22  16.37

(  25.46, 3.02) (  27.46,  5.28)

0.120 0.004

 8.06  7.04

(  21.98, 5.86) (  18.00, 3.92)

0.251 0.203

 8.73  7.19

(  22.73, 5.28) (  18.11, 3.72)

0.217 0.192

 0.11  0.31

(  0.45, 0.23) (  0.58,  0.04)

0.523 0.023

 0.16  0.28

(  0.50, 0.17) (  0.54,  0.02)

0.324 0.036

Note: All OCT measures were separately analyzed. In the adjusted model, variables were controlled for age, gender, and eye. RIE: Recent illness episode; NRIE: Non-recent illness episode. β: linear regression coefficient. CI: Confidence interval.

peripapillary RNFL thickness, macular inner ring thickness and macular volume. However, the most relevant finding is that differences in retinal parameters with respect to controls were only significant for NRIE patients but not for RIE patients. The differences found with respect to controls in our NRIE patients could be analogous to the findings of Lee et al. (2013), who reported differences in RNFL and macular thickness as well as in macular volume between controls and what they term “chronic” and “longterm chronic” patients with schizophrenia, but not for “acute” patients. When studying patients in the first years of illness, however, Chu et al. (2012) did not observe differences in RNFL thickness or in macular volume between patients and controls, as happens with our RIE subsample. Nevertheless, neither of these two studies is directly comparable with ours. In the Lee et al. (2013) study patients with an illness episode lasting up to two years were defined as “acute”, while in our study it is not illness duration but time since an acute psychotic episode what differentiates between the patient subgroups. In the Chu et al. (2012) study, patients in the early years after disease onset (mean illness duration of 4.4 years) were studied, thus the time elapsed since the last psychotic episode was not taken into account; furthermore, this study also included a significant proportion of patients (11 out of a total sample of 49) with schizoaffective disorder. Schizophrenia is a chronic disorder, and has been hypothesized to be associated with axonal loss and thus decreased retinal thickness (Ascaso et al., 2010; Lee et al., 2013). A potential explanation for the negative findings in RIE patients in the present study could be related to inflammation. Inflammatory processes are thought to increase retinal thickness. For example, Stock et al. (2011) detected an increased retinal thickness following cataract surgery, proposing inflammation as a cause. It could be hypothesized that inflammatory processes happening during acute

psychotic episodes may increase retinal thickness, thus masking the effects of axonal loss in patients with schizophrenia. Similar mechanisms have been proposed for other neuropsychiatric disorders. Thus, in a study of multiple sclerosis, a disorder characterized by inflammation and neuroaxonal degeneration, Balk and Petzold (2014) discussed that optic neuritis may mask the subtle thinning of retinal layers associated with global CNS atrophy. Our group has also reported an increased macular volume in patients with mild cognitive impairment compared with controls, in contrast with the decreased volume found in Alzheimer's disease patients when compared with controls, hypothesizing that inflammatory processes may be at stake in the prodromal phases of Alzheimer's disease (Ascaso et al., 2014). Inflammatory processes have been described in acute episodes of schizophrenia, both in first-episode (Garcia-Bueno et al., 2014) and in chronic patients with schizophrenia (Martinez-Gras et al., 2011). As previously reported, these inflammatory processes could be reflected in retinal structures. Using a novel free-water neuroimaging method, Pasternak et al. (2012) have suggested that neuroinflammation, accompanied by excessive extracellular volume, is more prominent than axonal degeneration in patients with a first psychotic episode. Therefore, due to these putative neuroinflammatory processes, it would be conceivable to find an increased volume of nervous tissue in patients with a recent psychotic episode, such as those in the RIE subsample of our study. Under these circumstances, the reduction of peripapillary RNFL thickness and macular volume associated with schizophrenia may not be observable due to the acute neuroinflammatory process, in accordance with Balk and Petzold’s (2014) suggestion. On the other hand, in patients without a recent episode of illness, changes suggesting axonal degeneration may be apparent, as observed in our NRIE subsample, and perhaps in some of the “chronic” and

Please cite this article as: Ascaso, F.J., et al., Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes. Psychiatry Research (2015), http://dx.doi.org/10.1016/j.psychres.2015.07.028i

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F.J. Ascaso et al. / Psychiatry Research ∎ (∎∎∎∎) ∎∎∎–∎∎∎

“long-term chronic” patients of the Lee et al. (2013) sample. Future, longitudinal studies should assess the presence of neuroinflammatory markers to test this explanatory hypothesis. In our study, all quadrants in the total patient sample and in the NRIE subgroup exhibited RNFL thinning; however, these differences were only significant for some quadrants. We cannot provide an explanation regarding differential effects on the quadrants, or on possible differences between the two eyes. However, previous studies in schizophrenia (Chu et al., 2012; Lee et al., 2013) as well as other neuropsychiatric disorders (Motchos et al., 2011; Kirbas et al., 2013; Shi et al., 2014) have also found differences between quadrants. In these studies several hypotheses were proposed in order to explain these differential effects, but none of them has been proven to date. Finally, in contrast to Lee et al. (2013), we found no relationship between abnormal OCT retinal parameters and illness duration. A possible methodological explanation to these contradictory results is the fact that in the Lee et al. (2013) paper it is not clear whether results were age-corrected. Age may be a confounding factor, since a thinning of retinal structures is observed with increasing age (Alamouti and Funk, 2003; Parikh et al., 2007). From a conceptual point of view, Lee et al. (2013) suggested that their findings could be a consequence of the progression of neurodegenerative changes that are measurable in the retina. However, in contradiction with classical theories about schizophrenia being a progressive disease, and based on more recent neuroimaging findings, some authors advocate the hypothesis that pathological changes documented in patients with schizophrenia may not be progressive (Zipursky et al., 2013). In fact, there is ongoing controversy in the field regarding neurodegenerative versus neurodevelopmental pathophysiological models in schizophrenia. Although the RNFL alterations found in NRIE patients in this study are similar to those observed in Parkinson’s or Alzheimer's diseases and could suggest neurodegenerative pathology in schizophrenia, only longitudinal OCT studies may help clarify the underlying neurobiological processes at play (Pantelis et al., 2005; Kochunov and Hong, 2014). In the meantime, this study shows the potential of OCT to document retinal changes that could be considered as markers of the biological stage of the disorder. A potential limitation of this study is the difference between the mean antipsychotic doses in the two patient samples. As expected, the mean dose of antipsychotic medication was higher in RIE than in NRIE patients. The differences were not statistically significant, but this may be due to the limited sample size in the two patient subgroups. Although it could be argued that potential neuroinflammation in retinal structures in RIE patients might be related to antipsychotic medication (Haupt, 2006; ContrerasShannon et al., 2013), meta-analysis suggests an anti-inflammatory effect of antipsychotics (Tourjman et al., 2013). Another possible limitation is the relatively small sample size, especially in the patient subsamples. Nonetheless, we report statistically significant differences between patients and controls, and also between the RIE and NRIE patient subsamples and controls. In addition, the effect size was ‘moderate’ (from 0.5 to 0.8) for most parameters, and ‘large’ (from 0.8 to 2.0) for several others (Cohen, 1988). Therefore, it is conceivable that the differences observed in this study may be found to be even more marked in larger samples. In conclusion, this study confirms that, compared to controls, patients with schizophrenia have a reduced peripapillary RNFL thickness, macular inner ring thickness and macular volume as documented by means of OCT. For the first time, we report that these differences between patients and controls were only observed in patients with non-recent episodes of schizophrenia, but not in those with a recent psychotic episode. The finding of differences in OCT parameters between RIE and NRIE patients should

be considered as preliminary results to be tested in future longitudinal studies. To date, there are very few reports exploring OCT parameters in patients with schizophrenia and all of them are cross-sectional, thus providing limited insight regarding the longitudinal course of these parameters as the illness progresses. Similarly, the conjecture that the observed differences could be influenced by neuroinflammatory processes taking place during psychotic exacerbations should also be explored, given its potential applicability in the search for biological markers of schizophrenia. Finally, the potential of OCT, a non-invasive, relatively inexpensive imaging technique, to document changes in the retina might also be helpful in studying other hypotheses such as current neurodevelopmental theories of schizophrenia.

Role of the funding source This research was supported in part by the Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM) of the Instituto de Salud Carlos III, and by Madrid’s Regional Government (S2010/BMD-2422 AGES) and European Union Structural Funds.

Contributors All the authors worked collectively to develop the protocols and methods described in this paper. F.J.A. suggested the rationale and acted as research coordinator. L.C. had special input in all aspects of this study, including the literature search. A.L. led the research group. N.C., M.A.Q, C.D.L.C., L.G.G., and J.A.C. had responsibility for the fieldwork, checked the accuracy of methods in the draft, and significantly contributed to the interpretation of results. F.J.A., L.C., A.L., P.J.M., R.R.J., A.B., R.L.A. and J.S. wrote the first draft, placed it in context and interpreted the results. J.S. designed and carried out the statistical analysis. All authors read and approved the final report.

Conflicts of interest All authors declare there are no potential financial, personal, or organizational conflicts of interest for this particular study.

Acknowledgment We thank the Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM) of the Instituto de Salud Carlos III, and the Instituto de Investigación Hospital 12 de Octubre, the Madrid Regional Government and European Union Structural Funds.

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Please cite this article as: Ascaso, F.J., et al., Retinal nerve fiber layer and macular thickness in patients with schizophrenia: Influence of recent illness episodes. Psychiatry Research (2015), http://dx.doi.org/10.1016/j.psychres.2015.07.028i