Table of Contents Author Guidelines Submit a Manuscript
Journal of Ophthalmology
Volume 2018, Article ID 7314308, 5 pages
https://doi.org/10.1155/2018/7314308
Research Article

Psychological Aspects and Depression in Patients with Symptomatic Keratoconus

11st Department of Ophthalmology, Medical School of University of Athens, Athens, Greece
2Department of Ophthalmology, Medical School of University of Ioannina, Ioannina, Greece
3Department of Ophthalmology, Medical School of University of Larisa, Larisa, Greece
4Royal Eye Infirmary, Dorset County Hospital, Dorchester, UK

Correspondence should be addressed to Marilita M. Moschos; rf.oohay@atiliramsohcsom

Received 26 September 2017; Revised 26 December 2017; Accepted 17 January 2018; Published 29 May 2018

Academic Editor: Sotiria Palioura

Copyright © 2018 Marilita M. Moschos et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose. To assess the psychological status of keratoconus sufferers and to determine the relationship between depression and visual impairment in this group of patients. Methods. Fifty-six patients with keratoconus and forty-seven age- and gender-matched healthy control subjects were retroprospectively analyzed. Every participant underwent a complete ophthalmological examination. Keratoconus diagnosis was confirmed with corneal topography and tomography. Zung Depression Inventory Questionnaire and Patient Health Questionnaire-9 (PHQ-9) were completed by everyone. Results. Visual acuity (logMAR 0.53 ±0.30 versus 0.11 ± 0.16), PHQ-9 score (10.20 ± 4.00 versus 5.40 ± 5.01), and Zung score (46.52 ± 8.70 versus 38.53 ± 8.41) showed a statistically significant difference between keratoconus patients and healthy controls ( for all). Worse visual acuity was strongly correlated with older individuals (rho = 0.339, ) and higher PHQ-9 (rho = 0.765, ) and Zung score (rho = 0.672, ). Conclusion. Depressive disorders appear to be directly associated with keratoconus, both in frequency and intensity. Worse visual acuity and older age could be identified as predictive factors for their emotional status. Moreover, the disease itself could be recognized as an independent risk factor for depression development, underlying the need for close monitoring and supportive management. To the best of our knowledge, our study is the first in the literature to elaborate the association between keratoconus and depression, by assessing two different questionnaires simultaneously.

1. Introduction

Keratoconus (KC) is a noninflammatory, progressive, and bilateral but usually asymmetric corneal disorder, characterized by stromal thinning, iron deposition in the epithelial basement membrane, breaks in Bowman’s layer, steepening of central cornea, and in more advanced stages by corneal ectasia or even acute stromal oedema (hydrops) [13]. Its exact etiology and pathogenesis remain unknown. Its prevalence is reported to range from 0.3 to 2,300 per 1,00,000 in Russia and central India, respectively [13].

In the early stages, symptomatology is usually vague, with blurred vision, due to changes in refractive error and photosensitivity, being the major patients’ complains, thus needing corneal topography to confirm the diagnosis [2]. In more advanced stages, severe visual impairment is present due to irregular astigmatism, myopia, corneal scarring, and hydrops.

Depression is a growing public health disorder worldwide, affecting especially the elderly and patients with chronic health problems, such as cancer, chronic heart disease, and chronic obstructive pulmonary disease [47]. Depression is associated with increased morbidity and mortality, or suicidal attempts [8]. Although the disease could be easily identified and effectively treated in early stages [9, 10], it usually goes undetected and insufficiently treated for long periods of time [1113]. In primary care, numerous questionnaires have been used for screening depression, including among others Geriatric Depression Scale [14], Hospital Anxiety and Depression Scale [15], 9-item Patient Health Questionnaire (PHQ-9) [16], Zung Depression Inventory-Self-Rating Depression Scale (Zung SDS) [17], Beck Depression Inventory [18], Hamilton Rating Scale for Depression [19], 12- or 36-item Short Form Health Survey [20], and the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes [21].

Visual impairment is a result by numerous disorders, affecting crucially patients’ quality of life, and is regarded as one of the most common chronic causes of psychological distress, particularly in the elderly [22]. It is well established that self-reported decline in visual function is accompanied by depressive symptoms [23, 24], whereas the association between visual acuity and depression remains controversial [2327].

Several studies have evaluated the aforementioned association, detecting depression in patients with age-related macular degeneration [25], glaucoma [28], retinitis pigmentosa [29], and Stargardt disease [30]. As for the KC, studies demonstrated controversial conclusions. Gorskova et al. identified a positive correlation only in women [31], while Woodward et al. rejected the existence of such an association [32].

As early detection and appropriate treatment of depression could inhibit effectively its progression to more severe stages, the purpose of our study was to examine the association of KC and depression, using for first time both PHQ-9 and Zung Depression Inventory (Zung SDS) questionnaires, and to identify whether worse objective vision in KC patients, expressed by visual acuity, is associated with the severity of depression.

2. Materials and Methods

In this case control study, we included 56 KC patients (61% male) and 47 (64% male) age- and gender-matched healthy control subjects (CL). The KC subjects were recruited from the Laboratory of Electrophysiology, 1st Department of Ophthalmology, University of Athens, Greece.

The CL population consisted of subjects that referred to the outpatient department of ophthalmology for ocular examination and who had no systemic or ocular disorders. All the individuals were Caucasian, middle aged, and nonsmokers. Furthermore, none of them suffered from diabetes mellitus, hypertension, glaucoma, cataract, or any other ocular disorder that could contribute to visual deterioration.

The study was performed according to the Helsinki Declaration and was approved by the ethical committee of our hospital, General Hospital of Athens “G. Gennimatas.” Written informed consent was obtained by everyone that took part in the study.

All the participants were examined thoroughly, clinically, and topographically and completed the PHQ-9 and Zung SDS questionnaires, translated and validated in Greek. Corrected distance visual acuity (CDVA) was measured with Snellen charts (measured in decimals). For KC patients their usual best correction (spectacles or contact lenses) was utilized. The values were converted in a logarithm of the minimum angle of resolution (logMAR) scale for statistical purposes, and mean CDVA score was used in the statistical analysis. Slit-lamp biomicroscopy examined the existence of stromal corneal thinning, Vogt striae, or a Fleischer ring. Retinoscopy after pupil dilation (20 minutes after phenylephrine 2.5% and cyclopentolate 1% drops had been instilled in the eye) determined the presence or absence of retroillumination signs of KC, such as the oil droplet sign and scissoring of the red reflex.

The criteria used in KC diagnosis included (1) distortion of the corneal surface; (2) visual acuity reduction; (3) stromal thinning within central cornea, using a comprehensive ophthalmic examination including, visual acuity measurement, and corneal imaging; (4) presence of Vogt striae; and (5) presence of cone upon Scheimpflug topography with irregular astigmatism. In order to assign a subject to KC group, it was needed both the presence of at least one clinical sign of KC and a confirmatory videokeratographic map, with an asymmetric bowtie with skewed radial axis above and below the horizontal meridian (AB/SRAX) pattern [1].

Zung SDS questionnaire is a short self-rating scale regarding the affective, psychological, and somatic symptoms of depression [17, 33]. It consists of 20 questions which address the most commonly found diagnostic criteria of depression during patients’ interviews. Ten questions are worded positively and the rest negatively. Each one is scored on a scale of 1–4 (a little of the time to most of the time) according to the frequency of each feeling during the preceding week. Total scores range from 20 to 80. Scores below 49 are regarded normal, whereas 50–59 exhibit mild, 60–69 moderate, and over 70 severe depression [3436].

PHQ-9 depression scale is a questionnaire used for screening, identification, and evaluation of depression, with well-established validity and reliability [16, 3739]. It assesses patient’s emotional status over the past two weeks, by scoring each of the 9 criteria of the Diagnostic and Statistical Manual of Mental Disorders- IV (DSM-IV) [40]. The responses are rated from “0” (not at all) to “3” (nearly every day). Total score is the sum of all the answers, ranging from 0 to 27, with elevated values indicating more severe depressive symptoms. Scores less than 5 demonstrate the absence of a depressive disorder, 5 to 9 exhibit mild, 10 to 14 moderate, and over 15 severe depression [16].

Statistical comparisons between patients and controls were performed using Mann–Whitney–Wilcoxon (MWW) test, after confirmation of nonnormality with a Kolmogorov–Smirnov test. The correlations of the Zung SDS score and the PHQ-9 score to CDVA, age, and sex were analyzed by the Spearman correlation test. Statistical analysis was performed using the SPSS 24.0 software (IBM SPSS Inc., Chicago, IL, USA). A value less than 0.05 was considered statistically significant.

3. Results

The demographic and clinical data of the participants are summarized in Table 1. The KC group consisted of 56 subjects, whereas the CL group comprised 47 participants. No significant differences existed in mean age (41 ± 7 years versus 42 ± 9 years, resp.) and gender status (61% male versus 64% male, resp.) between the groups.

Table 1: Demographic and clinical characteristics of patients with keratoconus and controls.

Subjects with KC, compared to CL subjects, had significantly elevated both PHQ-9 score (10.20 ± 4.00 versus 5.40 ± 5.01, ) and Zung SDS score (46.52 ± 8.70 versus 38.53 ± 8.41, ). Moreover, CDVA in KC patients was significantly worse compared to CL (CDVA logMAR 0.53 ± 0.30 versus 0.11 ± 0.16, ).

According to PHQ-9 score, 12.5% of KC patients did not suffer from depression, while 46.4% encountered mild, 28.6% moderate, and 12.5% severe depressive symptoms. Zung SDS score detected no depressive symptomatology in 58.9% of the KC patients, mild symptomatology in 33.9%, and moderate in 7.2% of them.

In Table 2 are presented the intercorrelations among the examined parameters in the KC group. Older participants had worse CDVA (rho = +0.339, ) and elevated PHQ-9 score and Zung SDS score (rho = +0.444, and rho = +0.422, , resp.). No significant correlations were associated with age. Patients with worse CDVA presented significantly higher PHQ-9 score and Zung SDS score ( for both). Finally, PHQ-9 score was positively and strongly correlated with Zung SDS score (rho = 0.907, ).

Table 2: Intercorrelations among the examined parameters in patients with keratoconus.

4. Discussion

In the present study, we demonstrated that depression occurs more frequently and with greater intensity in KC patients compared to age and gender-matched healthy control subjects. The possible association between KC and depression had not been thoroughly investigated. Although the hypothesis that KC is accompanied by depression has been rejected by Woodward et al. [32], this association appeared to demonstrate a gender bias [31]. Cingu et al. reported significant improvement of anxiety after cross-linking (CXL) in KC patients; however, this intervention did not appear to influence the depressive status of KC patients [41]. To the best of our knowledge, our study is the first to report a significant association between depression and KC, regardless of the participants’ age and gender, by assessing two different questionnaires simultaneously.

Low visual acuity attributed to conditions, such as age-related macular degeneration (ARMD) [26] and retinitis pigmentosa [29], has been associated been associated with depression. We demonstrated that worse objective visual function, expressed by lower CDVA, is mildly (0.339) but significantly () correlated with older age and with more intense depressive symptoms. Previous studies using solely the PHQ-9 questionnaire suggested self-reported visual deterioration, rather than lower best corrected visual acuity (BCVA) correlation with depression [23, 24]. The differences could be at least partly attributed to the fact that Morse [23], and Zhang et al. [24], examined the association of visual impairment and depression in a population of US citizens, regardless of the presence or not of an ocular disorder and without taking into account the causes of vision loss. The KC participants in our study did not suffer from other common causes of depression, and therefore our findings suggest that not only visual impairment, but also the disease itself plays a key role in the development of depression.

Interestingly, we found that PHQ-9 score and Zung SDS score were positively and strongly intercorrelated (rho = +0.907, ) in the KC population. Although PHQ-9 usefulness in assessing and grading depression in visually impaired people is well established [42], Zung SDS appears to be a valuable tool in screening depression in adults [17], while its usefulness in grading depression severity remains controversial [43]. In our study, both questionnaires showed consistency and sensitivity in detecting depressive symptoms in KC patients.

Although depression can be readily diagnosed and treated, especially in early stages, it can easily remain undetected and therefore untreated for prolonged periods [9, 10, 44]. Eye care professionals should be aware of the increased prevalence of depression in patients with visual impairment, especially with growing age. Screening tools, such as PHQ-9 and Zung SDS questionnaires, could help ophthalmologists detect depressive symptoms even in early stages and thus urge prompt referral for psychiatric evaluation and possible treatment. It is important to note that in visually impaired patients, depression may cause poorer adherence to treatment, which in turn accelerates the progression of irreversible vision loss, resulting in a more pronounced depressive status [45, 46].

Our study included KC patients with measured CDVA, effectively detected depression using short, easily administered, and well-validated tools such as PHQ-9 and Zung SDS, and it was the first to underline the role of KC itself in the development of depression. Possible limitation of our study is the fact that the KC subjects were in different disease stages which impedes the assessment of disease duration on presence and severity of depression.

5. Conclusions

Keratoconus patients encounter more often depressive symptoms compared to healthy subjects without visual impairment. The frequency and the severity of the symptoms correlate with patients’ age and CDVA, suggesting that worse vision and older age (at presentation) in KC patients could be identified as predictive factors of their emotional status. Finally, our study demonstrates the usefulness of PHQ-9 and Zung SDS questionnaires as a screening tool for depression in KC patients and underlines the need for close monitoring and supportive management of this vulnerable population.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this article.

References

  1. Y. S. Rabinowitz, “Keratoconus,” Survey of Ophthalmology, vol. 42, no. 4, pp. 297–319, 1998. View at Publisher · View at Google Scholar · View at Scopus
  2. M. Romero-Jiménez, J. Santodomingo-Rubido, and J. S. Wolffsohn, “Keratoconus: a review,” Contact Lens and Anterior Eye, vol. 33, no. 4, pp. 157–166, 2010. View at Publisher · View at Google Scholar · View at Scopus
  3. N. S. Gokhale, “Epidemiology of keratoconus,” Indian Journal of Ophthalmology, vol. 61, no. 8, pp. 382-383, 2013. View at Publisher · View at Google Scholar · View at Scopus
  4. A. J. Mitchell, M. Chan, H. Bhatti et al., “Prevalence of depression, anxiety, and adjustment disorder in oncological, haematological, and palliative-care settings: a meta-analysis of 94 interview-based studies,” Lancet Oncology, vol. 12, no. 2, pp. 160–174, 2011. View at Publisher · View at Google Scholar · View at Scopus
  5. S. Herbst, R. H. Pietrzak, J. Wagner et al., “Lifetime major depression is associated with coronary heart disease in older adults: results from the National Epidemiologic Survey on Alcohol and Related Conditions,” Psychosomatic Medicine, vol. 69, no. 8, pp. 729–734, 2007. View at Publisher · View at Google Scholar · View at Scopus
  6. K. Wilhelm, P. Mitchell, T. Slade et al., “Prevalence and correlates of DSM-IV major depression in an Australian national survey,” Journal of Affective Disorders, vol. 75, no. 2, pp. 155–162, 2003. View at Publisher · View at Google Scholar · View at Scopus
  7. E. J. Wagena, W. A. Arrindell, E. F. M. Wouters et al., “Are patients with COPD psychologically distressed?” European Respiratory Journal, vol. 26, no. 2, pp. 242–248, 2005. View at Publisher · View at Google Scholar · View at Scopus
  8. K. H. Abate, “Gender disparity in prevalence of depression among patient population: a systematic review,” Ethiopian Journal of Health Sciences, vol. 23, no. 3, pp. 283–288, 2013. View at Publisher · View at Google Scholar
  9. M. E. Thase and T. Denko, “Pharmacotherapy of mood disorders,” Annual Review of Clinical Psychology, vol. 4, no. 1, pp. 53–91, 2008. View at Publisher · View at Google Scholar · View at Scopus
  10. M. P. Pignone, B. N. Gaynes, J. L. Rushton et al., “Screening for depression in adults: a summary of the evidence for the U.S Preventive Services Task Force,” Annals of Internal Medicine, vol. 136, no. 10, pp. 765–776, 2002. View at Publisher · View at Google Scholar
  11. L. Del Piccolo, A. Saltini, and C. Zimmermann, “Which patients talk about stressful life events and social problems to the general practitioner?” Psychological Medicine, vol. 28, no. 6, pp. 1289–1299, 1998. View at Publisher · View at Google Scholar · View at Scopus
  12. A. J. Mitchell, A. Vaze, and S. Rao, “Clinical diagnosis of depression in primary care: a meta-analysis,” The Lancet, vol. 374, no. 9690, pp. 609–611, 2009. View at Publisher · View at Google Scholar · View at Scopus
  13. J. W. Williams, C. A. Kerber Jr., C. D. Mulrow et al., “Depressive disorders in primary care: prevalence, functional disability, and identification,” Journal of General Internal Medicine, vol. 10, no. 1, pp. 7–12, 1995. View at Publisher · View at Google Scholar · View at Scopus
  14. J. Wancata, R. Alexandrowicz, B. Marquart et al., “The criterion validity of the Geriatric Depression Scale: a systematic review,” Acta Psychiatrica Scandinavica, vol. 114, no. 6, pp. 398–410, 2006. View at Publisher · View at Google Scholar · View at Scopus
  15. A. S. Zigmond and R. P. Snaith, “The hospital anxiety and depression scale,” Acta Psychiatrica Scandinavica, vol. 67, no. 6, pp. 361–370, 1983. View at Publisher · View at Google Scholar · View at Scopus
  16. K. Kroenke, R. L. Spitzer, and J. B. Williams, “The PHQ-9: validity of a brief depression severity measure,” Journal of General Internal Medicine, vol. 16, no. 9, pp. 606–613, 2001. View at Publisher · View at Google Scholar · View at Scopus
  17. W. W. Zung, “A self-rating depression scale,” Archives of General Psychiatry, vol. 12, no. 1, pp. 63–70, 1965. View at Publisher · View at Google Scholar · View at Scopus
  18. A. Schrag, M. Jabanshahi, and N. P. Quinn, “What contributes to depression in Parkinson’s disease?” Psychological Medicine, vol. 31, no. 1, pp. 65–73, 2001. View at Publisher · View at Google Scholar · View at Scopus
  19. E. Cubo, B. Bernard, S. Leurgans et al., “Cognitive and motor function in patients with Parkinson's disease with and without depression,” Clinical Neuropharmacology, vol. 23, no. 6, pp. 331–334, 2000. View at Publisher · View at Google Scholar · View at Scopus
  20. S. H. Paz, D. R. Globe, J. Wu et al., “Relationship between self-reported depression and self-reported visual function in Latinos,” Archives of Ophthalmology, vol. 121, no. 7, pp. 1021–1027, 2003. View at Publisher · View at Google Scholar · View at Scopus
  21. M. Tournier, Y. Moride, T. Ducruet et al., “Depression and mortality in the visually-impaired, community-dwelling, elderly population of Quebec,” Acta Ophthalmologica, vol. 86, no. 2, pp. 196–201, 2008. View at Publisher · View at Google Scholar
  22. C. Q. Huang, B. R. Dong, Z. C. Lu et al., “Chronic diseases and risk for depression in old age: a meta-analysis of published literature,” Ageing Research Reviews, vol. 9, no. 2, pp. 131–141, 2010. View at Publisher · View at Google Scholar · View at Scopus
  23. A. R. Morse, “Vision function, functional vision, and depression,” JAMA Ophthalmology, vol. 131, no. 5, pp. 667-668, 2013. View at Publisher · View at Google Scholar · View at Scopus
  24. X. Zhang, K. M. Bullard, M. F. Cotch et al., “Association between depression and functional vision loss in persons 20 years of age or older in the United States, NHANES 2005-2008,” JAMA Ophthalmology, vol. 131, no. 5, pp. 573–581, 2013. View at Publisher · View at Google Scholar · View at Scopus
  25. A. Augustin, J. A. Sahel, F. Bandello et al., “Anxiety and depression prevalence rates in age-related macular degeneration,” Investigative Opthalmology and Visual Science, vol. 48, no. 4, pp. 1498–1503, 2007. View at Publisher · View at Google Scholar · View at Scopus
  26. J. R. Evans, A. E. Fletcher, and R. P. Wormald, “Depression and anxiety in visually impaired older people,” Ophthalmology, vol. 114, no. 2, pp. 283–288, 2007. View at Publisher · View at Google Scholar · View at Scopus
  27. K. J. Hayman, N. M. Kerse, S. J. La Grow et al., “Depression in older people: visual impairment and subjective ratings of health,” Optometry and Vision Science, vol. 84, no. 11, pp. 1024–1030, 2007. View at Publisher · View at Google Scholar · View at Scopus
  28. S. Skalicky and I. Goldberg, “Depression and quality of life in patients with glaucoma: a cross-sectional analysis using the Geriatric Depression Scale-15, assessment of function related to vision, and the Glaucoma Quality of Life-15,” Journal of Glaucoma, vol. 17, no. 7, pp. 546–551, 2008. View at Publisher · View at Google Scholar · View at Scopus
  29. M. Moschos, A. Chatzirallis, and I. Chatziralli, “Psychological aspects and depression in patients with retinitis pigmentosa,” European Journal of Ophthalmology, vol. 25, no. 5, pp. 459–462, 2015. View at Publisher · View at Google Scholar · View at Scopus
  30. M. M. Moschos, E. Nitoda, and A. Lavaris, “Estimation of depression prevalence in patients with Stargardt disease using PHQ-9 and Zung scores,” European Journal of Ophthalmology, vol. 26, no. 3, pp. 268–272, 2016. View at Publisher · View at Google Scholar · View at Scopus
  31. E. N. Gorskova, E. N. Sevost’ianov, and N. A. Baturin, “Results of psychological testing of patients with keratoconus,” Vestnik Oftalmologii, vol. 114, no. 6, pp. 44-45, 1998. View at Google Scholar
  32. M. A. Woodward, T. S. Blachley, and J. D. Stein, “The association between sociodemographic factors, common systemic diseases, and keratoconus: an analysis of a nationwide heath care claims database,” Ophthalmology, vol. 123, no. 3, pp. 457–465, 2016. View at Publisher · View at Google Scholar · View at Scopus
  33. M. Kleinstaueber, “Zung depression inventory,” in Encyclopedia of Behavioral Medicine, M. D. Gellman and J. R. Turner, Eds., Springer, New York, NY, USA, 2013. View at Google Scholar
  34. L. G. Branch, A. Horowitz, and C. Carr, “The implications for everyday life of incident self-reported visual decline among people over age 65 living in the community,” Gerontologist, vol. 29, no. 3, pp. 359–365, 1989. View at Publisher · View at Google Scholar · View at Scopus
  35. H. Buch, T. Vinding, M. La Cour et al., “Prevalence and causes of visual impairment and blindness among 9980 Scandinavian adults: the Copenhagen City Eye Study,” Ophthalmology, vol. 111, no. 1, pp. 53–61, 2004. View at Publisher · View at Google Scholar · View at Scopus
  36. D. T. Hartong, E. L. Berson, and T. P. Dryja, “Retinitis pigmentosa,” The Lancet, vol. 368, no. 9549, pp. 1795–1809, 2006. View at Publisher · View at Google Scholar · View at Scopus
  37. K. Kroenke, R. L. Spitzer, J. B. Williams et al., “The patient health questionnaire somatic, anxiety, and depressive symptom scales: a systematic review,” General Hospital Psychiatry, vol. 32, no. 4, pp. 345–359, 2010. View at Publisher · View at Google Scholar · View at Scopus
  38. R. L. Spitzer, K. Kroenke, and J. B. Williams, “Validation and utility of a self-report version of PRIME-MD: the PHQ primary care study. Primary care evaluation of mental disorders: Patient Health Questionnaire,” JAMA, vol. 282, no. 18, pp. 1737–1744, 1999. View at Publisher · View at Google Scholar · View at Scopus
  39. R. L. Spitzer, J. B. Williams, K. Kroenke et al., “Validity and utility of the PRIME-MD patient health questionnaire in assessment of 3000 obstetric-gynecologic patients: the PRIME-MD Patient Health Questionnaire Obstetrics-Gynecology Study,” American Journal of Obstetrics and Gynecology, vol. 183, no. 3, pp. 759–769, 2000. View at Publisher · View at Google Scholar · View at Scopus
  40. H. Chacón-López, F. J. Pelayo, M. D. López-Justicia et al., “Visual training and emotional state of people with retinitis pigmentosa,” Journal of Rehabilitation Research and Development, vol. 50, no. 8, pp. 1157–1168, 2013. View at Publisher · View at Google Scholar · View at Scopus
  41. A. K. Cingu, Y. Bez, Y. Cinar et al., “Impact of collagen cross-linking on psychological distress and vision and health-related quality of life in patients with keratoconus,” Eye and Contact Lens, vol. 41, no. 6, pp. 349–353, 2015. View at Publisher · View at Google Scholar · View at Scopus
  42. E. L. Lamoureux, H. W. Tee, K. Pesudovs et al., “Can clinicians use the PHQ-9 to assess depression in people with vision loss?” Optometry and Vision Science, vol. 86, no. 2, pp. 139–145, 2009. View at Publisher · View at Google Scholar · View at Scopus
  43. E. J. Lee, J. B. Kim, I. H. Shin et al., “Current use of depression rating scales in mental health setting,” Psychiatry Investigation, vol. 7, no. 3, pp. 170–176, 2010. View at Publisher · View at Google Scholar · View at Scopus
  44. R. J. DeRubeis, S. D. Hollon, J. D. Amsterdam et al., “Cognitive therapy vs medications in the treatment of moderate to severe depression,” Archives of General Psychiatry, vol. 62, no. 4, pp. 409–416, 2005. View at Publisher · View at Google Scholar · View at Scopus
  45. B. W. Rovner, R. J. Casten, and W. S. Tasman, “Effect of depression on vision function in age-related macular degeneration,” Archives of Ophthalmology, vol. 120, no. 8, pp. 1041–1044, 2002. View at Publisher · View at Google Scholar
  46. B. L. Brody, A. C. Gamst, R. A. Williams et al., “Depression, visual acuity, comorbidity, and disability associated with age-related macular degeneration,” Ophthalmology, vol. 108, no. 10, pp. 1893–1900, 2001. View at Publisher · View at Google Scholar · View at Scopus