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Effect of cataract surgery on cognitive function in elderly: Results of Fujiwara-kyo Eye Study

  • Kimie Miyata,

    Roles Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft

    Affiliation Department of Ophthalmology, Nara Medical University, Kashihara, Nara, Japan

  • Tadanobu Yoshikawa,

    Roles Writing – review & editing

    Affiliation Department of Ophthalmology, Nara Medical University, Kashihara, Nara, Japan

  • Masayuki Morikawa,

    Roles Data curation, Investigation

    Affiliation Mie Prefectural Mental Care Center, Tsu, Mie, Japan

  • Masashi Mine,

    Roles Methodology

    Affiliation Department of Ophthalmology, Nara Medical University, Kashihara, Nara, Japan

  • Nozomi Okamoto,

    Roles Project administration

    Current address: Department of School Psychology, Development Science & Health Education, Hyogo University of Teacher Education, Hyogo, Japan

    Affiliation Department of Community Health and Epidemiology, Nara Medical University, Kashihara, Nara, Japan

  • Norio Kurumatani,

    Roles Funding acquisition, Project administration

    Current address: Department of Epidemiology and Preventive Medicine, Nara Medical University, Kashihara, Nara, Japan

    Affiliation Department of Community Health and Epidemiology, Nara Medical University, Kashihara, Nara, Japan

  • Nahoko Ogata

    Roles Project administration, Supervision, Writing – review & editing

    ogata@naramed-u.ac.jp

    Affiliation Department of Ophthalmology, Nara Medical University, Kashihara, Nara, Japan

Effect of cataract surgery on cognitive function in elderly: Results of Fujiwara-kyo Eye Study

  • Kimie Miyata, 
  • Tadanobu Yoshikawa, 
  • Masayuki Morikawa, 
  • Masashi Mine, 
  • Nozomi Okamoto, 
  • Norio Kurumatani, 
  • Nahoko Ogata
PLOS
x

Abstract

Purpose

To determine whether there is a significant association between prior cataract surgery and cognitive function in an elderly Japanese cohort.

Setting

Nara Medical University, Nara, Japan.

Design

The Fujiwara-kyo Eye Study was a cross-sectional epidemiological study.

Methods

The subjects were ≥ 68-years who lived in the Nara Prefecture and responded to recruitment notices. All of the subjects received comprehensive ophthalmological examinations, and answered questionnaires on their socio-demographic and medical history including prior cataract surgery. The association between prior cataract surgery and cognitive function was determined.

Results

A total of the 2764 subjects whose mean age was 76.3±4.8 years (±standard deviation) was studied. Of these, 668 individuals (24.2%) had undergone cataract surgery. Of these, 150 (5.4%) had dementia as determined by the Mini-Mental State Examination (MMSE) score ≤23, and 877 individuals (31.7%) had mild cognitive impairment (MCI; MMSE score 24–26). The subjects who had prior cataract surgery had significantly lower odds ratio (OR) of having MCI (OR = 0.78, 95% confidence interval; CI 0.64–0.96, P = 0.019) than those who had not had cataract surgery after adjusting for age, sex, body mass index, education, hypertension, diabetes, depression, and history of stroke. The OR was still lower when the visual acuity was also added to the adjusted factors (OR 0.79, 95% CI 0.64–0.97, P = 0.025). However, prior cataract surgery did not contribute significantly to the low OR for dementia.

Conclusions

Cataract surgery may play a role in reducing the risk of developing MCI independently of visual acuity but not for dementia.

Introduction

The number of older individuals is rapidly increasing worldwide, and the cost of medical care and social security benefits have correspondingly increased. It is known that both visual and cognitive impairments increase with advancing age [13], and these impairments will contribute to the cost of medical care. The incidence of dementia was estimated to be 15% and mild cognitive impairment (MCI) was 13% in individuals ≥65 years in Japan in 2010. Thus, 28% of individuals ≥65 years have some degree of cognitive impairments [4]. Visual and cognitive impairments can limit the activities of daily living and the quality of life (QOL), and earlier studies [58] and population-based epidemiological studies [914] involving older individuals have shown that there is a strong association between visual impairments and cognitive function. We have also found a significant association between visual impairments and cognitive function in elderly Japanese [3].

Cataract is the most common eye disorder that disturbs the visual acuity in the elderly. Because cataracts are the leading cause of reversible blindness, cataract surgery may be one strategy for decreasing the number of individuals with cognitive impairments.

Thus, purpose of this study was to determine whether there is a significant association between cataract surgery and cognitive function in the elderly.

Subjects and methods

The Fujiwara-kyo Study

A detailed description of the Fujiwara-kyo Study has been reported elsewhere [1518]. Briefly, this was a cohort study whose purpose was to identify factors related to the maintenance of a healthy life, prevention of physical weakness, and improvements of the functional capacities and the QOL of an elderly population in Japan [1518]. The subjects consisted of residents of the Nara Prefecture who were ≥65-years-old and were living independently in their own homes. The first examinations were performed in 2007 on 4,206 participants. The examinations included a basic interview to obtain socio-demographic data, overall medical conditions, and histories of medical treatments.

The Fujiwara-kyo Eye Study

An ophthalmological examination was not conducted in the initial survey in 2007. The Fujiwara-kyo Eye study was conducted for the first time as part of the Fujiwara-kyo Study at the second survey between February to November 2012. The data presented in this manuscript were collected from the examinations done in 2012. The subjects recruited at the initial survey in 2007 were ≥ 65-years and were 5-years older in 2012. Eighty new subjects ≥ 65-years were recruited during the survey in 2012.

The surveys were conducted in accordance with the tenets of the Declaration of Helsinki, and the protocol was approved by the Ethics Review Board of Nara Medical University. A signed informed consent form was obtained from all participants. When participants had difficulties reading or understanding the written informed consent form, medical staff members helped them understand the informed consent. If participants could not understand the informed consent, they were not included in this study without obtaining proxy consent from a legally authorized representative. We did not have any participants who assumed and agreed the informed consent but could not conduct MMSE.

Visual acuity and slit-lamp examinations for cataract

The uncorrected and corrected visual acuities of both eyes were measured with a Landolt ring chart at 5 m. The refractive errors were measured by an autoref/keratometer (ARK-700A, Nidek, Gamagori, Aichi, Japan), and these values were used when the best-corrected visual acuity (BCVA) was measured. The BCVA of the better seeing eye was recorded as the BCVA, and the decimal BCVA was converted to the logarithm of the minimum angle of resolution (logMAR) units for the statistical analyses. The slit-lamp examination was performed by an ophthalmologist to determine the status of the crystalline lens.

Self-administered cataract questionnaire

A prior cataract surgery was determined by the self-administered questionnaire. The eyes were divided into those with and those without a cataract surgery. The subjects who had undergone cataract surgery in at least one eye were placed in the cataract surgery group for the person wise analyses.

Two hundred and four randomly selected participants were examined by slit-lamp to verify the accuracy of the self-administered questionnaires regarding the cataract surgery. For this, the presence of the crystalline lens or an implanted intraocular lens was determined to confirm that the answer to the self-administered questionnaire was correct. The Kappa coefficient between self-administered questionnaires and diagnosis based on the slit-lamp examination was excellent at 0.95.

Cognitive and depression examinations

The Mini-Mental State Examination (MMSE) was used as a cognitive function test. This test is commonly used for dementia screening [19], and it consists of 5 downstream items; orientation, memory, attentiveness for calculations, speech function, and design capacity. This test was performed by verbal questioning of 5 to 10 minutes duration by skilled clinical psychologists. The maximum score for the MMSE is 30 points, and individuals with a score of ≤ 23 points were classified as having dementia, those with a score of 24–26 points were classified as having mild cognitive impairments (MCI), and those with a score of ≥27 points were classified as having normal cognitive function [3, 20, 21].

The presence of symptoms of depression was evaluated by a self-administered questionnaire by the Geriatric Depression Scale (GDS-15).

Socio-demographic data and general information

The educational level, medical history, and information on medications being used were determined from the answers to the self-administered questionnaire. Hypertension was based on a self-reported diagnosis and current antihypertensive therapy. Diabetes mellitus was defined based on self-reported diagnosis, current anti-diabetic therapy, and fasting plasma glucose and glycated hemoglobin levels.

Statistical analyses

The significance of the differences in the cognitive status by age and BMI were determined by analysis of variance. The differences in the sex and prevalence of hypertension, diabetes, depression, and stroke between the cognitive statuses were determined by chi-square tests. The differences in the BCVA by the cognitive statuses were analyzed by unpaired t-tests. Multivariate statistical models were used to analyze the following as covariates; the variables associated with cognitive impairment in Table 1 (P <0.25) for model 1 and all variables shown in Table 1 for model 2. Statistical analyses were performed with SPSS (version 22.0; SPSS Inc., Chicago, IL). A P <0.05 was taken to be significant.

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Table 1. Basic and clinical characteristics of 2764 participants by cognitive status.

https://doi.org/10.1371/journal.pone.0192677.t001

Results

Data was available on 2,764 individuals on the status of the crystalline lens or prior cataract surgery (S1 Table). All of these individuals had been examined by MMSE. The mean age of subjects was 76.3 ± 4.8 years (mean ± standard deviation, SD). Of the 2,764 subjects, 5.4% were placed in the dementia group, 31.7% in the MCI group, and 62.8% in the normal cognitive function group. The mean age of the dementia group and the MCI group was significantly higher than that of the normal cognitive function group (P <0.001, Table 1). The number of subjects with ≥13 years of education was lower in the dementia group (13.3%) and the MCI group (18.2%) than that in the normal cognitive function group (26.1%; P <0.001, Table 1). The mean BCVA was significantly worse in the dementia group and the MCI group than that in the normal cognitive function group (P <0.001, Table 1).

Associations between visual acuity and cognitive impairment by cataract status

There were 24.2% of the subjects in the prior cataract surgery group. Dementia was present in 4.7% and MCI in 32.4% in this group. Dementia was present in 7.6% and MCI was present in 29.5% in the no cataract surgery group. The mean BCVA was significantly better in the normal cognitive function group than in the MCI and the dementia groups in both the prior cataract surgery group (P for trend = 0.01) and no cataract surgery group (P for trend < 0.01, Table 2).

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Table 2. Associations between visual acuity and cognitive impairment by cataract status.

https://doi.org/10.1371/journal.pone.0192677.t002

Association between cataract surgery and cognitive status

In the multivariate logistic regression analyses, the odds ratio (OR) for MCI was significantly lower in the prior cataract surgery group than in the no cataract surgery group (OR 0.78; P = 0.019, model 1, Table 3 and S2 Table). In addition, when the BCVA was included as a variant, the OR for MCI was still significantly lower in the cataract surgery group than that in the no cataract surgery group (OR, 0.79; P = 0.025, model 2, Table 3 and S2 Table).

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Table 3. Odds ratio for association between cataract surgery and cognitive status.

https://doi.org/10.1371/journal.pone.0192677.t003

In the multivariate logistic regression models, the OR for dementia was not significantly different between the cataract surgery group and the no cataract surgery group after adjusting for confounding factors except for the BCVA (OR 1.10; P = 0.64, model 1, Table 3 and S2 Table). When the BCVA was included as a variant, the OR for dementia was still not significant (model 2, Table 3 and S2 Table).

Discussion

Our results showed that prior cataract surgery significantly reduced the risk of having MCI (OR = 0.78) but did not reduce the risk for dementia. Cataracts are frequent in the elderly and are the leading cause of visual impairments in the elderly worldwide. An earlier study reported that there was a significant correlation between the visual acuity and cognition [22], and subjects with good visual acuity had a 63% lower risk for developing dementia over an 8.5-year period [23]. Similarly, elderly individuals with decreased visual acuity were 5 times more likely to show diminished cognitive performance than elderly individuals with good vision [23]. We also reported earlier that the prevalence of both cognitive and visual impairments increased with increasing age in this cohort [3]. Furthermore, subjects with mild visual impairments (BCVA >0.2 logMAR unit) had 2.4 times higher risk of having dementia than those without visual impairments after adjusting for age, sex, and length of education. These results indicate that it is important to maintain good visual acuity to reduce the risk of developing dementia, however the effects of cataract surgery on preventing cognitive impairment were not analyzed in the Fujiwara-kyo study.

For patients whose poor vision can be attributed to cataracts, surgical intervention may not only improve their vision but also improve their mental status [2430]. Ishi et al. reported that cataract surgery significantly improved the vision-related QOL in elderly patients, and cognitive impairments and depressive mental status also improved in parallel with the improvement in the vision-related QOL [29]. However, Elliott et al [31] found that vision improvement after cataract surgery or refractive correction (eye glasses) did not improve the short-term cognitive function.

A report from UK [32] emphasized the use of cataract surgery in those with both normal and impaired cognition, and it was reported that both groups had significant improvements in the visual outcomes. Cognitive impairment may, however, limit the visual improvements following cataract surgery. We also found that the mean BCVA was significantly better in the normal cognitive function group than that in the cognitive impaired group in both the prior cataract surgery and no cataract surgery groups. Thus, patients with impaired cognition benefit from cataract surgery but not to the same extent as patients with normal cognition.

We evaluated both dementia and MCI and found that 37.2% of the subjects had MCI. This was comparable to the prevalence of MCI that was reported to be 42% in an older population in the United Kingdom [33].

The results of an earlier study showed that cognitive and visual function improvements could not be attributed to cataract surgery per se, and the investigators concluded that cataract surgery does not affect cognitive function [34]. However, our results demonstrated that individuals who had cataract surgery were less likely to have MCI but not dementia, and it was independent of the improved visual acuity. This is probably because MCI is a preventable and reversible condition [35, 36].

We showed earlier in the HEIJO-KYO Cohort that cataract surgery with the implantation of an IOL was significantly associated with a lower incidence of MCI in multivariate statistical models adjusting for visual BCVA and several major causes of cognitive impairments [21]. In the HEIJO-KYO Cohort, we did not have sufficient number of participants with dementia who had MMSE score of ≤23. Thus, in the current study, we divided cognitive impairment subjects into those with dementia and those with mild cognitive impairment and found the differences.

Cataract surgery markedly increases the amount of light reaching the retina. This is important because light is a primary environmental cue for regulating the biological clock, and a desynchronization of the circadian rhythm can predispose the individual to cognitive impairments [37, 38]. Ayaki et al. reported that cataract surgery improved the sleep quality by increasing light transmittance needed to maintain the circadian rhythm [39]. Thus, we suggest that the increase in light impinging on the retina might be one mechanism for preventing cognitive impairments.

There are some limitations in this study. First, this was a cross-sectional study which precludes assessments of causality although earlier pretest–posttest studies supported the beneficial effects of cataract surgery on cognitive functions. Thus, further longitudinal studies of longer durations are needed. Second, we used MMSE to determine the dementia and MCI. To diagnose dementia and MCI accurately, MMSE may not be enough. However this was a survey study, and extensive examinations of cognitive function were limited.

In conclusion, cataract surgery may be important in reducing the risk of developing MCI but not for dementia independently of the improvements of the visual acuity.

Supporting information

S1 Table. Minimal dataset for basic and clinical characteristics.

https://doi.org/10.1371/journal.pone.0192677.s001

(XLSX)

S2 Table. Odds ratio for the association between cataract surgery and cognitive status.

https://doi.org/10.1371/journal.pone.0192677.s002

(XLSX)

Acknowledgments

We thank the participants and supporting organizations in the Fujiwara-kyo Study. We also thank Professor Emeritus Duco Hamasaki of the Bascom Palmer Eye Institute for advices and suggestions.

References

  1. 1. Mitchell P, Cumming RG, Attebo K, Panchapakesan J. Prevalence of cataract in Australia: the Blue Mountains eye study. Ophthalmology. 1997;10: 581–588.
  2. 2. Ferri CP, Prince M, Brayne C, Brodaty H, Fratiglioni L, Ganguli M, et al; Global prevalence of dementia: a Delphi consensus study. Alzheimer's Disease International. Lancet. 2005;17;366: 2112–2117. pmid:16360788
  3. 3. Mine M, Miyata K, Morikawa M, Nishi T, Okamoto N, Kawasaki R, et al. Association of Visual Acuity and Cognitive Impairment in Older Individuals: Fujiwara-kyo Eye Study. Biores Open Access. 2016;5: 228–234. pmid:27610269
  4. 4. Cabinet Office, Government of Japan. Annual Report on the Aging Society 2012. Cabinet Office, Government of Japan; 2013. Available from: www8.cao.go.jp/kourei/english/annualreport/2012/2012pdf_e.html (cited June 30, 2016).
  5. 5. Reischies FM, Geiselmann B. Age related cognitive decline and vision impairment affecting the detection of dementia syndrome in old age. Br J Psychiatry. 1997;171: 449–451. pmid:9463604
  6. 6. Anstey KJ, Lord SR, William P. Strength in the lower limbs, visual contrast sensitivity, and simple reaction time predict cognition in older women. Psychol Aging. 1997;12: 137–144. pmid:9100274
  7. 7. Clemons TE, Rankin MW, McBee WL; Age-Related Eye Disease Study Reseach Group. Cognitive impairment in the age-related eye disiease study: AREDS report. Arch Opthalmol. 2006;124: 537–543.
  8. 8. Busse A, Sonntag A, Bischkopf J, et al. Adaptation of dementia screening for vision-impaired older persons: administration of the Mini-Mental State Examination (MMSE). J Clin Epidemiol. 2002;55: 909–915. pmid:12393079
  9. 9. Lindenberger U, Baltes PB. Sensory functioning and intelligence in old age: a strong connection. Psychol Aging. 1994;9: 339–355. pmid:7999320
  10. 10. Anstey KJ, Luszcz MA, Sanchez L. A reevaluation of the common factor theory of shared variance among age, sensory function, and cognitive function in older adults. J Gerontol B Psychol Sci Soc Sci. 2001;56: 3–11.
  11. 11. Anstey KJ, Luszcz MA, Sanchez L. Two-year decline in vision but not hearing is associated with memory decline in very old adults in a population-based sample. Gerontology. 2001;47: 289–293. pmid:11490149
  12. 12. Valentijn SA, van Boxtel MP, van Hooren SA, Bosma H, Beckers HJ, Ponds RW, et al. Change in sensory functioning predicts change in cognitive functioning: results from a 6-year follow-up in the Maastricht aging study. J Am Geriatr Soc. 2005;53: 374–380. pmid:15743277
  13. 13. Gussekloo J, de Craen AJ, Oduber C, et al. Sensory impairment and cognitive functioning in oldest-old subjects: the Leiden 85+ Study. Am J Geriatr Psychiatry. 2005;13: 781–786. pmid:16166407
  14. 14. Tay T, Wang JJ, Kifley A, Lindley R, Newall P, Mitchell P. Sensory and cognitive association in older persons: findings from an older Australian population. Gerontology. 2006;52: 386–394. pmid:16921251
  15. 15. Iki M, Fujita Y, Tamaki J, Kouda K, Yura A, Kadowaki E, et al. Design and baseline characteristics of a prospective cohort study for determinants of osteoporotic fracture in community-dwelling elderly Japanese men: the Fujiwara-kyo osteoporosis risk in men (FORMEN) study. BMC Musculoskelet Disord. 2009;10: 165. pmid:20030855
  16. 16. Fujita Y, Iki M, Tamaki J, Kouda K, Yura A, Kadowaki E, et al. Renal function and bone mineral density in community-dwelling elderly Japanese men: the Fujiwara-kyo Osteoporosis Risk in Men (FORMEN) Study. Bone. 2013;56: 61–66. pmid:23684959
  17. 17. Nezu S, Okamoto N, Morikawa M, Saeki K, Obayashi K, Tomioka K, et al. Health-related quality of life (HRQOL) decreases independently of chronic conditions and geriatric syndromes in older adults with diabetes: the Fujiwara-kyo Study. J Epidemiol. 2014;24: 259–66. pmid:24814506
  18. 18. Okamoto N, Morikawa M, Tomioka K, Yanagi M, Amano N, Kurumatani N. Association between tooth loss and the development of mild memory impairment in the elderly: the Fujiwara-kyo Study. J Alzheimers. 2015;44: 777–786.
  19. 19. Folstein MF, Folstein SE, McHugh PR. ‘Mini-Mental State’ a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res. 1975;12: 189–198. pmid:1202204
  20. 20. Pol Psychiatr. Is the Montreal Cognitive Assessment (MoCA) test better suited than the Mini-Mental State Examination (MMSE) in mild cognitive impairment (MCI) detection among people aged over 60? Meta-analysis. 2016;50: 1039–1052.
  21. 21. Miyata K, Obayashi K, Saeki K, Tone N, Tanaka K, Nishi T, et al. Higher Cognitive Function in Elderly Individuals with Previous Cataract Surgery: Cross-Sectional Association Independent of Visual Acuity in the HEIJO-KYO Cohort. Rejuvenation Res. 2016;19: 239–243. pmid:26414122
  22. 22. Spierer O, Fischer N, Barak A, Belkin M. Correlation Between Vision and Cognitive Function in the Elderly: A Cross-Sectional Study. Medicine (Baltimore). 2016;95: e2423.
  23. 23. Rogers MA, Langa KM. Untreated poor vision: a contributing factor to late-life dementia. Am J Epidemiol. 2010;171: 728–735. pmid:20150357
  24. 24. Grodstein F, Chen J,Hankinson SE. Cataract extraction and cognitive function in older women. Epidemiology 2003;14: 493–497. pmid:12843777
  25. 25. Applegate WB, Miller ST, Elam JT, Freeman JM, Wood TO, Gettlefinger TC. Impact of cataract surgery with lens implantation on vision and physical function in elderly patients. JAMA 1987;257: 1064–1066. pmid:3806895
  26. 26. Tamura H, Tsukamoto H, Mukai S, Kato T, Minamoto A, Ohno Y, et al. Improvement in cognitive impairment after cataract surgery in elderly patients. J Cataract Refract Surg 2004;30: 598–602. pmid:15050255
  27. 27. Jefferis JM, Mosimann UP, Clarke MP. Cataract and cognitive impairment: A review of the literature. Br J Ophthalmol 2011;95: 17–23. pmid:20807709
  28. 28. Gray CS, Karimova G, Hildreth AJ, Crabtree L, Allen D, O’connell JE. Recovery of visual and functional disability following cataract surgery in older people: Sunderland Cataract Study. J Cataract Refract Surg 2006;32: 60–66. pmid:16516780
  29. 29. Ishii K, Kabata T, Oshika T. The impact of cataract surgery on cognitive impairment and depressive mental status in elderly patients. Am J Ophthalmol. 2008;146: 404–409. pmid:18602079
  30. 30. Anstey KJ, Lord SR, Hennessy M, Mitchell P, Mill K, von Sanden C. The effect of cataract surgery on neuropsycho- logical test performance: A randomized controlled trial. J Int Neuropsychol Soc. 2006;12: 632–639. pmid:16961944
  31. 31. Elliott AF, McGwin G Jr, Owsley C. Vision-enhancing interventions in nursing home residents and their short-term effect on physical and cognitive function. J Am Geriatr Soc. 2009;57: 202–208. pmid:19170783
  32. 32. Jefferis JM, Taylor JP, Clarke MP. Does cognitive impairment influence outcomes from cataract surgery? Results from a 1-year follow-up cohort study. Br J Ophthalmol. 2015;99: 412–417. pmid:25287367
  33. 33. Ward A, Arrighi HM, Michels S, Cedarbaum JM. Mild cognitive impairment: disparity of incidence and prevalence estimates. Alzheimers Dement 2012;8: 14–21. pmid:22265588
  34. 34. Hall TA, McGwin G Jr, Owsley C. Effect of cataract surgery on cognitive function in older adults. J Am Geriatr Soc. 2005;53: 2140–2144. pmid:16398899
  35. 35. Grande G, Cucumo V, Cova I, Ghiretti R, Maggiore L, Lacorte E, el al. Reversible Mild Cognitive Impairment: The Role of Comorbidities at Baseline Evaluation. J Alzheimers Dis. 2016;51: 57–67. pmid:26836169
  36. 36. Koepsell TD, Monsell SE. Reversion from mild cognitive impairment to normal or near-normal cognition: risk factors and prognosis. Neurology. 2012;79: 1591–1598. pmid:23019264
  37. 37. Kondratova AA, Kondratov RV. The circadian clock and pathology of the ageing brain. Nat Rev Neurosci. 2012;13: 325–335. pmid:22395806
  38. 38. Coogan AN, Schutova´ B, Husung S, Furczyk K, Baune BT, Kropp P, et al. The circadian system in Alzheimer’s disease: Disturbances, mechanisms, and opportunities. Biol Psychiatry. 2013;74: 333–339. pmid:23273723
  39. 39. Ayaki M, Muramatsu M, Negishi K, Tsubota K. Improvements in sleep quality and gait speed after cataract surgery. Rejuvenation Res. 2013;16: 35–42. pmid:23145881