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ORIGINAL ARTICLE
Year : 2017  |  Volume : 4  |  Issue : 4  |  Page : 104-108

The effect of spherical refractive error on tear volume


1 Department of Optometry and Visual Sciences, Faculty of Optometry and Visual Sciences, Al-Neelain University, Khartoum, Sudan
2 Department of Optometry and Visual Sciences, Associate Professor of Optometry, Faculty of Optometry and Visual Sciences, Al-Neelain University, Khartoum, Sudan

Date of Web Publication7-Jun-2019

Correspondence Address:
Dr. Reem Hassan Abd Almajeed
Department of Optometry, Faculty of Optometry and Visual Sciences, AlNeelain University, Khartoum
Sudan
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DOI: 10.4103/bijo.bijo_14_18

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  Abstract 


Background: Dry eye disease (DED) is the most common multifactorial annoying ocular surface disorder, of various ocular symptoms, ranging from eye discomfort, dryness, itching, irritation, and foreign body sensation up to noticeable visual disturbance. Eventually ends with reducing quality of life. Optical refractive quality might deteriorate in these DED individuals, especially in hot-dry-windy climates like in Sudan.
Aim: This study aims to determine the influence of spherical refractive errors (REs) on the tear volume and DED.
Materials and Methods: In a comparative cross-sectional hospital-based study 90 (n = 90) participants were included; all were free from any ocular or systemic diseases and not using contact lenses. They were of equal numbers of hypermetropes and myopes of mixed gender; males and females, with their ages range between (18-28) years. The mean ages in both groups of RE states were 21.97 ± 2.35 and 22.55 ± 3.29 hypermetropes and myopes, respectively. The study was performed at Makkah Eye complex (MEC), Khartoum, Sudan, from May to July 2015; where the participants were recruited from the general refraction clinics at MEC. All individuals were subjected to the full eye examination. The Schirmer's test was used for all the participants. SPSS statistical analysis program was used to analyze the data.
Results: Dry eye was found in 26.6% on hypermetropic patients and 1.1% myopic patients. In this study, the spherical REs showed a significant difference between males (16.6%) and females (12%) P = 0.001.
Conclusion: REs may be considered to be one of the risk factors to cause dry eye condition. Correcting RE may reduce the risk factor of dry eye, and that may reduce its prevalence.

Keywords: Dry eye disease, dryness, hypermetropia, myopia, Schirmer's test, spherical refractive error, tear volume


How to cite this article:
Abd Almajeed RH, Elawad ME. The effect of spherical refractive error on tear volume. Albasar Int J Ophthalmol 2017;4:104-8

How to cite this URL:
Abd Almajeed RH, Elawad ME. The effect of spherical refractive error on tear volume. Albasar Int J Ophthalmol [serial online] 2017 [cited 2019 Jun 19];4:104-8. Available from: http://www.bijojournal.org/text.asp?2017/4/4/104/259770




  Introduction Top


Dry eye disease (DED) is a commonly encountered diagnosis in ophthalmology, but is poorly understood, difficult to define and lacks a unique diagnostic test. The International Dry Eye WorkShop recently defined DED as “a multifactorial disease of the tears and ocular surface that results in symptoms[1] of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolality of the tear film and inflammation of the ocular surface.”[1] Dry eye symptoms belong to the most frequently encountered ocular problems that patients complain about in the daily practice of eye care.[2] Although these symptoms rarely lead to severe problems threatening vision, they may be one of the most common symptoms causes decreasing the quality of vision. The reported prevalence of dry eye is diverse, with questionnaire-based surveys documenting rates ranging from 14.4% to 33% of the population sampled.[3],[4],[5],[6]

Studies which also involve tests of tear function including Schirmer's test, tear breakup time (TBUT), fluorescein staining, or rose Bengal staining for the determination of dry eye have found generally lower prevalence rates.[7] Limitations in comparisons of studies in different populations include different age distribution of the population, definitions of dry eye, or methodology. Most studies of dry eye are confined to developed nations and older populations, with resultant lack of ethnic diversity.[5]


  Materials and Methods Top


In a comparative cross-sectional hospital-based study 90 (n = 90; 180 eyes) participants were included, all were free from any ocular or systemic diseases and not using contact lenses. The participants were recruited to form the general refraction clinics at Makkah Eye Complex (MEC) Khartoum, Sudan, from May to July 2015. The selected individuals were divided into two groups; one included 45 patients with myopia (myopia was defined in this study, as a spherical equivalent [SE] of at least −0.5 diopters “D”). The other group included equal numbers of 45 individuals (hypermetropia was defined as a SE of at least +1.0 D).[8] Both in mixed gender, males and females.

The age of the participants ranged from 18 to 28 years; the mean ages in both groups of refractive error (RE) states were 21.97 ± 2.35 and 22.55 ± 3.29 hypermetropes and myopes, respectively. The total of the 90 individuals (n = 180 eyes) had spherical REs from ± 0.50 to ± 4.50 diopters.

A comprehensive clinical examination was performed, which included vision tests by Snellen's E-test chart using projected Snellen's Chart by Chart Projector (CP; Chart Projector, CP-770; NIDEK CO., LTD. 34–14 Maehama, Hiroishi-cho, Gamagori, Aichi 443-0038, JAPAN; www.nidek.com) to measure the visual acuity and recorded in decimal forms. Then, ophthalmoscopy and refraction were done by autorefractometer (AR 510 A, NIDEK; model 9000 Japan), and direct ophthalmoscope (Heine ophthalmoscope and retinoscope (HEINE QUALITY IN GERMANY HEINE and USA LTD 10 Innovation Way, Dover, NH 03820, USA) plus TLS series Trial frame and TLS series Trial Set of lenses from Topcon Full Diameter Trial Sets (Topcon Corporation; 1 Chome-5-2 Azusawa, Itabashi, Tokyo 174-0051, Japan www.topcon.co.jp/en/). Then, slit-lamp biomicroscopic examinations were done by Haag-Streit Slit Lamp (Haag-Streit Diagnostics-Slit Lamp BQ 900/870 18./2014-11; HAAG-STREIT AG Gartenstadtstrasse 10 3098 Koeniz, Switzerland, www.haagstreit.com) for all candidates.

Schirmer's test to measures basic tear function and volume was done by Schirmer's paper strips (Sigma Pharmaceuticals, 955 236th St NE, Ste 1 North Liberty, IA; 52317; E-mail: sales@sigmapharmaceuticals.com) inserted into the eye for ≥2 min up to 5 min[9] after the explanation of the procedure to each participant. The tear volume results were checked by the denoted amount of wetting on the strips scale. The grade was taken as (1) normal which is ≥15 mm wetting, (2) mild which is 14–9 mm wetting, (3) moderate which is 8–4 mm wetting, and (4) severe which is <4 mm wetting.

Data analysis was done by “Statistical Analysis” by Statistical program for social sciences (SPSS) version 20 (Manufactured by IBM SPSS Inc., PASW Statistics for Windows, Version 20.0; 2009. Chicago: SPSS Inc., IL, USA). Categorical variables were analyzed using frequencies and percentage. Continuous variables were summarized using mean, percentile, range, and standard deviation (SD). Statistically significant differences and associations were determined by P < 0.05.

Ethical approvals were obtained from Al-Neelain University, Khartoum Sudan Ethical committee, and Makkah Research Center.


  Results Top


A total of 90 (180 eyes) participants' eyes with mean age of 22.26 ± 2.86 years old were included in this study. Males were 48 (53.3%) and 42 (46.7%) were female. The total participants were divided into two groups; each group comprised 45 individuals. Group (A) was hypermetropia patients and Group (B) was myopic patients.

The mean age of Group A (GA) was 21.97 ± 2.35 (18–25), (males 23 [51.1%] and females 22 [49.9%]) and Group B (GB) was 22.55 ± 3.29 (17–28), (males 25 [55.5%] and females 20 [44.5%]). Vision range: 0.57 ± 0.23 (0.20–1.00) in GA and 0.55 ± 0.23 (0.10–1.00) in GB. Sphere equivalent range was 1.78 ± 0.98 (0.50–4.50) in GA whereas 1.54 ± 1.12 (0.50–4.00) in GB. Tear volume (mean ± SD) range was 1.78 ± 0.98 (0.50–4.50) in GA, 18.41 ± 4.26 (1–25) in GB [Table 1].
Table 1: Description of the demographic and clinical data of the studied groups (n=45)

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In the myopia group, the mean age was 21.97 ± 2.35, males 23 (51.1%) and females 22 (49.9%), their vision mean was 0.57 ± 0.23, and SE mean was 1.78 ± 0.98, tear volume 13.18 ± 5.00. While in the hypermetropia group, the mean of age was 22.55 ± 3.29, males 25 (55.5%) and females 20 (45.5%), their vision mean was 0.55 ± 0.23, and SE mean was 1.54 ± 1.12, tear volume 18.41 ± 4.26 [Figure 1].
Figure 1: Mean of tear volume of spherical refractive error subjects

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A paired sample t-test was used to compare between tear volume myopic and hypermetropic patients. The test showed a significant difference between them; df (89) t = −7.2, P < 0.001. Pearson's correlation was used to find the relation between tear volume myopic and hypermetropic patients. The test yielded no significant correlation, r = (0.087) P (0.413) [Figure 2] and [Table 2].
Figure 2: Correlation between tear volume of spherical refractive Error (Hypermetropic/Myopic) subjects

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Table 2: Measurements of tear quantity

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An independent sample t-test was used to compare between hypermetropic genders and tear volume. The test showed no significant difference between them, t (−1.4) f = 648, P > 0.001, whereas myopic patients showed a significant difference between them t (4.0) F (0.449) P < 0.001 [Table 3]. Kruskal–Wallis test was used to find the association between the study groups' genders and tear volume. The test showed statistically difference between them, X1 (2) = 13.816, P = 0.000 in myopic genders, and nonsignificant in hypermetropic genders X1( 2) =1.994, P = 0.158 [Table 3].
Table 3: Comparison of hypermetropic and myopic tear measurements with gender

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  Discussion Top


Overview

Patients with DED often complain about poor vision, which is not easily measurable.[10]

As optical quality could be affected by low tear volume or tear production which can be checked easily by simple tear assessment tests[11],[12] such as Schirmer's test or TBUT.[13] These assessment tests purely focus on the dynamics of the tear film after a blink and its important role in the optical quality of the eye. It was noted that patients with DED report large optical aberrations as compared with normal eyes.[14] There are strong associations between DED and its severity with REs.[15]

The participants in the current study were a pit young population, with a mean age of was 22.26 ± 2.86 years, similar to the young- and middle-aged adults, in Norway study by Midelfart et al., 2002.[16] While it was in contrary with the population-based study of 2520 elderly Americans residents of Salisbury, Maryland, aged ≥65 years;[17] and the hospital-based study at a Tertiary Care Center in 400 elderly Indians,[18] Furthermore, the Japanese elderly population study by Uchino et al.[19] The results of this study were succeeded to demonstrate a correlation between REs and eye dryness level [Table 2] which was in line with Fahmy and Aldarwesh, 2018; in Saudi young adults.[20]

Regarding the gender differences in REs, our study revealed that REs had higher values in males than females, and this agreed with Gomez-Salazar et al., 2017[6] and disagreed with Castro et al., 2018[21] in their largest population-based Brazilian study (3107 participants from the five geopolitical regions of Brazil) where the prevalence of dry eye patients was 26.4% for males and 73.6% for females.[21] Our study was disagreed with[17] who report a higher incidence of myopia and hypermetropia in females rather than male.

This concept of decreased tear production and occurrence of dry eye in females was to some extent in line with Lamberts et al., 1979,[22] who demonstrated that the tear production decreased significantly in women in their menopausal ages (50–59 years of age group) as menopause causes estrogen deficiency and consequent change in the local hormonal milieu of lacrimal gland. The study revealed that most of the RE patients – both hypermetropic and myopic – had normal average tear volume (65.5% in hypermetropes and 51.1% myopes). The mean normal tear volume in each group was 13.18 ± 5.00 and 18.41 ± 4.26, respectively.

Forty-three (47.8%) participants had excessive tears volume. Twenty-four (26.6%) had dry eye (DED), and this is agreed with Fahmy and Aldarwesh and Uchino et al., 2006,[19],[20] who report that DED is prevalent among young adults with RE.[20]

In the myopia group, the mean age was 21.97 ± 2.35, males 23 (51.1%) and females 22 (49.9%), their vision mean was 0.57 ± 0.23, and SE mean was 1.78 ± 0.98, tear volume 13.18 ± 5.00. While in the hypermetropia group, the mean of age was 22.55 ± 3.29, males 25 (55.5%) and females 20 (45.5%), their vision mean was 0.55 ± 0.23, and SE mean was 1.54 ± 1.12, tear volume 18.41 ± 4.26 [Figure 1]. This result supported that the concept reported by Fahmy and Aldsrwesh; 2018, in their association between dry eye and RE.[20] The is no significant differences between volumes of tear production between myopes and hypermetropes. In the present study, 12% of females had dry eye compared to 16.6% of males and the difference was statically significant; P > 0.001, most studies reported a higher prevalence of dry eye in females than males,[23],[24] and Gayton; 2009,[25] Gayton all reported that female gender is considered to be risk one of the factors of dry eye same as age. Although Schein OD and colleagues (1997).[4] and Shah and Jani[18] in their population-based study of 2520 elderly Americans residents of Salisbury, Maryland, aged ≥65 years; (65–84 years), and hospital-based study at a Tertiary Care Center in 400 elderly Indians.[18] Respectively, both concluded that DED is not only associated with race or sex but only associated with older age as DED were found common among the elderly.[18],[4]

Although the above comment was against the comment with Wang et al. 2016,[26] in which they demonstrated low tear volume in teenagers with myopia.[26] This current study finding of DED prevalence in those with spherical REs in consistent with the observation by (Moss et al., in 2000,[23] and again with Moss et al., in 2004[27] all postulated that persons with REs have an increased tendency to rub their eyes and feel foreign substance into the eye that predisposes to tear film instability; hence, these individuals may be susceptible to external eyes inflammation and more DED.[28]

The current study demonstrated that DED was more prevalent in hypermetropic (26.6%) than myopic (1.1%), we have no definite explanation for this observed phenomenon despite to suggestion by Shimmura et al.; 1999[29] and this agreed with Sahai and Malik; 2005.[24]

The differences between the average of Schirmer test volume with hypermetropia and myopia were found to be statistically significant as revealed by t-test, (P > 0.001).

The authors suggested that it would be a worthwhile incitation to incorporate REs studies in all DED in the future studies.

In the estimated rate of refractive status in the USA; Sperduto et al., 1983 found that myopia was the higher REs in Americans between 12 and 54 years of age.[17],[30] This was significantly lower for male participants than for female participants and blacks than for whites.[17]


  Conclusion Top


The studied postulated that there is association between REs and dry eye. Persons with REs have an increased tendency to rub their eyes and feel foreign substance into the eye that predisposes to tear film instability. The findings of this study demonstrated that dry eye was more prevalent in hypermetropic than myopic patients', and males have a higher value than females. Correcting the RE may help reducing dry eye occurrence.

Acknowledgments

Authors would like to thank MEC for their cooperation and permitting to use their parameters for this study; also thank all the participants who accept to join into this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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  [Table 1], [Table 2], [Table 3]



 

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