Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 29  |  Issue : 2  |  Page : 107-112

Refractive Changes in Pregnant Nigerian Women


1 Department of Ophthalmology, Federal Medical Centre, Owerri, Imo State, Nigeria
2 Department of Ophthalmology, Imo State University, Orlu, Imo State, Nigeria

Date of Submission01-Dec-2020
Date of Decision16-Feb-2021
Date of Acceptance20-Mar-2021
Date of Web Publication18-Jan-2022

Correspondence Address:
Dr. E C Nwajei
Central Hospital Sapele, Delta State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njo.njo_47_20

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  Abstract 


Objective: The aim of the study is to determine the changes in refraction that occur amongst healthy pregnant women in South-Eastern Nigeria. Materials and methods: This was a hospital-based prospective longitudinal study. Forty-six healthy pregnant women and an equal number of healthy nonpregnant women, designated as cases and controls, respectively, were recruited from the antenatal clinic (ANC) of Federal Medical Centre Owerri and followed up from the first trimester of pregnancy to 6 weeks postpartum. All participants underwent ocular examinations and intraocular pressure measurement using Perkins handheld applanation tonometer and refraction (subjective and objective). These examinations were repeated and recorded during the second trimester, third trimester, and 6 weeks postpartum follow-up visits. Data obtained were entered and analyzed using the Statistical Package for Social Science version 21. P < 0.05 was considered statistically significant. Results: A myopic shift in the mean refraction of the pregnant women as the pregnancy advanced was observed. This change in the refractive state was however not statistically significant (P = 0.14) and it did not have any significant effect on their distance visual acuity (P ≥ 0.11) and near visual acuity (P ≥ 0.10). Conclusion: Normal pregnancy is associated with changes in refraction; nonetheless, these change maybe innocuous and gradually resolves following delivery. Clinicians may need to delay spectacle correction for pregnant women who experience visual symptoms from physiological changes in refraction unless it is deemed necessary.

Keywords: Healthy females, pregnancy, refractive status


How to cite this article:
Nwajei E C, Achigbu E O, Nkwogu F U, Ogborogu E U, Dike K C. Refractive Changes in Pregnant Nigerian Women. Niger J Ophthalmol 2021;29:107-12

How to cite this URL:
Nwajei E C, Achigbu E O, Nkwogu F U, Ogborogu E U, Dike K C. Refractive Changes in Pregnant Nigerian Women. Niger J Ophthalmol [serial online] 2021 [cited 2022 May 22];29:107-12. Available from: http://www.nigerianjournalofophthalmology.com/text.asp?2021/29/2/107/335919




  Introduction Top


Pregnancy, though a period endowed by nature, maybe associated with multiple physiological and pathological changes throughout the body. These changes are usually transient although they may occasionally become permanent.[1],[2] Physiological changes occurring in pregnancy involve the reproductive, cardiovascular, hormonal, metabolic, hematological, immunological, and visual systems[3] with hormonal changes being the most prominent systemic change. These hormonal changes occur as a result of increased secretion of estrogen and progesterone by the maternal endocrine glands and the placenta throughout pregnancy.[4],[5] The increased elaboration of these hormones results in physiological changes such as increase in maternal blood volume and circulation, relaxation of vascular smooth muscles, and hypertrophy of various organs and tissues in the body.[6]

Ocular changes associated with pregnancy are not uncommon and have been attributed to the physiological changes occurring in pregnancy.[7] These changes are usually marked in the third trimester of pregnancy and coincides with the peak period of estrogen and progesterone production. However, they are often transient because the hormone levels return to the prepregnancy state 6 to 8 weeks postpartum.[8],[9] They include eyelid changes (chloasma, ptosis), decrease in conjunctival capillaries and increase in venules granularity, dry eyes, increase in cornea thickness and curvature, and a decrease in cornea sensitivity. There may also be progression and development of ocular pathologies such as diabetic retinopathy, toxoplasmosis retinitis, peripheral vitreochorioretinal dystrophies, macular edema, and central serous chorioretinopathy.[2] These changes may impact the visual needs of the pregnant woman causing ocular discomfort and influencing the use of preexisting medications. Some conditions, such as ptosis and cortical blindness, may pose a serious risk to the pregnant woman’s quality of life.

This study seeks to add to the existing knowledge on the relationship between pregnancy and refraction. particularly among Nigerian women, and also provide useful data that would assist clinicians in counseling and managing pregnant women who experience changes in their visual status.


  Materials and methods Top


This was a hospital-based prospective longitudinal study carried out in the Obstetrics and Gynaecology Department of Federal Medical Centre (FMC) Owerri. Forty-six healthy pregnant women designated as cases were recruited from the antenatal clinic of FMC Owerri and followed up from the first trimester of pregnancy to 6 weeks postpartum. The same number of age-matched healthy nonpregnant women (controls) were also recruited for the study.

Sample size calculation

The sample size was determined using the formula for quantitative variables in a case control survey:

n = (r + 1/r) × SD2 (Zb + Za/2)2/d2

where n is the minimum sample size and r is the ratio of control to cases. For this study, the ratio of control to cases was 1. SD is the standard deviation (was derived from previous studies[10]). Zb is the standard normal variate for power (which was 1.28 for 90% power). Za/2 is the standard normal variate for level of significance (which was 1.96 at 95% confidence interval). The parameter d is the expected mean difference between case and control. Therefore,

r = 1

Zb= 1.28 at 90% power

Za/2 = 1.96 at 95% confidence level

SD[10] = 0.54

d[10] = 0.38

Therefore,

n = (1+1/1) × 0.542(1.28 + 1.96)2/0.382

n = 2 × 0.29(3.24)2/0.144

n = 6.089/0.144

n = 42.28

Therefore, the sample size for refractive status assessment in this study was 42. This was increased to 46 to accommodate for possible 10% attrition.

Forty-six pregnant women (cases) and 46 age-matched nonpregnant women (controls) were selected for the study.

Inclusion criteria

Pregnant women 18 years and above and age-matched controls, who are of African descent, with no existing or previous ocular pathology (e.g., corneal scar, glaucoma, ocular hypertension, uveitis, choroidal effusion, intraocular tumor and ocular hypotony) or ocular surgeries (e.g., corneal repairs or refractive surgeries) and without diabetes mellitus, gestational diabetes mellitus, hypertension or preeclampsia, and mental illness who consented to participate in the study.

Exclusion criteria

Females less than 18 years, not of African descent, with existing or previous ocular pathology (e.g., corneal scar, glaucoma, ocular hypertension, uveitis, choroidal effusion, intraocular tumor, and ocular hypotony) or ocular surgeries (e.g., corneal repairs or refractive surgeries) diabetesmellitus, gestational diabetes mellitus, hypertension or preeclampsia, mental illness, and females who declined to participate were excluded from the study.

Ethical consideration

In line with the Helsinki’s declaration, informed written consent and ethical clearance were obtained from all participants and the institutional review board of FMC Owerri. respectively.

Data management

Data were collected using an open-ended questionnaire. Information on participants’ demographics, that is, age, place of residence, occupation, parity, and marital and educational status, were noted.

The Snellen chart placed at 6 m from the patient was used for assessing the distance visual acuity of the patients. Similarly, the Rayner reading chart, placed at 40 cm, was used for assessing the near visual acuity and values of both the distance and the near visual acuity converted to Logrithim of the Minimum Angle of Resolution (LogMAR) for the purpose of statistical analysis. Accoson sphygmomanometer and stethoscope were used for assessing the blood pressure. Refraction was done in a dark room by the researcher; objective refraction (streak retinoscopy method) was assessed at a distance of two-thirds of a meter using the Welch Allyn retinoscope. Subjective refraction was assessed immediately after to determine the refractive status of the participant. Anterior segment examination was then performed with a pen torch and magnifying loupe. Intraocular pressure (IOP) measurement was thereafter assessed with Perkins handheld applanation tonometer (Haag-Streit) and measurements were taken between 8 am and 10 am to avoid diurnal variation in IOP. Posterior segment examination was done using Heine Omega 100 indirect ophthalmoscope after pupillary dilatation with 1% tropicamide. These examinations were subsequently repeated and recorded during the second trimester, third trimester, and at 6 weeks postpartum visits for the pregnant women.

Data collected were coded and entered into a database using the Statistical Package for Social Science version 21. Data were validated by double entry and compared for missing values and data entry errors. Any difference between the first and the second file was resolved by referring to the questionnaire.

The results were described using simple statistics (mean, median, frequency, percentages) and presented in the tabular form. Comparison of variables was done with t test and analysis of variance (ANOVA). P ≤ 0.05 was considered statistically significant


  Results Top


Fifty-five pregnant women (cases) and 55 age-matched nonpregnant women (controls) were recruited for the study, but nine pregnant women were lost to follow up (five delivered elsewhere, two withdrew voluntarily from the study after consultations with their families, one was completely unreachable, while another suffered a miscarriage). Of the 46 pregnant women followed up during the study period, 67.1% were aged from 24 to 35 years. The sociodemographic characteristics of the participants are shown in [Table 1].
Table 1 Demography of cases and controls

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The mean unaided visual acuity observed for the pregnant women was −0.01 (6/6) for both eyes. This progressively decreased to the third trimester, followed by an improvement in the visual acuity 6 weeks postpartum. There was, however, no statistically significant difference in unaided distance visual acuity between the pregnant and nonpregnant women (P ≥ 0.12).

[Table 3] gives information comparing the mean near visual acuity of the case group and control group. The mean visual acuity for the cases observed was 0.211 ± 0.10 (N5) for both eyes. There was neither any remarkable change in the near vision of the pregnant women during pregnancy and 6 weeks after delivery nor, statistically significant, difference in their near vision when compared with their nonpregnant counterparts (P ≥ 0.15).
Table 2 Comparison of uncorrected distance visual acuity (LogMAR) of cases and controls

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Table 3 Comparison of the unaided near visual acuity (LogMAR) of cases and controls

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[Table 4] gives the changes in refraction of the pregnant women during pregnancy and 6 weeks after delivery. There was a myopic shift in the mean spherical equivalent across the three trimesters of pregnancy with some degree of reversal 6 weeks after delivery. This reversal was, however, not statistically significant (P ≥ 0.222).
Table 4 Changes in refractive status of the cases during pregnancy and postpartum

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[Table 5] gives information comparing the mean distance visual acuity of pregnant women before and after correction in the three trimesters. Although there was an improvement in the mean visual acuity of the pregnant women after refraction, the change in visual acuity was not statistically significant (P ≥ 0.07). In addition, 93.5% (43 patients) did not experience any visual disturbance during pregnancy, while two (4.3%) patients who used spectacles and one (2.2%) who did not use spectacles prior to pregnancy complained of visual symptoms.
Table 5 Comparison of distance visual acuity (LogMAR) before and after refraction (cases)

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[Table 6] gives information comparing the mean near visual acuity of pregnant women before and after refraction. The mean visual acuity for the cases observed was 0.21 ± 0.10 (N5). There was neither any remarkable change in the near vision of the pregnant women during pregnancy and 6 weeks after delivery nor any difference in their near vision following refraction. Overall, there was no statistically significant difference in near visual acuity (VA) with or without correction (P = 1.00).
Table 6 Comparison of the near visual acuity (LogMAR) before and after refraction (cases)

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  Discussion Top


The sociodemographic characteristics of this study population is akin to several studies with respect to age and racial composition,[10],[11],[12],[13] but contrasts with studies by Pilas-Pomykalska,[14] Akar[15] and Efe[16] in racial composition as their subjects were Caucasian females. The educational level and place of residence of the subjects were largely similar to the findings reported in other studies.[10],[14],[15]

The distance visual acuity was slightly reduced as pregnancy advanced and returned to the first trimester value in the postpartum period [Table 2]. This change in distance visual acuity was however not statistically significant and is in keeping with studies by Balasubramanian et al.[17] and Ebeiege et al.[10] This change may be attributed to physiological alteration in the central corneal thickness and curvature of the cornea as well as the lens.[18],[19],[20]

The near visual acuity, however, remained fairly stable throughout pregnancy. Majority of the participants were in the pre-presbyopic age, and so the stable near vision is not surprising. Moreover, their ability to accommodate may also contribute to the near normal visual acuity in the cases similar to the controls.

Following refraction, the mean spherical equivalents of the pregnant and nonpregnant women in the index study showed low power myopia, which was similar to a study conducted in Enugu[21] and New York,[22] but contrasts with studies conducted in Mid-Western Nigeria,[10] where a hyperopic state was reported among pregnant women.

The myopia observed among the pregnant women in this study increased as pregnancy advanced; however, this increasing myopic shift was not statistically significant. This is similar to studies conducted in Canada,[23] New York,[22] India,[16] Tehran,[24] and Nigeria,[10],[21] where a myopic shift in the refractive state of pregnant women was documented. This change alone may not be adequate to warrant a spectacle or contact lens prescription. However, it may affect preexisting prescriptions[17],[25] or cause contact lens intolerance.[26] Refraction had no significant impact on the visual acuity (distance and near) of the participants. This agrees with other studies.[10],[17],[27] The mean spherical equivalents of the refraction done were lower than −0.25DS and these powers are hardly prescribed as most people live and cope effectively with such minor errors. In addition, most of the pregnant women were not presbyopic and so their near vision was intact. Moreover, the myopic shift may likely improve their near vision. This is corroborated by findings in Tables 5 and 6 that showed no significant difference in the visual acuity before and after refraction. However, a small proportion of the participants who use spectacles complained about visual disturbances during the study. In contrast, Mehdizadehkashi and coinvestigators[25] observed that majority of the pregnant women in their study experienced statistically significant visual disturbances especially in the afternoon. However, the aforementioned study was a cross-sectional study and the change in visual acuity observed was marked in the afternoon. This change may be attributed to fatigue. Furthermore, as no refraction was performed, it is not clear if the change in visual acuity observed was influenced by a change in the refractive state of the pregnant women. They however reported that the visual acuity returned to their prepregnancy state postpartum.[24]{Table 6}

The myopic shift observed may be attributed to increased fluid absorption by the cornea and lens as a result of the hyperpermeable state induced by the influence of estrogen and progesterone during pregnancy.[28],[29],[30] It has been postulated that the change in refraction observed in pregnancy is due to the role of estrogen and progesterone and the former’s effect on modulation of the renin angiostesin aldosterone system.[31],[32] The combined effect of progesterone and estrogen also increases the permeability of the corneal and lenticular membrane, thus increasing their susceptibility to hydration,[25] with resultant increased steepening of corneal curvature,[19] increased central cornea thickness,[20] and, in effect, a myopic shift. Similarly, hydration of the lens results in increased lenticular curvature which also causes a myopic shift.[33] As a result of this change in refraction, pregnant women may complain of reduction in vision (particularly distance vision), observe that their spectacles are no longer effective,[17] or present with contact lens intolerance.[2] It may be advisable for the clinician to withhold spectacles or contact lens correction until 6 to 8 weeks postpartum when stable postpartum refraction can be achieved.[5]A change in the refractive status of pregnant women compared to nonpregnant controls was noted; however, this change in refraction was not statistically significant. This is also in agreement with other studies.[16],[26],[34] Although there were remarkable differences in the mean refractive power of the cases and the controls in the third trimester when fluid retention is greatest, the results of this study implies that the change may not be significant enough to warrant spectacle prescription.


  Conclusion and recommendation Top


This study showed that pregnancy can induce a change in the refractive status of the eyes toward a myopic shift that virtually returns to its prepregnancy level during the postnatal period. However, these refractive changes did not induce any statistically significant change in the distance and near visual acuity of the pregnant women. These changes in refraction are often transient and may require no treatment and resolve in the postnatal period,[8],[9] and hence clinicians may need to withhold new spectacle prescriptions and employ counseling in the management of healthy pregnant women experiencing changes in refraction.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Balasubramanian K, Gayatri Nagarajan G. A prospective study of changes in the refractive system of Eye during pregnancy. Intern J Sci Study 2017;5:89-92.  Back to cited text no. 17
    
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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