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Background: Islamic Ramadan is the month of fasting, in which intake of food and drink is restricted from sunrise until sunset. The objective of the present study was to find out the effect of altered eating habits during Ramadan fasting on ocular refractive and biometric properties.
Methods: In this prospective case series, 40 eyes of 22 healthy volunteers with a mean age of 60.55 ± 12.20 years were enrolled. Patients with any systemic disorder and eyes with pathology or previous surgery were excluded. One month before Ramadan (at 8.00 am), during Ramadan fasting (at 8.00 am and 4.00 pm) and one month later during the non-fasting period (at 8.00 am), ocular refractive and biometric characteristics were measured using an autokeratorefractometer (Auto-Kerato-Refractometer KR-8900; Topcon Co, Tokyo, Japan) and contact ultrasonic biometry (Nidek Echoscan US 800; Nidek Co, Tokyo, Japan).
Results: Anterior chamber depth was significantly increased during fasting compared with baseline measurements and returned to baseline one month after Ramadan (3.22 ± 0.07 mm and 4.33 ± 0.17 mm for non-fasting and fasting, respectively; p < 0.001). The anterior chamber depth measurements were significantly larger at 8.00 am during fasting compared with 4.00 pm (p = 0.01). Axial length was significantly decreased during fasting and returned to baseline one month after Ramadan (23.09 ± 0.14 mm and 22.65 ± 0.18 mm, for non-fasting and fasting, respectively; p < 0.001). Intraocular lens power calculations were significantly increased during fasting and returned to baseline one month after Ramadan (SRK-T formula: 21.46 ± 0.27 D and 22.92 ± 0.46 D, for non-fasting and fasting, respectively; p < 0.001). There were no significant differences in spherical equivalent, corneal astigmatism, mean keratometry and flatter and steeper corneal radii of curvature between time intervals.
Conclusions: Ramadan fasting is associated with statistically significant alterations in anterior chamber depth and axial length that result in both statistically and clinically significant changes in intraocular lens power calculations. Therefore, relying on measurements taken during this month might lead to refractive errors after cataract surgery.
Ramadan is the month during which Muslims fast from sunrise until sunset. Any type of food and drink, smoking and sexual intercourse are not allowed during the day. The type of food and drink taken between sunset and sunrise is fairly similar to non-fasting days. At sunset, people usually break their fast with a small cup of hot water and then eat their usual food and drinks. Several minutes before sunrise, people usually eat some food with a considerable amount of drink to suffer fasting during the day. The Islamic calendar is a lunar calendar and Ramadan occurs at different times in the seasonal year. The present study was conducted when Ramadan fell on August and September in a tropical climate.
People practising fasting are subjected to significant changes in their normal feeding, sleeping and behavioural patterns. Several investigators have studied the effect of these changes on body homeostasis;1 however, there are only a few reports in the literature regarding the effects of Ramadan fasting on the eye, most of which investigated intraocular pressure (IOP) and basal tear secretion. Accordingly, Kayikcioglu and Guler2 and Indriss, Anas and Hicham3 found no significant effect on IOP. Dadeya and colleagues4 found significantly lower IOP values during fasting at all four times of day studied, whereas Kerimoglu and colleagues5 showed that during Ramadan fasting, the IOP increase in the early morning period and decrease before sunset compared with non-fasting. Kerimoglu and colleagues5 found that basal and reflex tear secretion increase in the early morning; however, Kayikcioglu, Erkin and Erakgun6 found that religious fasting in the winter season did not affect basal tear secretion. Kerimoglu and colleagues5 found no significant differences in the corneal and anterior chamber parameters during fasting and non-fasting periods.
To the best of our knowledge, there is no report about changes in axial length and intraocular lens (IOL) power calculations during fasting. Because any significant changes in refraction or biometry could confound clinical decisions regarding refractive surgery or IOL power determination, we conducted this study to evaluate the effect of Ramadan fasting on refractive and biometric features of the eye.
MATERIALS AND METHODS
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- MATERIALS AND METHODS
Forty eyes of 22 healthy volunteers (12 male) with a mean age of 60.55 ± 12.20 years (range, 40 to 87) were enrolled. All participants fasted on all days of the Ramadan and all took the pre-dawn meal and drink. Premenopausal women, who do not fast during their menstruation period, were excluded. Patients with any systemic disorder and eyes with pathology or previous surgery were excluded. Informed consent was obtained from the participants after giving detailed information and the study protocol was approved by the local ethics committee.
Spherical equivalent refraction, mean keratometry, flatter (R1) and steeper (R2) corneal radii of curvature, corneal astigmatism, anterior chamber depth (ACD), axial length and IOL power calculations with SRK-2 and SRK-T formulae were measured one month before Ramadan (at 8.00 am), during Ramadan fasting (at the middle of the month of Ramadan; at 8.00 am [about three hours after the pre-down meal] and 4.00 pm [3.5 to four hours before sunset]) and one month after Ramadan (at 8.00 am) during the non-fasting period.
Biometric data were evaluated with contact ultrasonic biometry (non-immersion) using a Nidek Echoscan US 800 (Echoscan US-800; Nidek Co, Tokyo, Japan) after instilling one drop of tetracaine 0.5% in each eye. Six measurements per eye were taken and averaged. The measurements with standard deviations greater than 0.12 mm were discarded and the process was repeated until the standard deviation was no greater than 0.12 mm. In ultrasonic biometry, axial length is defined as the distance from the anterior cornea to the inner limiting membrane of the retina and the ACD is defined as the distance from the posterior corneal surface to the anterior lens surface.
The keratometry and cycloplegic refraction (using 0.5% cyclopentolate hydrochloride) were determined using an autokeratorefractometer (Auto Kerato-Refractometer KR-8900; Topcon Co, Tokyo, Japan). Three consecutive readings were taken per eye and averaged. The spherical equivalent (SE) was determined by adding half the minus cylinder to the sphere.
Statistical analysis was performed using the Statistical Package for Social Sciences software version 17 (SPSS Inc, Chicago, IL, USA). A clustered analysis was applied, in which each participant was considered as a cluster to adjust for the dependency of measurements in the fellow eye. The Gaussian distribution assumption was tested using the Kolmogorov and Smirnov method. All samples succeeded in passing the normality test. The repeated-measures analysis of variance (ANOVA) was used to test the significance of the mean values before fasting and the values at each time interval thereafter. Measurements of the non-fasting periods were compared with those at the same hour (8.00 am) during the fasting day. The measurements at 8.00 am and 4.00 pm during the fasting day were compared with each other. A p-value of 0.05 or less was considered statistically significant.
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There were no significant differences in spherical equivalent, corneal astigmatism, mean keratometry, and flatter and steeper corneal radii of curvature between time intervals (Table 1). The spherical equivalent (mean ± SEM) was -0.006 ± 0.30 D (range, -2.75 to 3.75 D), 0.13 ± 0.32 D (range, -2.25 to 4.25 D) and 0.15 ± 0.31 D (range, -2.75 to 4.00 D) before Ramadan, on fasting and after Ramadan, respectively. ACD and IOL power calculation measurements were significantly increased during Ramadan fasting compared with baseline measurements and returned to baseline one month after Ramadan. Axial length was significantly decreased during Ramadan fasting compared with baseline measurements and returned to baseline one month after Ramadan (Tables 1 and 2). Age and sex showed no significant effect.
Table 1. Ocular biometric data recorded before, during and after Ramadan
| ||Before Ramadan||On fasting (morning)||On fasting (evening)||After Ramadan||p-value|
|Spherical equivalent (D)||-0.006 ± 0.30||0.13 ± 0.32||0.24 ± 0.32||0.15 ± 0.31||0.471|
|Mean keratometry (D)||44.03 ± 0.29||44.01 ± 0.30||44.01 ± 0.29||44.01 ± 0.28||0.899|
|Corneal astigmatism (D)||0.60 ± 0.06||0.58 ± 0.08||0.61 ± 0.08||0.56 ± 0.09||0.528|
|R1 (mm)||7.69 ± 0.05||7.69 ± 0.05||7.70 ± 0.05||7.70 ± 0.05||0.863|
|R2 (mm)||7.52 ± 0.09||7.59 ± 0.05||7.59 ± 0.05||7.59 ± 0.05||0.414|
|Axial length (mm)||23.09 ± 0.14||22.65 ± 0.18||22.83 ± 0.17||23.00 ± 0.15||<0.001|
|ACD (mm)||3.22 ± 0.07||4.33 ± 0.17||3.72 ± 0.15||3.16 ± 0.07||<0.001|
|SRK-2 formula (D)||21.15 ± 0.21||22.50 ± 0.41||21.92 ± 0.32||21.49 ± 0.29||<0.001|
|SRK-T formula (D)||21.46 ± 0.27||22.92 ± 0.46||22.32 ± 0.37||21.78 ± 0.32||<0.001|
Table 2. p-values for pairwise comparisons calculated using Bonferroni post hoc multiple comparison test†
|Before Ramadan – on fasting (morning)||<0.001||0.001||0.002||0.001|
|Before Ramadan – after Ramadan||0.125||1||0.818||1|
|On fasting (morning) – on fasting (evening)||0.513||0.010||0.225||0.325|
|On fasting (morning) – after Ramadan||0.006||<0.001||0.008||0.007|
The ACD measurements were significantly larger at 8.00 am during fasting compared with 4.00 pm (p = 0.01); however, the differences in axial length, SRK-2, and SRK-T formulae were not statistically significant (Table 2).
There were significant correlations between changes in axial length or ACD after fasting (8.00 am) and the resultant changes in SRK-2 or SRK-T formulae (Table 3). Decrease in axial length was significantly correlated with increase in ACD and IOL power calculations (Pearson correlation coefficient: -0.64 [for ACD] and -0.80 [for either formula]). The increase in ACD was significantly correlated with the increase in IOL power calculation (Pearson correlation coefficient: -0.64 and -0.67, for SRK-2 and SRK-T formulae, respectively). Stepwise multiple linear regression analysis revealed that the axial length was the only independent factor associated with changes in IOL power calculations (ACD and age did not show any significant association).
Table 3. Correlation between changes in different biometric parameters recorded at 8 am on fasting and baseline
| ||ACD (fasting-baseline)*||SRK-2 (fasting-baseline)*||SRK-T (fasting-baseline)*|
|AL (fasting-baseline)||-0.64 (0.002)||-0.80 (<0.001)||-0.80 (<0.001)|
|ACD (fasting-baseline)|| ||0.64 (0.002)||0.67 (0.001)|
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A number of factors can affect post-cataract surgery refractive outcome. Inaccurate axial length measurements remain the most important biometric factor responsible for post-operative refractive errors followed by imprecision in ACD and keratometric measurements.7–10 Therefore, in the present study, we focused on the evaluation of these factors to uncover the causes for probable IOL power measurement changes during Ramadan fasting.
We found that axial length significantly decreased during Ramadan fasting. Theoretically, the dehydration occurring during fasting periods can shrink the vitreous humour and subsequently decrease the axial length.2 In addition, vitreous dehydration might result in changes in its acoustic properties leading to inaccurate axial length measurement with ultrasonic instruments, which assume a predetermined average value for sound speed in the vitreous.
Another notable finding in the present study was the greater ACD in the morning compared with in the evening on a fasting day. To suffer the effects of dehydration, people intentionally drink a remarkable amount of fluid at the pre-dawn meal. We measured ACD at 8.00 am nearly three hours after the pre-dawn meal. Therefore, water loading at the pre-dawn meal might be the cause of increased ACD in the morning. It is known that oral water loading transiently elevates IOP probably through an increase in aqueous formation or depression in the aqueous outflow facility.11 This effect might also inflate the anterior chamber in the morning, while the effect is decreased in the evening because of the gradual dehydration that occurs during the day. These diurnal fluctuations were not observed for axial length measurements. Our results suggest that the ACD might be influenced by daily fluctuations of water intake and hydration status of the body, while alterations in axial length might follow a more chronic pattern.
In the present study, Ramadan fasting did not affect corneal keratometry, which verifies the previous report by Kerimoglu and colleagues.5 Although the spherical equivalent showed a slight hyperopic shift in accordance with the observed decrease in axial length, the differences were not statistically significant. In principle, dehydration during the fasting month might lead to refractive changes in the crystalline lens through either change in the refractive index, lens thickness, radii of curvature or a combination thereof. These changes in combination with possible changes in the refractive index of the dehydrated vitreous could offset the refractive consequences of a change in axial length resulting in little or no change in refraction.
The IOL power measurements were significantly higher during Ramadan fasting compared with baseline. The mean differences ranged from 0.77 to 1.46 dioptres that were considered both clinically and statistically significant (Table 1). The changes in IOL power measurements were highly correlated with changes in axial length, while the statistical analysis suggests that changes in axial length lead to variations in IOL power measurements. The measurements in the morning were higher than those in the evening; however, the difference did not reach statistical significance. In the present study, we only applied the available SRK-2 and SRK-T formulae for IOL power calculation. The IOL power calculation might be confounded even more if we had used the Haigis or Holladay 2 formula that incorporates actual ACD measurements in IOL power calculations.
In conclusion, Ramadan fasting can confound the IOL power calculation and might lead to post-operative refractive errors. Based on the results of the present study, we suggest that the IOL power calculation should not be performed during Ramadan fasting and should be postponed until recovery of vitreous dehydration. The present study is limited by its relatively small sample. In addition, it was performed during August and September in a tropical climate. Because the Islamic calendar is lunar and Ramadan occurs at different times in the seasonal year, the outcomes might not be applicable when Ramadan occurs in colder climates.