|Year : 2019 | Volume
| Issue : 2 | Page : 48-53
Effect of yoga ocular exercises on intraocular pressure
Satish Kumar Gupta, S Aparna
Department of Optometry, Sankara Academy of Vision, Sankara College of Optometry, Sankara Eye Hospital, Bengaluru, Karnataka, India
|Date of Submission||27-Jun-2019|
|Date of Acceptance||23-Sep-2019|
|Date of Web Publication||09-Dec-2019|
Satish Kumar Gupta
Brien Holden Institute of Optometry and Vision Sciences, L V Prasad Eye Institute, Gullapalli Pratibha Rao Campus, Near Kali Mandir, Don Bosco Nagar (PO), Kismathpur, Hyderabad - 500 086, Telangana
Source of Support: None, Conflict of Interest: None
Background: Glaucoma is the second leading cause of global blindness and is the leading cause of irreversible visual loss. Hence, it becomes very important in guiding the designs of glaucoma screening, treatment, and intraocular pressure (IOP) control methods. Hence, the aim of this study was to analyze the effect of yoga ocular exercises on IOP.
Materials and Methods: Thirty-one undergraduate optometry students (62 eyes) who satisfied the inclusion criteria after a baseline comprehensive eye examination were selected for the study and were assigned to two groups: an exercise group (n = 15) and a control group (n = 16). A baseline IOP measurement was done for both groups. The exercise group performed yoga ocular exercises for 30 min/day for 5 days a week for up to 6 weeks. IOP was measured for both eyes for all participants at the end of each week for up to 6 weeks.
Results: In the exercise group, there was a highly statistically significant reduction in IOP in both eyes (p = 0.000 in the right eye [RE] and p = 0.001 in the left eye [LE]). Whereas in the control group, there was an insignificant change in IOP (p = 0.751 in the RE and p = 0.809 in the LE).
Conclusions: The yoga ocular exercises induce a significant reduction in IOP and hence can be considered as a nonpharmacological intervention for lowering the IOP for the management and treatment plan of various ocular diseases or disorders associated with ocular hypertension.
Keywords: Colloid osmotic pressure, glaucoma, intraocular pressure, ocular hypertension, osmosis, yoga ocular exercises
|How to cite this article:|
Gupta SK, Aparna S. Effect of yoga ocular exercises on intraocular pressure. Yoga Mimamsa 2019;51:48-53
| Introduction|| |
The human eye is a closed ball filled with clear jelly (vitreous humor) in the posterior segment behind the crystalline lens and clear fluid (aqueous humor) in the anterior segment in front of the lens. The aqueous humor is produced continuously in the posterior chamber by the ciliary body. It gradually flows through the pupil into the anterior chamber and drains continuously through the trabecular meshwork located at the angle of anterior chamber, just in front of the iris where it meets the cornea. This continuous and gradual mechanism of aqueous humor production and drainage determines the normal intraocular pressure (IOP). Various large and population-based epidemiologic studies have revealed the normal IOP ranges between 10 and 21 mmHg, with the mean IOP to be 15.50 ± 2.60 mmHg (“Intraocular Pressure,” 2019). The IOP maintains the shape of the eyeball, and the aqueous humor along with the vitreous humor keeps the eyeball inflated. For instance, air inside a balloon maintains its shape and keeps it inflated (Fountain, 2012). The IOP is influenced by several factors such as diurnal variation (Brubaker, 1991; Liu & Weinreb, 2011), blood pressure and ocular perfusion pressure (Liu, Gokhale, Loving, Kripke, & Weinreb, 2003), aqueous humor kinetics (Heiting, 2018), physical exercises (Bakke, Hisdal, & Semb, 2009; Read & Collins, 2011; Vieira, Oliveira, Andrade, Bottaro, & Ritch, 2006), musical instruments (Goss, 2012; Schmidtmann, Jahnke, Seidel, Sickenberger, & Grein, 2011; Schuman et al., 2000), drugs or certain medications (Drance, 1964; Mertz, 2016; Pardianto, 2005), ocular trauma, disease and disorders (Heiting, 2018).
Several studies have concluded that the elevated IOP, clinically known as ocular hypertension, plays a major role in optic nerve (CN II) damage (Cohen & Pasquale, 2014; Davis, Crawley, Pahlitzsch, Javaid, & Cordeiro, 2016; Gupta, Agarwal, Saxena, Agrawal, & Agarwal, 2009; Weinreb, Aung, & Medeiros, 2014). In case if IOP rises beyond the normal range, it causes mechanical damage to the optic nerve and thus the reduction in the visual field occurs, leading to glaucoma. Glaucoma is a multifactorial optic neuropathy, where there is a characteristic acquired loss of retinal ganglion cells (nerve fibers) and atrophy of the optic nerve head with corresponding visual field damage and may or may not be associated with a risk factor of raised IOP (Cohen & Pasquale, 2014; Davis et al., 2016; Gupta et al., 2009; Weinreb et al., 2014). Glaucoma may lead to permanent painless vision loss and ultimately blindness without any signs or symptoms in the early stages. Therefore, often glaucoma is also called “the silent thief of eye sight” (Berdahl, 2017; Dubow & Slonim, 2017).
Glaucoma is second to cataract as a leading cause of global blindness and is the leading cause of irreversible visual loss (Tham et al., 2014). The global prevalence of glaucoma in population aged 40–80 years is 3.54%, with the prevalence of primary open-angle glaucoma being highest in Africa (4.20%) and the prevalence of primary closed-angle glaucoma being highest in Asia (1.09%) (Tham et al., 2014). In 2013, the number of people (aged 40–80 years) with glaucoma worldwide was estimated to be 64.3 million, and is estimated to be increasing to 76.0 million in 2020 and 111.8 million in 2040, primarily affecting people residing in Asia and Africa (Tham et al., 2014). Medical therapy aimed at reducing IOP is the primary treatment for glaucoma; however, it is unknown if medical therapy alone is sufficient to achieve the target IOP levels in glaucoma patients (Gyasi et al., 2014). It is found that the current medical regimen is insufficient to reduce IOP to target levels as defined in the Advanced Glaucoma Intervention Study (Gyasi et al., 2014). These estimates become very important in guiding the designs of glaucoma screening, treatment options besides medical regimen, IOP control methods to achieve the target IOP, and related public health strategies. Till date, there is no permanent cure for glaucoma because the lost eye sight cannot be restored. The reason behind is that the damaged optic nerve fibers cannot regenerate their neurons. However if diagnosed early and treated, the eyes can be protected against the serious loss of eye sight (“Facts About Glaucoma,” 2015). Once the IOP is controlled, the progression of vision loss can be slowed down. Therefore, it is very important to control the IOP.
Yoga balances and harmonizes the body, mind, and emotions through the regular practice of asanas, pranayama, mudra, bandha, shatkarma, and meditation (Saraswati, 2009a, 2009b). However, some yoga postures which involve inverted positions, i.e., headstand postures, induce a significant increase in IOP within 1 min which can affect the patients with glaucoma and those who are at a high risk of glaucoma or its progression or ocular hypertensive patients (Baskaran et al., 2006; Jasien, Jonas, Gustavo De Moraes, & Ritch, 2015; Jasien & Ritch, 2015). The IOP values dropped back to the baseline values within 2 min after returning to the normal sitting position (Jasien et al., 2015; Jasien & Ritch, 2015).
Yoga ocular exercises are recommended by yoga practitioners with the purpose of maintaining the normal eye health and well-being. It is reported that there is a significant decrease in the IOP after a short-term practice of yoga ocular exercises for about 5 min (Dimitrova & Trenceva, 2017). Till date, further studies analyzing the prolonged effects of yoga ocular exercises in larger population groups are lacking. Hence, this study was designed to analyze the effects of yoga ocular exercises on IOP.
| Materials and Methods|| |
This prospective study was done enrolling the optometry college students in Bengaluru, India. Permission was obtained from the college and hospital authorities in accordance with the tenets of the Declaration of Helsinki. An informed consent was obtained from each participant after an explanation of the nature of study. A total of 32 participants were recruited by randomized controlled trial design (Charan & Biswas, 2013; Rodríguez del Águila & González-Ramírez, 2014) who underwent a comprehensive eye examination and general health examination. Those who met the inclusion criteria, i.e., best-corrected visual acuity better than or equal to 20/20 (6/6), normal body mass index, normal blood pressure (90/60–120/80 mm Hg) (“Blood Pressure Chart,” 2008), and normal IOP (10–21 mm Hg) (“Intraocular Pressure,” 2019) were enrolled into the study. Participants with any systemic disease or disorder, ocular pathology, surgery, ocular hypertension (IOP >21 mmHg), and high ammetropia (≥ ±6.00 D) were excluded from the study (Dimitrova & Trenceva, 2017). One participant was excluded for having ocular hypertension. The rest of the participants (n = 31) with a total of 62 eyes were assigned to two groups by randomization: an exercise group (n = 15; 30 eyes) and a control group (n = 16; 32 eyes). The groups were divided in such a way that there was no statistically significant difference in the baseline mean IOP between both the groups (p > 0.05).
A trained yoga instructor guided the participants in the exercise group to to perform yoga ocular exercises. Each session of yoga ocular exercises involved the following ten steps in a sequence: palming, blinking, sideways viewing, front and sideways viewing, diagonal viewing, rotational viewing, preliminary nose-tip gazing, near and distant viewing, concentrated gazing (Trataka), and acupressure point on the palm (Saraswati, 2009a; Yoga, 2017). The participants in exercise group practiced yoga ocular exercises for 30 min/day from 8:30 to 9:00 AM for 5 days a week for up to 6 weeks. The regularity and frequency of the participants for practicing yoga were strictly monitored.
The examiner (SKG) was masked regarding the recruitment of the participants into an exercise group or a control group and did all the IOP measurements using the Keeler Goldmann Applanation Tonometer. IOP was measured for both eyes for all participants at the end of each week. The IOP was measured at the same time interval (12:00 P.M.–1:00 P.M.) during each measuring day to keep an eye on the diurnal variation of the IOP and to obtain the accurate measurement. A total of three IOP measurements were taken for each eye for all participants during each measurement to ensure the within-participant variability, and the average of three measurements was taken into consideration for analysis purpose. Each IOP measurement was obtained in the original form and was not corrected by central corneal thickness (CCT) or pachymetry values in order to prevent the introduction of further errors in IOP measurements.
The data input and statistical analysis were done by using the International Business Machine Statistical Package for the Social Sciences (IBM SPSS Statistics) V 23.0 for Microsoft Windows developed by the IBM Corporation, Armonk, New York, USA. The data followed a normal distribution, and unpaired t-test was used to analyze the differences in participants' clinical characteristics between exercise group and control group. The ANOVA test, as well as the Bonferroni test, was used to analyze the differences as well as variation in IOP measurement in both groups. p < 0.05 was considered statistically significant.
| Results|| |
The mean age of exercise group was 21.07 ± 1.75 (19–24 years), with six males and nine females. Similarly, the mean age of control group was 20.94 ± 1.69 (18–24 years), with seven males and nine females.
There were statistically insignificant differences in participants' clinical characteristics between two groups as well as in baseline mean IOP between the right eye (RE) and left eye (LE) in both groups [Table 1]. In addition, there was a statistically insignificant difference in the baseline mean IOP between both groups (p = 0.200 in the RE and p = 0.177 in the LE; unpaired t-test).
|Table 1: Clinical characteristics of the participants: Mean±standard deviation|
Click here to view
[Figure 1] (ANOVA and Bonferroni test) shows that the participants in exercise group had a highly significant reduction of mean IOP in RE between the baseline measurement (16.93 ± 2.25 mmHg) and measurement after 6 weeks (13.20 ± 2.24 mmHg; p = 0.000). Whereas the participants in control group had an insignificant difference in mean IOP in the RE between the baseline measurement (16.00 ± 2.06 mmHg) and measurement after 6 weeks (15.69 ± 1.88 mmHg; p = 0.751).
|Figure 1: Comparison of the mean IOP of RE between two groups (weekly basis). *p = Statistically significant (p < 0.05). IOP, Intraocular pressure; RE, Right eye|
Click here to view
Similarly, [Figure 2] (ANOVA and Bonferroni test) also shows that the participants in exercise group had a highly significant reduction of mean IOP in the LE between the baseline measurement (16.87 ± 1.95 mmHg) and measurement after 6 weeks (13.13 ± 2.80 mmHg; p = 0.001). Whereas the participants in the control group had an insignificant difference in mean IOP in the LE between the baseline measurement (15.94 ± 2.20 mmHg) and measurement after 6 weeks (16.00 ± 1.89 mmHg; p = 0.809).
|Figure 2: Comparison of the mean IOP of LE between two groups (weekly basis). *p = Statistically significant (p < 0.05). IOP, Intraocular pressure; LE, Left eye|
Click here to view
| Discussion|| |
The results from the current study indicate a significant decrease in IOP after a regular practice of yoga ocular exercises for a period of 6 weeks. The yoga ocular exercises are also associated with a short-term decrease in IOP, showing a significant decrease in IOP after short-term (5 min) yoga ocular exercise (Dimitrova & Trenceva, 2017). In this regard, the yoga ocular exercises not only cause an acute pressure lowering effect, but also initiate a long-term sustaining effect till the yoga ocular exercises are regularly performed. The proposed scientific explanation of the action of yoga ocular exercises on eyes has been described as follows: palming relaxes and revitalizes the extraocular muscles and stimulates the circulation of the aqueous humor; blinking exercise emboldens the blinking reflex to become spontaneous, inducing relaxation of the extraocular muscles; the sideways viewing relaxes the tension of the extraocular muscles strained by constant near work, preventing and correcting the squint (mostly phoria); front and sideways viewing encourages the coordination of medial and lateral recti muscles; diagonal viewing balances the superior rectus, inferior rectus, superior oblique, and inferior oblique muscles; rotational viewing restores the balance in the extraocular muscles around the eyeball and improves the coordinated activity of both eyeballs and its muscles; preliminary nose-tip gazing encourages the accommodating and focusing power of the ciliary muscles; the benefits of near and distant viewing are similar to that of preliminary nose-tip gazing exercise, but the range of movements is further increased; intense concentrated gazing balances the nervous system, relieving nervous tension, anxiety, depression, and insomnia, thus improving the memory and helping to develop good concentration; acupressure point in the palm gives relief to eye fatigue and helps in sound eye health (Saraswati, 2009a, 2009b; Yoga, 2017).
The mechanism of IOP reduction due to these exercises can be complex. There is constant movement of eyes during the day and partly movement during the night; however, there occur small deviations from the primary position due to these movements. However, while practicing the yoga ocular exercises (all exercises except palming), the bulbomotor muscles/extra-ocular muscles are maximally and continuously stretched in all directions that dramatically increases the metabolic demand of the muscular tissues (Dimitrova & Trenceva, 2017). As a result, an increment in the intra-orbital blood circulation occurs and it acts as a pump for a more efficient intra-orbital venous outflow (Martin, Harris, Hammel, & Malinovsky, 1999; McMonnies, 2016). In addition, “palming” may have a vasodilatory effect on episcleral veins and thus trigger the circulation and outflow of aqueous humor (Dimitrova & Trenceva, 2017). It is believed that “Palming” has greater efficacy over other yoga ocular exercises for IOP reduction.
The reasons why the yoga ocular exercises result in reduced IOP in both short and long term are yet to be fully explicated; however, it seems possible that the properties of IOP reduction during yoga ocular exercises might be similar to that of isotonic (dynamic) exercises. Yoga ocular exercises can be referred to as isotonic/dynamic exercises of extra-ocular muscles (skeletal muscles), where both the concentric contraction (shortening) and eccentric contraction (elongation) of extra-ocular muscles occur (Hilton, 2003; McMonnies, 2016). The osmotic mechanistic properties of dynamic exercise-induced hypotension were investigated deeply in order to establish the primary mechanism by which the IOP gets reduced (Martin et al., 1999). Previous studies had already shown that neither plasma osmolality nor hypocapnia (a state of reduced carbon dioxide in the blood) accounted for the IOP decline and that selective and nonselective ocular β-adrenergic blockade was ineffective in altering the exercise-induced IOP reduction (Hilton, 2003). In Martin's study, identical exercises were performed under the conditions of varying hydration level and osmotic fluid intake in order to best determine which factors were most closely correlated with IOP reduction (Martin et al., 1999). Of those which were measured, only colloid osmotic pressure (COP), which is linked to capillary ultrafiltration, was directly associated to IOP changes during the dynamic exercise; hematocrit, total plasma osmolarity, and plasma protein concentration failed to show a correlation to IOP reduction (Martin et al., 1999). In terms of the eye, this correlation offers three explanations for IOP decline [Figure 3]:
|Figure 3: The schematic representation of the colloid osmotic pressure hypothesis for the mechanism of IOP reduction due to yoga ocular exercises (dynamic exercises). EOMs, Extraocular muscles; IOP, Intraocular pressure|
Click here to view
- Osmotic changes in the retinal and uveal vasculature may incur ocular dehydration
- An increase in COP may reduce the formation of aqueous through reduced ultrafiltration and hence IOP decline
- An increase in COP may act directly on the hypothalamus resulting in IOP reductions through an unspecified reflex response.
The first hypothesis which could potentially result in ocular dehydration and then decreased vitreous volume is the most likely explanation for the IOP decline (Hilton, 2003; Martin et al., 1999; McMonnies, 2016).
It is suggested that in IOP, measurements should be corrected based on measured CCT measurements (Ehlers, Bramsen, & Sperling, 1975). However, there is a large body of evidence which suggests that it is inappropriate to correct IOPs given that there are many factors besides CCT that have an impact on IOP (Al Busaidi, 2018; Kaushik, Pandav, Banger, Aggarwal, & Gupta, 2012; Tonnu et al., 2005). Even if one assumes that the measured IOP is precise enough, adjusting for accuracy remains a problem due to lack of an accurate and accepted algorithm. Although many correction algorithms exist, none are adequately validated or universally accepted. Therefore, for selecting an IOP correction formula arbitrarily, one runs the risk of introducing further errors into the equation rather than reducing them. A growing understanding of corneal biomechanics suggests that this IOP correction based on CCT is not reliable (Al Busaidi, 2018). It may produce a more accurate IOP reading for some patients, but there is no way to know which patients those are. One 580-μm cornea may be altering the IOP reading very differently than another, depending on the biomechanical properties of the individual corneas. Hence, the obtained IOP measurements were independent of CCT and did not undergo any correction factor with respect to the pachymetry measurements.
One limitation of the study is that the reduction in IOP was within the normal variation. Besides, it was not able to assess if the reduced IOP in the exercise group sustained over a period of time or reverted back to its baseline values after cessation of yoga exercises because of the limited time period for the study to be carried out and completed. Further studies are required to estimate these effects.
To the best of our knowledge, this is the first report concerning the long-term effect of yoga ocular exercises on IOP. Further studies evaluating the long-term effects of yoga ocular exercise involving larger population groups of different age groups, clinical trials on glaucoma, as well as ocular hypertensive patients are necessary to establish the potential benefits of yoga ocular exercise for the prevention, treatment, and management of various ocular diseases associated with ocular hypertension.
| Conclusions|| |
The yoga ocular exercises induce a significant reduction in IOP. It can be a useful tool for purposely lowering IOP for the management and treatment plan of various ocular diseases or disorders associated with ocular hypertension such as glaucoma. Therefore, these findings conclude that yoga ocular exercises might be considered as a nonpharmacological intervention for lowering IOP.
The authors acknowledge the principal of SCO, Aditya Goyal, and the faculties Diwakar Rao, Namratha Hegde, Vandana Kamath, Jasmine C Kumpuckal, and Tapas Kumar De for their valuable assistance during the various stages of this study. We also express special thanks to Ms. Krupa Patel and Mr. Ankur Patel (yoga instructors) for guiding the participants for yoga ocular exercises, which is the backbone of this study. We also acknowledge Raman Prasad Sah for valuable suggestions during the preparation of the manuscript.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Al Busaidi, A. S. (2018). Corneal thickness: It's time we all get rid of the correction factor from the glaucoma equation! Oman Journal of Ophthalmology
(1), 1-2. doi.org/10.4103/ojo.OJO_220_2017.
Bakke, E. F., Hisdal, J., & Semb, S. O. (2009). Intraocular pressure increases in parallel with systemic blood pressure during isometric exercise. Investigative Ophthalmology and Visual Science
(2), 760-764. doi.org/10.1167/iovs.08-2508.
Baskaran, M., Raman, K., Ramani, K. K., Roy, J., Vijaya, L., & Badrinath, S. S. (2006). Intraocular pressure changes and ocular biometry during sirsasana (headstand posture) in yoga practitioners. Ophthalmology
(8), 1327-1332. doi.org/10.1016/j.ophtha.2006.02.063.
Brubaker, R. F. (1991). Flow of aqueous humor in humans. Investigative Ophthalmology & Visual Science
Charan, J., & Biswas, T. (2013). How to calculate sample size for different study designs in medical research? Indian Journal of Psychological Medicine
(2), 121-126. doi.org/10.4103/0253-7176.116232.
Cohen, L. P., & Pasquale, L. R. (2014). Clinical characteristics and current treatment of glaucoma. Cold Spring Harbor Perspectives in Medicine
(6), a017236. doi.org/10.1101/cshperspect.a017236.
Davis, B. M., Crawley, L., Pahlitzsch, M., Javaid, F., & Cordeiro, M. F. (2016). Glaucoma: the retina and beyond. Acta Neuropathologica
(6), 807-826. doi.org/10.1007/s00401-016-1609-2.
Dimitrova, G., & Trenceva, A. (2017). The short-term effect of yoga ocular exercise on intra-ocular pressure. Acta Ophthalmologica
(1), e81-e82. doi.org/10.1111/aos.12850.
Drance, S. M. (1964). Effect of oral glycerol on intraocular pressure in normal and glaucomatous eyes. Archives of Ophthalmology
(4), 491-493. doi.org/10.1001/archopht.1964.00970020491009.
Ehlers, N., Bramsen, T., & Sperling, S. (1975). Applanation tonometry and central corneal thickness. Acta Ophthalmologica
(1), 34-43. doi.org/10.1111/j.1755-3768.1975.tb01135.x.
Gupta, S. K., Agarwal, P., Saxena, R., Agrawal, S. S., & Agarwal, R. (2009). Current concepts in the pathophysiology of glaucoma. Indian Journal of Ophthalmology
(4), 257-266. doi.org/10.4103/0301-4738.53049.
Gyasi, M. E., Andrew, F., Adjuik, M., Kesse, E., Kodjo, R. A., & Herndon, L. (2014). The effect of medical therapy on IOP control in Ghana. Ghana Medical Journal
(3), 148-152. doi.org/http://dx.doi.org/10.4314/gmj.v48i3.6
Hilton, E. (2003). Exerc-eyes: Effects of exercise on ocular health. Clinical
Jasien, J. V, & Ritch, R. (2015). Practical tips: Avoiding inversions – Intraocular pressure changes and common yoga poses. Glaucoma Now
, (1), 10-11.
Jasien, J. V., Jonas, J. B., Gustavo De Moraes, C., & Ritch, R. (2015). Intraocular pressure rise in subjects with and without glaucoma during four common yoga positions. PLoS ONE
(12), 1-16. doi.org/10.1371/journal.pone.0144505.
Kaushik, S., Pandav, S. S., Banger, A., Aggarwal, K., & Gupta, A. (2012). Relationship between corneal biomechanical properties, central corneal thickness, and intraocular pressure across the spectrum of glaucoma. American Journal of Ophthalmology
(5), 840-849. doi.org/10.1016/j.ajo.2011.10.032.
Liu, J. H., & Weinreb, R. N. (2011). Monitoring intraocular pressure for 24 h. The British Journal of Ophthalmology
(5), 599-600. doi.org/10.1136/bjo.2010.199737.
Liu, J. H., Gokhale, P. A., Loving, R. T., Kripke, D. F., & Weinreb, R. N. (2003). Laboratory assessment of diurnal and nocturnal ocular perfusion pressures in humans. Journal of Ocular Pharmacology and Therapeutics
(4), 291-297. doi.org/10.1089/108076803322279354.
Martin, B., Harris, A., Hammel, T., & Malinovsky, V. (1999). Mechanism of exercise-induced ocular hypotension. Investigative Ophthalmology and Visual Science
McMonnies, C. W. (2016). Intraocular pressure and glaucoma: Is physical exercise beneficial or a risk? Journal of Optometry
(3), 139-147. doi.org/10.1016/j.optom.2015.12.001.
Mertz, B. P. (2016). Intraocular pressure. In: Drug Discovery and Evaluation: Cham, Switzerland: Springer International Publishing. Pharmacological Assays
Pardianto, G. (2005). Intraocular pressure measure on normal eyes. Mimbar Ilmiah Oftalmologi Indonesia
Read, S. A., & Collins, M. J. (2011). The short-term influence of exercise on axial length and intraocular pressure. Eye
(6), 767-774. doi.org/10.1038/eye.2011.54.
Rodríguez del Águila, M. M., & González-Ramírez, A. R. (2014). Sample size calculation. Allergologia et Immunopathologia
(5), 485-492. doi.org/10.1016/j.aller.2013.03.008.
Saraswati, S. S. (2009a). Asana Pranayama Mudra Bandha
ed.). Bihar: Yoga Publications Trust.
Saraswati, S. S. (2009b). Yoga Nidra
ed.). Bihar: Yoga Publications Trust.
Schmidtmann, G., Jahnke, S., Seidel, E. J., Sickenberger, W., & Grein, H. J. (2011). Intraocular pressure fluctuations in professional brass and woodwind musicians during common playing conditions. Graefe's Archive for Clinical and Experimental Ophthalmology
(6), 895-901. doi.org/10.1007/s00417-010-1600-x.
Schuman, J. S., Massicotte, E. C., Connolly, S., Hertzmark, E., Mukherji, B., & Kunen, M. Z. (2000). Increased intraocular pressure and visual field defects in high resistance wind instrument players. Ophthalmology
(1), 127-133. doi.org/10.1016/s0161-6420(99)00015-9.
Tham, Y. C., Li, X., Wong, T. Y., Quigley, H. A., Aung, T., & Cheng, C. Y. (2014). Global prevalence of glaucoma and projections of glaucoma burden through 2040: A systematic review and meta-analysis. Ophthalmology
(11), 2081-2090. doi.org/10.1016/j.ophtha.2014.05.013.
Tonnu, P. A., Ho, T., Newson, T., El Sheikh, A., Sharma, K., White, E., & Garway-Heath, D. F. (2005). The influence of central corneal thickness and age on intraocular pressure measured by pneumotonometry, non-contact tonometry, the Tono-Pen XL, and Goldmann applanation tonometry. British Journal of Ophthalmology
(7), 851-854. doi.org/10.1136/bjo.2004.056622.
Vieira, G. M., Oliveira, H. B., Andrade, D. T., Bottaro, M., & Ritch, R. (2006). Intraocular pressure variation during weight lifting. Archives of Ophthalmology
(9), 1251-1254. doi.org/10.1001/archopht.124.9.1251.
Weinreb, R. N., Aung, T., & Medeiros, F. A. (2014). The pathophysiology and treatment of glaucoma: A review. Journal of the American Medical Association
(18), 1901-1911. doi.org/10.17851/1983-36188.8.131.52-205.
[Figure 1], [Figure 2], [Figure 3]