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眼科醫學會臨床論文 首頁 > 醫療新知 > 眼科醫學會臨床論文

中華民國眼科醫學會雜誌論文

第四十三卷第四期289-296頁中華民國93年12月發行 

Preliminary Observations on the Efficacy of Ocular Divergence Exercise for the Relax of Accommodation 

 

以眼球外展運動來放鬆調節力的臨床觀察

 

林超群

Dr. Chao-chyun Lin M.D. Ophthalmologist

林立菁

Dr. Grace L. Lin M.D., BSc.(Bio-med)

林立華

Janice Lin BSc.(Bio-med)

  

Abstract

Purpose:  To study the effect of targeted divergence exercise on eye strain and relax of accommodation. 

 

Method:  60 myopic volunteers were recruited through poster advertisement and allocated into the test (41) and control (19) groups by order of presentation.  The subjects were blinded to their allocations.  All subjects wore a vision training device containing convex prism lenses (test) or plano lenses (control) and watched television at a three meter distance for ten sessions lasting one hour each over a three week period.  Their refractive error and pupil size were measured before and after each session.  Adverse symptoms were measured through questionnaires completed after each session.

 

Results:  After the tenth session, the test group showed a mean reduction in measured refractive error of 0.28±0.03D, while the Controls showed a mean reduction of 0.06±0.03D.  A paired t-test yielded a significant difference in mean reduction between the groupsmean difference=0.22±0.05D, paired t=4.323, p=0.000.  The measured pupil size in both groups did not reduce following training, thus showing the improvement in vision was not a result of pinhole effect by pupil miosis.  The subjects experienced brief, fully reversible discomfort in initial sessions only. 

 

Conclusion:  We found a statistically significant reduction in measured refractive error, likely due to the relax of accommodation or the reversal of over accommodation (e.g. pseudomyopia ), when test subjects performed ocular divergency exercise using the ocular training device.  Longitudinal studies are needed to evaluate the long term effect of ocular divergency vision training on myopic progression.

 

Keywords: myopia, prism, accommodation, convergency

 

  

Introduction

 

Considerable human and medical resource is expended each year on the prevention of myopia in Taiwanese children.  Despite this, the myopic-population has steadily increased over the years1, 2.  Excluding the use of cycloplegic agents, orthokeratology, or LASIK, there is currently no alternative method that successfully prevents myopic progression. 

 

Due to the widespread availability of prescription glasses and contact lenses, myopia is not commonly considered a debilitating illness.  However, approximately 20% of the myopic population has refractive errors of –6.00 D or worse, which places them in the category of high myopia, and hence more susceptible to structural anomalies of the eyes including retinal degeneration, and retinal detachment3, 4.  Therefore, high myopia should be considered a disease that requires treatment and prevention.

 

 

Background

 

To produce a sharp image at close distances, the eye requires the use of intra ocular muscles for accommodation, as well as the use of extra ocular muscles for convergence.  When the eyes converge, the contraction of the extra ocular muscles leads to increased pressure within the vitreous body, forcing the posterior pole of the eyes to expand outwards, and thus increase the axial length 5. 

 

A clear image on the retina is vital to the emmetropization of the eye during the growth period.  Until approximately the age of 10, the crystal lens of the human eye grows towards a thinner and flatter shape.  After the age of 10, axial growth continues if the eye is subjected to too much close work.  Therefore, myopia commonly occurs around the age of 10, due to the loss of the “compensating action” of the flattening of the crystal lens.  The progression of myopia generally slows down after puberty.

 

With excessive close work, the prolonged contraction of ciliary muscles during accommodation limits the growth of the eyes in the equatorial direction.  This leads to two phenomena: a) The obstruction of the “flattening” growth pattern of the crystal lens, hence affecting its ability to reduce the degree of myopia; and b) The tension of the equatorial section causing an increase in pressure on the axis of the eye, leading to the lengthening of the eyeball6.  Both phenomena lead to the development of myopia.

 

Findings from animal studies have shown that myopic defocus leads to the shortening of the axis of the eye, while hyperopic defocus lengthens it.  However, clinical observations of subjects with prescription glasses reveal a more complicated situation.  Research conducted by Ong et. Al7 did not show a marked difference between spectacle-wearers who wore their spectacles all day and those who removed them for close work.  As such, it appears that in humans the over exposure to near-work causes an increased dependence on accommodation, and hence Accommodative Hysteresis.  The resulting image on the retina is unclear, leading to the lengthening of the eye axis7 and the progression of myopia.

In myopic patients, the refractive error is the combined result of axial myopia (caused by excess axial length) and refractive myopia (caused by accommodation tonus), where axial myopia contributes the larger portion.  In pseudo-myopia, due to accommodation spasm, the refractive error contributed by refractive myopia can be more intense than that of the average myopic patients.  Currently there is no conclusive clinical data on the relationship between dynamic divergence exercise and reduction in refractive myopia.  Studies in the past that also investigated the effectiveness of visual training exercises for improving vision, such as exercises of the eyeball, Qi-Qong, acupuncture and the Biofeedback method3, 4 have demonstrated some improvement in visual acuity.  However they were unable to confirm that these methods were able to improve the refractive error of myopic patients.

 

The present study involves the initial stages of investigation into a non-pharmaceutical, non-invasive method of inducing divergence ocular exercise for the relaxation of accommodation.  Initial results have shown significant reduction in refractive myopia.  Further research is being planned to study the long term effect on myopic progression.

 

 

Methods

 

60 healthy myopic volunteers with no other eye history were recruited through poster advertisements at local schools and universities.  There were 21 males and 39 females, aged between 15 and 25 years, with an average age of 19 (see graph 1).  The subjects were divided into the Test Group (the first 41 to volunteer) and the Controls (the other 19).

 

At the initial consultation the subjects’ eye history and examination were obtained.  Their visual acuity was measured objectively and subjectively at this consultation.  When the prescription of the glasses was unsuitable for the eyes (with a deviation over ±0.50 D), they were replaced with appropriate prescriptions. 

 

The subjects were blinded to their allocation.  During training a prototype of a visual training device was used (see picture 1).  The test device contained convex prism lenses of +0.5D & 5D, which rotated at 90 degrees between the BASE in and BASE down positions for fixed periods of time (9 seconds and 6 seconds respectively.)  The control group wore devices, which were identical in appearance and lens rotation, but containing plano lenses.  The subjects wore their prescribed glasses under the vision training device during the training sessions.

 

Each subject underwent 10 vision-training sessions either daily or on alternative days until 10 sessions were completed.  Measurements of the refractive error and astigmatism (in spherical equivalent) were taken just prior to, and 10 minutes after each session using an autorefractometer and a phoroptor and eye-chart projector.  During each session, all subjects watched television for one hour at a 3-meter distance.  Symptoms of discomfort were measured by questionnaires.

 

The objective measurements were taken using the CANON R10. The subjective measurements of refractions were taken using the TOPCON CV300 Phoropter, and the ACP-8 eye-chart projector.  Targets on the eye-chart appeared one at a time to avoid the subjects remembering the sequence of the targets.  Each patient’s refractive status was also assessed with the Duochrome test (Red-green test) by the same experienced technician in order to maintain a consistent standard of measurement. The horizontal diameters of the pupils were measured from the monitor of the autorefractometer and calculated using ratios.

 

At the end of the tenth session, after both objective and subjective measurements have been taken, a cycloplegic agent (Mydrin-p: 0.5% Tropicamide + 0.5% Phenylephrine HCl ) was used before a second set of objective and subjective measurements were taken.  The cycloplegic drop was administered 3 times at 5-minute intervals, and the ‘after’ measurements were taken 30 minutes after the drops were instilled. 

 

 

  

Results

The subjects’ refractive errors, measured by the phoroptor and eye-chart projector, before the first session and after the tenth session were compared.

 

After the tenth training session, 27% of eyes in the Test subjects showed no reduction in refractive error, compared with 68% in the Controls. (see Table 1)

 

The Test group showed a mean reduction in refractive error of 0.28±0.03D, while the Controls showed a mean reduction on 0.06±0.03D.  A paired t-test yielded a significant mean reduction between the Test and Control groups (mean difference = 0.22±0.05D; paired t = 4.323, p = 0.000). (See Table 2)

 

Table 3 shows the mean refractive error after ten sessions with and without the application of cycloplegic agents.  In the test subjects, the mean refractive error post training was –4.93 D, which is close to the value measured after cycloplegic agent was administered (-4.92 D).  Therefore, the cycloplegic agent did not produce significant additional reduction in refractive error in the subjects.  (See Table 3.)

 

 

 

 Pupil Diameter

 

Measurements of pupil diameter taken prior to and following each training session showed that there was no significant change in average pupil size in the test group, and there was a slight decrease in average pupil size in the controls.  Table 4 shows that the average pupil diameter in the test group increased rather than decreased with successive sessions, and shows that the improvements in vision and the lowered degree of myopia was not a result of pinhole effect by pupil miosis.  (See Table 4. and Table 5.)

 

 

Adverse Effects

 

Within the 41 test subjects, 5 were able to adjust from the first session with ease and no symptom of discomfort.  The remaining 36 subjects (88%) experienced an assortment of symptoms (some subjects experienced two or more symptoms).  As shown in Table 6, 20 subjects experienced dizziness, 21 experienced soreness of the eyes, and 20 experienced double vision.  At the second training session the number of subjects who experienced discomfort reduced to 18 (43.9%), and the number steadily decreased to 7 (17%) by the third session, and 2 (4.9%) by the fifth session. 

 

All subjects were able to fully recover from the symptoms of discomfort within 5-30 minutes after each training session.  From the sixth session onwards, none of the subjects showed any symptom of discomfort.  (See Table 6.)

 

 

 

Discussion

 

After ten sessions of ocular divergence training, the average reduction in refractive error in Test subjects was 0.28±0.03D, compared with 0.06±0.03D in Control subjects.  The reduction was significant, and parallels the results of Yang 17 who with the administration of the cycloplegic agent Tropicamide was able to lower myopia in patients by an average of 0.25D. 

 

In past studies10, 11, 14, 15, Plus Lenses or Bifocal Lenses have been used to replace accommodation, in the hope of achieving relaxation of the ciliary muscle and hence slowing down the rate of myopic progression, while Prisms were used in attempt to avoid the over-convergence of the eyes.  However, these methods did not achieve a significant reduction in refractive error of the patients.  We hypothesize that the lack of convincing result could be due to the fact that the prisms chosen were not strong enough to induce a significant degree of divergence; and the fact that the lenses were immobile fixtures and were unable to periodically induce the exercise of extra and intra ocular muscles to allow for relaxation of accommodation.

 

Pupil diameter can often influence the result of subjective measurements.  Shih 18 reported that methods of Qi-Qong and acupuncture are able to stimulate the parasympathetic nerves, causing pupil miosis, which leads to improved vision.  However, prolonged stimulation of the parasympathetic nerves can in fact increase accommodation, and accelerate the rate of myopic progression18.  There was no corresponding reduction in pupil diameter associated with the reduction in refractive error in this study, in fact a slight dilation of the pupils was seen.  This shows that the improvement in vision was not a result of pinhole effect by pupil miosis, but by the relax of accommodation tonus. 

 

In summary, we found a statistically significant relax of accommodation when subjects performed ocular divergence exercise using the ‘ocular training device’.  The decrease in measured refractive error achieved was comparable to that obtainable through instillation of cycloplegic drops.  The effect of the refractive error improvement was not dependent on pupil miosis and resultant pin-hole effect, as shown by the increased pupil diameter of the test subjects. 

 

This method of ocular divergence exercise was effective in producing relaxation of accommodation.  Longitudinal studies are needed to observe if long-term, regular training has an effect in the reduction of eye-strain and computer vision syndrome, the prevention and treatment of pseudo-myopia or the alleviation of myopic progression.

 

 

   

 

Reference

 

Lin LLK, Shih YF, Hsiao CK, Chen CJ, Lee LA, Hung PT. Epidemiologic study of the prevalence and severity of myopia among schoolchildren in Taiwan in 2000.  J Formos Med Assoc 2001; 100: 684-91. A number of subjects experienced two or more symptoms.

Chang SHC, Shih YF, Lin LLK. A review of myopia studies in Taiwan. The Official Journal of the Ophthalmologic Society of Taiwan the Republic of China, 1999; 383: 313-26.

Grosvenor T, Goss DA. Clinical Management of Myopia. Butterworth Heinemann. 1999.

Dr. Schmid, Klaus. Myopia Manual 2003. http://www.myopia-manual.de

Green, Peter R. Mechanical considerations in myopia: Relative effects of accommodation, convergence, intraocular pressure, and the extraocular muscles. American Journal of Optometry & Physiological Optics. 1980; 5712:902-14

Mutti DO, Zadnik K, Fusaro RE, Friedman N, Sholtz RI, Adams AJ. Optical and structural development of the crystalline lens in childhood. Investigative Ophthalmology &Visual Science. January 1998; 391: 120-33.

Ong E, Grice K, Held R, Thorn F, Gwiazda J. Effects of spectacle intervention on the progression of myopia in children. Optometry and Vision Science. 1999; 766: 363-9.

Chung K, Mohidin N, O’Leary DJ. Undercorrection of myopia enhances rather than inhibits myopia progression. Vision Research. 2002; 42: 2555-9.

Eulenberg, Alexander. The case for the preventability of myopia. I See. http://www.i-see.org/prevent_myopia.html

Shotwell, Alan J. Plus lenses, prisms, and bifocal effects on myopia progression in military students. American Journal of Optometry & Physiological Optics. 1981; 585: 349-54.

Shotwell, Alan J. Plus lenses, prisms, and bifocal effects on myopia progression in military students, Part II. American Journal of Optometry & Physiological Optics. 1984; 612: 112-7.

Goss, David A. Attempts to reduce the rate of increase of myopia in young people. American Journal of Optometry & Physiological Optics. 1983; 5910: 828-41.

Goss, David A. Effect of spectacle correction on the progression of myopia in children – a literature review. J Am Optom Assoc 1994; 65: 117-28.

Leung JTM, Brown B. Progression of myopia in Hong Kong Chinese schoolchildren is slowed by wearing progressive lenses. Optometry and Vision Science. 1999; 766:346-54.

Brown B, Edwards MH, Leung JTM. Is esophoria a factor in slowing of myopia by progressive lenses? Optometry and Vision Science. October 2002; 7910:638-42.

Edwards MH, Li RWH, Lam CSY, Lew JKF, Yu BSY. The Hong Kong progressive lens myopia control study: Study design and main findings. Investigative Ophthalmology & Visual Science. September 2002; 439:2852-8.

Yang,Y., Woung L., Chiang, H., Jian,Y & Shih, Y.. The effect of tropicamide versus atropine on the refractive errors of myopic children. The Official Journal of the Ophthalmologic Society of Taiwan the Republic of China,2000; 393:240-6.

Shih Feng Shih. The effect of Qi-Qong Ocular Exercise on Accommodation. Chinese Journal of Physiology 1995; 381:35-42

Ehrlich, David L. Near vision stress: Vergence adaptation and accommodative fatigue. Ophthal. Physiol. Opt. 1987; 74:353-7

   

Graph 1.  Age Distribution of Subjects

 

 

Graph 2.  Distribution of Refraction Error in the Test Group Prior to First Training

Session

 

 

 

Picture 1. Subject wearing “ocular divergence exercise” device.

 

 

 

 

 

 

 

 

Number of Eyes

Reduction in refractive Error

Test (total: 82)

Control (total: 38)

≤0.00 D

22

26

0.25 D

28

9

0.50 D

22

3

0.75 D

9

0

1.00 D

0

0

1.25 D

1

0

 

Table 1.  Number of eyes showing reduction in refractive error

  

Groups

N

Mean

Std Dev

SEM

Test

82

0.2774

0.2778

0.0307

Control

38

0.0592

0.2050

0.0333

Difference

 

0.2182

 

0.0505

 

Table 2.  Mean reduction in refractive error

 

 

Mean Refractive Error

 

Before the 1st Session

After the 10th Session -

Without Cycloplegic Agent

After the 10th Session –

With Cycloplegic Agent

Test

5.22D

4.93D

4.92D

Control

4.51D

4.45D

4.37D

 

Table 3.  Mean Refractive Error After 10 Training Sessions - With And

Without Application of Cycloplegic Agent   

Table 4.  Average Pupil Diameter in Test Subjects 

Table 5.  Average Pupil Diameter in Control Subjects

Table 6.  Number of Test Subjects Experiencing Symptoms During Training.

  

以眼球外展運動來放鬆調節力的臨床觀察

 

 

林超群 林立菁 林立華

 

目的:以眼球外展運動來放鬆眼球及放鬆調節力之臨床試驗

 

方法:以刊登海報方式募集了60位患有近視之自願者,並將其分為實驗組(41人)與對照組(19人)。分組結果未告知自願者。所有自願者均戴用外觀相同但內含不同鏡片之視力訓練儀器(實驗組為稜凸透鏡,對照組為平光鏡片);並在三星期內,於三公尺距離觀看電視ㄧ小時,共十次。每次訓練前後,均量取近視度數與瞳孔大小。訓練時之不適症狀則以問卷方式於每次訓練後調查。

 

結果:十次訓練後,實驗組平均減少0.28±0.03D,對照組平均減少0.06±0.03D。兩組間有十分具統計學意義之差異(mean difference=0.22±0.05D, paired t=4.323, p=0.000)。每次訓練後,兩組之瞳孔大小均未縮減,顯示度數之降低並非針孔效應之影響。訓練初期之短暫不適症狀,於訓練中期均已消失。

 

結論:本實驗發現,戴用稜凸透鏡之實驗組,與對照組之度數變化有具統計學意義之差異。此差異應為放鬆調視或過度調視(如假性近視)的改善所引起。進一步的臨床觀察:「長期利用此種眼球外展運動,來減緩近視加深的速度」,則正在進行中。

 

                         

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