JOURNAL OF EVIDENCE BASED MEDICINE AND HEALTHCARE

Table of Contents

2019 Month : September Volume : 6 Issue : 35 Page : 2411-2414

CLINICAL STUDY OF CORRELATION BETWEEN DEGREE OF MYOPIA AND AXIAL LENGTH OF EYEBALL IN MYOPIC PATIENTS.

Damayanti Mallappa Suranagi1, Theerthavathi Gowdanakatte Lingadevaru2

1. Associate Professor, Department Ophthalmology, Karnataka Institute of Medical Sciences, Hubli, Karnataka.
2. 3rd Year Postgraduate, Department of Ophthalmology, Karnataka Institute of Medical Sciences, Hubli, Karnataka.

Corresponding Author:
Dr. Theerthavathi G. L.,
D/o. G. M. Lingadevaru,
Gowdanakatte, Mattihalli Post, Kasaba Hobli,
Tiptur Taluk, Tumkur- 572201, Karnataka.
E-mail: theerthavathisneha@gmail.com
DOI: 10.18410/jebmh/2019/493

ABSTRACT
BACKGROUND
The refractive error around the globe has been estimated to be around 800 million to 2.4 billion. Refractive errors are the most common cause of visual disorders. Amongst them myopia is the most common disorder. As per the 2001-02 national survey on blindness in India, refractive errors accounts for 19.7% of total blindness.

METHODS
Anterior segments of 150 eyes of patients were examined using slit lamp biomicroscope. The visual acuity, cycloplegic refraction, retinoscopy, fundoscopy were done for all the selected patients after obtaining an informed consent. The axial lengths that were obtained using A-scan were correlated with the degree of myopia. They were further sub classified on the basis of age, sex, familial factors and complications.

RESULTS
In this study, out of 150 eyes Females constituted 65.06% of the total cases while males constituted 34.93% of the total cases. Subjects having less than -6D constituted 69.9% of the cases. The degree of myopia progressively increased with increase in axial lengths particularly in those with greater than -6D. Myopia of greater than -15D was commonly associated with degenerative changes. Severity increases with increase in axial lengths. Lower degrees of myopia have good corrected visual acuities while the longer axial lengths having higher grades of myopia had worst corrected visual acuities.

CONCLUSIONS
All patients showed an increase in the axial length, which was greater for highly myopic eyes. High degrees of myopia associated with complications may require careful follow up.

KEYWORDS
Myopia, Visual Acuity, Refraction, Axial Length, A-Scan

How to cite this article

Suranagi DM, Lingadevaru TG. Clinical study of correlation between degree of myopia and axial length of eyeball in myopic patients. J. Evid. Based Med. Healthc. 2019; 6(35), 2411-2414. DOI: 10.18410/jebmh/2019/493

BACKGROUND

Refractive errors are the most common cause of visual disorders. Amongst them myopia is the most common disorder. Myopia or short-sightedness is a type of refractive error in which parallel rays of light coming from infinity are focused in front of the retina when accommodation is at rest.1 It affects all the age groups, ethnic groups, genders and causes blindness. Myopia is a global health problem associated with not only vision impairment but also blinding complications. Myopia can be classified into-

  1. Axial myopia: It occurs due to the increase in antero-posterior length of the eyeball. It is the commonest form.
  2. Curvatural myopia: It occurs due to increased curvature of the cornea, lens or both.
  3. Positional myopia: It is produced by anterior placement of crystalline lens in the eye.
  4. Index myopia: It results from increase in the refractive index of crystalline lens associated with nuclear sclerosis.
  5. Myopia due to excessive accommodation occurs in patients with spasm of accommodation.1

Ultrasonography A - scan measures the axial length i.e., antero posterior diameter of the eyeball with high degree of accuracy. It utilizes ultrasonic frequencies of 10 MHZ. Based on the degree of myopia, it can be again classified into two types namely simple myopia (-0 to -6 dioptres), pathological myopia (>-6 dioptres).

As per the 2001-02 national survey on blindness in India, refractive errors accounts for 19.7% of total blindness.2 Studies from the early 2000s from India have quoted prevalence of myopia in children is 7.4% by Murthy et al. and 4.1% by Dandona et al.3,4 Studies in adults have found myopia prevalence ranging from 19.4% in Taiwan to 41.8% in Japan.5,6 It is a condition occurring as a result of increased global axial length or increased refractive power 

of anterior segment but the former being the more important. Von Jeager first described congenital myopia in 1855. Studies have revealed that myopia is found more often in females than males and also prevalence of myopia increased with age, with a maximum of 67.2% in the age group between 30 to 40 years.7 Higher degrees of myopia are known to have higher axial lengths and complications like lattice degeneration, posterior staphyloma, retinal detachment, vitreous opacities, and retinal tears. High myopia can have a profound effect on the visual acuity of the patient and can cause blindness.8 Myopia also poses medical burden with increased incidence of glaucoma and cataracts in those myopic individuals.9

We wanted to study the correlation between axial length, age, sex and complications associated with the degree of myopia.

 

METHODS

This is a cross sectional study conducted on 150 eyes of the patients attending the outpatient department of Ophthalmology at Karnataka institute of medical sciences, Hubli. Ethical clearance is obtained from the institution.

 

Inclusion Criteria

All patients attending the outpatient department of Ophthalmology, Karnataka Institute of Medical Sciences, Hubli, for diminished vision within the age group of 10 to 60 years, with pseudophakia, and with diabetes and hypertension were included in the study.

.

Exclusion Criteria

Patients with corneal pathologies, lenticular opacities, glaucoma, retinitis pigmentosa and uveitis were excluded.

 

Methodology

A clinical study on patients with complaints of blurring of vision attending the outpatient department of Ophthalmology, Karnataka institute of medical sciences and who are willing to participate in the study. After taking written informed consent a detailed history regarding their complaints, the onset, duration of complaints, past history of wearing spectacles and family history is to be enquired. The patients are to be screened in the outpatient department. Preliminary examination of visual acuity for distance is to be determined with Snellen’s chart and pinhole improvement is noted. Cycloplegic refraction is done for patients in the age group of 10 to 15 years &retinoscopy is performed in all the patients included in the study. Refraction readings are to be determined with a retinoscope in a dark room and subjective correction is to be given. Retinoscopy readings are to be done after using a cycloplegic like cyclopentolate (0.5 to 1%) and they are called for post mydriatic refractive correction after 3 days. For auto refractometer, three consecutive autorefractor measurements were performed and the average value was used for analysis. The patients were reviewed again for assessment of subjective dioptric refractive acceptance. They were then be prescribed appropriate refractive correction for refractive error. The results of objective refractometry technique will be compared to the results of subjective dioptric acceptance of refractive correction. The following measurements with dioptres (D) will be recorded for analysis: 1. Spherical Power 2. Cylindrical Power 3. Spherical Equivalent (Spherical Power + (0.5× Cylindrical Power) 4. Axis. Those patients with myopia are segregated and subjected for slit lamp examination and fundus examination with direct or indirect ophthalmoscope. The patients are then explained the procedure of axial lengths using A scan are determined. The axial length so obtained are co-related with degree of myopia. They are then further sub-classified on basis of age, sex, familial factors and complications.

 

RESULTS

In the present study, axial lengths of 150 eyes were measured using the A scan ultrasonography.

 

Gender

No. of Cases

Percentage

Males

29

34.93%

Females

54

65.06%

Total

83

100

Table 1. Proportion of Myopia in the Two Genders

 

Degree of Myopia

No. of Eyes

No. of Patients

Percentage

0 to -3D

82

41

54.66%

-4 to -6D

23

14

15.33%

-7 to -9D

23

15

15.33%

-10 to -12D

06

04

04%

-13 to -15D

04

03

02.66%

-16 to -18D

08

04

05.33%

-19 to -21D

04

02

02.66%

Total

150

83

 

Table 2. Correlation Between the Degree of Myopia and Number of Patients

 

Degree of Myopia

Range of Axial Length

No. of Eyes

Percentage

0 to -3D

21 to 25 mm

74

49.33%

-4 to -6D

22 to 26 mm

30

20%

-7 to -9D

23 to 27 mm

22

14.66%

-10 to -12D

22 to 24 mm

10

06.66%

>12D

26 to 30 mm

14

09.33%

Total

 

150

 

Table 3. Correlation Between Range of Axial Length and Degree of Myopia

 

The above table shows that the shorter axial lengths associated with lower degrees of myopia when compared to the longer axial lengths associated higher degrees of myopia. It is seen that, as the axial length increases, dioptric power also increases.

 

Myopic Fundus Features

No. of Eyes

Percentage

Myopic crescent

50

33.3%

Tessellated fundus

54

36%

Vitreous changes

26

17.3%

Choroid degenerative changes

10

06.6%

Fuchs’s spots

06

04%

Peripheral retinal degeneration

04

02.66%

Total

150

 

Table 4. Number and Percentage of Myopic Eyes Showing Fundus Changes

The above table shows that tessellated fundus was present in maximum number of eyes (54) 36% whereas, peripheral retinal degeneration was present in only 2.66% eyes.

 

Family History

No. of Cases

Percentage

Present

22

26.5%

Absent

61

73.4%

Total

83

 

Table 5. Incidence of Family History

 

Ocular Condition

No. of Eyes

Percentage

Nystagmus

02

01.33%

Divergent squint

04

02.66%

Keratoconus

02

01.33%

Diabetic retinopathy

04

02.66%

Pigment degeneration

10

06%

Night blindness

00

00%

Macular scar

04

02.66%

Total

26

 

Table 6. Number of Myopic Cases with

Associated Ocular Condition

 

The above table shows that 6% of myopic cases are associated with pigment degeneration.

 

Visual Improvement

No. of Eyes

Percentage

 

6/6 - 6/9

72

48%

6/12 – 6/18

32

21.33%

6/24 – 6/36

25

16.66%

6/60 – CF 3 mtr

12

08%

CF 2 mt - CF 1 mt

06

04%

No improvement

03

02%

Total

150

 

Table 7. Degree of Visual Improvement with Glasses

 

The above table shows that 48% of the total eyes had improvement of vision up to 6/6-6/9 whereas, no improvement in vision was observed in 2%.

 

Complications

No. of Eyes

Percentage

Choroidal haemorrhage

00

00%

Retinal detachment

04

02.66%

Complicated cataract

00

00%

Posterior staphyloma

02

01.38%

Macular scar

04

02.66%

CNVM

02

01.38%

Total

12

 

Table 8. Number of Myopic Eyes Showing Complications

 

The above table shows that 2.66% of eyes had retinal detachment and macular scar whereas, none of the patients had choroidal haemorrhage and complicated cataract.

 

DISCUSSION

In the present study, patients having 0 to -3D of myopia and -3 to -6 D accounts for 69.9% in this study.

 

 

Low Myopia< -6D

High Myopia>-6D

Tron10 (computation)

22.19 – 28.08

24.88 – 38.18

Deller11 (radiology)

20.5 – 26.0

25.5 – 28.5

Stenstorm12 (radiology)

22.0 – 28.0

23.5 – 29.50

Sorsby et al13 (computation)

22.01 – 28.0

25.01 – 37.0

Table 9. Range of Axial Length in Low and High Myopia

 

Yang J, Song X, Wang Y14 in their paper published in 1997 observed that ultrasound biometry to be the best method of axial length measurement. Reports by Hauff W,15 using 10 MHz sound probe for A scan biometry enabled measurements of the axial lengths of the eye to within an accuracy of 0.1 mm. In present study, it was noted that the degree of myopia progressively increased with increase in axial length especially, >-6D. Beyond, -6D a definite relationship between the axial length and degree of myopia was seen. Every degree of myopia corresponded to approximately an increase by 0.39 mm in the axial length. Nicolcescu AM16 concluded that axial myopia is the most frequent form of myopia. In this study of axial myopia, 34.93% of the subjects were males and 65.09% were females. Studies conducted by Wang17 et al reveal a higher prevalence of myopia in females compared to males in all age groups.

 

Age Group

Females

Males

43-54

47.50

37.80

55-64

26.50

23.40

65-74

15.90

13.30

Table 10. Gender Difference in Refraction Wang17 et al

 

In the present study, the majority of cases having shorter axial lengths had myopia of less than -6D and showed mainly a physiological fundus. All eye >-15D had pathological myopic fundus changes. The incidence and severity of complications showed an increase in the axial lengths and the degree of myopia. Similar findings have been reported by Curtin BJ.18 He reports an increase frequency of crescents with increase in axial lengths. In the present study, tessellated fundus and optic disc crescent were found out to be the most common posterior pole findings. Karlin DB19 reported that the frequency of crescents increased with axial length until all eyes larger than 29 mm had crescents. Pigmentary degeneration was seen commonly in 51-60 and >60 age groups.

 

CONCLUSIONS

The majority cases of myopia were observed in females. There exists a statistical correlation between axial length and degree of myopia. Longer axial lengths were associated with high degree of myopia and shorter axial lengths were associated with low degree of myopia. Also, high degrees of myopia were associated with complications and compromised quality of life due to poor vision when compared to low degrees of myopia associated with less complications and good quality of life due to good vision.

 

REFERENCES

  1. Khurana AK. Comprehensive ophthalmology. 4th Anshan Publishers 2007.
  2. Park K. Park’s textbook of preventive and social medicine. 19th Jabalpur: Banarsidas Bhanot Publishers 2007: p. 337.
  3. Dandona R, Dandona L, Srinivas M, et al. Refractive error in children in a rural population in India. Invest Ophthalmol Vis Sci 2002;43(3):615-622.
  4. Murthy GV, Gupta SK, Ellwein LB, et al. Refractive error in children in an urban population in New Delhi. Invest Ophthalmol Vis Sci 2002;43(3):623-631.
  5. Xu L, Li J, Cui T, et al. Refractive error in urban and rural adult Chinese in Beijing. Ophthalmology 2005;112(10):1676-1683.
  6. Cheng CY, Hsu WM, Liu JH, et al. Refractive errors in an elderly Chinese population in Taiwan: the Shihpai Eye Study. Invest Ophthalmol Vis Sci 2003;44(11):4630-4638.
  7. van Rens GHMB, Arkell SM. Refractive errors and axial length among Alaskan Eskimos. Acta Ophthalmologica 1991;69(1):27-32.
  8. Abrams DM. Duke-Elders practice of refraction. 10th Elsevier 1993:53-64.
  9. Saw SM, Gazzard G, Shih-Yen EC, et al. Myopia and associated pathological complications. Ophthalmic Physiol Opt 2005;25(5):381-391.
  10. Tron EJ. The optical elements of the refractive power of the eye. In: Ridley F, Sorsby A, eds. Modern trends in ophthalmology. New York: Hoeber Press 1940: p. 245.
  11. Deller JFP, O’Conner AD, Sorsby A. X-ray measurement of diameter of living eye. Proc R Soc Lond 1947;134(877):456-465.
  12. Stenstrom S. Investigation of the variation and the correlation of the optical elements of human eyes. Am J Optom Arch Am Acad Optom 1948;25(10):218-232.
  13. Sorsby A, Leary GA. A longitudinal study of refraction and its components during growth. Spec Rep Ser Med Res Counc (GB) 1969;309:1-41.
  14. Yang J, Song X, Wang Y. The measurement of eye axial length by ultrasound. Zhongguo Yi Liao qi xu Za Zhi 1997;21(1):24-25.
  15. Hauff W. Biometry--an exact method for the measurement of the axial length of the eye. Wien Klin Wochenschr 1983;95(8):271-274.
  16. Nicholcescu AM. Biometric variation of the ocular globe in myopia Oftalmologia 2001;54(4):43-46.
  17. Wang Q, Klein BE, Klein R, et al. Refractive status in the Beaver Dam Eye Study. Invest Ophthalmol Vis Sci 1994;35(13):4344-4347.
  18. Curtin BJ, Karlin DB. Axial length measurements and fundus changes of the myopic eye. Am J Ophthalmol 1971;71(1 Pt 1):42-53.
  19. Karlin DB, Curtin BJ. Peripheral chorioretinal lesions and axial lengths of the myopic eye. Am J Ophthalmol 1976;81(5):625-635.