What does the Myopia or Nearsightedness Actually Mean?
Myopia (also known as Nearsightedness and Shortsightedness) is a most common refractive condition where the distant object appears to be blurred and the near object clear. In medical parlance, the eye having excessive refractive power for the axial length (AL). This may be due to the increased axial length or increased dioptric power of one or more of its refractive medium. So the correct term would be something like this “Incident parallel light from an infinity are brought to focus in front of the retina (macula) with accommodation at rest”.
Prevalence in India?
In fact, a recent study shows the prevalence of myopia has been reported to be as high as 70-90% in some Asian population among 16-18 – years – old high school students1)Pan CW, Ramamurthy D, Saw SM. Worldwide prevalence and risk factors for myopia. Ophthalmic Physiol Opt. 2012;32:3–16. [PubMed].
The earliest survey conducted in India in the 1970’s by Jain et al., has shown a prevalence of myopia of 4.79% among the school children in Chandigarh. It was higher in urban population (6.9%) in comparison to rural population (2.77%)2)Jain IS, Jain S, Mohan K. The epidemiology of high myopia: Changing trends. Indian J Ophthalmol. 1983;31:723–8. [PubMed]. Murthy et al.,assessed the prevalence of refractive error and related visual impairment in school going children 5-15 years of age, in an urban population in New Delhi and reported a prevalence of 7.4% of myopia3)Murthy GV, Gupta SK, Bachani D, Jose R, John N. Current estimates of blindness in India. Br J Ophthalmol. 2005;89:257–60. [PMC free article][PubMed].
What causes Myopia?
Excessive and concentrated near point work is the chief causes of nearsightedness or myopia. If one keeps away from any kind of near task like reading or writing for a considerable length of time, myopia may decrease. Overuse of the eyes causes their distance vision to be blurred this is because, after a prolonged use of near work, the eyes are unable to refocus to see the distance clearly. This constant visual stress may lead to a permanent reduction in the distance over a period of times.
A number study proves that the percentage of nearsightedness in youngsters is greater during the school year than at the end of long vacations, a time of few books and long hours outdoors.
The Sydney Myopia Study (SMS) and the Singapore Cohort Study for the risk factors for myopia (SCORM) are as follows4)Ip JM, Saw SM, Rose KA, et al. Role of near work in myopia: findings in a sample of Australian school children. Invest Ophthalmol Vis Sci 2008; 49: 2903–29105)Saw SM, Carkeet A, Chia KS, Stone RA, Tan DT. Component dependent risk factors for ocular parameters in Singapore Chinese children. Ophthalmology 2002; 109: 2065–2071.:
Children who read continuously for more than 30 min had a higher incidence of myopia. Children who performed near work at <30 cm distance were 2.5 times likely to be more myopic. Children who read more than two books per week were also three times likely to have higher myopia. Children who read more than 2 h per day were 1.5 times likely to have higher myopia. For every book read per week the axial length elongation was more by 0.04 mm. However, several other studies failed to find any significant correlation between near work and myopia.
Inheritance plays a major role in refractive myopia. A strong family history of nearsightedness double times increases the chance of developing it. And also certain health conditions such as diabetes raises the risk of myopia
Common signs and symptoms:
As we described earlier, in myopia near objects appears clearer and the distance is fuzzy and blurred. Children’s cannot see the blackboard clearly at the school whereas adults cannot see the street signs clearly while driving.
Other signs may include:
– Eye strain
– Squinting of eyes to make out distance clear
– Need to sit closer to the television, movie screen or the front of the classroom
– Holding books very close while reading
Degrees of Myopia:
- 0 = normal or emmetropic
- -0.25 to -3.00 D = mild nearsightedness
- -3.25 to -6.00 D = moderate nearsightedness
- -6.25 to -10.00 D = severe nearsightedness
- -10.25 D or higher = extreme nearsightedness
How do your eye care professionals determine your power?
With your routine yearly check-ups, your optometrist performs a thorough eye exam, which will include a procedure to find your refractive power. The nearsighted person can easily read the near point chart but finds trouble in reading the distance (Snellen chart).
A standard eye examination may include:
– Visual acuity (VA), both at a distance, and near
– Eye pressure measurement (Tonometry)
– Refraction test, to determine the correct prescription for glasses
– Retinal examination (Fundoscopic Exam)
– Slit-lamp exam of the structures at the front of the eyes
– Colour vision test, to look for possible colour blindness
– Tests of the muscles that move the eyes
Treatment options of Nearsightedness?
Nearsightedness can be corrected with eyeglasses, contact lenses or refractive surgery. Depending on how strong your prescription, you may need to wear your glasses or contact lenses. The higher the number is, the more you’re nearsighted.
Correction with glasses?
Generally, nearsightedness is corrected with minus lenses. if we place minus lens in front of the eye, the image will be pushed and brought focus to the retina.
Other available correction options?
Refractive surgery often eliminates or reduces glasses and contact lenses. The goal of refractive surgery is to improve natural vision and thereby improve quality of life through minimized dependence on external eyewear. Types of surgeries for refractive errors,
– LASIK, or laser in-situ keratomileusis.
– PRK, or photorefractive keratectomy.
– LASEK, or laser epithelial keratomileusis.
– RLE stands for refractive lens exchange. Other names include PRELEX, clear lens exchange (CLE), clear lens extraction (CLE), and refractive lens replacement (RLR).
References [ + ]
|1.||↑||Pan CW, Ramamurthy D, Saw SM. Worldwide prevalence and risk factors for myopia. Ophthalmic Physiol Opt. 2012;32:3–16. [PubMed]|
|2.||↑||Jain IS, Jain S, Mohan K. The epidemiology of high myopia: Changing trends. Indian J Ophthalmol. 1983;31:723–8. [PubMed]|
|3.||↑||Murthy GV, Gupta SK, Bachani D, Jose R, John N. Current estimates of blindness in India. Br J Ophthalmol. 2005;89:257–60. [PMC free article][PubMed]|
|4.||↑||Ip JM, Saw SM, Rose KA, et al. Role of near work in myopia: findings in a sample of Australian school children. Invest Ophthalmol Vis Sci 2008; 49: 2903–2910|
|5.||↑||Saw SM, Carkeet A, Chia KS, Stone RA, Tan DT. Component dependent risk factors for ocular parameters in Singapore Chinese children. Ophthalmology 2002; 109: 2065–2071.|