Myopia: What does Nearsightedness Mean? | Eyesdisorder

Eye Test- Myopia

Myopia Definition

Short Answer Myopia is an eye disorder, nearsightedness, shortsightedness, one can only able to see the near objects clearly.

Detailed Answer Myopia is a defect in our eye in which one can only able to see the near objects(i.e objects close to his eyes) clearly that is why myopia is also known as nearsightedness or also as a Shortsightedness all are the same.

Myopia causes distant objects to be blurry and unclear.

What does Nearsightedness Mean?

Scientific Explanation In normal cases light that enters in our eye will form an image on the retina but in the case of the Myopia instead of the retina, light focuses in front of the retina causes to see only near objects.

Let us understand Myopia with diagram

  

Normal Eye Diagram

Normal Eye Ray Diagram

Myopia Eye

Myopia Diagram

How does the light propagates inside a myopia eye? (Near Objects)

The light from the nearer object travels in the usual way. It gets focused on the retina only. No problems there.

How does the light propagates inside a myopia eye? (Far Objects)

First of all the light rays from a faraway object coming towards the eye are almost parallel to each other. And when these rays enter the eye, they get converged in front of the retina instead of on the retina. This is the reason for the blurriness.

What causes the light to converge in front of the retina rather than on the retina?

The larger size of the eyeball is one of the reasons which results in this eye defect. Due to the elongated eyeball, the distance between the lens and the retina is more than the usual. Because of this larger distance between the two, the image is formed in front. 

Well one thing we must note here is that the lens functions in its usual way. It does its work neatly as it is supposed to. The only thing is that the image is formed at a different position.

Causes of Myopia/ Nearsightedness

• Age of the person.

• It can be caused genetically.

• Environmental factors.

• Also caused according to the type of job and stress level on your eye. 

Symptoms of Myopia/ Nearsightedness

• Blur far Vision is the main symptom of myopia.

• Headaches.

• More eye strain.

• As Myopia is nearsightedness you can see near objects clearly but far object becomes unclear or different from near objects in the initial stages.

Prevention of Myopia/ Nearsightedness

• Myopia is prevented by proper eye care and a healthy diet plan. Nowadays it is becoming more frequent in children and teenagers because of our daily unhealthy routine.

• Glasses and Contact Lenses.

• Antimuscarinic medications slow down the worsening of myopia.

• Other methods are also there which include the Scleral reinforcement surgery.

From above all mentioned methods healthy diet, wearing Glasses and Contact lenses are on top and from these two wearing glasses are more used because of the following reasons:-

•  Less complicated.

•  Fast results.

•  Cheap.

How do we overcome myopia defect?

It can be corrected by using a concave lens. We place a concave lens in front of the myopic eye.

What does this biconcave lens do?

It refracts light, but its main objective is to make sure that the image is formed on the retina only. By changing its shape, the lens controls the direction of the propagation of light. This ability of the lens to change its focal length is defined as the accommodation power of the eye.

Detailed Explanation using Diagram

Correction of Myopia using a Concave Lens

As we are able to see from the above diagram that the concave lens of a particular focal length helps to remove the myopia defect in the eye. The concave lens helps the light to fall on the retina of the eye and make a clear image of the near as well as far objects.

Why concave lens?

We know that the concave lens diverges the light and these divergent rays fall on the lens at such an angle such that they refract and come together on the retina and not in front of the retina.

How to calculate the focal length and power of the lens for myopia eye?

Far point of the myopic person = 145 cm. After this distance vision starts to blurry due to myopia.

Formula to calculate the focal length(f)

  1/f =1/v – 1/u

By putting the values,

v = -145cm (distance of the image/ far distance) 

   u= -infinity (distance of the object)

  1/f = 1/(-145) - 1/-(infinity)

f= - 145cm = -1.45 m

Formula to calculate Power(P)

P= 1/focal length (for 'f' in m)P= 100/focal length (for 'f' in cm)

p= 1/-1.45

p= -0.68D