The theory of black holes in the universe construes the theory of the hole in the eye yet without any interdependence of course.
The black hole is a region in space where gravity is so strong that nothing can escape from it, not even light. Now we really don’t know what lies inside the black hole and similar is our eye. Looking at a person’s eye we can only see the exterior of the eye that is the Cornea, the Iris, and the Pupil. We can say that the pupil is the black hole in your eye.
It is the gap in the Iris that does not absorb light unlike the black hole in the space, but it allows the light to reach the posterior surface of your eye. The contradiction is that light does not escape the black hole in space but with the human eye, it is a little different.
You must have noticed when pictures clicked using flashlights in dark, our eye resembles vampire’s eyes. This happens because the flashlight entering the eye reflects from the retina. Although the Choroid layer prevents internal reflectance of rays, unlike the black holes in the space, light that enters your eyes also leaves your eyes.
Lights rays are received by the photoreceptors present in the retina. Receptors convert the light rays into signals that reach our brain to form an image. But in the process, the extra light is reflected back. The blood vessels in the anterior surface of the eye give it a red color. Not everyone gets those flashy vampire eyes because the size of the pupil is different for every person.
The pupil expands or contracts depending upon the amount of light. If the light is excess the pupil contracts to restrict light rays from getting in the eyes, like when you suddenly come out in Sun from darkroom your pupil will become small wherein if you enter into a dark room your pupil expands to allow more light to reach the retina in order to be able to see. Thus its size may vary from 2mm to 8mm.
As the size of the pupil is not the same among people, so is the PD? First, we need to define PD.
Pupillary Distance is the distance from the nose bridge to the pupil of the left eye or the right eye also called the monocular PD. The distance between pupils of both eyes is known as binocular PD or simply PD. This distance also varies from person to person.
Pupils’ function is to control the light entering the eye but accurate pupillary measures are vital for efficient vision. In the process of making the prescription lenses, the pupillary distance is very important to measure for the accuracy and comfort of vision
To understand the importance of PD in making your prescription lenses we need to explore the making of a lens and before that, we need to understand the physics of light. When light passes through any medium it bends to a certain angle which depends on the indices of the medium. In the case when the incident ray is perpendicular to the boundary, the light travels in the same direction without bending into the other medium. A mirror is one such medium through which light travels at the same angle. The same physics applies to ophthalmic lenses.
The point from which light passes through the ophthalmic lens without bending is called the optical center. The science of accurate vision depends on accurate alignment. For light to travel straight through the ophthalmic lens and the pupil of the eye it is important to obtain the following steps:
- Measure correct Monocular and binocular vision using a PD meter or PD scale.
- Marking of the PD on the demo glass of the prescription frame.
- Make the person wear the glasses to verify the accuracy of marking. If the marking (usually a small cross) does not fall over the pupil of the patient, the optician may need to repeat the process all over again until accurate marking is achieved.
- Fitting of lens such that the optical center aligns PD marking on the lens.
It is the job of the optician to take accurate PD measures on the frame. If he fails to do so the patient may suffer from discomfort, poor or blurry vision, headaches, and other such symptoms.
While purchasing online gives you the comfort of ordering from the ease of your home it may reduce the accuracy of vision of your prescription glasses. Knowing your PD is not enough. Even if you are aware of your PD measure without verifying PD marking on demo glass with a person’s pupil, it may not result in utmost accuracy. Thus, it is more appropriate to visit your local optician to get your tailor-made pair of glasses.
Finally, the eye is the smallest organ but every little part of the eye has its own marvelous functionalities that enable us to see the life around us.
