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Following the Light – Part III: Iris, pupil and lens


3 min


AmblyoPlay - Following The Light Part III
AmblyoPlay - Following The Light Part III

Click here for Part 1 (On the origin of light) and here for part 2 (The cornea) of our current blog series. Further into the eye we will now cover the iris and the pupil, and the lens.

Iris – the Gatekeeper for the Light

Do you still remember the Part 1 when you were sitting at your garden on a summer sunny day? If you do, imagine that you move into a dark place now. Probably most of you will know what happens next, am I right? Your pupil will suddenly enlarge. Why is that? Well, it is one of the reflexes that adjust the amount of light that enters deeper into the eye. It is basically what a shutter on your camera does. Arguably the most beautiful tissue in our bodies, the iris, is a muscle around the pupil. In dark environments it obviously relaxes so that more light can enter and vice versa. As its reflex originates from deep brain structures, very close to where important centres for breathing are, pathological pupillary reflex may sometimes be the very first sign of potentially very serious illnesses and a good clue of brain damage (and the depth of (un)consciousness levels) in cases of head trauma. Pupillary reflex can also be affected in certain poisonings and what is more, some substances even cause specific pupils – making choosing the right treatment ever so slightly easier.

Accommodating with lens for best vision at near – and far!

Let us go back to your garden now. Imagine you were just looking at the birds somewhere at the distance and then you suddenly decided to have a look at your smartphone. And you do and the very moment you shift your gaze onto your smartphone an important process in eye takes place. Your lens changes its shape. Our lens becomes more round so that it bends the light slightly more when we want to see things that are close to our eyes. Contrary, when we want to focus objects in the distances it becomes flatter so that it bends the light slightly less. Therefore, we can see clearly at every imaginable distance. This process is called accommodation and it is of major importance for everyday life. We will cover more on that in the next blog. The lens is also one of the most frequently affected structures in the eye.

Cataract – most known enemy of an eye lens

I am sure most of you have heard about the disease called cataract, have you not? It is a condition that causes the lens to cloud and is usually caused by degenerative changes due to age. It has got an interesting name, the cataract. It is derived from Latin and Greek, which would mean, in translation, waterfall and down-rushing, respectively. It is a normal process that happens with ageing although certain medications may accelerate it. When visual acuity is affected to the extent that it interferes with everyday life, cataract extraction is required. The surgery is safe, simple and very effective and perfect visual acuity is usually restored within days.

Our journey continues – next time!

Stay tuned as in the next blog we will summarize the action of the cornea and the lens, and talk about the refraction and most important refractive errors, that most of you have already encountered of will you encounter in your lives.

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Missed few parts of the series? Check them out:


Part I: On the Origin of Light

Part II: The Cornea

Part IV: Refraction and the Eye Globe

Part V: The retina (and the vitreous)

Part VI: The Retina, continued

Part VII: From retina to the brain

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