Ocular injuries after solar exposure

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A digression on the “Astigmatism series”.

Summer is here and many of you had already been on holiday or you are thinking about that, preparing everything to enjoy a well-deserved time for rest :-)

Do not forget to put in the suitcase sunglasses for all your family members (adults and children). Just as you do not forget the sun protection lotions, sunglasses are something indispensable to enjoy some safe holiday.

Think about the time that you are going to be performing outdoor activities, without your eyes being protected. Furthermore, there are more harmful radiations in the beach, because we have to add the ones that are reflected in the sea; but many surfaces reflect those harmful rays (sand, buildings, sidewalks,…). Even in cloudy days, with high clouds, the solar radiation that crosses them is nearly the same one that when there are no clouds at all. Only rain, fog and low clouds reduce UV radiation in a significant way.

Any tissue of the eye, as it happens with the skin, can be burnt. Solar UVA or UVB radiations on the tissues cause a cellular death process and a transformation of cell DNA, which can create irreversible disorders. Therefore, we must take care of our eyes by wearing lenses that comply with health regulations of visual quality. In the case of European sunglasses, the CE mark identifies glasses fulfilling quality regulations.

Atmospheric ozone is a barrier against very detrimental UVC radiation and other UV types; and this moderates the quantity of UVB that arrives to the earth (more harmful than UVA).
The constant slimming of ozone layer causes an increase of the UVB radiation that we receive daily. So, while this keeps being like that (unfortunately), we will have to do everything in our power to protect our eyes.

Some injuries that are caused in the eye due to solar radiation are the following ones:

IN CONJUNCTIVA (5)

• Squamous cell carcinomas
• Pterygium
• Pinguecula

IN CORNEA (1)
Cornea and crystalline lens absorb most of UVA and UVB radiation that get into the eye, damaging these structures; therefore, if a person has got a keratoconus or she has undergone a refractive surgery, her cornea will be thinner and it will be able to absorb less radiation, so, this radiation might get into the eye, causing some injuries.

• Painful superficial keratitis
• Photokeratitis or snow blindness
• Climatic droplet keratopathy or Spheroidal Degeneration

IN AQUEOUS HUMOR (4)
The aqueous humor of the anterior chamber has a lot of Vitamin C (ascorbic acid), which is responsible for filtering UV radiation, and this way, achieving that the least amount possible of radiation gets to the crystalline lens.

• A prolonged exposure to sunlight decreases the quantity of vitamin C in the aqueous humor.

IN CRYSTALLINE LENS (8)
The same as solar exposure can cause that your skin aged sooner, the same happens with the lens; it might suffer from a premature aging, because of the damages in DNA.

• Cataratas

IN RETINA (10)
Looking directly at sun (in a eclipse or not), without adequate eye protection, causes a photochemical damage of the photoreceptors, inducing a burn at macular level (area of maximum vision of the retina) and being the reason of an irreversible blindness.

• Early development of Macular degeneration
• Melanomas

A little bit of basic ocular anatomy… What is the eye surrounded by?

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As I wrote in the last post, in this one I am going to briefly explain those structures surrounding the eye; they are as important as the eye itself, because if any of them are not in perfect condition, the visual information can not be adequately processed.

LACRIMAL SYSTEM AND EYELIDS

EYELIDS protect the eye against any element that “wants” to get in. There is a reflex that cause that, when we simply touch the eyelashes, the eyelid closes. This is a “little inconvenience” when we want to position contact lenses onto the cornea (1) or simply when we need to put some drops on the eyes.
Also, they cover the eye when we sleep and, along with the pupil, control the quantity of light that gets into the eye.

If blinkings are not frequent (they are different in each people, but, the average frequency might be 1 blinking for every 5 seconds), the tear is not totally extended by all the cornea (1) and thus the cornea is not correctly lubricated, causing problems of clear vision, reddening and stinging of eye, discomfort with the contact lenses, and so on.
But all these problems are also caused, when the eyelids are not completely closed in each blink, that is, when we blink and the eyelids margins do not touch. Many people blink that way, and they do not know it. In fact, my eyelids blinked wrongly before I started my degree; one day, as I was doing my practice, one colleage let me know it.

People using computers in a frequent basis, usually suffer these problems and in general, everybody that work many hours doing tasks that involve looking at near distance. These people concentrate so much on their tasks, that they “forget” to blink. This paper shows an interesting guide about how to blink consciously the correct way so to automate it and thus to avoid present or future ocular problems.

The TEAR serves to protect the cornea, cleaning and moisturizing our eyes. The Lacrimal Glands (in upper eyelids) produce tears that flow over the cornea (1). The tears drain into two small openings at the inside corner of the upper and lower eyelids called the Lacrimal Puncta. The tears drain into the tear ducts (Canaliculus) and then into the Lacrimal Sac and finally into the back of your nose and throat (Nasolacrimal Duct). Now you can understand why when we cry, “we cry with our nose, too”.


If many tears are produced and they are not correctly drain (Epiphora), the tears will drain down the face rather than through the nasolacrimal system. It is the feeling that the eye is always watery, with many tears.
Sometimes an obstruction is present in any of these ducts owing to a infection, this causes an inflammation of Lacrimal Sac (Dacryocysititis). Some babies suffer this infection (20-30 percent) and some adults, mainly women, because of aging.

Besides the Lacrimal Gland, there are some sebaceous glands in the eyelids, that produce the lipid layer of the tear. If any of them gets blocked, it might cause the following disorders:

- Stye: It is a red lump in the eyelid margin, very painful. It is caused by an infection of the sebaceous glands at the base of the eyelashes, with more or less depth. If it is deep, its treatment is more difficult.
- Blepharitis: It is an inflammation and irritation of the margins of the eyelids, due to an allergic, infectious, seborrheic, irritable or mixed reason. It usually occurs in both eyes at the same time, and it is recurrent.
- Chalazion: It is a hard and painless inflammation of some little sebaceous glands in the eyelid margin. It usually disappears in a few months, but it sometimes remains, develops into a cyst and its size increases. When this occurs, it causes aesthetic problems and, what is worse, might compress the cornea and modify vision. If they are small, they usually just need a corticoids injection, but if they are big, sometimes a little surgery is required to extirpate them.


MUSCLES

In one hand, six EXTRAOCULAR MUSLES (EOM) are surrounding the eyeball and anchor it to the orbit. The extraocular muscles control eye movement and allow to lead them wherever we want (while reading, practicing sports, driving,…).


The Superior (2) (top) and Inferior (3) (bottom) Rectus Muscles control the eye’s vertical movement (up and down).
The Medial Rectus (4) and Lateral Rectus Muscles (5) control the eye’s lateral movement (from side to side).
The Superior Oblique (6) and Inferior Oblique Muscles (8) help rotate the eyes inward and outward in order to balance the sideways tilts of the head (they cause an opposite movement to eye).

All six of these extraocular muscles work together to move the eye. They coordinate so that the eyes are always aligned.

Any trauma in any orbit bone may cause a partial or total paralysis of any of these six muscles:
- If it is a partial paralysis we are before a Paresis or partial loss of movement owing to the weakness of one of them.
- If it is a total paralysis we are before a Paralysis or complete loss of the muscle function that causes restricted movement.
In any of these previous conditions, the eye movements in both eyes are not synchronous and thus cross-eyed or strabismus may appear and, consequently, double vision (but I will explain this later on).


In the other hand, we also have PALPEBRAE MUSCLES, which give eyes their shape and allow to open or close our eyes voluntary or involuntary manner.

If any of the muscles described is altered, it may cause the following conditions:
- The upper eyelid is dropped (Ptosis)
- When the previous condition happens or when there is a recession of the eyeball, the eyes seem smaller (Enophthalmos).
- Or, alternatively, when the eyes are more opened that what is usual or the eyeball bulges anteriorly out of the orbit, they seem bigger (Exophthalmos).
- The lower eyelid folds inward (Entropion), and this causes discomfort because the eyelashes rub against the cornea constantly (Trichiasis).
- Or, alternatively, the lower eyelid folds outward (Ectropion), drying the conjunctiva and the cornea, as the eye can not close totally (Lagophtalmos).


Well, my intention with this post is not for you learn these odd scientific concepts, but that these problems are familiar to you, and as with the previous post, if for whatever reason someone mentions these terms, you have where you can look them up to know what they talked about.


In the upsets of the palpebrae muscles I have preferred not to show directly the pictures just in case they are disgusting to any of you.

RELATED POSTS
A little bit of basic ocular anatomy… Eye or Ocular Globe
A little bit of basic ocular anatomy… The Retina.