Oops, I squinted! Is it over after I “squinted”? Where did the foreign object that got into my eye go…

Autumn is here and the wind is getting cooler. It is still beautiful to go out and enjoy the autumn scenery during the National Day holiday. But you are the wind and I am the sand, and tears flow when they enter my eyes.

So, where do the sand, debris and other foreign objects that enter the eyes go? I believe many people have this question in their minds, so let's talk about it today.

Where do foreign objects go when they enter the eye?

First, let's understand the structure of our eyes. The conjunctiva is a thin, transparent mucous membrane that connects the eyelids to the eyeball. It is divided into the palpebral conjunctiva (a layer of conjunctiva inside the upper and lower eyelids, marked in green in the picture), the bulbar conjunctiva (a layer of mucous membrane on the surface of the white eyeball, marked in yellow in the picture), and the fornix conjunctiva (between the palpebral conjunctiva and the bulbar conjunctiva, marked in red in the picture). With the palpebral fissure as the opening and the cornea (marked in blue in the picture) as the base, these three types of conjunctiva form a semi-enclosed sac-like space, the conjunctival sac, and most foreign bodies enter our conjunctival sac.

Figure 1 The blue line represents the corneal surface, the green line represents the palpebral conjunctiva, the yellow line represents the bulbar conjunctiva, and the red line represents the fornix conjunctiva (Source: Reference 3)

Most foreign bodies will be located in the conjunctival sac of the lower eyelid after entering the ocular surface. Most of the foreign bodies in the conjunctival sac of the lower eyelid can be flushed out through protective mechanisms such as blinking and reactive tearing . In addition, the lower eyelid is relatively easy to open, and most people can also remove foreign bodies in the conjunctival sac of the lower eyelid in front of a mirror.

Some foreign bodies are located in the conjunctival sac of the upper eyelid, and the contact area between the upper eyelid conjunctiva and the cornea is large. Once the foreign body enters and adheres to the upper eyelid conjunctiva, it is easy to rub and irritate the cornea, causing a strong and persistent foreign body sensation, accompanied by eye pain, fear of opening the eyes, tears and other irritating symptoms. It is very difficult to completely turn up the upper eyelid by yourself. Some people are used to rubbing their eyes in an attempt to rub out the foreign body, but they do not know that rubbing the eyes will aggravate the damage of the foreign body to the corneal epithelium. Not only can the foreign body not be rubbed out, but the foreign body sensation and pain will become more and more severe .

Figure 2 Foreign body in the upper eyelid conjunctiva (Source: Reference 4)

A foreign body sensation ≠ a foreign body

Common foreign objects that enter the conjunctival sac include eyelashes, sand, small metal particles, plant debris, flying insect remains, contact lens fragments , etc.

Our eyes have a defense mechanism. When foreign matter enters the conjunctival sac, it will cause reactive tearing and frequent blinking. Some tiny foreign matter will be washed out of the eye with blinking and tears, so if a foreign matter suddenly enters the eye, you will feel much better after blinking a few times and shedding tears.

There are also some tiny foreign bodies hidden in corners and are difficult to find, and our eyes will produce secretions to wrap them. Even if they are not washed away by tears at the time, they will be discharged along with the eye secretions in the next few days.

Ophthalmology emergency departments often encounter patients with foreign bodies in their eyes, who rush to see the doctor in tears. Some patients have clear foreign bodies, and doctors can find the foreign bodies through slit lamp examination and remove them completely, and the discomfort symptoms are quickly relieved. Some doctors do not find clear foreign bodies, but patients just feel that there are "foreign bodies" in their eyes, and wonder if the foreign bodies have hidden behind the eyeballs and the doctors have not found them?

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If we look at the anatomical diagram of the conjunctival sac, we can see that the conjunctival sac ends at the front of the eyeball, so it is almost impossible for foreign matter to break through the barrier of the fornix conjunctiva and run to the back of the eyeball. So why do patients feel that there is a "foreign body" in their eyes?

To be precise, this is a foreign body sensation, which is one of the most common symptoms in ophthalmology. Having a foreign body sensation does not necessarily mean that there is a foreign body in the eye , especially when a foreign body enters the ocular surface, causing irritant conjunctivitis or corneal epithelial damage, which will not subside or heal so quickly after the foreign body is removed. It is normal for the foreign body sensation to last for several hours or even a day or two after the foreign body is removed, but this foreign body sensation generally has a clear trend of gradually easing and subsiding. If the foreign body sensation still persists and does not show a trend of easing, you need to see an ophthalmologist for a follow-up visit in a timely manner.

These 2 foreign bodies enter the eye

Be careful!

Of course, in daily life there are still some foreign bodies that do not enter the conjunctival sac. They enter the eyes at a certain speed and angle. They are not intercepted by eyelashes and eyelids and directly hit our black eyeballs and embed themselves on the surface of the black eyeballs. They are called corneal foreign bodies.

Corneal foreign bodies mostly come from rapidly projecting objects. The most common ones seen in outpatient clinics are the use of angle grinders, cutters, crushers, striking objects, etc., which cause metal (iron filings, aluminum filings) or non-metallic fragments (ceramic tiles, stones) to be projected onto the cornea.

High-risk people who use these machines often do not seek medical attention in time after symptoms appear, and only go to the ophthalmology department when obvious redness, eye pain, and decreased vision occur. At this time, metal corneal foreign bodies are often rusted and cause obvious corneal inflammation, infiltration, and even erosion, which increases the difficulty for doctors to remove corneal foreign bodies and increases the risk of corneal infection and even perforation. If the corneal foreign body happens to be located in the pupil area, the corneal scar formed later will permanently affect vision.

Figure 3: Corneal metal rust foreign body (Source: Reference 5)

Figure 4 Source of black foreign bodies under the cornea from the Merck Manual of Diagnosis and Treatment (Source: Reference 6)

If the foreign body is faster and more powerful, it is enough to penetrate our cornea and sclera and enter the eyeball and remain in the eyeball, which is called an intraocular foreign body. This is a very serious eye injury.

Among open ocular injuries, the incidence of intraocular foreign body injury is 18%~41%. According to the nature of the foreign body, intraocular foreign bodies are divided into two categories: magnetic foreign bodies and non-magnetic foreign bodies . Non-magnetic foreign bodies include metal foreign bodies (copper, zinc, aluminum, nickel, etc.) and non-metallic foreign bodies. In addition to stones, glass, plastics, slag, and ceramics, non-metallic foreign bodies also include plant foreign bodies (twigs, bamboo thorns, wheat awns, beans, paper scraps, etc.) and animal foreign bodies (eyelashes, insect limbs, hair, etc.). Intraocular foreign bodies destroy the integrity of the eyeball and are prone to cause infectious endophthalmitis, uveitis, severe visual impairment, etc., which are extremely harmful to the eyes and visual function. Once it occurs, it is necessary to seek medical attention as soon as possible and surgically remove the intraocular foreign body.

Figure 5 Orbital CT shows foreign bodies in the eye, showing metal artifacts. (Source: Reference 7)

Finally, here are two questions that everyone must want to know:

1. What should we do if foreign objects enter our eyes?

①Don’t rub your eyes, don’t rub your eyes, don’t rub your eyes.

② If you are crying a lot, let the tears flow for a while.

③If there is clean drinking water around you, you can try to rinse your eyes with water. When rinsing your eyes, pry open the lower eyelid. It would be best if you can completely lift up the upper eyelid. If not, do not force it.

④ If the foreign body sensation is significantly reduced after tearing or flushing the eyes, you can temporarily observe and do not need to rush to see a doctor. If the foreign body sensation is still strong, seek help from an ophthalmologist in time.

⑤ People who frequently operate angle grinders, cutters, and crushers should seek medical attention immediately if they experience a foreign body sensation that cannot be relieved.

⑥ There is a "folk method" of using "horsetail" or "hair" to scrape off foreign matter on the surface of the eye, but it is absolutely not advisable.

2. How to prevent foreign objects from entering the eyes?

① Reduce the time spent outdoors in windy weather.

② If you need to go out in windy weather, you can wear sunglasses for protection.

③ Wear goggles when operating angle grinders, cutters, crushers and other machines that are prone to projectiles.

References

[1] Ocular Trauma Group, Ophthalmology Branch, Chinese Medical Association. Expert consensus on the diagnosis and treatment of intraocular foreign body injuries in China (2021) [J]. Chinese Journal of Ophthalmology, 2021, 57(11): 819-824.

[2] Li Fengming, Xie Lixin. Chinese Journal of Ophthalmology[M]. 3rd edition. Beijing: People's Medical Publishing House, 2014:134.

[3]https://www.brainkart.com/article/Conjunctiva--Basic-Knowledge_25973/

[4]https://decisionmakerplus.net/dg-post/t15-12xs-foreign-body-in-conjunctival-sac/

[5]https://imagebank.asrs.org/file/16336/metal-foreign-body-on-the-cornea

[6]https://www.msdmanuals.com/professional/injuries-poisoning/eye-trauma/corneal-abrasions-and-foreign-bodies

[7]https://ar.inspiredpencil.com/pictures-2023/intraocular-foreign-body

Planning and production

Author: Liu Gang, deputy chief physician of ophthalmology, Qilu Hospital, Shandong University, Qingdao Branch

Review丨Liu Xiufen, deputy chief physician of ophthalmology, Bethune First Hospital, Jilin University

Planning丨Yinuo

Editor: Yinuo

Proofread by Xu Lai and Lin Lin