Causes of Eye Pain: What Your Eyes May Be Trying to Tell You

Eye pain is one of those symptoms I never think should be dismissed simply because it seems minor at first. I have found that people use the phrase “eye pain” to describe many completely different sensations: burning after hours in front of a computer, a sharp feeling as though something is trapped beneath the eyelid, pressure behind the eye, tenderness around the socket, throbbing associated with a headache, or deep pain that seems to come from somewhere inside the eye itself. Those differences matter because the causes of eye pain range from relatively simple surface irritation to conditions that need urgent medical attention.

What makes eye pain especially confusing is that the intensity of discomfort does not always tell me how serious the underlying problem might be. A tiny corneal abrasion can be extremely painful because the cornea is densely supplied with sensory nerves, while some potentially serious eye disorders may initially produce surprisingly subtle symptoms. Researchers studying ocular pain have also shown that eye discomfort can arise through different mechanisms, including direct stimulation of pain-sensitive tissues, inflammation, nerve injury, and abnormal processing of pain signals.

For that reason, when I think about the causes of eye pain, I look beyond the simple question of whether an eye “hurts.” I want to know where the discomfort is located, how quickly it started, whether vision has changed, whether the eye is red, whether light makes the pain worse, and whether symptoms such as headache, nausea, discharge, swelling, or pain with eye movement are also present. This article explains the major possibilities, the warning signs I would never ignore, how doctors investigate eye pain, and where nutritional supplements such as Retina Clear may—and may not—fit into an overall eye-health strategy.

Understanding What Eye Pain Can Actually Feel Like

One of the first things I pay attention to is the quality of the pain. Burning, stinging, scratchiness, grittiness, or the sensation of something being stuck in the eye often directs attention toward the ocular surface—the cornea, tear film, conjunctiva, or eyelids. Dry eye, environmental irritation, blepharitis, contact-lens problems, and corneal injuries commonly produce this type of discomfort. Dry eye in particular may cause burning, scratchiness, redness, blurred vision, and light sensitivity when the tears are insufficient or do not function properly.

A deeper aching or pressure sensation can point in another direction. Pain associated with inflammation inside the eye, severe increases in eye pressure, inflammation around the eye, or certain neurological problems may feel less like surface irritation and more like something occurring behind or inside the eyeball. Some people also describe pain when looking from side to side or moving the eye. That particular detail can be important because pain with eye movement may occur in some optic-nerve, orbital, or inflammatory disorders, especially when accompanied by altered vision.

I also keep in mind that the nervous system can blur the boundaries between eye pain, facial pain, and headache. Sensory pathways involving the trigeminal nerve serve large portions of the face, eye, cornea, and surrounding structures. As a result, migraine, cluster headache, sinus-related discomfort, trigeminal neuralgia, and other neurological conditions may produce pain that a person genuinely perceives as coming from the eye. Clinical studies of people presenting with eye pain have found both ophthalmic and neurological causes, reinforcing why the location of pain alone cannot establish a diagnosis.

The Most Common Causes of Eye Pain

When I look at the broad picture, disorders affecting the surface of the eye are among the most frequent reasons for eye discomfort. In a study examining more than 2,600 adults evaluated for eye pain at ophthalmology and neurology clinics, inflammatory eye conditions—including dry eye, blepharitis, conjunctivitis, keratitis, uveitis, chalazion, and scleritis—accounted for a large proportion of ophthalmic causes. The exact likelihood of any condition obviously varies between populations, but the study illustrates how many different disorders can generate a similar complaint.

Dry eye is particularly important because it can produce much more than a vague sensation of dryness. Tears provide lubrication, nourishment, protection, and a smooth optical surface. When tear production falls or tears evaporate too quickly, the exposed ocular surface can become irritated and inflamed. I may then notice burning, stinging, scratchiness, intermittent blurring, redness, sensitivity to light, or discomfort that increases during prolonged reading and screen use. Age, contact-lens use, certain medications, environmental conditions, autoimmune disorders, and problems affecting the eyelids or tear glands can all contribute.

Corneal problems are another major source of pain. The cornea is extraordinarily sensitive, so even a relatively small scratch can hurt far more than its size would suggest. Corneal abrasion may follow rubbing, a fingernail injury, dust, debris, plant material, or improper contact-lens handling. Keratitis— inflammation of the cornea—can be even more concerning, particularly when infection is involved. The National Eye Institute notes that contact-lens-associated infections are an important cause of keratitis and that corneal conditions can produce pain, redness, watering, light sensitivity, and blurred vision.

Eyelid disorders can also make an eye surprisingly uncomfortable. Blepharitis, clogged meibomian glands, styes, and inflammation around the lash line may disrupt the oily layer of the tear film. When that happens, tears can evaporate too rapidly and leave the corneal surface exposed between blinks. I may see crusting, irritation, swollen eyelid margins, burning, or fluctuating vision, especially first thing in the morning or after long periods of concentrated visual work.

Conjunctivitis is another familiar possibility, although itching and discharge can sometimes be more prominent than true pain. Viral and bacterial infections may produce redness and irritation, while allergic conjunctivitis typically creates itching, tearing, and swelling. Significant pain, major light sensitivity, or loss of vision is less typical of uncomplicated conjunctivitis and deserves closer evaluation because those symptoms can signal involvement of deeper or more sensitive eye structures.

To make the distinctions easier to understand, I find it helpful to compare some of the more recognizable symptom patterns. This is not a diagnostic chart—the same symptom can appear in several conditions—but it illustrates why accompanying symptoms are so valuable.

Dry Eye, Screen Use, and Eye Strain

Modern routines have made dry-eye-type discomfort and visual fatigue exceptionally familiar. When I concentrate on a computer, tablet, or phone for a long period, I tend to blink less often and sometimes less completely. That gives tears more time to evaporate and can destabilize the ocular surface. The National Eye Institute recognizes prolonged use of computers, tablets, and smartphones as one factor associated with dry-eye symptoms.

Traditional “eye strain,” or asthenopia, can produce aching around the eyes, tiredness, difficulty focusing, headaches, blurred vision, and discomfort after visually demanding work. Uncorrected refractive errors, poorly positioned screens, glare, inadequate lighting, long periods of close focusing, and problems coordinating the eyes can all contribute. Ordinary digital eye strain does not normally damage the eye, but repeated or severe discomfort can be a useful signal that the visual environment, glasses prescription, ocular surface, or focusing system needs attention.

What I would avoid doing is automatically blaming every case of eye pain on screen time. It is an easy explanation, particularly for people who spend most of the day on devices, but genuine eye disease can occur in someone who also happens to use a computer heavily. Persistent one-sided pain, substantial redness, worsening symptoms, pain with eye movement, severe light sensitivity, or loss of vision deserves more than a screen-break experiment.

Corneal Injury, Foreign Bodies, and Contact-Lens Problems

Whenever eye pain begins suddenly after something gets into the eye, I immediately think about the cornea. Dust, sand, metal fragments, makeup particles, fingernails, tree branches, and other materials can scrape the delicate corneal epithelium. Because corneal nerves are highly sensitive, the resulting pain can be intense and may be accompanied by uncontrollable tearing, blinking, redness, or difficulty keeping the eye open.

A sensation that something remains trapped under the eyelid may come from an actual foreign body or from a scratch that continues to stimulate the nerves even after the object has disappeared. This is why aggressive rubbing is something I would avoid. If chemicals enter the eye, the situation becomes even more urgent: immediate irrigation is generally the priority, followed by emergency medical guidance. Penetrating injuries, high-speed metal fragments, and significant blunt trauma also require professional evaluation rather than home treatment.

Contact lenses deserve special attention because they alter the environment immediately over the cornea. Sleeping in lenses that are not intended for overnight wear, poor lens hygiene, exposing lenses to contaminated water, wearing them beyond the recommended replacement schedule, or continuing to wear them through significant redness and pain can increase the risk of corneal infection. A painful red eye in a contact-lens wearer should be taken seriously, particularly if there is light sensitivity, discharge, or reduced vision.

Inflammation Inside the Eye: Uveitis and Scleritis

Some of the causes of eye pain arise deeper than the ocular surface. Uveitis is inflammation involving the uvea—the middle layer of the eye—and sometimes neighboring structures. Depending on which part of the eye is affected, symptoms can include eye pain, redness, blurred vision, floaters, and sensitivity to light. These symptoms may appear suddenly, and untreated inflammation can threaten vision.

Uveitis is particularly interesting because it is not a single disease with one cause. It may be associated with infections, inflammatory or autoimmune disorders, and other systemic diseases, while in some cases a clear cause is never identified. Conditions associated with uveitis can include inflammatory arthritis, sarcoidosis, Behçet disease, lupus, psoriasis, inflammatory bowel disease, certain infections, and other disorders. That connection is one reason an ophthalmologist may ask questions that initially seem unrelated to the eye, such as whether a patient has joint pain, skin problems, mouth ulcers, or a history of infection.

Scleritis is another inflammatory cause worth knowing about. The sclera is the tough white outer coat of the eyeball, and inflammation there can cause significant deep, boring pain and tenderness. Some forms are associated with systemic inflammatory disease. Deep pain that is intense, persistent, or accompanied by significant redness should not automatically be treated as ordinary irritation, because differentiating surface inflammation from deeper inflammatory disease usually requires an eye examination.

Glaucoma and Sudden Pressure-Related Eye Pain

The relationship between glaucoma and pain is often misunderstood. The most common form, open-angle glaucoma, typically progresses gradually and often causes no noticeable early symptoms. A person can therefore have glaucoma without experiencing painful eyes at all. That is why regular dilated eye examinations remain important, particularly for people with established risk factors.

Acute angle-closure glaucoma is different. In this situation, drainage of fluid from the front of the eye becomes abruptly blocked and eye pressure can rise quickly. The National Eye Institute lists intense eye pain, a red eye, blurred vision, and nausea among the warning symptoms that require immediate medical care. This is one of the situations in which waiting to see whether the eye feels better the next morning can be dangerous.

I also think it is important not to assume that a subjective feeling of “pressure behind the eye” automatically means elevated intraocular pressure. Migraine, sinus discomfort, eye strain, inflammation, and other conditions can create a pressure-like sensation. Actual eye pressure is measured using tonometry during an eye examination. Symptoms alone cannot reliably tell someone whether intraocular pressure is high, which is another reason persistent or unusual eye pain deserves objective evaluation.

Migraine, Headache, and Pain That Feels Like It Comes From the Eye

Not every painful eye has an eye disease. Migraine is a particularly important example because pain can concentrate around, above, or behind one eye. Depending on the individual, migraine may also involve nausea, sensitivity to light and sound, visual disturbances, or worsening pain with physical activity. In specialist studies of people presenting with eye pain, neurological causes—including migraine—have represented an important part of the overall diagnostic picture.

Cluster headache can produce an even more dramatic pattern, often causing severe unilateral pain centered around the eye together with tearing, nasal symptoms, eyelid changes, or agitation. Neuralgias and other facial pain syndromes can also be perceived around the eye because sensory pathways overlap. These disorders illustrate why an apparently healthy-looking eye does not necessarily mean the pain is imaginary or insignificant.

At the same time, I would never diagnose a new headache pattern by assumption. New severe headache with eye pain, vision loss, weakness, confusion, difficulty speaking, drooping of the face, a new unequal pupil, or other neurological changes requires urgent assessment. The objective is not simply to determine whether the eye itself is abnormal but to identify whether the pain reflects an ophthalmic, neurological, vascular, orbital, or systemic process.

Optic-Nerve and Neuropathic Eye Pain

Some eye pain originates from the nervous system rather than straightforward irritation or inflammation of the ocular surface. Optic-nerve disorders can produce pain, particularly discomfort associated with moving the eye, and may occur alongside changes in visual sharpness, contrast, or color perception. Because the optic nerve carries visual information from the retina to the brain, eye pain accompanied by a new reduction in vision deserves prompt evaluation, even when the front of the eye looks normal.

There is also growing recognition of neuropathic ocular pain. In these cases, abnormalities in sensory nerve function can cause burning, aching, sensitivity to wind or light, or severe discomfort that seems disproportionate to visible findings on a routine examination. Damage, inflammation, or altered signaling in corneal and trigeminal nerve pathways may contribute, and some people develop symptoms following ocular surface disease or eye surgery.

This area is important because simply adding more lubricating drops may not fully solve pain driven predominantly by abnormal nerve signaling. Researchers distinguish between nociceptive pain, in which active tissue irritation or injury stimulates pain receptors, and neuropathic pain, in which dysfunction or injury within the sensory nervous system itself contributes to the pain experience. Chronic eye pain can therefore require a broader, individualized strategy involving ophthalmology and, in selected situations, neurology or pain specialists.

Warning Signs I Would Never Ignore

Most episodes of mild eye irritation will not turn out to be medical emergencies, but the consequences of missing certain disorders are serious enough that I prefer a cautious approach. The National Eye Institute specifically advises urgent medical attention for intense eye pain associated with conditions such as acute angle-closure glaucoma, and it recommends urgent assessment for serious corneal symptoms or injuries.

I would be especially concerned when pain is sudden, severe, rapidly worsening, or accompanied by a significant change in sight. Marked light sensitivity, profound redness, nausea or vomiting, major trauma, chemical exposure, swelling around the eye, or inability to move the eye normally can also change the urgency considerably. A painful red eye in someone wearing contact lenses is another situation I would not casually ignore because infectious keratitis can potentially progress.

The warning signs I would treat particularly seriously include:

• Sudden or significant loss of vision together with eye pain
• Severe eye pain with a very red eye, blurred vision, nausea, or vomiting
• Significant trauma, a penetrating injury, chemical exposure, or an object embedded in the eye
• Severe light sensitivity, rapidly worsening pain, or inability to keep the eye open
• Painful redness in a contact-lens wearer, particularly with blurred vision or discharge
• Pain with eye movement accompanied by new visual loss or neurological symptoms
• Fever, major eyelid swelling, protrusion of the eye, or difficulty moving the eye
• A sudden severe headache associated with eye pain and neurological abnormalities

How Doctors Work Out What Is Causing Eye Pain

When I think about diagnosing eye pain, the medical history is almost as important as the eye examination. A clinician may want to know whether the discomfort started suddenly or gradually, whether one or both eyes are affected, whether vision has changed, what the pain feels like, whether light worsens it, and whether the patient uses contact lenses. Recent injury, eye surgery, medication use, allergies, autoimmune disease, infection, headache history, and neurological symptoms can all shift the diagnostic possibilities.

The physical examination can then narrow the field dramatically. Visual acuity may be tested first because a change in vision alters the level of concern. A slit lamp allows detailed examination of the eyelids, tear film, conjunctiva, and cornea. Fluorescein dye can reveal corneal abrasions and surface damage, while measurements of intraocular pressure can help identify pressure-related problems. A dilated examination allows the clinician to inspect deeper structures, including the retina and optic nerve.

Additional tests depend entirely on what the initial evaluation suggests. Dry-eye testing may include tear production, tear-film stability, and detailed assessment of the eyelids and ocular surface. The National Eye Institute describes slit-lamp examination, Schirmer testing, and tear break-up time among tools used when dry eye is suspected. Imaging, laboratory studies, neurological evaluation, visual-field testing, or other specialized investigations may be appropriate when inflammation, optic-nerve disease, orbital disorders, glaucoma, or systemic disease is suspected.

Treatment Depends on the Cause, Not Just the Pain

Something I think is crucial to understand is that eye pain is a symptom, not a diagnosis. Treating discomfort without identifying its source can sometimes mask the real problem. Mild dry eye may respond to artificial tears and environmental adjustments, while inflammatory dry eye may require prescription therapy. Corneal infections can require antimicrobial treatment, uveitis may require medications that control inflammation, and acute angle closure requires emergency pressure-lowering treatment.

This is also why I am cautious about using leftover prescription eye drops. Steroid eye drops, for example, can be valuable when prescribed for appropriate inflammatory conditions, but unsupervised steroid use can worsen certain infections and create other complications. Likewise, redness-relief drops are not a substitute for investigating a persistently painful red eye. The correct treatment can only be chosen once the likely cause has been established.

For chronic ocular discomfort, treatment sometimes has to address several factors simultaneously. A person may have tear-film instability, eyelid-gland dysfunction, inflammation, environmental triggers, and sensitized corneal nerves at the same time. Reviews of ocular surface pain therefore emphasize individualized and sometimes multimodal management rather than expecting one universal therapy to solve every painful-eye complaint.

Can Supplements Help? My Perspective on Retina Clear

Nutritional supplements occupy an interesting but sometimes misunderstood place in eye health. Nutrition unquestionably matters to the normal function of the eyes, retina, nerves, blood vessels, and other tissues. Certain vitamins, minerals, carotenoids, and fatty acids participate in biological processes important to vision. However, supporting nutritional health is very different from treating unexplained eye pain, and that distinction becomes especially important when supplements are marketed specifically for vision.

A product such as Retina Clear, for example, may be positioned as an eye-health supplement intended to complement a person’s nutritional routine. When I evaluate a formula like this, I would look closely at its exact ingredient list, serving sizes, manufacturer information, quality testing, warnings, and whether the amounts of individual nutrients are consistent with established safety guidance. I would not assume that the name “Retina Clear” itself establishes effectiveness, and I would not treat the product as a replacement for an ophthalmic examination.

The important question is what supplements can realistically accomplish. If a person’s diet is deficient in a nutrient essential to normal eye function, correcting that deficiency can obviously be relevant to overall health. Certain specific nutritional formulations have also been studied for particular diagnosed retinal conditions. That does not mean the same nutrients have been proven to relieve corneal injury, acute glaucoma, uveitis, optic neuritis, infection, migraine, or other causes of eye pain.

I therefore view Retina Clear—or any comparable eye supplement—as potentially supportive rather than therapeutic unless good clinical evidence exists for the exact formula and the exact condition being discussed. If the product contains antioxidants, carotenoids, vitamins, minerals, botanical extracts, or other nutrients, their effects should be considered individually rather than assuming that combining many ingredients automatically creates a clinically proven treatment. The evidence for one standardized formulation cannot automatically be transferred to a different proprietary blend.

Safety deserves equal attention. Supplements can cause adverse effects, duplicate nutrients already present in multivitamins, and interact with medicines or medical conditions. The U.S. Food and Drug Administration explains that dietary supplements are regulated differently from drugs and are generally not FDA-approved for safety and effectiveness before they are marketed. The FDA also recommends discussing supplement use with a healthcare professional.

For someone who has unexplained eye pain, my priority would therefore remain finding the cause first. No supplement should delay urgent evaluation of severe pain, vision loss, acute redness, trauma, infection, or neurological symptoms. Once serious causes have been ruled out and a diagnosis is established, a person can have a much more useful conversation with an ophthalmologist, optometrist, physician, or registered dietitian about whether Retina Clear or another nutritional product makes sense alongside—not instead of—evidence-based care.

Practical Ways I Protect My Eyes From Avoidable Irritation

Not every cause of eye pain can be prevented, particularly autoimmune inflammation, migraine, neurological disease, or inherited anatomical risk factors. Still, many everyday contributors to ocular-surface irritation are modifiable. I pay particular attention to hydration of the ocular surface, sensible screen habits, contact-lens hygiene, protective eyewear, and avoiding unnecessary exposure to smoke, strong airflow, dust, and irritants.

Screen-related discomfort is one area where small behavioral changes can make a meaningful difference. Taking periodic breaks from sustained near work allows blinking patterns to normalize and focusing muscles to relax. A comfortable viewing distance, an appropriate glasses prescription, controlled glare, and avoiding extremely dry airflow around the face may also reduce unnecessary strain. When dryness persists despite these adjustments, I would rather have the ocular surface examined than simply keep increasing the amount of over-the-counter drops.

A few habits I consider especially worthwhile are:

• Taking regular visual breaks during prolonged computer or phone use and consciously blinking more completely.
• Following contact-lens cleaning, replacement, and wear instructions carefully and never ignoring significant pain or redness while lenses are in use.
• Wearing appropriate eye protection during construction, yard work, sports, or tasks where debris can fly toward the face.
• Avoiding rubbing an eye that may contain a foreign body.
• Scheduling comprehensive eye examinations at intervals recommended for age, medical history, symptoms, and individual risk.
• Protecting the eyes from excessive smoke, wind, dust, and other sources of irritation whenever practical.

Why Persistent Eye Pain Deserves Proper Evaluation

One of the biggest mistakes I see people make with eye symptoms is waiting for a dramatic emergency before taking persistent discomfort seriously. Eye pain does not have to be unbearable to justify evaluation. Recurrent pain can interfere with reading, computer work, driving, concentration, sleep, and quality of life even when vision still seems normal. Chronic ocular surface and neuropathic pain research has increasingly emphasized that persistent eye discomfort can represent a genuine pain disorder requiring careful assessment.

At the same time, I would not want anyone reading an article like this to become frightened by every brief episode of irritation. The goal is perspective rather than alarm. Mild dryness after hours of computer work is very different from sudden severe pain with blurred vision and vomiting. A scratchy feeling in both eyes during allergy season creates a different clinical picture from deep pain in one eye with reduced color vision or marked sensitivity to light.

The most useful approach is to pay attention to the combination of symptoms, their severity, how quickly they appeared, and whether they are changing. Persistent discomfort merits routine professional evaluation, while severe or vision-threatening patterns deserve urgent care. That balance allows common problems to be managed sensibly without overlooking the relatively uncommon situations where time matters.

Final Thoughts on the Causes of Eye Pain

After looking at the many possible causes of eye pain, the main lesson I take away is that the symptom is far more varied than it initially sounds. Dry eye, digital strain, eyelid inflammation, corneal abrasion, contact-lens complications, infection, uveitis, glaucoma, migraine, optic-nerve disorders, and neuropathic pain can all produce discomfort around the eye, yet their treatment and urgency are very different.

I also think it is worth resisting the temptation to diagnose eye pain by a single symptom. A burning sensation might suggest dry eye, but the full picture matters. Pressure does not automatically mean glaucoma. Pain behind an eye does not automatically mean sinus trouble. And an eye that looks relatively normal from the outside can still be associated with neurological or deeper ophthalmic conditions. Vision changes, significant redness, severe pain, light sensitivity, trauma, nausea, or neurological symptoms should always raise the level of concern.

When symptoms are mild and clearly linked to temporary irritation, simple measures may be enough. When pain persists, recurs, intensifies, or appears with other warning signs, professional examination is the safer route. Supplements such as Retina Clear may have a place in a broader nutrition strategy for some people, but they should remain exactly that—supportive products, not substitutes for finding and treating the actual cause of eye pain.

Disclaimer

This article is intended for general educational and informational purposes only. It is based on established eye-health information and medical literature, but it is not designed to diagnose eye disease, determine the cause of an individual’s symptoms, or provide personalized treatment instructions.

Eye pain can occasionally signal a condition requiring urgent treatment. Anyone experiencing severe or rapidly worsening eye pain, sudden vision changes, major redness, trauma, chemical exposure, nausea or vomiting with eye pain, significant swelling, neurological symptoms, or other concerning changes should seek appropriate professional or emergency medical care rather than relying on information from an online article.

The discussion of Retina Clear and dietary supplements is also educational and should not be interpreted as a recommendation, endorsement, or guarantee of effectiveness. Supplement ingredients and formulations can change, individual responses vary, and supplements can interact with medicines or health conditions. Anyone considering an eye-health supplement should review the current label and discuss it with a qualified healthcare professional, particularly when an eye disorder has already been diagnosed.

References

The sources below were selected because they come primarily from the National Eye Institute, the U.S. Food and Drug Administration, PubMed-indexed medical literature, and peer-reviewed ophthalmology research rather than general health blogs or commercial supplement websites. They provide the evidence base used to develop the medical information in this article.

The National Eye Institute resources are particularly useful for understanding dry eye, corneal disease, uveitis, glaucoma, symptoms requiring urgent treatment, and diagnostic testing. The PubMed-listed studies provide additional clinical context on ocular surface pain, neuropathic pain, referred eye pain, and the differential diagnosis of pain around an apparently normal eye.

For supplement-related statements, I relied on FDA information describing the regulation and safe use of dietary supplements. These sources are included because understanding the difference between dietary supplementation and medical treatment is especially important when discussing unexplained eye pain.

1. National Eye Institute — Dry Eye
   Symptoms, causes, diagnosis, and treatment of dry eye disease.
   National Eye Institute: Dry Eye
2. National Eye Institute — Causes of Dry Eye
   Evidence-based information on medications, health conditions, age, and other factors that can contribute to dry eye.
   National Eye Institute: Causes of Dry Eye
3. National Eye Institute — Testing for Dry Eye
   Overview of slit-lamp examination, Schirmer testing, and tear break-up time.
   National Eye Institute: Testing for Dry Eye
4. National Eye Institute — Corneal Conditions
   Medical information on corneal injuries, keratitis, dry eye, allergies, symptoms, and circumstances requiring urgent care.
   National Eye Institute: Corneal Conditions
5. National Eye Institute — Uveitis
   Information on uveitis symptoms, causes, complications, diagnosis, and treatment.
   National Eye Institute: Uveiti
6. National Eye Institute — Glaucoma
   Evidence-based overview of glaucoma, including emergency symptoms associated with acute angle closure.
   National Eye Institute: Glaucoma
7. National Eye Institute — Glaucoma and Eye Pressure
   Explanation of intraocular pressure, aqueous-fluid drainage, optic-nerve damage, and glaucoma risk.
   National Eye Institute: Glaucoma and Eye Pressure