Acutely or at the early sign includes painful, photophobic, red and watery eye. This is due to active corneal inflammation resulting in vascular invasion and stromal necrosis which can be diffuse or localized. This cause the pinkish discoloration of what was a clear transparent normal corneal tissue (called "Salmon patch of Hutchinson").

Chronically or the end result will cause blurring of vision secondary to corneal stromal scarring, presence of ghost vessel and thinning of the cornea especially if it involves the visual axis.

Interstitial keratitis (IK) is corneal scarring due to chronic inflammation of the corneal stroma. Interstitial means space between cells i.e. corneal stroma which lies between the epithelium and the endothelium. Keratitis means corneal inflammation.

Patients typically present within one week of surgery with eye pain, photophobia, conjunctivitis, or excessive tear production.

DLK is predominantly associated with Lasik, as the creation of a flap creates a potential space for cells to accumulate. Individuals with atopic conditions with pre-existing allergic conjunctivitis, or ocular rosacea, are more prone to developing the condition after surgery. Some authors have reported that moderate to severe eye allergies and chronic allergic conjunctivitis are an absolute contraindication to the LASIK procedure. This is in distinction to findings of earlier studies. Keratitis can also occur after photorefractive keratectomy (PRK), although because it occurs in the setting of infection, it is distinct from the sterile infiltrates of DLK. DLK can also occur following myopic keratomileusis, in which a disc of corneal tissue is removed, shaped and sutured back into place, although this technique is more historical, having been replaced by Lasik and PRK.

Neurotrophic keratitis (NK) is a degenerative disease of the cornea caused by damage of the trigeminal nerve, which results in impairment of corneal sensitivity, spontaneous corneal epithelium breakdown, poor corneal healing and development of corneal ulceration, melting and perforation.

Neurotrophic keratitis is classified as a rare disease, with an estimated prevalence of less than 5 in 10,000 people in Europe. It has been recorded that on average, 6% of herpetic keratitis cases may evolve to this disease, with a peak of 12.8% of cases of keratitis due to herpes zoster virus.

The diagnosis, and particularly the treatment of neurotrophic keratitis are the most complex and challenging aspects of this disease, as a satisfactory therapeutic approach is not yet available.

Corneal ulcers are extremely painful due to nerve exposure, and can cause tearing, squinting, and vision loss of the eye. There may also be signs of anterior uveitis, such as miosis (small pupil), aqueous flare (protein in the aqueous humour), and redness of the eye. An axon reflex may be responsible for uveitis formation—stimulation of pain receptors in the cornea results in release inflammatory mediators such as prostaglandins, histamine, and acetylcholine.

Sensitivity to light (photophobia) is also a common symptom of corneal ulcer.

In the acute stage of the disease, a catarrhal conjunctivitis is present, with signs of ocular pain, usually blepharospasm, increased lacrimation, and photophobia. Miosis is also usually present. After a few days, this will progress to a keratitis and iridocyclitis. Other ocular problems may also occur, including conjunctival and corneal oedema, and aqueous flare.

After an acute flare-up, no clinical signs of disease may be seen for a prolonged period, which can vary from a few hours to a few years. With frequent acute incidents, though, additional clinical signs may be seen, including anterior and posterior synechiae, poor pupillary responses, cataracts, and a cloudy appearance to the vitreous humour.

Corneal neovascularization (CNV) is the in-growth of new blood vessels from the pericorneal plexus into avascular corneal tissue as a result of oxygen deprivation. Maintaining avascularity of the corneal stroma is an important aspect of corneal pathophysiology as it is required for corneal transparency and optimal vision. A decrease in corneal transparency causes visual acuity deterioration. Corneal tissue is avascular in nature and the presence of vascularization, which can be deep or superficial, is always pathologically related.

Corneal neovascularization is a sight-threatening condition that can be caused by inflammation related to infection, chemical injury, autoimmune conditions, post-corneal transplantation, and traumatic conditions among other ocular pathologies. Common causes of CNV within the cornea include trachoma, corneal ulcers, phylctenular keratoconjunctivitis, rosacea keratitis, interstitial keratitis, sclerosing keratitis, chemical burns, and wearing contact lenses for over-extended periods of time. Superficial presentations of CNV are usually associated with contact lens wear, while deep presentations may be caused by chronic inflammatory and anterior segment ocular diseases.

Corneal neovascularization is becoming increasingly common worldwide with an estimated incidence rate of 1.4 million cases per year, according to a 1998 study by the Massachusetts Eye and Ear Infirmary. The same study found that the tissue from twenty percent of corneas examined during corneal transplantations had some degree of neovascularization, negatively impacting the prognosis for individuals undergoing keratoplasty procedures.

This classic herpetic lesion consists of a linear branching corneal ulcer (dendritic ulcer). During eye exam the defect is examined after staining with fluorescein dye. The underlying cornea has minimal inflammation.

Patients with epithelial keratitis complain of foreign-body sensation, light sensitivity, redness and blurred vision.

Focal or diffuse reduction in corneal sensation develops following recurrent epithelial keratitis.

In immune deficient patients or with the use of corticosteroids the ulcer may become large and in these cases it is called geographic ulcer.

Primary infection most commonly manifests as blepharoconjunctivitis i.e. infection of lids and conjunctiva that heals without scarring. Lid vesicles and conjunctivitis are seen in primary infection. Corneal involvement is rarely seen in primary infection.

A patient with TSPK may complain of blurred vision, dry eyes, a sensation of having a foreign body stuck in the eye, photophobia (sensitivity to bright light), burning sensations and watery eyes. On inspection with a slit lamp, tiny lumps can be found on the cornea of the eye. These lumps can be more easily seen after applying fluorescein or rose Bengal dye eye-drops. The lumps appear to be randomly positioned on the cornea and they may appear and disappear over a period of time (with or without treatment).

TSPK may affect one or both eyes. When both eyes are affected, the tiny lumps found on the cornea may differ in number between eyes. The severity of the symptoms often vary during the course of the disease. The disease may appear to go into remission, only to later reappear after months or years.

The symptoms of fungal keratitis are blurred vision, a red and painful eye that does not improve when contact lenses are removed, or on antibiotic treatment, increased sensitivity to light (photophobia), and excessive tearing or discharge. The symptoms are markedly less as compared to a similar bacterial ulcer.

Signs: The eyelids and adnexa involved shows edema and redness, conjuctiva is chemosed. Ulcer may be present. It is a dry looking corneal ulcer with satellite lesions in the surrounding cornea. Usually associated with fungal ulcer is hypopyon, which is mostly white fluffy in appearance. Rarely, it may extend to the posterior segment to cause endophthalmitis in later stages, leading to the destruction of the eye. (Note: Fungal endophthalmitis is extremely rare)

Keratitis is a condition in which the eye's cornea, the clear dome on the front surface of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following symptoms: pain, impaired eyesight, photophobia (light sensitivity), red eye and a 'gritty' sensation.

Equine recurrent uveitis (ERU), also known as moon blindness, recurrent iridocyclitis or periodic ophthalmia, is an acute, nongranulomatous inflammation of the uveal tract of the eye, occurring commonly in horses of all breeds, worldwide. The causative factor is not known, but several pathogeneses have been suggested. It is the most common cause of blindness in horses. In some breeds, a genetic factor may be involved.

Vernal keratoconjunctivitis (VKC) or spring catarrh is a recurrent, bilateral, and self-limiting inflammation of conjunctiva, having a periodic seasonal incidence.

According to Mackie's classification, neurotrophic keratitis can be divided into three stages based on severity:

1. "Stage I:" characterized by alterations of the corneal epithelium, which is dry and opaque, with superficial punctate keratopathy and corneal oedema. Long-lasting neurotrophic keratitis may also cause hyperplasia of the epithelium, stromal scarring and neovascularization of the cornea.

2. "Stage II:" characterized by development of epithelial defects, often in the area near the centre of the cornea.

3. "Stage III:" characterized by ulcers of the cornea accompanied by stromal oedema and/or melting that may result in corneal perforation.

Corneal ulcer, or ulcerative keratitis, is an inflammatory or more seriously, infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and the agrarian societies. In developing countries, children afflicted by Vitamin A deficiency are at high risk for corneal ulcer and may become blind in both eyes, which may persist lifelong. In ophthalmology, a corneal ulcer usually refers to having an infectious cause while the term corneal abrasion refers more to physical abrasions.

Signs and symptoms of corneal abrasion include pain, trouble with bright lights, a foreign-body sensation, excessive squinting, and reflex production of tears. Signs include epithelial defects and edema, and often redness of the eye. The vision may be blurred, both from any swelling of the cornea and from excess tears. Crusty buildup from excess tears may also be present.

"Acanthamoeba" keratitis is a rare disease in which amoebae invade the cornea of the eye. It may result in permanent visual impairment or blindness.

Some infections may scar the cornea to limit vision. Others may result in perforation of the cornea, (an infection inside the eye), or even loss of the eye. With proper medical attention, infections can usually be successfully treated without long-term visual loss.

Red eye, swelling of conjunctiva and watering of the eyes are symptoms common to all forms of conjunctivitis. However, the pupils should be normally reactive, and the visual acuity normal.

In the United States, it is nearly always associated with contact lens use, as "Acanthamoeba" can survive in the space between the lens and the eye. To prevent the condition, contact lenses must be properly disinfected before wearing, and should be removed when swimming or surfing.

However, there have been many cases of "Acanthamoeba" in those who do not wear contact lenses, elsewhere in the world.

Infectious keratitis can be bacterial, fungal, viral, or protozoal. Remarkable differences in presentation of the patient allows presumptive diagnosis by the eye care professional, helping in institution of appropriate anti-infective therapy.

Those with conjunctivitis may report mild irritation or scratchiness, but never extreme pain, which is an indicator of more serious disease such as keratitis, corneal ulceration, iridocyclitis, or acute glaucoma.

Thygeson's superficial punctate keratopathy (TSPK; also "Thygeson Superficial Punctate Keratitis") is a disease of the eyes. The causes of TSPK are not currently known, but details of the disease were first published in the Journal of the American Medical Association in 1950 by the renowned American Ophthalmologist, Phillips Thygeson (1903–2002) - after whom it is named.