These discolorations have led to the term "sun fungus". Pathophysiology
In cases of tinea versicolor caused by the fungus Malassezia furfur, lightening of the skin occurs due to the funguss production of azelaic acid, which has a slight bleaching effect. Diagnosis
Tinea versicolor may be diagnosed by a potassium hydroxide (KOH) preparation and lesions may fluoresce copper-orange when exposed to Woods lamp. The differential diagnosis for tinea versicolor infection includes:
Progressive macular hypomelanosis
Pityriasis alba
Pityriasis rosea
Seborrheic dermatitis
Erythrasma
Vitiligo
Leprosy
Syphilis
Post-inflammatory hypopigmentation

Treatment
Treatments for tinea versicolor include:

Topical antifungal medications containing selenium sulfide are often recommended. Ketoconazole (Nizoral ointment and shampoo) is another treatment. It is normally applied to dry skin and washed off after 10 minutes, repeated daily for two weeks. Ciclopirox (ciclopirox olamine) is an alternative treatment to ketoconazole, as it suppresses growth of the yeast Malassezia furfur. Initial results show similar efficacy to ketoconazole with a relative increase in subjective symptom relief due to its inherent anti-inflammatory properties. Other topical antifungal agents such as clotrimazole, miconazole, terbinafine, or zinc pyrithione can lessen symptoms in some patients. Additionally, hydrogen peroxide has been known to lessen symptoms and, on certain occasions, remove the problem, although permanent scarring has occurred with this treatment in some people. Clotrimazole is also used combined with selenium sulfide. Oral medications are viewed as a second-line of treatment for pityriasis versicolor in the event of widespread, severe, recalcitrant or recurrent cases.
Diagnosis
AS is usually diagnosed through visual inspection by an ophthalmologist or optometrist using a slit lamp. Differential diagnoses
Several conditions can have a similar color and appearance. Limbus sign is caused by dystrophic calcification at the corneal limbus, and can be confused with AS in geriatric populations. Anterior embryotoxon is a congenital widening of the corneal limbus. Posterior embryotoxon is a congenital thickening and anterior displacement of schwalbes line.Other conditions with similar appearance, but differing in color are limbal ring, and Kayser–Fleischer ring. Treatment
In the elderly, arcus senilis is a benign condition that does not require treatment. The presence of an arcus senilis in males under the age of 50 may represent a risk factor for cardiovascular disease, and these individuals should be screened for an underlying lipid disorder. The opaque ring in the cornea does not resolve with treatment of a causative disease process, and can create cosmetic concerns. Epidemiology
In men, AS is increasingly found starting at age 40, and is present in nearly 100% of men over the age of 80. For women, onset of AS begins at age 50 and is present in nearly all females by age 90.