Coats white ring

Coats white ring (Fig 6-4) refers to a small (1 mm or less in diameter) circular or oval area of discrete gray-white dots seen in the superficial corneal stroma and representing iron-containing fibrotic remnants of a metallic foreign body. Once these lesions mature and are free of any associated inflammation, they do not change; hence, therapy with corticosteroids or other anti-inflammatory agents is not indicated.

Spheroidal degeneration

Spheroidal degeneration is characterized by the appearance in the cornea, and sometimes in the conjunctiva, of translucent, golden-brown, spheroidal deposits in the subepithelium, Bowman layer, or superficial stroma (Fig 6-5). The condition has been reported under different names, including actinic keratopathy, climatic droplet keratopathy, Bietti nodular dystrophy, and Labrador keratopathy. In primary spheroidal degeneration, the deposits are bilateral and initially located in the nasal and temporal cornea. With age, they can extend onto the conjunctiva in the interpalpebral zone. The primary degeneration is unrelated to the coexistence of other ocular disease. In rare cases, generally in childhood, the spheroidal deposits extend across the interpalpebral zone of the cornea, producing a noncalcific band-shaped keratopathy. The etiology is controversial, but the deposits may develop from UV radiation–induced alteration of preexisting structural connective tissue components or from the synthesis of abnormal extracellular material in limbal conjunctiva. Secondary spheroidal degeneration is associated with ocular injury or inflammation. The deposits aggregate near the area of corneal scarring or vascularization. All cases show extracellular, proteinaceous, hyaline deposits with characteristics of elastotic degeneration; these deposits are thought to be secondary to the combined effects of genetic predisposition, actinic exposure associated with temperature extremes, age, and perhaps various kinds of environmental trauma other than sunlight, such as dust and wind. The deposit composition is not lipid, despite its “oil droplet” appearance. Medical therapy is not of much value, but ocular lubrication is recommended to address uneven layering of the tear film over affected areas. In cases of central corneal involvement, superficial keratectomy or phototherapeutic keratectomy (PTK) using an excimer laser may be indicated.

Figure 6-4 Coats white ring (arrow), which should not be confused with map-dot-fingerprint dystrophy.

(Courtesy of W. Craig Fowler, MD.)

Figure 6-5 Spheroidal degeneration.

(Courtesy of Cornea Service, Paulista School of Medicine, Federal University of São Paulo.)

Iron deposition

Most iron lines are related to abnormalities of tear pooling due to ocular surface irregularities (Fig 6-6). Often, the clinician can see these lines only by using red-free or diffuse illumination with a cobalt-blue filter before instilling fluorescein. A Fleischer ring, representing iron deposition in keratoconus, is one of many corneal iron lines associated with epithelial irregularities (see Chapter 7, Fig 7-27). This ring is extremely useful as a diagnostic sign in mild or early cases of keratoconus. The Hudson-Stähli line, generally located at the junction of the upper two-thirds and lower one-third of the cornea, is ubiquitous. Iron lines are also associated with keratorefractive surgery. Following radial keratotomy, visually insignificant iron lines are noted in the inferior paracentral cornea in approximately 80% of patients and are commonly characterized as a “tear star.” Corneal iron lines are summarized in Table 6-3.

Calcific band keratopathy

Calcific band keratopathy is a degeneration of the superficial cornea that involves mainly the Bowman layer. The degeneration begins as fine, dustlike, basophilic deposits in the Bowman layer. These changes are usually first seen peripherally, in the 3- and 9-o’clock positions. Eventually, the deposits may coalesce to form a horizontal band of dense calcific plaques across the interpalpebral zone of the cornea (Fig 6-7). Small cracks can occur in the band as a result of fractures in the calcium deposits. In addition, small, lucent holes, representing corneal nerves that penetrate the Bowman layer, can be seen throughout the opacity.

Figure 6-6 Iron deposition (iron line) (arrow) due to irregularity of the tear film, which results from subepithelial fibrosis.

(Courtesy of Robert W. Weisenthal, MD.)

Table 6-3 Corneal Deposits

The condition can be idiopathic, but the chief known causes are

• chronic ocular (usually inflammatory) disease such as uveitis in children, interstitial keratitis, severe superficial keratitis, and phthisis bulbi

• hypercalcemia due to hyperparathyroidism, vitamin D toxicity, milk-alkali syndrome, sarcoidosis, or other systemic disorders

• hereditary transmission (primary hereditary band keratopathy, with or without other anomalies)

• elevated serum phosphorus level with normal serum calcium level (may occur in patients with renal failure, particularly if they are not receiving appropriate treatment to lower serum phosphate concentrations)

• chronic exposure to mercurial vapors or to mercurial preservatives (phenylmercuric nitrate or acetate) in ophthalmic medications (the mercury causes changes in corneal collagen that result in the deposition of calcium)

• silicone oil, instilled in an aphakic eye

Figure 6-7 Band keratopathy, displaying a horizontal calcific plaque with a lucid interval between the limbus and small lucent holes representing corneal nerves that penetrate the Bowman layer.

Band keratopathy may also result from the deposition of urates in the cornea. The urates appear brown, unlike the gray-white calcific deposits, and may be associated with gout or hyperuricemia.

A workup (eg, serum electrolytes and urinalysis) to rule out associated metabolic or renal disease should be considered. Underlying conditions, such as keratoconjunctivitis sicca or renal failure, should be treated or controlled as much as possible, which may reduce or control the deposition of calcium or at least help reduce the recurrence of band keratopathy. The calcium can usually be removed from the Bowman layer by chelation with a neutral solution of disodium EDTA, which can be warmed to speed up the chemical chelation. The usual concentration of EDTA (0.05 mol/L), 0.5%–1.5%, can be obtained through a compounding pharmacy. The epithelium overlying the calcium needs to be removed before the chelating solution is applied. Any cylindrical tube that approximates the corneal diameter (eg, corneal trephine) can facilitate the process by acting as a reservoir to confine the chelating solution to the desired treatment area; however, this is not always necessary. With the reservoir in place, very gentle surface agitation with a truncated cellulose sponge (mechanical debridement) may further enhance the release of the impregnated calcium. Certain types of calcium deposits can be removed with forceps alone. In any case, the deposit should be excised carefully to avoid further damage to the Bowman layer. A fibrous pannus may be present along with extensive calcific band keratopathy, especially if silicone oil is responsible; neither EDTA nor scraping will remove such fibrous tissue. A bandage contact lens can be helpful postoperatively until the epithelium has healed. Band keratopathy can recur but may not do so for years, at which time the treatment may be repeated. PTK using an excimer laser is not advised as primary treatment, because calcium ablates at a different rate than stroma and thus could produce a severely irregular surface. If there is residual opacification after the initial EDTA chelation, PTK may be used.

Jhanji V, Rapuano CJ, Vajpayee RB. Corneal calcific band keratopathy. Curr Opin Ophthalmol. 2011;22(4):283–289.

Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.