T UBERÍA DE PVC CORRUGADO

This concept becomes easy to understand if one imagines the cornea as a silver mylar balloon. By looking at your reflection at the flat surface of the balloon, you will notice that the image can be distorted by either pulling or pushing the sides of the balloon, because by doing so, you change the curvature of the center. Always remember that the cornea is one whole integral structure. Flattening of one meridian causes a corresponding steepening in the meridian 90 degrees away and vice versa. This effect is seen in pterygium, scars from peripheral corneal perforations, effect of sutures after cataract surgery, peripheral thinning disorders and others.

Principles of Management:

Corneal scars, as a rule, are permanent. There are no medical therapies available to turn scar tissue to normal corneal tissue. Depending on the location, size and degree of visual involvement, management is geared towards two goals, either improvement of vision or cosmetic or both. To improve vision, management is usually surgical which may range from manual excision to laser removal to corneal transplantation. To improve appearance, corneal scars may be covered with cosmetic contact lenses, dyed by tattooing or by corneal transplantation. (Fig 19)

Corneal edema due to endothelial damage or dysfunction is also permanent because the cells do not regenerate. Definitive treatment is by doing a corneal transplantation. The role of medical therapy is to minimize pain and discomfort and to prevent secondary infections. If it is due to high eye pressure, then the therapy should be directed towards lowering the pressure to appropriate levels.

Corneal deposits due to systemic metabolic disorders or from corneal dystrophy may recur after a corneal transplant since the underlying condition is not corrected. Corneal transplantation is reserved only for those conditions with significant visual loss. Calcium deposits can be removed by chelation since the location is superficial while deeper ones like lipid and heme cannot be removed. Corneal transplantation may be the only option.

In treating corneal melting, the underlying etiology should immediately be addressed. Surgical management is usually done later to treat sequelae, unless it is for an emergency procedure to restore the integrity of the globe. Corneal transplantation is usually done.

Corneal masses are usually treated by surgical removal if the indications for surgery are present. Sometimes corneal grafts are also used to restore corneal clarity.

Dry eye syndrome is treated by using topical lubricating agents and/or by preserving existing natural tears by preventing tear drainage. With adequate lubrication, the health of the corneal epithelium will be restored.

Moreover, all other possible risk factors that may aggravate tear quality should be removed or minimized.

This principle also holds true in treating toxic keratitis.

There are several options when treating corneal disorders with abnormal shape or curvature in order to improve vision. Goal is to correct the refractive errors so that the image will be sharply focused on the retina.

This is done by employing optical appliances or by surgically altering the cornea so that the shape will be restored to normal. Depending on the indications, choices may include glasses and contact lenses, incisional or laser refractive procedures, or corneal grafting and transplantation.

SUMMARY

The main function of the cornea is to transmit and refract light. If the normal anatomy of the cornea is altered, it will lead to blurring of vision.

Disorders that can disrupt the normal transmission of light are corneal scars, corneal edema, corneal deposits, corneal melt and corneal tumors. Scars are caused by infection, trauma, exposure, vascularization or can be congenital. Corneal edema can be congenital, due to surgical and non surgical trauma or due to chronic glaucoma. Deposits in the cornea can be caused by metabolic products, calcium, hemoglobin, iron, lipids, proteins, amyloid and other amorphous substances. Corneal melting caused by vitamin A deficiency, chemical burn or autoimmune diseases can lead to permanent corneal scarring. Masses on the cornea like dermoid, pterygium and neoplasia can block the transmission of light or alter the shape of the cornea.

Disorders of the cornea that can disturb the refraction of light includes dry eye disease, corneal epithelial dysfunction, and corneal disorders that affect its normal size, shape and curvature.

Management of these disorders involves the restoration of the cornea’s normal anatomy primarily through corneal tissue transplantation; excision of abnormal growths or tissues; control or removal of etiologic and contributing factors; surgical interventions to improve corneal shape and curvature and use of optical appliances to enhance the transmission and refraction of light into the eye.

REFERENCES 1. Krachmer JH, Mannis MJ, Holland EJ. (eds) Cornea Vol 1 to 3.

2. Smolin G, Thoft RA. (eds) The Cornea 3rd ed.

SELF- TEST 1. The main refractive component of the eye is:

A. tear film B. cornea C. lens D. retina

2. The water content of the normal cornea is:

A. 60%

B. 67%

C. 78%

D. 90%

3. The following affects the normal refraction of light into the eye, EXCEPT:

A. quality of the corneal surface B. radius of curvature of the cornea C. index of refraction

D. color of the iris

4. The major causes of corneal scarring in the Philippines is/are:

A. corneal infection and trauma B. anterior segment dysgenesis C. Stevens Johnson Syndrome D. trachoma

5. Which statement about the corneal endothelium is FALSE?

A. the human corneal endothelium retains its mitotic activity throughout life

B. the corneal endothelium is responsible for actively pumping water out of the corneal stroma C. the corneal endothelium is a monolayer of cells lining the posterior surface of the cornea D. the corneal endothelium can be damaged by intraocular surgery

6. What is the main mechanism of corneal scarring in a patient suffering from measles?

A. direct invasion of the cornea by measles virus B. misdirection of eye lashes towards the cornea

C. exposure of the cornea due to poor lid closure with secondary bacterial infection D. deposition of blood in the cornea

7. Which substance is usually deposited at the Bowman’s Layer of the cornea?

A. iron B. lipid C. amyloid D. calcium

8. Peripheral corneal lesions can cause blurring of vision by:

A. blocking the transmission of light

B. inducing astigmatism by changing the central corneal curvature C. decreasing tear production

D. increasing central corneal thickness

9. Steepening of the cornea caused by keratoconus leads to what form of refractive error?

A. myopia and astigmatism B. presbyopia

C. hyperopia and astigmastism D. monocular diplopia

10. The following are treatments options on the cornea to improve vision, EXCEPT:

A. Hard contact lenses B. corneal transplantation C. excimer laser photoablation D. corneal tattoo

Answer to Self Test:

1. B 2. C 3. D 4. A 5. A

6. C 7. D

8. B

9. A

10. D

Pictures:

Fig. 1 Theory of Corneal Transparency Fig. 2 Radius of curvature the cornea

Fig. 3 (L) Typical appearance of corneal scar (R) Hypertrophic scar

Fig. 4 (L) Active fungal keratitis (R) Active bacterial keratitis

Fig. 5 (L) Corneal perforating injury (R) Sutured corneal perforating injury

Fig 6 Exposure keratopathy secondary to lagophthalmos due to CN 7 palsy

Fig. 7 Congenital hereditary endothelial dystrophy (CHED)

Fig. 8 Post cataract extraction corneal edema

Fig. 9 Corneal dystrophy (L) Granular Type 3 ( R ) Avelino Stromal

Fig. 10 Lipid keratopathy secondary to herpes simples keratitis

Fig. 11 Calcific band keratopathy

Fig. 12 Corneal staining secondary to heme deposition

Fig. 13 Autoimmune peripheral corneal melting

Fig. 14 Acute chemical burn

Fig. 15 (L) Dermoid Choristoma (C) Corneal and conjunctival neoplasia ( R ) Pterygium

Fig. 16 Dry eye disease with ocular surface damaged (stained with Rose Bengal dye)

Fig. 17 Severe dry eye disease with ocular surface damage due to Stevens-Johnson syndrome

Fig. 18 (L) Keratoconus with acute hydrops ( R) Slit lamp view of corneal profile in keratoconus

Fig. 19 Clear corneal graft. Post penetrating keratoplasty (full thickness corneal transplant).

Note radial 10-0 nylon sutures.

DISTURBANCE IN VISION