SCLERA

  Basic Knowledge, Function, Morphology, Neurovascular supply, 

    Examination Methods, Color Changes, 

    Staphyloma and Ectasia, Staphyloma, Ectasia, 

    Trauma, Inflammations, Classification

Sclera

Gerhard K. Lang

➽_Basic Knowledge

➽ _Function

The sclera and the cornea form the rigid outer covering of the eye

All six ocular muscles insert into the sclera

➽ _Morphology

The sclera is fibrous, whitish-opaque, and consists of nearly a cellular connective tissue with a higher water content than the cornea.

The sclera is thickest (1mm) anteriorly at the limbus of the cornea, where it joins the corneal stroma, and at its posterior pole.

It is thinnest (0.3mm) at the equator and beneath the insertions of the rectus muscles.

The site where the fibers of the optic nerve enter the sclera is known as the lamina cribrosa.

In the angle of the anterior chamber, the sclera forms the trabecular network and the canal of Schlemm.

The aqueous humor drains from there into the intrascleral and episcleral venous plexus through about 20 canaliculi

➽ _Neurovascular supply

Vortex veins and the short anterior and posterior ciliary arteries penetrate the sclera.

The ciliary nerves pass through the sclera from

posterior to anterior

➽_Examination Methods

  The anterior portion of the sclera about as far back as the equator can be examined directly with a slit lamp.

Evaluation of the sclera posterior to the equator requires indirect methods such as ultrasound.

Transillumination can provide evidence of possible abnormal changes in the posterior sclera.

However, thismethod is not as precise as an ultrasound study.

➽_Coluor changes

The sclera is normally a dull white, like porcelain.

Altered color suggests one of the following changes:

1)   _Conjunctival and/or ciliary injection and inflammation will give the sclera a red appearance.

2)   _A sclera that is very thin will appear blue because of the underlying choroid (this occurs in the newborn, in osteogenesis imperfecta, and following inflammation; see Fig 1).

3)   _In jaundice, the sclera turns yellow.

4)   _In ochronosis (alkaptonuria), the sclera will take on brownish color. 

This should be distinguished from pigmented changes in the conjunctiva.

➽_Staphyloma and Ectasia

Staphyloma refers to a bulging of the sclera in which the underlying uveal tissue in the bulge is also thinned or degenerated.

By far the most common form is posterior staphyloma in severemyopia, a bulging of the entire posterior pole of the eyeball (Fig. 6.1).

Staphyloma can also occur secondary to scleritis (see Fig. 6.4).

                          

Ectasia is a thinning and bulging of the sclera without uveal involvement, as can occur secondary to inflammation.

Both staphyloma and ectasia are secondary or incidental findings.

No treatment is available.

➽_Trauma

The sclera is frequently involved in penetrating trauma. 

Deep injuries that extend far posteriorly usually also involve the choroid and retina.

Surgery to treat larger injuries extending 8mmpast the limbus should also include a retinal repair

(retinal cryopexy or retinal tamponade).

➽_Inflammations

Inflammations are the most clinically significant scleral changes encountered in ophthalmologic practice.

They more often involve the anterior sclera (episcleritis and anterior scleritis) than the posterior sclera (posterior scleritis).

       

  ➽_Classification

Forms of scleral inflammation are differentiated as follows:

1)   _Location

Anterior or posterior—i.e., anterior or posterior to the equator of

the globe.

2)   _Depth

_Superficial (episcleritis)

_ Deep (scleritis)

3)   _Nature

_Diffuse (usually scleritis)

_ Circumscribed or segmental (episcleritis)

_ Nodular, with formation of small mobile nodules

   (scleritis and episcleritis)

_ Necrotizing (scleritis only)

_ Nonnecrotizing (scleritis only)

With Regards

   👨l_Abdulbast Al-gabry💫