June 2013 Online Photo Diagnosis
2013 Online Photo Diagnosis
Patrick J. Caroline, FAAO, & Mark P. André, FAAO
Changes in Keratoconus
1931, Professor Alfred Vogt at the University of Zurich described in
detail the classic biomicroscopic findings in keratoconus. Von der
Heydt and Appelbaum classified the corneal changes into seven
distinct types of tissue alterations. These changes may appear at
varying periods throughout the course of the condition and may not be
present in all cases of keratoconus.
month’s online photo shows vertical striae, a series of
parallel, whitish lines in the deep stroma. They are most likely
tension lines caused by apical stretching of the corneal lamellae and
are most often orientated vertically; however, they can often be
aligned in the meridian of the greatest curvature (Figure 1).
Figure 1. Vertical striae represent tension lines caused by apical stretching.
Most often the striae are seen in the region of the corneal apex
before it becomes densely scarred. Crossing systems of striae may
produce a lattice-like design (Figure 2).
Figure 2. The presence of vertical striae is often the first positive slit lamp finding noted in keratoconus.
As a rule, the lines do not
cross at the same level. Vertical or Vogt's striae can often be the
earliest slit lamp finding noted in keratoconus. Some clinicians
believe that the diagnosis of keratoconus cannot be made without the
presence of vertical striae.
the early stages of keratoconus, apical thinning is often difficult
to detect with the slit lamp. Other positive slit lamp findings often
precede that of apical thinning, and therefore other findings may be
more helpful in detecting early forms of the condition.
an eye that has advanced keratoconus is viewed in optic section, the
thickness of the corneal apex may be reduced to one-third that of the
periphery (Figure 3).
Figure 3. Optic section of a keratoconus eye with significant apical thinning.
It may be difficult to keep the entire section
in exact focus at one time because of the excessive corneal
curvature. In the later stages of the condition, this can lead to
Munson’s sign, in which an angular curve is present by the
lower lid margin when the patient looks down (Figure 4).
Figure 4. Munson’s sign in advanced keratoconus.
ring is a yellow-brown or olive green pigmented line that partially
or completely encircles the base of the cone (Figure 5).
Figure 5. Yellow-brown or olive-green pigmented iron line (Fleischer’s ring) in moderate keratoconus.
It is the
result of a deposition and collection of iron (haemosiderin) anterior
to Bowman's layer in the adjacent epithelium. The broken or
interrupted ring occurs in approximately 50 percent of keratoconus
cases, and the ring is often best viewed under blue light
illumination with the slit lamp (Figure 6).
Figure 6. A Fleischer’s ring is often best visualized under the blue light illumination of the slit lamp.
in Bowman’s Layer
opacities form at or near the apex of the cone and represent
structural breaks in Bowman's layer resulting in irregular
superficial opacities and scars (Figure 7).
Figure 7. In this case of unilateral keratoconus, the corneal opacities seen on the right eye (left images) represent structural breaks in Bowman’s layer. Note the normal thickness and optical clarity of the left eye (right images).
The opacities begin as grayish dots located at the level of Bowman's layer. Later, the
spaces between the opacities become opaque, and an irregular
superficial opacity forms (Figure 8).
Figure 8. Corneal histology shows the breaks in Bowman’s layer and the subsequent accumulation of fibrillar connective tissue within the spaces.
These changes result when
fibrillar connective tissue fills in the spaces where there are
ruptures in Bowman’s layer. In advanced cases, these may
account for a considerable loss of visual acuity secondary to the
induced, irregular astigmatism and loss of corneal clarity (Figure
Figure 9. In the advanced stages of the condition, the ruptures in Bowman’s layer can account for significant visual loss due to corneal opacification and induced irregular astigmatism.
Visibility of the Corneal Nerve Fibers
corneal nerve fibers may become more visible in certain cases of
keratoconus, seen as a network of grayish lines with corpuscle-like
nodes at the point of branching (Figure 10).
Figure 10. The corneal nerve fibers in keratoconus may be more easily visualized.
It is likely not because
the nerve fibers are more numerous, but only that they are more
easily seen due to density changes of the corneal nerve fibers.
Because a similar clinical picture is often seen in both normal
corneas and in keratitis (Figure 11), an increased visibility of the
corneal nerve fibers cannot be considered a singular distinction of
Figure 11. The increased visualization of the nerves is made possible by an increase in fibril density of the superficial nerve. In some cases the fibers can create localized elevations in the epithelium that will result in a negative staining pattern with fluorescein.
in Descemet’s Membrane
ruptures in Descemet's membrane occur in approximately 5 percent of
patients who have keratoconus. The ruptures are characterized by a
crescent-shaped tear in Descemet's membrane and endothelium at the
apex of the cone (Figure 12).
Figure 12. Ruptures or tears in Descemet’s membrane permit aqueous to pass into the stroma, resulting in significant corneal edema and opacification.
Aqueous from the anterior chamber
passes through the tear, resulting in corneal edema and opacification
(hydrops) (Figure 13).
Figure 13. Corneal histology of a rupture in Descemet’s membrane.
The extent of the opacification varies with
the size and extent of the rupture. In most cases the endothelium
recovers, and within days begins a slow but steady deturgescence of
the corneal opacification, a process that can take weeks to months
Figure 14. In most cases the endothelium recovers and the tear closes. The cornea then begins the slow weeks-to-months process of deturgescence.
Following resolution of the hydrops, the rolled edges
of the tear in Descemet's are visible. Corneas that do not regain
transparency may require corneal transplant surgery (Figure 15).
Figure 15. In some cases the cornea fails to clear and surgical intervention, in the form of a corneal transplant, is required.
brilliant reflex is seen at the apex of the cone and accounts for the
characteristic "dewdrop" or crystalline appearance. The
intensified reflective properties are related to the increased
curvature of the posterior corneal surface that may appear as a
convex mirror (Figure 16).
Figure 16. A bright reflex can be seen at the apex of the cone called the endothelial cup reflex. This is related to the increased curvature of the posterior corneal surface.
Keratoconus Case is Different
the years, the slit lamp has provided practitioners with tremendous
insight into the multitude of corneal changes that occur in
keratoconus. However, it is important to remember that the various
slit lamp findings may appear at different stages throughout the
course of the condition. In addition, not all of the classic slit
lamp findings may appear in every case of keratoconus.
A. Textbook and Atlas of Slit Lamp Microscopy of the Living Eye, J.
Springer, Berlin 1931.
der Heydt, R. Slit Lamp Observation in Keratoconus, Transactions of
the American Ophthalmologic Society 28: 352-361 1930.
A. Keratoconus, Achieves of Ophthalmology, 15 (5): 900-921, 1936
Contact Lens Spectrum, Volume: 28 , Issue: June 2013, page(s): 11