The topographical map indicates any distortions or scarring in the cornea, with keratoconus revealed by a characteristic steepening of curvature that is usually below the centerline of the eye. The technique can record a snapshot of the degree and extent of the deformation as a benchmark for assessing its rate of progression. It is of particular value in detecting the disorder in its early stages when other signs have not yet presented. Stages
Once keratoconus has been diagnosed, its degree may be classified by several metrics:
The steepness of greatest curvature from mild (< 45 D), advanced (up to 52 D) or severe (> 52 D);
The morphology of the cone: nipple (small: 5 mm and near-central), oval (larger, below-center and often sagging), or globus (more than 75% of cornea affected);
The corneal thickness from mild (> 506 μm) to advanced (< 446 μm).Increasing use of corneal topography has led to a decline in use of these terms. Treatment
Lenses
In early stages of keratoconus, glasses or soft contact lenses can suffice to correct for the mild astigmatism. As the condition progresses, these may no longer provide the person with a satisfactory degree of visual acuity, and most practitioners will move to manage the condition with rigid contact lenses, known as rigid, gas-permeable, (RGP) lenses.
A dural arteriovenous fistula (DAVF) or malformation is an abnormal direct connection (fistula) between a meningeal artery and a meningeal vein or dural venous sinus. Signs and symptoms
The most common signs/symptoms of DAVFs are:
Pulsatile tinnitus
Occipital bruit
Headache
Visual impairment
PapilledemaPulsatile tinnitus is the most common symptom in patients, and it is associated with transverse-sigmoid sinus DAVFs. Carotid-cavernous DAVFs, on the other hand, are more closely associated with pulsatile exophthalmos. DAVFs may also be asymptomatic (e.g. cavernous sinus DAVFs). Location
Most commonly found adjacent to dural sinuses in the following locations:
Transverse (lateral) sinus, left-sided slightly more common than right
Intratentorial
From the posterior cavernous sinus, usually draining to the transverse or sigmoid sinuses
Vertebral artery (posterior meningeal branch)

Causes
It is still unclear whether DAVFs are congenital or acquired. Current evidence supports transverse-sigmoid sinus junction dural malformations are acquired defects, occurring in response to thrombosis and collateral revascularization of a venous sinus. Diagnosis
Cerebral angiography is the diagnostic standard. MRIs are typically normal but can identify venous hypertension as a result of arterial-venous shunting. Classification
Borden Classification
The Borden Classification of dural arteriovenous malformations or fistulas, groups into three types based upon their venous drainage:
Type I: dural arterial supply drains anterograde into venous sinus. Type II: dural arterial supply drains into venous sinus. High pressure in sinus results in both anterograde drainage and retrograde drainage via subarachnoid veins. Type III: dural arterial supply drains retrograde into subarachnoid veins. Type I
Type I dural arteriovenous fistulas are supplied by meningeal arteries and drain into a meningeal vein or dural venous sinus.