Welcome back. As we dive deeper into the eye,
we're going to be talking about, now, disease,
pathologies associated with the anterior chamber and uvea,
and we're going to start actually with corneal diseases.
So remember that the cornea is composed of a stratified squamous
non-keratinizing epithelium overlying a stroma and it has to be very clear,
it needs to be translucent to light.
At the same time, it needs to have some refractile properties.
So the organization of the cornea and the way that it's formed,
is actually quite important for normal focusing of light
and allowing light to come through and hit the retina.
There are a number of diseases that are indicated here in the red box
that can occur or can affect the cornea.
So pinguecula, pterygium, keratoconus, and band keratopathy,
and we're going to discuss those four in the following slides.
So pinguecula and pterygium are really degenerative conditions
affecting the conjunctiva and we'll start with pinguecula.
So the pinguecula is basically a little yellow patch on the bulbar conjunctiva,
so this is not the palpebral conjunctiva but the conjunctiva that's normally over the sclera,
over the whites of the eyes, and it's typically near the limbus
and it typically begins near the nasal side of the eye.
How is this happening?
Well, it's degenerative and the exposures to strong sunlight or dust or wind,
things that are going to be physically abrading or injuring potentially the surface of the corneum
and actually it's more of the conjunctiva than the corneum even in this case.
The pathology is related to degeneration of collagen fibers of the conjunctiva
and that degeneration of the collagen fibers there is going to give a coalescence,
a precipitation that we can visualize as to kind of a little yellow plaque.
The clinical manifestations, so usually when these occur, both eyes have been affected.
They've been out in the dust or the wind or in the strong sunlight together.
It tends to be stationary, it doesn't wander around on the eye
and it usually starts at the nasal side,
so in general, it may be cosmetically disfiguring or cosmetically unattractive,
but really doesn't have significant consequences in terms of the ability of the eye to see.
As opposed to a pterygium.
So a pterygium also involves the conjunctiva and it is a degenerative change,
but it's degeneration where the conjunctiva now
which is a highly vascularized membrane proliferates and it goes hyperplasia.
So what's causing this?
Same things as caused the pinguecula, exposure to strong sunlight, dry heat, dust, etcetera,
that's causing an inflammatory response that is then reflected in hyperplasia,
an overgrowth of the conjunctiva.
So this is actually something that will be felt in the eye and will have a foreign body sensation.
It can, actually, by having retractions, some scarring that happens secondary to the hyperplasia,
can actually cause double vision,
can actually pull the eye ever so slightly and so you don't get total axial alignment.
And it can also cause blurred vision if it gets involves over areas where light is coming through,
say it extends on to the pupil. So this is kind of a wing-shaped fold of conjunctiva over the corneum.
You can also have abnormal curvature of the cornea, this is keratoconus.
And there is severe thinning and bulging of the cornea, this eye,
instead of being round is almost pyramidal in shape.
The exact cause for keratoconus is not known.
It can be associated with a variety of either congenital defects
such as Down Syndromes or Ehlers-Danlos.
Can be associated with allergies, can be associated with inflammatory states
like retinitis pigmentosum. Peak incidents tends to be in the juvenile years from 10 to 25.
Clinical manifestations as you can imagine, the cornea is malshaped.
So now we're going to have abnormal refraction of light coming in,
so the vision will become blurred or distorted.
We will tend to have myopia because we will tend to focus the light not on the retina,
but before the retina so you'll tend to have more near-sightedness.
Because there is some asymmetry related to this, you may even have astigmatism,
and because of the malshape of the cornea, we will also pull on the muscle,
the smooth muscle that's going to be in the iris,
that will allow us to have normal miosis or mydriasis.
And so these patients typically have photophobia
because we have pulled open the muscles of the iris
and we have an enlarged pupil and they walk into bright light it's like, oh, my gosh.
So they will photophobia.
Band keratopathy is a complication of inflammation of the uvea.
It can also be caused because of glaucoma,
so increased pressure in the posterior chamber, anterior chamber;
and also by inflammation of the conjunctiva.
What it is, is as indicated here on the image,
it forms a band across the center of the cornea due to calcium deposition,
and clearly this is going to have an impact in the ability of the eye to transmit,
the cornea to transmit light appropriately.
There can be familial syndromes, genetic basis for this occurring,
and it can be a complication, an acquired complication of various metabolic situations
including hypercalcemia, too much calcium, hyperphosphatemia, and/or hyperuricemia.
Clearly, with this band of deposited calcium in the cornea,
you're going to have diminished visual acuity.
It will feel as if there's something there, so there will be a foreign body sensation
and again, we will tend to hold open the pupil and so there will be photophobia.
And with that, we've looked at diseases of the cornea specifically,
as well as some of the conjunctiva.