Friday, December 14, 2007

4.11 Broken windshields

Occasionally there are intriguing cases of blurred vision. And the reasons for which become obvious, once the optics is understood. It is all a matter of the broken windshield, i.e., the cornea, really.

Remember that the projection of images onto the retina requires that the cornea, the crystalline lens, and the vitreous all remain optically clear. Any opacities can cast shadows on the retina. The most obvious and commonly seen are cases of cataracts and floaters. Less obvious is corneal anomalies.

Here is one case with a chief complaint of glare. The cornea has previously undergone RK, i.e., radial keratotomy, with 8 incisions on the cornea:
Here you can see 4 bright radiating lines. They are part of the 8 RK incisions. The cornea is thinner under each cut thereby allowing more light to pass through. This is the reason why this patient sees star burst when looking at any point source of light, e.g., headlights from the approaching automobiles. The edges of the upper left incision is also irregular and it passes over the macula - not an agreeable situation for driving at night.

Yet another example is the multiple dark shadows seen in the image below:
And the source of these dark spots is shown in the following image:
The white areas are a form of corneal dystrophy. The opacities may decrease or increase in intensity causing vision change.

Other types of not-so-subtle broken windshields include:
This is a case of recurrent corneal erosion with pain and decreased vision. And in another, a very common case of superficial punctate keratitis (SPK):
The tiny green spots are areas with epithelial defects, often appearing in very dry eyes.

And of course there are infiltrates from inflammation due to contact lens over-wear:
In this case, an infiltrate slightly to the left of the pupillary area is detected.

Most superficial corneal defects from infection and inflammation can be treated medically and the recovery is almost all total.

Irregular corneas that severely limit vision from, e.g., keratoconus or corneal scarring, may need to be replaced with donor corneas.

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