At the ophthalmology clinic, 61-year-old Pedro presents with vision impairment that has been progressive over the past couple of years. He denies experiencing any pain. His past medical history is significant for type 2 diabetes mellitus. Physical examination shows bilateral clouding of the lens.
Next to him, 68-year-old Eileen comes in. She complains that, about an hour ago she started experiencing excruciating pain in her right eye, accompanied by blurry vision and seeing halos around bright lights. Eileen also tells you that she has since vomited twice. On clinical examination, her right eye is red, with a dilated pupil that fails to react to light. Her left eye appears unremarkable.
Based on the initial presentation, both Pedro and Eileen have some form of eye condition. But first, a bit of physiology. If we take a closer look at a cross-section of an eye, we can see that it’s split into three different chambers: anterior, posterior, and vitreous. The anterior chamber includes the area from the cornea to the iris. The posterior chamber is a really narrow space between the iris and the lens. Finally, the much larger vitreous chamber includes the space between the lens and the back of the eye.
Now, both the anterior and posterior chambers are located in the anterior segment of the eye, while the vitreous chamber is part of the posterior segment of the eye. Both chambers in the anterior segment, that is, the anterior and posterior chambers, are filled with a clear watery fluid called aqueous humor, while the vitreous chamber is filled with a clear but thicker fluid called the vitreous humor.
Okay, let’s start with what’s probably the most common group of eye conditions, so refractive errors. Normally, when the eye is in a relaxed state, the refractive power of the cornea and lens help focus light onto the retina. The retina is like a movie screen and the distance from the projector is the axial length of the eye. If it’s too close or too far from the projector, the image will end up looking blurry or out of focus. When the lens and cornea can focus light perfectly on the retina, it’s called emmetropia.