The endothelial cells pump fluid to keep the cornea clear. They act as a pump that controls how much fluid sits in the corneal layers. Clear layers let light pass and focus properly. When too many cells are lost, fluid builds up. The cornea then swells and turns cloudy, and vision drops. That is why the surgeon wants a cell count before surgery.
The number of endothelial cells is an indicator of corneal health. Cells that are too few, enlarged, or irregular can point to disease. They also warn that the cornea may not withstand the stress of eye surgery. Specular microscopy photographs these cells at great magnification so they can be counted. A slit-lamp attachment can take still photographs, or a video camera can display the cells on a screen. An image from that screen is saved in the medical record. The count helps the surgeon build a treatment plan. A very low count may push the surgeon to change technique or to warn the patient that the cornea may cloud after surgery.
Remember the endothelium as the cornea's water pump. Lose the pump and the cornea clouds, so a count taken before surgery can change the surgical plan. Handle the slit lamp gently and take a sharp, well-focused image, because blurred cells cannot be counted. Knowing what specular microscopy counts, and why, belongs to the biometry content area of the COA exam.
Incorrect Answers
- A. The cornea as a whole bends light, but that focusing power comes from its curved front surface. The endothelial cells help only by keeping the tissue clear enough for light to pass.
- B. The watery part of the tears comes from the lacrimal gland, which sits above and outside the eye. Corneal cells do not make tears.
- D. Pain and touch are carried by corneal nerves that run mostly in the front layers of the cornea. Sensation is not the endothelium's job, and it is not what a photograph counts.
Testing Pearls
- The corneal endothelium is the innermost cell layer and works as a fluid pump.
- Specular microscopy or photography magnifies those cells so they can be counted.
- Few, enlarged, or irregular cells suggest disease and a weaker response to surgery.
- Corneal swelling from pump failure makes the cornea cloudy and blurs vision.
- The count is taken before cataract or other intraocular surgery to judge how the cornea will cope.
References
- American Academy of Ophthalmology. Ophthalmic Medical Assisting: An Independent Study Course. Chapter 10, Adjunctive Tests and Procedures.
