Reviewing ocular specialty testing
Familiarize yourself with anterior and posterior testing in your practice
Endothelial cell count or specular microscopy determines the cell density of the corneal endothelial layer. The cell density of an eye will generally vary.
Most people in their 40s will have a cell density between 2,300 and 3,100 cells/mm2; patients in their 60s experience a cell density of 2000 to 2800 cells/mm2.
While cell loss may be a part of aging, patients may need to be monitored for potential development of Fuch’s dystrophy.
Corneal pachymetry measures cornea thickness and can play an important role in glaucoma diagnosis and in determining candidacy in refractive surgery.
The average corneal pachymetry reading is 540 µu. A thinner cornea may prevent a patient from having LASIK or could indicate a higher intraocular pressure (IOP) than Goldmann applanation tonometry would read.
Corneal topography maps the cornea. The two main methods of testing are Placido disc and Scheimpflug.
The three-dimensional image given by either method can show abnormal curvature, whether steep or flat, and can also track changes in the surface of the cornea. As with most things, red means “danger,” so large amounts of red in the image shows very steep curvature, which could indicate keratoconus.
Wavefront aberrometry can pinpoint potential visual problems in the eye’s refractive system. When light passes through the cornea and crystalline lens, rays can be distorted, resulting in diminished sight.
The pattern of aberrometry is a diagnostic tool to help determine candidacy of refractive procedures. It can also be useful in predicting positive outcomes of intraocular lens (IOL) upgrades.
Axial length measurements (A scans) provide the distance between the anterior pole of the eye and the retinal surface. This measurement is useful in calculating the IOL positioned during cataract surgery.