instrumental focus

An indispensable Technology

No longer complicated, specular microscopy becomes a mainstay.

PAUL KARPECKI, O.D., F.A.A.O.

The specular microscope is one of the most valuable instruments used in clinical practice. With it, most optometrists see a significant amount of anterior segment disease. In fact, it is quite surprising how often it helps us discover pathology, adjust patients' contact lenses or behavior, or simply track disease progression.

One of the most useful applications of the specular microscope is in the detection and management of endothelial disease. Endothelial disease has a variety of causes and the damage is irreversible, resulting in corneal edema, clouding, loss of vision and eventual decompensation. Because these cells seldom mitose, but rather spread to cover damaged areas of the cornea, cell count is essential to proper management, as is the quality of cell structure.

Endothelial cell features can only be observed with specular microscopy providing high magnification (approximately 200x) and high-definition. One such device that offers the latest in endothelial cell analysis is the CellChek XL system (Konan Medical USA, Torrence, Cal.)

Under the microscope

The CellChek XL has auto-focus to easily line up a specific location for precise imaging and hence measurements, regardless of the patients gaze position, and instantly acquires the image and data information. Once an image is captured, the microscope automatically archives the file on a 80GB hard drive, thus allowing the clinician to follow trends across multiple patient visits.

The CellChek XL

The device has two key measurement tools for specular microscopy; a screening mode (CellScreen) and a full specular microscopy scan. The screening mode helps us to determine who may need further specular testing, while the full scan provides cell count, polymegethism data (the change from the typical uniform cell size) and pleomorphism data (change from the typical hexagonal cell geometry of the cell).

The diagnostic device also gives pachymetry readings to correlate with the findings, such as corneal edema. Clinicians can then utilize the information to effectively diagnose or monitor progression of various corneal dystrophies, a poor contact lens candidate or one that may benefit from a different type of lens.

The microscope can identify patients at risk for endothelial decompensation with cataract surgery, or a history of iritis. For example, using the CellChek XL, we image all patients who are contemplating or currently wearing contact lenses. If we find a patient whose cell count is low, polymegethism is elevated or pleomorphism is low, we immediately educate the patient about the findings. Depending on the findings, we may advise the patient to consider a silicone hydrogel lens because of better oxygen permeability, or we may conclude that the patient is not a suitable candidate for contact lens wear.

Value in screening

In my practice, we also use the specular microscope to screen patients who are considering cataract surgery. Data from the device tell us if the patient's endothelial health will support an IOL procedure, or if Descemet's stripping with endothelial keratoplasty (DSEK) should be performed simultaneously. The microscope also can identify patients who have a history of iritis and are at risk for endothelial decompensation with cataract surgery.

Some refractive surgery patients' postoperative vision problems may have resulted from preoperative endothelial health issues.¹ The CellChek system could have helped identify these inappropriate LASIK candidates.

The CellChek also has been indispensable in helping us identify corneal edema, such as bullous keratopathy and persistent or unexplained corneal swelling or haze. In one case, where a patient was referred for Fuch's dystrophy, we determined that the patient actually had pigmentary dispersion.

From research to practice

Specular microscopy was once quite complex, and obtaining good measurements was difficult. The technology was primarily used in research and by cornea specialists, but it has now become a mainstream technology in primary eye-care practices because of the automated assessments and its ability to follow progression. With the cell counts and pachymetry data provided by this technology, we are better able to diagnose disease and manage everything from contact lens wearers and surgical candidates to patients with corneal dystrophies. OM

1. Ventura AC, Wäti R, Böhnke M. Corneal thickness and endothelial density before and after cataract surgery. Br J Ophthalmol. 2001 Jan;85(l):18–20.