Scheimpflug corneal topography takes two-dimensional optical cross-sectional images from the cornea with the help of a rotating camera. The Pentacam system generates three-dimensional images from the two-dimensional front and back surface images of the cornea. The total corneal densitometry measured with the Scheimpflug system is the sum of epithelial, stromal, and endothelial light scattering. Corneal densitometry software computes the corneal densitometry value based on measurements of light scattered back from the cornea over a 12 mm diameter area. Individual calculations are made in four concentric zones (0–2, 2–6, 6–10, and 10–12 mm) centered on the apex of the cornea.[8]. Values in the outermost zone of 10–12 mm were not included in the study because they had poor reliability and repeatability [8].
It is known that an increase in the space between collagen fibrils or an increase in the amount of keratocyte in the cornea increases corneal light scattering and thus corneal densitometry [9]. Many topical drugs used and diseases can affect the cornea and impair corneal health. Stimulation of keratocyte proliferation and activity due to prolonged use of topical IOP-lowering drugs leads to decreased cellular transparency[10] and increased reflectivity, as demonstrated by in vivo confocal microscopy[11]. Changes in corneal densitometry have been shown in corneal infections[12], and keratoconus[13].
All these studies reveal that corneal densitometry is a very sensitive indicator of corneal structural integrity, corneal health, or disease[12–15].
In our study, we aimed to evaluate possible changes in Scheimpflug corneal densitometry at 12 months after trabeculectomy in patients with POAG and to compare these measurements with healthy controls. Preoperative corneal densitometry values were found to be higher in glaucoma patients receiving medical treatment compared to healthy subjects. Long-term use of topical IOP-lowering drugs may have stimulated keratocyte proliferation and activity [10], which may be a reason for the increase in corneal densitometry. Postoperative corneal densitometry values were similar to normal cases in three different corneal regions compared with preoperatively.
The values at the 12th month after surgery were not different from the healthy group's corneal densitometry values. These results are likely to be with a better functioning endothelial cell and metabolic pump function at lower IOP levels, although there was no change in corneal thickness. Thus, corneal hydration, keratocyte activity, and corneal transparency can be achieved [16]. Another reason could be a reduced need for antiglaucoma medications following surgery. This eliminates the cumulative toxic effect of active compounds and their protective agents (BAC). In a potentially "healing" cornea, light backscatter and corneal transparency both change [17]. We believe that high intraocular pressure and the elimination of the negative effects of topical drugs on the cornea influenced our findings.On the other hand, these findings show that high IOP levels and the corneal effects of long-term use of topical antiglaucoma agents are reversible.
Total corneal densitometry is the sum of epithelial, stromal, and endothelial light scattering as measured by the Scheimpflug system [18]. In our study, we were able to evaluate backscatter in total corneal. Our study's limitation is that we were unable to evaluate these three distinct layers.Unfortunately, our device did not have a program to perform anterior, central, and posterior cornea segmentation, and it was paid. Lower IOP levels may result in improved endothelial cell and metabolic pump function, normalizing corneal hydration, keratocyte activity, and corneal transparency. Again, avoiding BAC can improve corneal epithelial health and thus corneal transparency. As a result, we believe that improved total densitometry results will reflect the health of all corneal layers.
In conclusion, corneal densitometry, an objective measure of corneal transparency, returns to normal in glaucoma patients 12 months after trabeculectomy surgery. This is due to a decrease in intraocular pressure and the discontinuation of topical antiglaucomatous agents, particularly those with preservative content. We can say that trabeculectomy surgery not only reduces intraocular pressure but also protects corneal health.