Evaluation of Corneal Endothelium Function by Combined Measurement of Corneal Volume and Specular Microscopy before and after Phacoemulsification

BCVA improved in all operated eyes. Median preoperative BCVA was 0.1 as it ranged from 0.01 to 0.70, median postoperative BCVA was 0.4with range from 0.02 to 0.80. A statistically significant (P= 0.001) increase in BCVA occurred postoperatively , Table (3).

Table 4: Correlation between cell density changes and corneal volume changes. r: Spearman correlation test value.

Changes in CD were tested for correlation to changes in corneal volume. Results showed that cell density change has reverse proportional correlation with corneal volume change as decrease in cell density post-operative lead to significant increase in corneal volume, Table (4).

Figure 1: Correlation between cell density changes and corneal volume changes.

DISCUSSION

Phacoemulsification has already shown as a minimally invasive surgical method, Nevertheless, endothelial compromise does occur after phacoemulsification as a result of traumatic stress on the cornea .⁹ Corneal injury is still an important complication as phacoemulsification is performedeven in eyes with poor corneal endothelial reservoir or a hard lens nucleus .¹⁰

Assessment of corneal endothelial cell morphology and density helps to provide vital information concerning corneal endothelial viability and function. Furthermore, itis an acceptance factor in practice and research through providing valuable information on this layer.¹¹  Alterationsin Endothelial mosaic are considered essential indicators of surgical trauma and are important in estimation of the safety of different surgical techniques. ⁸

Despite importance of these measurements, but it remains an anatomical not functional evaluation. Furthermore, measurements cover a very small area in the central cornea and do not represent the entire cornea. So, functional evaluation methods were suggested.

Assessment of corneal thickness is also limited to the area of pacymetry and has the same limitations of specular microscopy, despite being a functional test. Fluorophotometry is an invasive technique and is a complex procedure to be done in common practice. So, none of these procedures alone can be considered the ideal for evaluation of corneal endothelial function.

Scheimpflug cameras allow a more detailed study of the anterior segment. Suzuki et al.⁵introduced an assay of corneal volume using Pentacam® (Scheimpflug based instrument) as a possible new method for assessment of corneal endothelial damageresulting from phacoemulsification. In our work, we have used Sirius® 3D Rotating Scheimpflug Camera & Topography System, a readily available device at our institution.

Investigators compared different Scheimpflug based instruments for anterior segment imaging. Baradaran-Rafii et al.¹² used two Scheimpflug camera machines; Galilei® and Pentacam® to measure and compare anterior segment indices. Analyzed parameters includedaxial curvature, anterior and posterior best fit spheres (BFS), central corneal thickness (CCT), true corneal power, pupil diameter , anterior chamber (AC) depth, AC angle and AC volume . They found that there was a significant correlation between the Pentacam® and Galilei® in all measured parameters apart fromaverage pupil diameter, AC volume and AC angle.

Anayol et al. ¹³ compared the central corneal thickness and the thinnest corneal measurement among Galilei®, Pentacam® and Sirius® devices and observed that interchangeable use of pachymetry measurements obtained by different devices is not possible. They found that the measurements by the Galilei® were significantly higher when compared with those obtained by either the Pentacam® or the Sirius® systems and showed that Pentacam® and Sirius® systems agreed better with each other than with the Galilei®. They added that, difference observed among different studies can be attributed to the various software versions used in each study.

Kirchhoff et al.⁹ measured 3-mm corneal volume changes after cataract surgery with Orbscan and reported that corneal volume increased at six hours post-operative , and did not return to preoperative levels by24 hours post-operative . Short term central changes were then confirmed by Suzuki et al. ⁵  where the increased corneal volume that noticed early within the first week in the 3-mm diameter area, almost returned to the preoperative values at 1 month follow up. On the other hand, corneal volumes of 10 mm central rings  at one month were still significantly higher when compared with the pre-operative volmes.

Studies on corneal volume changes agree with previous studies on corneal pachymetric changes. Ravalico et al. ⁸ reported that post-phacoemulsification central corneal thickness returned to preoperative levels within one month post-operative . Another report by Doganay et al. ¹⁴ revealed that endothelial changes occur due to mechanical as well as traumatic stress during phacoemulsification. Furthermore, previous reports of increased corneal thickness following phacoemulsification have described a variable post-operative increase in thickness and were associated with loss of endothelial cell, with most corneas returning to normal thickness by 1 month.

Based on these reports, we have chosen to measure the long lasting corneal volume changes at 1 month postoperatively over a wide diameter (10 mm) area to test for widespread endothelial dysfunction following phacoemulsification. Follow up period of 1 month durationmay be sufficient for subsidenceof surgery-induced thermal or mechanical stromal injury. Moreover,cases with epithelial edema(i. e., increased IOP) after surgery were excluded from the study. So, in our study, the persistently increased corneal volume at 1 moth after surgery should be solely due to endothelial dysfunction.

Through literature review, factors that affect the corneal endothelial cell density and morphology may include: corneal disease, glaucoma, pseudoexfoliation, history of trauma age, race, ocular surgeries (cataract, refractive) ¹⁵,Type 2 Diabetes Mellitus ¹⁶, Years of contact lens wear ¹¹ and phakic intraocular lens implantation.¹⁷

 Patients with ocular surgery, ocular or systemic disease known to affect corneal endothelium were excluded from the study. We excluded patients with preoperative CD less than 1500 cell/mm², such patients may be inappropriate candidates for phacoemulsification surgery. We also excluded patients with intra operative or postoperative complications that may compromise corneal endothelium.

 The major outcome parameters in our study included changes in: mean endothelial cell density (CD) and mean corneal volume.

 Our measurements showed that the mean CD decreased by about 13.28 %, drop in CD was statistically significant (p<0.001), Table (4).

Ravalico et al.⁸ reported that the percentage of cell loss was 10.1 % in the ECCE group and 8.5% in the phacoemulsification group at 30 days post-operative . Suzuki et al. ⁵ reported that the central CD decreased for each of the 3 participating surgeons,differences between surgeons were insignificant. Through their diagrams, decreased CD ranged from 4% to 11%. We noticed that, the third surgeon, who has the least CD drop, used ophthalmic visco surgical device Healon5 in comparison to Healon and Viscoat used by other surgeons. He also used the least instrument parameters settings in comparison to other surgeons. Despite differences in CD drop between surgeons were statistically insignificant, but unifying surgical details may be important to decrease bias.

Regarding corneal volume changes in our study, we reported an average increase in corneal volume of 2.58 mm³(4.55%) at 1 month postoperatively, a result that was highly significant statistically (p <0.001).

Results reported by other authors varied according to the postoperative period at time of measurement. Kirchhoff et al.⁹ reported a significant (p <0.001) increase in the corneal volume (15.5%) 6 hours after phacoemulsification. An average drop of 5.05 mm3 (6.01%) then happened within 24 hours (values returned to almost half between pre operativeand 6 hours postoperative values), volume drop was also significant (p <0.001). Increased corneal volume was slightly higher than increased corneal thickness that increased  postoperatively by 13.9% that then decreased within 24 hagain by 6.6%. In their work, Suzuki et al.⁵ reported results of increased corneal volume 1 month afte rphacoemulsification. Through their diagrams, the percentage of increased volume did not exceed 3% for any of the 3 participated surgeons. A result that was close to our results.

When we compared changes in CD to changes in corneal volume, results showed that cell density change has reverse proportional correlation with corneal volume change as decrease in cell density postoperatively lead to significant increase in corneal volume (P= 0.001).

Relatively similar results were reported by Lundberg et al.¹⁸, as they found a strong correlation between the central corneal swelling at day 1 postoperative and the central corneal endothelial cell loss at 3 months. Rather than the corneal volume, they measured the central corneal thickness using both ultrasound pachymetry and Orbscan II. They concluded that measurement of the difference in pachymetry at day 1 postoperative is a useful way for assessment of the effects induced by the phacoemulsification procedure on the corneal endothelium.

In contrary to our reported correlation, Suzuki et al.⁵ mentioned that increases recorded for the 10-mm corneal volumes occurred similarly with included surgeons although a little decreasing rate for the central CD was noticed with the third surgeon. The correlation between these two parameters was analyzed among all subjects, but no statistically significant correlations were found.

Later on, Suzuki et al.¹⁰ introduced the VSI and concluded that it can be  helpful in assessment of the corneal endothelium functions  following phacoemulsification. In their study, an immediate post-operative increase in the VSI with slow decreasing as time passed, suggesting significant changes in the the residual corneal endothelium function  following phacoemulsification until it reaches a constant level.

These findings support a previous report by Ravalico et al.⁸ who used Anterior segment fluorophotometry, endothelial specular microscopy and ultrasonic pachymetry for evaluation of corneal endothelial function following cataract surgery . Their results indicated a significant increase in the endothelial pump function 7 days following phacoemulsification. Another support was the increased polymegathism and pleomorphism after cataract surgery that was supposed to be an anatomical and functional compensatory mechanism for decreased CD. ¹⁹

The software of the instrument used in our work (Sirius®) permits measurement of the corneal volume over 10 mm diameter area. So, evaluation of the VSI was beyond our study, as the calculation of Volume Stress Index was performed using the central CD value combined with the value of 3.0 mm corneal volume. Moreover, the described method of calculating the SVI has supposed that the CD of the central 1 mm², as measured by available specular microscopes, is representative of CD over the central area of 3 mm diameter (> 7.0 mm²), such point of criticism for VSI is considerable.

CONCLUSION

The corneal volume increase in central corneal ring of 10 mm after phacoemulsification procedure can be agood indicator of the degree of the endothelial damage in the area so corneal volume evaluation is very important for accurate endothelial function evaluation and combined evaluation with specular microscopy and corneal volume is more beneficial and accurate than specular microscopy alone.