Corneal Topography-Guided Penetrating Keratoplasty and Suture Adjustment

Post-penetrating keratoplasty astigmatism

Postoperative astigmatism is one of the common complications affecting visual outcomes after a penetrating keratoplasty. It can result from various factors related to host, donor and surgical technique, resulting in suboptimal visual outcome. While some of the measures taken during preoperative planning and during actual surgery can reduce the magnitude of postoperative astigmatism, postoperative correction of astigmatism is often required in cases with high degrees of astigmatism. When spectacles and contact lenses fail to provide optimal visual outcomes, various surgical techniques that include astigmatic keratotomy, compression sutures, toric intraocular lens placement, and laser refractive procedures can be considered. When none of these techniques are able to achieve a desired result with in the acceptable optical range, a repeat keratoplasty is considered a last option. We discuss the various causes and management of complication of postoperative astigmatism occurring after a full thickness corneal transplantation surgery.

Astigmatism Orientation After Deep Anterior Lamellar Keratoplasty for Keratoconus and Its Correlation With Preoperative Peripheral Corneal Astigmatism

PURPOSE

To evaluate the orientation of keratometric astigmatism (KA) after deep anterior lamellar keratoplasty (DALK) for keratoconus and its correlation with preoperative peripheral KA.

METHODS

This is a retrospective, single-center observational study including keratoconic patients undergoing DALK between January 2016 and January 2017 with regular astigmatism postoperatively. The orientation of postoperative KA was classified as with-the-rule (WTR), against-the-rule, or oblique and was correlated with the corresponding preoperative peripheral KA, calculated by the sinusoidal fitting of points of the axial keratometric power map at 8 mm diameter.

RESULTS

Forty-one keratoconic eyes were included, with the most common orientation of KA post-DALK being WTR (65.9%), followed by against-the-rule (19.5%) and oblique (14.6%). A significant correlation was found between preoperative peripheral KA and post-DALK KA regarding axis (P < 0.001, r = 0.88) and power (P = 0.0128, r = 0.23).

CONCLUSIONS

The axis of post-DALK astigmatism and to a lesser extent its respective power in keratoconic eyes can be predicted using the preoperative peripheral KA, with "WTR" being the most common astigmatic orientation.

Keratoconus: tissue engineering and biomaterials

Keratoconus (KC) is a bilateral, asymmetric, corneal disorder that is characterized by progressive thinning, steepening, and potential scarring. The prevalence of KC is stated to be 1 in 2000 persons worldwide; however, numbers vary depending on size of the study and regions. KC appears more often in South Asian, Eastern Mediterranean, and North African populations. The cause remains unknown, although a variety of factors have been considered. Genetics, cellular, and mechanical changes have all been reported; however, most of these studies have proven inconclusive. Clearly, the major problem here, like with any other ocular disease, is quality of life and the threat of vision loss. While most KC cases progress until the third or fourth decade, it varies between individuals. Patients may experience periods of several months with significant changes followed by months or years of no change, followed by another period of rapid changes. Despite the major advancements, it is still uncertain how to treat KC at early stages and prevent vision impairment. There are currently limited tissue engineering techniques and/or "smart" biomaterials that can help arrest the progression of KC. This review will focus on current treatments and how biomaterials may hold promise for the future.

Clinical validation of point-source corneal topography in keratoplasty

PURPOSE

To validate the clinical performance of point-source corneal topography (PCT) in postpenetrating keratoplasty (PKP) eyes and to compare it with conventional Placido-based topography.

METHODS

Corneal elevation maps of the anterior corneal surface were obtained from 20 post-PKP corneas using PCT (VU topographer, prototype; VU University Medical Center, Amsterdam, The Netherlands) and Placido-based topography (Keratron, Optikon 2000, Rome, Italy). Corneal surface parameters are calculated in terms of radius and asphericity. Corneal aberrations were characterized using standard Zernike convention. An artificial surface with quadrafoil feature (SUMIPRO, Almelo, The Netherlands) was measured and used as a reference to assess instrument performance compared with the gold standard.

RESULTS

The differences (mean ± std of PCT - Placido) found between the two types of topographers in measurements of post-PKP eyes are 0.02 ± 0.21 mm (p=0.64) for radius of curvature, 0.14 ± 0.49 (p=0.23) for asphericity, -0.19 ± 1.67 μm (p=0.61) for corneal astigmatism, -0.25 ± 1.34 μm (p=0.41) for corneal coma, 0.23 ± 0.82 μm (p=0.23) for corneal trefoil, and 0.15 ± 0.28 μm (p=0.02) for corneal quadrafoil. The PCT measured the artificial surface more accurate (rms error 0.16 μm; 0.12 eq. Dpt.) than the Placido-based topographer (rms error 1.50 μm; 1.15 eq. Dpt.).

CONCLUSIONS

PCT is more accurate than Placido-based topography in measuring quadrafoil aberration.

Timing of suture removal in sequential surgery: a pilot study

PURPOSE

To study the appropriate timing of corneal suture removal in sequential surgery (penetrating keratoplasty [PK]-phacoemulsification [PE]) procedures.

METHODS

In a pilot study, patients with a PK double running suture in place requiring cataract surgery were randomized to suture removal 1 month before PE or during PE (n = 14; 7 in each group). Visual acuity, refraction, manual keratometry, Pentacam analysis, biomicroscopy, biometry, endothelial cell count, and funduscopy were determined before suture removal/PE and after PE (except biometry). Outcome measures at 6 months were corneal refractive change (induced by PE plus suture removal) analyzed by conversion to corneal power vector, index of surface variance change, and postoperative spherical equivalent, corrected, and uncorrected visual acuity.

RESULTS

Average corneal refractive change induced was 1.63, -2.98 x 96 degrees in the preoperative suture removal group and 2.14, -2.84 x 90 degrees in the intraoperative suture removal group. Difference in parameters of the corneal power vector change were statistically significant but not clinically relevant (M, spherical component, 0.14 vs 0.72, P = 0.01, respectively; J, astigmatic component, 1.49 vs 1.42, P = 0.01, respectively). Postoperative spherical equivalent, index of surface variance change, and corrected and uncorrected visual acuity were not significantly different in the two groups.

CONCLUSIONS

Differences in refractive state and visual acuity of the eye are not observed between patients with PK continuous suture removal (1 month) before PE and during PE.

Importance of fixation, pupil center, and reference axis in ocular wavefront sensing, videokeratography, and retinal image quality

PURPOSE

To examine the impact of the location of the fixation target, pupil center, and reference axis of ophthalmic aberrometers and videokeratographers on the measurement of corneal aberrations relevant to vision.

SETTING

Clinical Research, Visual Optics Institute, College of Optometry, University of Houston, Houston, Texas, USA.

METHODS

The design features of a generic aberrometer and videokeratographer and their interaction with the eye were examined. The results provided a theoretical framework for experimental assessment of pupil translation errors on corneal aberrations relevant to vision and their correction in 129 eyes.

RESULTS

Two key principles emerged. First, the aberrometer's measurement axis must coincide with the eye's line-of-sight (LoS). Second, the videokeratographer's measurement axis (the vertex normal) must be parallel with the eye's LoS. When these principles are satisfied, the eye will be in the same state of angular rotation and direct comparison of measurements is justified, provided any translation of the pupil from the vertex normal is taken into account. The error incurred by ignoring pupil displacement in videokeratography varies between eyes and depends on the type of aberration and amount of displacement, with the largest residual correction root-mean-square wavefront error being 1.26 mum over a 6.0 mm pupil, which markedly decreases retinal image quality.

CONCLUSION

Translation of the pupil center with respect to the vertex normal in videokeratography should not be ignored in the calculation of the corneal first-surface, internal aberrations of the eye relevant to vision, or the design of refractive corrections based on videokeratography.

Refractive, topographic, tomographic, and aberrometric analysis of keratoconic eyes undergoing corneal cross-linking

PURPOSE

To report refractive, topographic, tomographic, and aberrometric outcomes 12 months after corneal cross-linking (CXL) in eyes with progressive advanced keratoconus.

DESIGN

Prospective, nonrandomized, single-center clinical study.

PARTICIPANTS

Twenty-eight eyes undergoing CXL between April and June 2006.

INTERVENTION

Riboflavin-ultraviolet A (UVA)-induced CXL included instillation of 0.1% riboflavin-20% dextrane solution 30 minutes before UVA irradiation and every 5 minutes for an additional 30 minutes during irradiation.

MAIN OUTCOME MEASURES

Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), sphere and cylinder refraction, topography, tomography, aberrometry, and endothelial cell count were evaluated at baseline and at 1, 3, 6, and 12 months follow-up.

RESULTS

Mean baseline UCVA and BSCVA were 0.17+/-0.09 and 0.52+/-0.17, respectively; 12-month mean UCVA and BSCVA were 0.27+/-0.08 and 0.72+/-0.16, a statistically significant difference (P<0.05). Mean spherical equivalent refraction showed a significant decrease of 0.41 diopters (D). Mean baseline simulated keratometry (SIM K) flattest and steepest meridians and SIM K average were 46.10, 50.37, and 48.08 D, respectively; at 12 months, 40.22, 44.21, and 42.01 D, respectively, were recorded, a difference that was significant for all 3 indices (P<0.05). Mean average pupillary power (APP) changed significantly from 47.50 to 41.04 D at 12 months (P<0.05) and apical keratometry (AK) from 58.94 to 55.18 D (P<0.05). The treated eyes showed no deterioration of the Klyce indices at 6 months postoperatively, whereas the untreated (contralateral) eyes did show deterioration. For a 3-mm pupil, there was a significant reduction (P<0.05) in whole eye (total), corneal, higher order, and astigmatic wavefront aberrations. A significant difference (P<0.05) in total coma and total spherical aberration after CXL was also observed. Mean baseline pupil center pachymetry and total corneal volume decreased significantly (P<0.05) to 470.09+/-29.01 microm and 57.17+/-3.21 mm(3) from baseline values of 490.68+/-30.69 microm and 59.37+/-4.36 mm(3), respectively. Endothelial cell counts did not changed significantly (P=0.13).

CONCLUSIONS

Corneal cross-linking seems to be effective in improving UCVA and BSCVA in eyes with progressive keratoconus by significantly reducing corneal APP, AK, and corneal and total wavefront aberrations at 1 year postoperatively.