Long-term changes in corneal surface configuration after penetrating keratoplasty

Corneal topography in keratoconus evaluated more than 30 years after penetrating keratoplasty: a Fourier harmonic analysis

The aim of this observational study was to examine the characteristics of anterior and posterior corneal topography in keratoconic eyes more than 30 years after penetrating keratoplasty (PK). Patients who maintained clear grafts for more than 30 years after PK were included and divided into the keratoconus (KC) group or other diseases (Others) group, based on the primary indication. Twenty-six eyes of 26 patients were included. The KC group and the Others group included 14 eyes and 12 eyes, respectively. The KC group participants were younger at the time of surgery (P = 0.03). No differences were found in best-spectacle-corrected visual acuity, keratometric power, and central-corneal-thickness. Based on corneal topography using Fourier harmonic analyses, regular astigmatism in the anterior cornea was significantly larger (P = 0.047) and the spherical component in the posterior cornea was significantly lower (P = 0.01) in the KC group. The area under the receiver operating characteristic curve of the spherical component, regular astigmatism, asymmetry component, and higher-order irregularity were 66.07%, 63.10%, 57.14%, and 59.23%, respectively, in the anterior cornea and 80.65%, 52.98%, 63.10%, and 63.99%, respectively, in the posterior cornea. Our results suggested that Fourier harmonic analysis of corneal topography could be useful for patients with KC long after PK.

Effect of Simulated and Real Spherical and Astigmatism Defocus on Visual Acuity and Image Quality Score

SIGNIFICANCE

Image simulation is a useful and efficient tool to explore the impact of spherical and astigmatic blur on visual acuity (VA) and image gradation. It could help to design new optical corrections more efficiently and rapidly.

PURPOSE

The purpose of this study was to compare the effects of simulated (convolution by an artificial eye) and real spherical and astigmatic defocus on VA and image gradation.

METHODS

Experiments were performed under highly controlled conditions: dynamic correction of the subjects' aberrations at 1 Hz and application of an artificial pupil. In experiment 1, Landolt C VA was measured in various conditions of spherical and astigmatism defocus. The amounts of spherical or positive astigmatic defocus oriented at 45° that gives a Landolt C VA of 0.0, 0.2, and 0.5 logMAR were measured in experiment 2. In experiment 3, the subjects scored the quality of the perceived image (three high-contrast 0.4 logMAR letters) with a five-item continuous grading scale.

RESULTS

Simulated blur was always more detrimental than optical blur. We measured a difference of 0.08 ± 0.03 and 0.11 ± 0.05 logMAR between both conditions, respectively, in presence of spherical and astigmatism defocus. An average ± standard deviation difference of 0.16 ± 0.06 D (i.e., spherical defocus) and 0.24 ± 0.15 D (i.e., astigmatism defocus) was observed between simulated and real optics blur to provide a given VA. The differences of image quality score between both conditions were, respectively, 15.13 ± 9.63 and 13.33 ± 4.83 for spherical and astigmatism defocus. Most of the differences were statistically significant.

CONCLUSIONS

We observed a difference of about 20 and 35% between simulated and real optics blur, respectively, in presence of spherical and astigmatism blur. However, the difference between both methods remains equal to or below the clinically significant difference.

Visual outcome of penetrating keratoplasty, deep anterior lamellar keratoplasty and Descemet membrane endothelial keratoplasty

PURPOSE

A single-center, cross-sectional study was designed to assess and compare objective and subjective quality of vision of patients intervened with penetrating keratoplasty (PK), deep anterior lamellar keratoplasty (DALK) and Descemet membrane endothelial keratoplasty (DMEK).

METHODS

Forty-six patients previously intervened with PK (22 eyes), DALK (7 eyes) and DMEK (17 eyes) were recruited. Visual evaluation included spherical and cylindrical refraction, distance corrected visual acuity (DCVA), photopic contrast sensitivity (CS), optical quality, measured with the HD Analyzer (objective scattering index [OSI], MTF cut-off and Strehl ratio), and ocular and corneal aberrometry, measured with the KR-1W Wavefront Analyzer.

RESULTS

Statistically significant between-group differences were found in age (p=0.006, DMEK patients were older) and time since surgery (p<0.001, longest time for PK patients). No statistically significant differences were found in DCVA between the techniques. Between-group differences were encountered in CS at 12 (p=0.007) and 18 (p<0.001) cycles per degree, with DMEK and DALK obtaining the best and worst outcomes, respectively. Differences in optical quality were found between the techniques (OSI, p=0.004; MTF cut-off, p=0.048; Strehl ratio p=0.022), with DMEK displaying the best outcomes. Highest and lowest values in ocular and corneal aberrations were for DALK and DMEK patients, respectively. Between-group differences were found in corneal astigmatism (p<0.001; -3.31±2.00 D in PK; -2.68±0.94 D in DALK; -1.09±0.62 D in DMEK).

CONCLUSION

Overall, DMEK proved superior over PK and DALK in terms of quality of vision, with PK offering slightly better outcomes than DALK in most visual function parameters under evaluation.

Long-term changes in corneal endothelial cell density after repeat penetrating keratoplasty in eyes with endothelial decompensation

PURPOSE

To compare the longitudinal changes in corneal endothelial cell density (ECD) and the incidence of postoperative complications between eyes with endothelial decompensation after repeat penetrating keratoplasty (RPK) and those after primary penetrating keratoplasty (PPK).

METHODS

Fifty-seven eyes with endothelial decompensation scheduled for RPK (RPK group) and 57 eyes with endothelial decompensation scheduled for PPK (PPK group) were enrolled. Corneal ECD was evaluated using a specular microscope at 1, 3, 6, 9, and 12 months, and every 6 months until 60 months postoperatively. Visual acuity (VA) and incidence of graft failure, graft rejection, or marked increase in intraocular pressure were examined.

RESULTS

Corneal ECD decreased gradually and percentage of cell loss at 60 months was approximately 73% in both groups; these did not differ significantly between groups throughout the follow-up (P ≥ 0.2209). The incidence of graft failure (52.6% in the RPK group and 36.8% in the PPK group), immune rejection, and marked increase in intraocular pressure did not differ significantly between groups (P ≥ 0.0898), although corrected VA was worse in the RPK group. The most common cause of graft failure in both groups was late endothelial failure. The outcomes were not significantly different between eyes that underwent a first RPK and those that underwent a second or subsequent RPK.

CONCLUSIONS

Corneal endothelial cell loss and complications are comparable between eyes with endothelial decompensation after RPK and those after PPK, although VA is worse in eyes after RPK. The outcomes after a first RPK did not differ from those after multiple RPKs.

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.

Postkeratoplasty corneal wavefront analysis of selective suture removal

PURPOSE

To analyze the corneal wavefront higher order aberrations (HOAs) after penetrating keratoplasty and selective suture removal.

METHODS

All patients undergoing penetrating keratoplasty by the same surgeon (R.K.F.) using identical suturing technique were retrospectively identified. Corneal HOAs were calculated at the week 6, week 10, 6-month, and final postoperative visits and compared with simulated corneal astigmatism, surface regularity index, surface asymmetry index, and best-corrected visual acuity.

RESULTS

Ninety-two eyes were identified. Total corneal HOAs declined from the week 6 visit to the final visit (week 6: 0.65, final: 0.50, P = 0.041). Final visit linear regression demonstrated correlations of surface asymmetry index and surface regularity index with total corneal HOAs (R = 0.51 and R = 0.45, respectively). No relationship for simulated corneal astigmatism or vision was found with total corneal HOAs (R = 0.003 and 0.30, respectively).

CONCLUSIONS

Total corneal HOAs are increased in the early postkeratoplasty course, possibly representing the optical consequences of surface irregularity. Because simulated keratometry provides no information in regard to corneal HOAs, measuring HOAs may be indicated in select cases. Total corneal HOAs perhaps provide a clinical representation of irregular astigmatism. The visual significance of these total corneal HOAs was not evident.

A review of astigmatism and its possible genesis

Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various aspects of this refractive error. We examine the components of astigmatism and the research into the prevalence and natural course of astigmatic refractive errors throughout life. The prevalence of astigmatism in various ethnic groups and diseases and syndromes is also discussed. We highlight the extensive investigations that have been conducted into the possible aetiology of astigmatism, however, no single model or theory of the development of astigmatism has been proven conclusively. Theories of the development of astigmatism based on genetics, extraocular muscle tension, visual feedback and eyelid pressure are considered. Observations and evidence from the literature supporting and contradicting these hypotheses are presented. Recent advances in technology such as wavefront sensors and videokeratoscopes have led to an increased understanding of ocular astigmatism and with continued improvements in technology, our knowledge of astigmatism and its genesis should continue to grow.

Zernike versus Fourier treatment tables for myopic patients having CustomVue wavefront laser in situ keratomileusis with the S4 excimer laser

PURPOSE

To compare the efficacy, predictability, and safety of Zernike-based versus Fourier-based treatment tables in myopic eyes 1 year after CustomVue wavefront laser in situ keratomileusis (LASIK) using the S4 excimer laser (Visx).

SETTING

Department of Ophthalmology, Stanford University School of Medicine, Stanford, California, USA.

METHODS

A prospective analysis of 32 eyes of 16 patients with myopia who had CustomVue LASIK with the S4 excimer laser was conducted using Zernike or Fourier treatment tables. Mean spherical equivalent (SE), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and higher wavefront analyses were determined.

RESULTS

The mean postoperative SE was -0.27 diopter (D) +/- 0.41 (SD) in Zernike-treated eyes and -0.20 +/- 0.29 D in Fourier-treated eyes. Twenty-eight of 32 eyes were available for analysis. Ninety-two percent of eyes in the Zernike group and all eyes in the Fourier group had 20/20 or better acuity (P = .85). Seventy-nine percent and 92%, respectively, were within +/-0.50 D of emmetropia (P = .68). All eyes in the Zernike group and 93% of eyes in the Fourier group had no change or gained at least 1 Snellen line of BSCVA (P = .85). Mean higher-order aberration values (mum) in the Zernike group and Fourier group were as follows: total root mean square, 0.91 and 0.99, (P = 0.95); defocus, 0.71 and 0.74, (P = 0.98); astigmatism, 0.15 and 0.31, (P = 0.81); coma, 0.21 and 0.20, (P = 0.99); trefoil, 0.11 and 0.11, (P = 1); and spherical aberration, 0.17 and 0.30, (P = 0.85), respectively.

CONCLUSIONS

Myopic eyes that had CustomVue LASIK had better visual outcomes in the Fourier group than in the Zernike group. Higher-order wavefront aberration results were similar between the 2 groups.

Quality of vision and graft thickness in deep anterior lamellar and penetrating corneal allografts

PURPOSE

To compare visual function after deep anterior lamellar keratoplasty (DALK) with visual function after penetrating keratoplasty (PK) for keratoconus and correlate this with corneal thickness.

DESIGN

Retrospective case series.

METHODS

Twenty-three patients (32 eyes) with unilateral or bilateral DALK or PK for keratoconus were analyzed for visual quality after suture removal. Evaluation included measurement of visual acuity, contrast sensitivity, and higher order aberrations (HOAs) (WaveScan; Visx, Santa Clara, California, USA). Readings were performed with both spectacle and rigid contact lens correction of refractive error. Total and residual stromal thickness after DALK was measured using optical coherence tomography (OCT) and correlated to visual quality.

RESULTS

Eyes after PK had better visual acuity than eyes after DALK (P = .018). Subgroup analysis of DALK eyes revealed that the level of visual acuity was related to the thickness of residual recipient corneal stroma. Eyes with a recipient corneal bed thickness of <20 microm had visual acuities similar to eyes with a PK, whereas those with a recipient thickness of >80 microm had a significantly reduced visual acuity (P = .0009). Contrast sensitivity was similar in DALK and PK eyes. There was no significant difference in HOAs between eyes with DALK or PK.

CONCLUSIONS

These data suggest that the main parameter for good visual function after DALK for keratoconus is the thickness of residual recipient stromal bed. An eye with a DALK with a residual bed of <20 microm can achieve a similar visual result as a PK.

Simultaneous Versus Sequential Penetrating Keratoplasty and Cataract Surgery

PURPOSE

To compare the surgical outcomes of simultaneous penetrating keratoplasty and cataract surgery with those of sequential surgery.

METHODS

Thirty-nine eyes of 39 patients scheduled for simultaneous keratoplasty and cataract surgery and 23 eyes of 23 patients scheduled for sequential keratoplasty and secondary phacoemulsification surgery were recruited. Refractive error, regular and irregular corneal astigmatism determined by Fourier analysis, and endothelial cell loss were studied at 1 week and 3, 6, and 12 months after combined surgery in the simultaneous surgery group or after subsequent phacoemulsification surgery in the sequential surgery group.

RESULTS

At 3 and more months after surgery, mean refractive error was significantly greater in the simultaneous surgery group than in the sequential surgery group, although no difference was seen at 1 week. The refractive error at 12 months was within 2 D of that targeted in 15 eyes (39%) in the simultaneous surgery group and within 2 D in 16 eyes (70%) in the sequential surgery group; the incidence was significantly greater in the sequential group (P = 0.0344). The regular and irregular astigmatism was not significantly different between the groups at 3 and more months after surgery. No significant difference was also found in the percentage of endothelial cell loss between the groups.

CONCLUSION

Although corneal astigmatism and endothelial cell loss were not different, refractive error from target refraction was greater after simultaneous keratoplasty and cataract surgery than after sequential surgery, indicating a better outcome after sequential surgery than after simultaneous surgery.