Control of astigmatism aided by intraoperative keratometry

Penetrating Excimer Laser Keratoplasty with vs without the Homburg Cross-Stitch Marker in Inexperienced Surgeons

BACKGROUND AND OBJECTIVES

The Homburg cross-stitch marker, according to Suffo, was developed in 2017 in the Department of Ophthalmology at Saarland University Medical Center. With this instrument, a surgeon can precisely define and mark the points of the first and second continuous cross-stitch sutures, according to Hoffmann. The aim of this retrospective study was to compare the functional outcomes of Hoffmann's double continuous cross-stitch suture in penetrating keratoplasty (PKP) with vs without the Homburg cross-stitch marker in inexperienced surgeons.

METHODS

A total of 130 eyes from 130 patients with central corneal scars, corneal dystrophies and advanced keratoconus were included. All eyes underwent elective excimer laser-assisted penetrating keratoplasty (excimer laser PKP) with a diameter of 8.0/8.1mm. In 65 eyes each, surgery was performed without (group 1) or with (group 2) the Homburg cross-stitch marker. Corrected distance visual acuity, topographic astigmatism, and refractive cylinder were obtained 6 weeks, 10 months post-PKP as well as 6 weeks after the first and after the second suture removal, respectively. The rate of early postoperative single interrupted suture addition was compared between the two groups.

RESULTS

Visual acuity, astigmatism and refractive cylinder values were significantly more favorable in group 2 (with device) compared to group 1 (without device) before and after suture removal. Postoperative single interrupted suture addition was performed in 34.4% of patients in group 1 compared to 10.6% in group 2 (P = 0.001, Fisher's Exact Test).

CONCLUSION

The use of the Homburg cross-stitch marker for excimer laser PKP in young cornea specialists results in significantly better visual acuity before and after suture removal, significantly lower astigmatism and cylinder value before suture removal, as well as a reduced necessity of early postoperative single interrupted suture addition.

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.

"Harmonization" of donor and recipient tomography in corneal transplantation

The applicability of donor and recipient tissue matching in corneal transplantation ("harmonization") to reduce residual astigmatism after keratoplasty was simulated using Matlab software. The height profile of the donor and recipient corneas was measured using the anterior segment optical coherence tomography (AS-OCT) Casia 2. After best fit of the donor button in the recipient bed the mean height difference as the mismatch, which had to be minimized, was derived from the height profile of the donor and recipient corneal front and back surfaces. The donor button was rotated in the recipient bed to extract the best fit situation where the mean height difference was minimized. After successful simulation, the procedure will be transferred to real measurement data.

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.

A new technique to mark the donor and host corneas in keratoplasty

A new technique is described to easily and accurately mark the donor and the host cornea in keratoplasty using simple, readily available instruments and utilizing a simple mathematical equation. This technique will allow for even distribution of the donor tissue in the recipient bed.

[The penetrating keratoplasty. A 100-year success story]

Ten precautions for prophylaxis of astigmatism in penetrating keratoplasty are recommended:1. The attempt should be made to determine donor topography for exclusion of previous refractive surgery, keratoconus/high astigmatism, and to allow for "harmonization" of donor and recipient topography.2. Donor and recipient trephination should be performed from the epithelial side with the same system, which is the prerequisite for congruent cut surfaces and angles in donor and recipient. For this purpose an artificial anterior chamber is used for donor trephination.3. Orientation structures in donor and host facilitate the correct placement of the first four or eight cardinal sutures to avoid horizontal torsion.4.A measurable improvement seems to be possible, using the Krumeich guided trephine system (GTS), the second generation Hanna trephine, and the Erlangen technique of nonmechanical trephination with the excimer laser.5. Horizontal positioning of the head and limbal plane are indispensable for state-of-the-art PKP surgery in order to avoid decentration, vertical tilt, and horizontal torsion.6. Graft size should be adjusted individually ("as large as possible, as small as necessary").7. Limbal centration should be preferred over pupil centration (especially in keratoconus).8. Excessive graft over- or undersize should be avoided to prevent stretching or compression of peripheral donor tissue.9. As long as Bowman's layer is intact a double running cross-stitch suture (according to Hoffmann) is preferred since it results in higher topographic regularity, earlier visual rehabilitation, and less suture loosening requiring only rarely suture replacement.10.Intraoperative keratoscopy should be applied after removal of lid specula and fixation sutures.

Laser in situ keratomileusis for the correction of residual ametropia after penetrating keratoplasty

PURPOSE

To evaluate the safety, efficacy, and predictability of excimer laser in situ keratomileusis (LASIK) to correct residual myopia and astigmatism after penetrating keratoplasty (PKP).

SETTING

Buzard Eye Institute, Las Vegas, Nevada, USA.

METHODS

Twenty-six eyes had LASIK at least 1 year after PKP. All eyes were followed for at least 6 months after LASIK; 22 eyes were followed for 12 months. Sutures were removed at a mean of 13 months post PKP. Laser in situ keratomileusis was performed with the Chiron Automated Corneal Shaper microkeratome (Bausch & Lomb) and the Visx Star excimer laser. Before LASIK, the mean spherical equivalent (SE) was -4.94 diopters (D) +/- 2.79 (SD) and the mean astigmatism was 2.71 +/- 2.33 D; all eyes had regular astigmatism or slightly decentered, irregular astigmatism.

RESULTS

At the last follow-up, the mean postoperative uncorrected visual acuity (UCVA) was 20/30, the mean SE was -0.35 +/- 0.65 D, and the mean residual astigmatism was 1.06 +/- 0.67 D. Eighty-six percent of patients had an SE within +/-1.00 D of emmetropia and a UCVA of 20/40 or better. Ten eyes (39%) had 1 or more enhancements, which were performed a mean of 6 months after the primary LASIK. Significant complications such as wound dehiscence, epithelial ingrowth, and corneal decompensation did not occur. At the last follow-up, 18% of patients lost 1 line of best corrected visual acuity and 27% gained 1 line.

CONCLUSION

Laser in situ keratomileusis appeared to be a reliable and safe procedure to correct residual myopia and astigmatism after PKP.

Centration of donor trephination in human corneal transplantation

PURPOSE

To develop and evaluate a new method to quantify centration of the trephined donor cornea relative to the limbus.

METHODS

After human donor corneas were trephined for penetrating keratoplasty, the remaining corneoscleral discs were stained and subjected to image analysis. The centration of the excised donor cornea relative to the limbus was calculated by measuring their centroids from the "captured" images.

RESULTS

Fifty-two corneoscleral discs were analyzed. The average deviation from the centre was 0.32 mm (SD, 0.18 mm). Neither surgeon nor the type of trephine significantly influenced the mean centroid deviation.

CONCLUSION

We have developed and evaluated a method to quantify centration of human donor cornea. In a small series, decentration did not correlate significantly with either the surgeon or the trephine.

Comparison of astigmatism after penetrating keratoplasty by experienced cornea surgeons and cornea fellows

PURPOSE

We compared surgically induced astigmatism after penetrating keratoplasty performed by supervised cornea fellows and experienced cornea surgeons.

METHODS

Data were collected by retrospective chart review of 166 cases (166 eyes) of penetrating keratoplasty: 63 performed by two cornea surgeons and 103 by four cornea fellows. Astigmatism was calculated using scalar and vector methods. Vector analysis was performed on 109 of 166 eyes. Two techniques were compared: intraoperative keratometry and suture adjustment and the torque-antitorque running suture technique with no intraoperative keratometry or suture adjustment.

RESULTS

Mean surgically induced scalar astigmatism changed from preoperative astigmatism by 3.27 diopters (fellows) and 2.94 diopters (attending surgeons). In 109 cases, surgically induced vector cylinder changed from peroperative astigmatism by 4.21 diopters at 98 degrees (fellows) and 4.25 diopters at 114 degrees (surgeons). Surgically induced vector astigmatism changed from preoperative astigmatism by 4.67 diopters at 93 degrees in the first 6 months (fellows) and by 3.79 diopters at 103 degrees in the second 6 months. Analysis of x-axis and y-axis components of the surgically induced vector cylinder showed that the majority of the astigmatism was induced in the y-axis and that this difference was significant (P < .001) in all comparisons, independent of technique or surgeon group.

CONCLUSIONS

Penetrating keratoplasty performed by supervised cornea fellows resulted in similar rates of surgically induced vector astigmatism, surface asymmetry, and surface regularity as that by experienced surgeons. Fellows induced significantly more with-the-rule astigmatism, but this tendency decreased with further training. Penetrating keratoplasty astigmatic outcomes were not significantly different whether or not intraopertive keratometry and suture adjustment were utilized. This study supports the concept that increased experience with corneal transplantation improves the outcome of penetrating keratoplasty by using the criterion of postoperative astigmatism as a measures.

Corneal transplant for keratoconus: results in early and late disease

PURPOSE

To evaluate the results and complications rates associated with corneal transplantation for keratoconus and assess the prospects of using penetrating keratoplasty at a much earlier stage.

SETTING

Buzard Eye Institute, Las Vegas, Nevada, USA.

METHODS

In this prospective clinical study, 104 eyes of 76 patients had corneal transplantation for keratoconus identified by corneal topography, keratometry, pachymetry, and/or retinoscopy. Sutures were removed at a mean of 15 months; mean follow-up was 42 months. All surgeries were performed by one surgeon using a torque-antitorque suture method. Eyes were grouped according to severity of the disease: early (n = 24); moderate (n = 47); high (n = 33). Preoperative keratometry was 40.00 to 49.00, 50.00 to 59.00, and 60.00 to 90.00 diopters (D), respectively. The criteria for corneal transplant were a best spectacle-corrected visual acuity of 20/40 or worse and keratoconus clearly identified by one of the above methods. Secondary procedures included repair of wound dehiscence (33 eyes, 31%), relaxing incisions (33 eyes, 31%), wedge resections (5 eyes, 5%), and automated lamellar keratoplasty (4 eyes, 4%).

RESULTS

Mean postoperative uncorrected visual acuity at last follow-up was 0.43 +/- 0.3 (20/50), with 46 eyes (44%) achieving 20/40 or better. Mean best corrected visual acuity (BCVA) at last follow-up was 0.83 +/- 0.2 (20/25). Sixty eyes (58%) achieved 20/40 or better BCVA at 1 month and 92 eyes (88%), at 3 months. At last follow-up, mean average keratometric astigmatism was 3.10 +/- 1.70 D, mean keratometry was 43.30 +/- 2.20 D, and mean spherical equivalent was -1.70 +/- 3.00 D. Complications included 21 graft rejections (20%); 19 were successfully treated with topical and oral steroids. No expulsive hemorrhage or endophthalmitis occurred.

CONCLUSIONS

The risk-benefit for corneal transplantation has been significantly altered by improved surgical and postoperative techniques. The improved results, low complication rate, and postoperative enhancement management indicate that corneal transplantation is a viable option early in the clinical course of keratoconus.

Long-term follow-up of a single continuous adjustable suture in penetrating keratoplasty

Penetrating keratoplasty was performed on 30 patients using a single adjustable continuous 10/0 nylon suture. Seventeen patients had astigmatism of 4.00 dioptre cylinders (DC) or more and were adjusted. The latest adjustment was at 32 weeks. Following adjustment there was a significant reduction in median post-keratoplasty astigmatism from 6.00 DC to 2.50 DC (p < 0.001). Thirteen patients, with astigmatism of 4.00 DC or less, were not adjusted. Median astigmatism for the non-adjusted group was 3.00 DC and for the entire group was 2.88 DC. Long-term refraction and suture status were monitored with time. Mean follow-up was 112 weeks (range 53-170 weeks). Over the study period the entire group showed significant 'long-term astigmatic drift' (LTAD), from 2.88 DC to 3.25 DC (median drift, 1.25 DC; range, 0.00-5.50 DC) (p < 0.001). Suture adjustment and suture removal showed no significant effect on LTAD. With suture removal between 32 and 84 weeks median LTAD was 1.50 DC. For suture removal after 84 weeks, median LTAD was also 1.50 DC, but the range of LTAD was 1.50 DC, compared with a larger range of 5.00 DC in the earlier suture removal group. The technique of single continuous adjustable sutures for penetrating keratoplasty is safe, effective in reducing astigmatism, but may need modification to further enhance long-term refractive stability.

Transverse keratotomy in postkeratoplasty astigmatism

Transverse relaxing incisions were made in 12 eyes with a mean corneal astigmatism of 10.7D following penetrating keratoplasty. A few days later the mean graft astigmatism had been reduced to 5.5D (p = 0.0022), the reduction being significantly correlated to the degree of astigmatism before the keratotomy was done (p = 0.0044). Thereafter the corneal contour remained fairly stable through a mean follow-up period of 28.1 months, although a tendency towards a further reduction of the astigmatism was indicated. The mean corrected visual acuity improved from 0.5 before the keratotomy to 0.7 at the last control visit (p = 0.0117).