Managing Post Keratoplasty Astigmatism

Corneal transplantation, when used in the correct setting, can significantly improve visual acuity and therefore quality of life. One of the barriers to good vision following keratoplasty is residual post operative surgical astigmatism. Following a thorough literature search, we present the different options available to readers, with regards to how post-operative astigmatism can be approached and managed in order to improve vision. We present available data from the literature, which in some areas are scarce, with a view to collating all of this information in one place, allowing comparison between different modalities of treatment.

Comparison of outcomes between cross-linking plus topoguided excimer laser ablation and intrastromal corneal ring segments for keratoconus

OBJECTIVE

To compare cross-linking (CXL) plus topography-guided photorefractive keratectomy (t-PRK) and intrastromal corneal ring segments (ICRS) in keratoconus patients, at 12 months of follow-up.

METHODS

This was a longitudinal, retrospective multi-center study. We included a referred sample of 154 eyes from 149 patients with grade I-III Amsler-Krümeich keratoconus with insufficient corrected-distance visual acuity (CDVA). In group 1 (CXL plus t-PRK, 87 eyes), another possible indication for surgery was evidence of progression. Group 2 (ICRS, 67 eyes) included only eyes with paracentral keratoconus (thinnest point at the inferotemporal quadrant) with coincident axes, and evidence of stabilization was required. A subgroup analysis was performed regarding the disease topographic phenotype. At 12 months postoperatively, visual, refractive, and topographic outcomes were evaluated.

RESULTS

Comparison of the outcomes between CXL plus t-PRK (group 1) and ICRS (group 2) showed similar improvements in CDVA (in group 1, CDVA improved 0.18 logMAR, and in group 2 0.12 logMAR, P = .18) and K2 (-2,45 [6.46] D in group 1 and -2.13 [1.67] D in group 2, P = .34) The improvement in cylinder power was greater in group 2 (-2.37 [2.07] D in group 2 versus -1.18 [2.63] D in group 1, P = .003); group 1 had a higher decrease in Kmax (- 3.26 [3.64] versus-1.74 [2.67], P = .001).

CONCLUSIONS

Both CXL plus t-PRK and ICRS were equally effective in improving CDVA and topographic parameters in a similar group of keratoconus patients at 12 months.

Intrastromal corneal ring segments: effect of depth of implantation in visual, refractive, and topographic outcomes in patients with keratoconus

PURPOSE

To evaluate visual, refractive, and topographic outcomes of intracorneal ring segment implantation in relation to the achieved segment depth, using the manual technique.

SETTING

Ophthalmology Department, Hospital de Braga, Braga, Portugal.

DESIGN

Retrospective cohort study.

METHODS

We obtained 104 eyes of 93 patients with keratoconus submitted to Ferrara intracorneal ring segment (ICRS) implantation, using a manual technique. Subjects were divided into 3 groups according to the achieved depth of implantation: 40% to 70% (Group 1), 70% to 80% (Group 2), and 80% to 100% (Group 3). Visual, refractive, and topographic variables were evaluated at baseline and 6 months. Topographic measurement was performed using Pentacam. Thibos-Horner and Alpins methods were used to analyze the vectorial change of refractive and topographic astigmatism, respectively.

RESULTS

We found a significant improvement of uncorrected distance visual acuity and corrected distance visual acuity in all groups at 6 months ( P < .005); no differences were observed regarding safety and efficacy indexes in the 3 groups ( P > .05). Manifest cylinder and spherical equivalent significantly reduced in all groups ( P < .05). Topographic evaluation showed a significant improvement of all parameters in the 3 groups ( P < .05). A shallower (Group 1) or deeper (Group 3) implantation was associated with topographic cylinder overcorrection, a higher magnitude of error, and a higher mean centroid postoperative corneal astigmatism.

CONCLUSIONS

ICRS implantation with the manual technique showed to be equally effective in visual and refractive outcomes despite the depth of implantation; however, shallower or deeper implants were associated with topographic overcorrection and a higher mean centroid postoperative astigmatism, which explain the lower topographic predictability associated with manual surgery for ICRS implantation.

Management of keratoconus: an updated review

Keratoconus is the most common corneal ectatic disorder. It is characterized by progressive corneal thinning with resultant irregular astigmatism and myopia. Its prevalence has been estimated at 1:375 to 1:2,000 people globally, with a considerably higher rate in the younger populations. Over the past two decades, there was a paradigm shift in the management of keratoconus. The treatment has expanded significantly from conservative management (e.g., spectacles and contact lenses wear) and penetrating keratoplasty to many other therapeutic and refractive modalities, including corneal cross-linking (with various protocols/techniques), combined CXL-keratorefractive surgeries, intracorneal ring segments, anterior lamellar keratoplasty, and more recently, Bowman's layer transplantation, stromal keratophakia, and stromal regeneration. Several recent large genome-wide association studies (GWAS) have identified important genetic mutations relevant to keratoconus, facilitating the development of potential gene therapy targeting keratoconus and halting the disease progression. In addition, attempts have been made to leverage the power of artificial intelligence-assisted algorithms in enabling earlier detection and progression prediction in keratoconus. In this review, we provide a comprehensive overview of the current and emerging treatment of keratoconus and propose a treatment algorithm for systematically guiding the management of this common clinical entity.

Corneal Hydrops - Aetiology and Advanced Therapeutic Strategies

Acute hydrops refers to sudden corneal edema caused by rupture of Descemet's membrane (DM) - often in progressive keratectasia. It leads to a sudden decrease in visual acuity, pain, and foreign body sensation as well as an increased glare sensation. Acute hydrops usually heals with scarring within months, but complications such as corneal perforation, infectious keratitis, and corneal vascularization may occur. The prevalence in keratoconus patients is 2.6 to 2.8%. Risk factors include keratoconjunctivitis vernalis, atopic dermatitis, high keratometry, male gender, and eye rubbing. Keratoplasty should be avoided in the acute phase. The prognosis of the graft is reduced, and after scar healing of the hydrops, wearing contact lenses or glasses may be possible again. Conservative therapy alone with lubricants and hyperosmolar eye drops, prophylactic antibiotic eye drops to prevent superinfection, and topical steroids was long considered the only possible form of treatment. However, healing under conservative therapy takes an average of over 100 days. In the meantime, there are different surgical strategies that rapidly shorten the healing and thus the recovery phase of the patients to a few days. If the DM is detached without tension, a simple injection of gas into the anterior chamber can already lead to reattachment and thus to almost immediate deswelling of the cornea. If the DM is under tension, predescemetal sutures combined with a gas injection into the anterior chamber can flatten the cornea and reattach the DM. Mini-Descemet membrane endothelial keratoplasty (mini-DMEK) allows for sutureless closure of the DM defect by transplantation of a small (< 5 mm) graft. In cases of particularly large DM tears and very pronounced hydrops, suture loosening and relapse may occur after the placement of predescemetal sutures. Mini-DMEK can then lead to permanent healing, but in contrast to simple corneal sutures, it is usually performed under general anesthesia and by aid of intraoperative optical coherence tomography. The very good results with regard to the rapid healing prove that surgical therapy makes sense in the vast majority of patients with acute hydrops and should be initiated quickly.

Refractive surgery after deep anterior lamellar keratoplasty: a review of the literature

PURPOSE

The main objective of this work is to present an updated review of the different surgical procedures for the correction of residual refractive errors following deep anterior lamellar keratoplasty (DALK) surgery.

METHODS

A review of the literature was conducted using PubMed, Web of Science, and Scopus databases. The search was conducted in January 2022 and was limited to articles published in peer-reviewed journals. The information extracted from each publication included sample size, mean follow-up time, pre- and post-operative uncorrected (UDVA) and corrected distance visual acuity (CDVA), pre- and post-operative refraction and spherical equivalent (SE), safety and efficacy indexes and complications.

RESULTS

Residual ametropias, mainly high astigmatism and myopia, and the resulting anisometropia are likely to occur following DALK. They become a limiting factor and may lead to unsatisfactory visual restoration, therefore affecting patients' quality of vision and life. Alternative surgical interventions may be required to treat this residual ametropia, such as corneal refractive surgery or intraocular lens implantation. A total of 47 relevant articles were studied in detail. Different refractive surgery techniques have been shown to be effective and safe for the correction of ametropia following the DALK procedure and to improve the patient's quality of vision, although more research is needed to confirm long-term results.

CONCLUSION

The final refractive technique will depend on different factors, such as the amount of ametropia, the condition of the cornea or the patient's individual needs, economics, and occupational demands.

Clinical, tomographic, and topometric outcomes of progressive thickness intracorneal ring segment implantations in duck-type keratoconus

Purpose

To evaluate the visual, refractive, tomographic, and topometric outcomes of progressive thickness intracorneal ring segment (PT-ICRS) implantation in duck-type keratoconus.

Methods

This retrospective study included eyes with oval (duck-type) keratoconus treated with PT-ICRS implantation. After the femtosecond laser tunnel creation, one PT-ICRS (Keraring AS 5 with 160° arc length) was implanted along the ectatic, inferior half of the cornea. Data of uncorrected and corrected distance visual acuity (UDVA and CDVA), refraction, asphericity (Q value), and keratometry (K) were compared pre- and postoperatively. Additionally, changes in the topometric indices of corneal irregularity were also evaluated after PT-ICRS implantation.

Results

Thirty-one eyes of 30 patients were included in the study with a mean follow-up time of 9.06 months (ranging between 6 and 18 months). UDVA improved from 0.85 ± 0.36 to 0.27 ± 0.14 logMAR (P = 0.001), and CDVA improved from 0.37 ± 0.22 to 0.13 ± 0.11 logMAR (P = 0.001). The mean spherical error decreased from -3.66 ± 2.60 to -1.60 ± 1.42 D (P = 0.001), and the mean cylindrical error decreased from -4.91 ± 2.65 to - 1.41 ± 1.31 D (P = 0.001). All topographic parameters measured from the anterior cornea demonstrated statistically significant improvements after PT-ICRS implantation (P = 0.001). K mean, K maximum, corneal astigmatism, and Q value showed a significant decrease. Besides the index of height asymmetry, all topometric indices were significantly reduced after PT-ICRS implantation. There were no loss of lines and no complications.

Conclusion

PT-ICRS implantation in duck-type keratoconus is an effective and safe treatment. This intervention improves the visual acuity, refractive error, topographical, and topometric parameters significantly by decreasing both eccentricity and steepness of the cone.

Evaluation of a new nomogram for Ferrara ring segment implantation in keratoconus

AIM

To evaluate the short-term clinical outcomes of Ferrara rings in keratoconus using an optimized nomogram developed after several years of research and retrospective analysis of clinical data.

METHODS

This prospective longitudinal non-comparative clinical trial evaluated 88 eyes of 88 patients (age 18-62y) with keratoconus diagnosis from two Spanish centers. Ferrara ring segment (AJL Ophthalmic) implantation was performed in all cases, using the mechanical procedure in 25 eyes (28.4%) and a femtosecond laser-assisted procedure in 63 eyes (71.6%). The ring segments implanted in each case were selected using a new optimized nomogram that considered variables such as anterior corneal asphericity and astigmatism or the discrepancy among astigmatism and coma orientations. Visual, refractive, corneal topographic, aberrometric, and pachymetric changes after surgery were evaluated during a 3-month follow-up.

RESULTS

The implants induced a significant refractive change as well as an improvement in uncorrected (UDVA) and corrected distance visual acuity (CDVA; P<0.001). Postoperative CDVA of 0.10 logMAR or better was achieved in 28.4% and 46.5% of eyes, respectively. Two eyes (2.3%) lost two or more lines of CDVA whereas a total of 53.5% of eyes gained lines of CDVA. A significant central anterior and posterior corneal flattening was induced (P≤0.003), with a significant reduction of anterior (P<0.001) and posterior corneal astigmatisms (P=0.048), and a change in anterior asphericity (P<0.001). Total primary coma (6 mm pupil) change was also statistically significant (preoperative 3.66±3.04 µm vs postoperative 2.33±2.26 µm, P<0.001). No significant differences were found in the effect of ring segments between cases implanted using the mechanical and femtosecond techniques (P≥0.101).

CONCLUSION

The implantation of Ferrara rings based on the nomogram evaluated is safe and effective for promoting a visual rehabilitation in keratoconus, with a relevant control of primary coma aberration.

Clinical evaluation of the effectiveness of asymmetric intracorneal ring with variable thickness and width for the management of keratoconus

PURPOSE

To evaluate the short-term clinical outcomes obtained with a new model of asymmetric intracorneal ring segments (ICRS) with variable thickness and base width in keratoconus.

SETTING

Four ophthalmologic centers in Spain.

DESIGN

Prospective multicenter longitudinal noncomparative clinical trial.

METHODS

Thirty-one keratoconus eyes of 25 patients (aged 15 to 50 years) that underwent implantation of ICRS of variable thickness and base (AJL-pro+) in 4 Spanish centers were enrolled. Visual, refractive, topographic, aberrometric, and pachymetric changes were evaluated during a 3-month follow-up. Complications were also recorded.

RESULTS

Statistically significant changes after surgery were observed in uncorrected distance visual acuity (P = .002) and corrected distance visual acuity (CDVA) (P = .005), as well as in spherical equivalent (P = .006). At 3 months postoperatively, no loss of 2 or more lines of CDVA was observed, whereas 48.4% (15) of eyes gained ≥1 line. Statistically significant changes were observed in the steepest and mean keratometric values (P ≤ .047) and in the magnitude of astigmatism (P < .001) of both anterior and posterior corneal surfaces. Likewise, a change to a less prolate shape of the anterior surface was found (P = .011). Primary coma was also reduced significantly at 1 month postoperatively (P = .001, mean reduction 40.1%). No serious implant-related complications occurred during the follow-up.

CONCLUSIONS

The implantation of intrastromal asymmetric ring segments of variable thickness and base width in keratoconus corneas induces a significant anterior corneal flattening, leading to refractive changes, a significant reduction of its prolate shape and irregularity, and improvement in patient CDVA.

Visual and Tomographic Outcomes of a 300° Arc-length ICRS Implantation in Moderate to Advanced Central Keratoconus

PURPOSE

To assess the outcomes of implanting a new 300° arc-length intrastromal corneal ring segment (ICRS) in moderate to advanced central hyperprolate keratoconus.

METHODS

Forty-two eyes with moderate to advanced central hyperprolate keratoconus were evaluated before and after implanting an inferior 300° ICRS (AJL Ophthalmic). The clinical measurements taken included manifest refraction, uncorrected (UDVA) and corrected (CDVA) distance visual acuity (logMAR scale), and corneal tomographic analysis (Sirius; Costruzioni Strumenti Oftalmici). Changes in the anterior and posterior corneal surfaces and the root mean square (RMS) for coma-like aberrations for a pupil size of 4.5 mm were evaluated. All examinations were performed before surgery and 6 months after surgery.

RESULTS

The mean UDVA improved from 1.12 ± 0.48 logMAR preoperatively to 0.73 ± 0.37 logMAR postoperatively (P < .0001). The mean CDVA changed from 0.33 ± 0.20 to 0.20 ± 0.11 logMAR (P < .0001). Postoperatively, the CDVA improved by two or more lines in 45.2% of the eyes and increased by one line in 19.04%, and none of the patients lost lines of CDVA. All of the anterior and posterior corneal tomographic parameters analyzed were significantly improved after surgery, except posterior flat keratometry, which remained unchanged. In 80.95% of the eyes, the postoperative mean keratometry was 50.00 diopters or less. The 6-month RMS for coma-like aberrations also declined significantly from 1.57 ± 0.68 to 1.06 ± 0.42 µm after surgery (P < .0001).

CONCLUSIONS

These results suggest that implanting a 300° arc-length ICRS is a safe and effective procedure for treating patients with moderate to advanced central hyperprolate keratoconus and clear cornea. [J Refract Surg. 2021;37(4):249-255.].