Refractive surgery for keratoconus

The efficacy of 2 different phakic intraocular lens implant in keratoconus as an isolated procedure or combined with collagen crosslinking and intra-stromal corneal ring segments: a systematic review and meta-analysis

PURPOSE

To compare the efficacy of phakic intra-ocular lenses in isolation or in combination with corneal crosslinking (CXL) and/or intra-stromal corneal ring segments (ICRS) in keratoconus.

METHODS

Data extracted from the publications meeting the selection. The outcome parameters included mean pre- and post-operative uncorrected distance visual acuity, corrected distance visual acuity (CDVA), sphere and cylinder of refraction and complications. Available data analyzed with Cochrane Review Manager.

RESULTS

A total of 23 studies including 464 eyes were included. All the parameters showed significant improvement in all subgroups other than CDVA in ACPIOL + CXL subgroup and cylinder in PIOL + CXL subgroups. There was not a significant difference between PCPIOL and ACPIOL in the outcomes, exception was more improvement of CDVA in "ACPIOL only" than" PCPIOL only" subgroup.

CONCLUSION

Both PCPIOLs and ACPIOLs are comparably safe and efficient options in management of KCN and their efficacy significantly improves when combined with CXL/ICRS.

Less Complex Contact Lens Required for a Patient With Keratoconus After Topography-Guided Photorefractive Keratectomy

ABSTRACT

In this report, we discuss contact lens (CL) fitting in a patient with a history of keratoconus (KC), before and after undergoing topography-guided photorefractive keratectomy (TG PRK). Before TG PRK, the patient failed multiple CL modalities and reported difficulty with his habitual CLs and inadequate spectacle-corrected visual acuity to perform his activities of daily living. In this case, a collaborative, comprehensive approach to visual management in a patient with KC was used, and after TG PRK was performed to improve his corneal contour and symmetry, our patient was fit with a standard soft CL and additionally had improved spectacle-corrected visual acuity.

Biaxial hyperelastic and anisotropic behaviors of the corneal anterior central stroma along the preferential fibril orientations. Part II: Quantitative computational analysis of mechanical response of stromal components

To study the hyperelastic and anisotropic behaviors of the central anterior stroma for patients with myopia, 40 corneal stromal specimens extracted after small incision lenticule extraction (SMILE) surgery were used in the biaxial extension test along two preferential fibril orientations. An improved collagen fibril crimping constitutive model with a specific physical meaning was proposed to analyze the hyperelasticity and anisotropy of the stroma. The effective elastic modulus of the two families of preferentially oriented collagen fibrils and the stiffness of the non-collagenous matrix along all three directions were compared according to the specific physical meaning of the parameters. Anisotropic behavior was found in the hyperelastic properties of the corneal anterior central stroma in the preferential fibril orientations. The stiffness of non-collagenous matrix is significantly larger in the optical axis direction than in the nasal-temporal (NT) and superior-inferior (SI) directions. Moreover, individual differences between males and females slightly impact on hyperelastic and anisotropic behaviors. The differences of these behaviors were significant in the comparison of the left and right eyes. These results have a guiding significance for the accurate design of surgical plans for refractive surgery according to a patient's condition and have a driving value for the further exploration of the biomechanical properties of the whole cornea.

Clinical and self-reported outcomes after multifocal intraocular lens implantation of patients with stable keratoconus

BACKGROUND

Multifocal intraocular lens (IOL) implantation is generally not considered in patients with keratoconus; however, it may provide good optical results in selected patients based on two case reports.

AIMS

To evaluate patient satisfaction and clinical outcomes in this patient population.

METHODS

This is a retrospective single-center, non-comparison study. All patients with frank keratoconus who had undergone a trifocal IOL implantation between 2016 and 2019 were invited to participate in this study (18 eyes of 9 patients were included). Postoperatively, refractive outcomes, contrast sensitivity, and ocular aberrations were recorded. A questionnaire was used for determining patient satisfaction and their quality of life. The mean follow-up time was 31.22 ± 6.38 months.

RESULTS

Postoperatively the patients' uncorrected distance visual acuity improved from 1.13 ± 0.93 logMAR to 0.10 ± 0.17 (p ˂ 0.001), corrected distance visual acuity went from 0.10 ± 0.11 to 0.05 ± 0.09 (p = 0.19), mean refractive spherical equivalent changed from -4.34 ± 4.31 to 0.05 ± 0.51 D (p ˂ 0.001), and manifest astigmatism from 2.44 ± 1.92 to 0.88 ± 1.81 D (p = 0.017). A postoperative MRSE of less than ± 0.50 D was achieved in 17 eyes (94%). Three eyes (17%) lost 1 line of best corrected visual acuity and no patient lost two or more lines. The patients were independent of glasses in 78% for all distances. One patient who required an IOL exchange due to photic phenomena was lost to follow-up.

CONCLUSIONS

Use of a trifocal IOL provided relatively predictable refractive outcomes and spectacle independence in most of this small cohort of patients with stable frank keratoconus.

Results of Follow-up in Pediatric Keratoconus Treated With Intracorneal Ring Segments Implantation Alone or in Combination With Corneal Cross-linking

PURPOSE

To report visual and topographic outcomes of pediatric keratoconus with intracorneal ring segments (ICRS) implantation alone or in combination with accelerated corneal cross-linking (A-CXL).

METHODS

A descriptive, retrospective observational study was performed. Medical records of patients younger than 18 years at Fundación Oftalmológica Nacional in Bogotá, Colombia, were reviewed. Demographic data, follow-up time, preoperative and postoperative uncorrected (UCVA) and best corrected (BCVA) visual acuity, manifest refraction, and tomography were evaluated. SPSS software (version 22.0; SPSS, Inc) was used for analysis.

RESULTS

Twenty-six eyes of 19 patients with a mean age of 16.5 ± 1.8 years were analyzed, and 16 were boys (84.2%). Median follow-up time was 39.6 months (inter-quartile range [IQR] = 30). Fifteen patients (78.9%) had a history of allergic conjunctivitis. Sixteen eyes (61.5%) received ICRS implantation with A-CXL and 10 eyes (38.4%) received ICRS implantation only. Global results (including ICRS implantation with A-CXL and ICRS implantation only) were: (1) median UCVA of 0.90 logarithm of the minimum angle of resolution (logMAR) (IQR = 0.85) preoperatively improved to 0.54 logMAR (IQR = 0.70) postoperatively; (2) median BCVA of 0.43 logMAR (IQR = 0.39) preoperatively improved to 0.30 logMAR (IQR = 0.26) postoperatively; and (3) median spherical equivalent of -5.37 diopters (D) (IQR = -5.28) preoperatively improved to -4.12 D (IQR = -3.57) postoperatively. There was a reduction in half of the sphere and cylinder. The median maximum keratometry was 54.40 D (IQR = 7.4) preoperatively and 49.80 D (IQR = 5.3) postoperatively. The median asphericity was -1.18 (IQR = 0.70) preoperatively and changed to -0.75 (IQR = 0.68) postoperatively. No patient presented with complications before or after surgery.

CONCLUSIONS

ICRS implantation only or in combination with A-CXL induced visual and topographic improvement in patients with keratoconus, which was maintained throughout the follow-up time. It seems to be a safe procedure to delay or avoid corneal transplantation in the pediatric population. [J Pediatr Ophthalmol Strabismus. 2022;59(2):118-127.].

Posterior Chamber Phakic Intraocular Lens Implantation for Refractive Correction in Corneal Ectatic Disorders: A Review

PURPOSE

To summarize the indications and outcomes of posterior chamber phakic intraocular lens (PIOL) implantation in corneal ectasias including keratoconus, pellucid marginal degeneration (PMD), post-refractive surgery, and post-keratoplasty ectasias.

METHODS

A review of the literature was conducted using the relevant keywords from various databases up to August 15, 2020. All pertinent studies were reviewed, and the relevant articles were studied in detail for efficacy, stability, predictability, and safety outcomes. In addition, visual quality, corneal biomechanical outcomes, complications, the role of posterior chamber PIOL in combination treatment, and comparison of posterior chamber PIOL with other PIOLs for ectasias were also evaluated.

RESULTS

A total of 30 relevant studies (13 prospective, 13 retrospective, 4 case reports) on the subject were studied and summarized. All studies showed a favorable refractive outcome. Quality of vision remained unaffected and no significant complications were reported in any of the studies.

CONCLUSIONS

Posterior chamber PIOLs represent a viable option in the treatment of mild to moderate and stable corneal ectasia in patients with contact lens intolerance who have low irregular astigmatism, a clear central cornea, and good preoperative corrected distance visual acuity. [J Refract Surg. 2021;37(5):351-359.].

Association of TIMP-1 and COL4A4 Gene Polymorphisms with Keratoconus in an Iranian Population

Purpose

Keratoconus (KC) is a bilateral and noninflammatory disease, characterized by progressive thinning and anterior protrusion of the cornea and may result in severe visual impairment due to irregular astigmatism. Matrix metalloproteinases (MMP) are the main group of enzymes that degrade extracellular matrix proteins including collagens; Type IV collagen is found in the corneal stroma. MMP enzymatic activity is inhibited by tissue inhibitor of metalloproteinase-1 (TIMP-1). A decrease in TIMP-1 level is associated with the development of KC. In the present study, we investigated the impact of COL4A4 rs2228557 C/T and TIMP-1 rs4898 C/T (X-chromosome) variants on the odds of KC development in a sample of Iranian population.

Methods

This case-control study was conducted on 140 patients with KC and 150 healthy control subjects. We used modified methods of Nested-PCR and ARMS-PCR in combination (Nested-ARMS-PCR) and confirmed their validity with RFLP-PCR.

Results

Significant differences were noticed between KC patients and healthy individuals regarding the genotype TY or T allele frequencies of rs4898 in the male subjects (OR = 0.43, 95%CI: 0.20-0.92, P = 0.03), whereas no significant differences were identified in the female subjects (OR = 1.07, 95%CI: 0.52-2.20, P = 0.85). The rs2228557, T allele was associated with KC (OR = 0.69, 95% CI: 0.50-0.97, P = 0.035).

Conclusion

In the rs2228557 variant, T allele acts as a protective factor from the disease and decreases the risk of KC compared with the C allele. Also, in our investigation about rs4898, we found that TY genotype or T allele decreased the risk of KC compared with the C allele in males and was a protective factor for KC in our population.

[Strength properties of rabbit cornea after femtosecond laser keratoplasty with and without different intracorneal implants]

AIM

to conduct a comparative experimental study of the effect of the use of intracorneal implants during femtosecond laser-assisted intrastromal pocket (IP) and intrastromal tunnel (IT) formation on the strength properties of the cornea.

MATERIAL AND METHODS

The experimental study was performed on 24 corneas of 12 rabbit eyes enucleated 1 month after slaughtering. All eyes were divided into 6 groups according to the method of operation. IP and IT were created with IntraLase FS 60 kHz femtolaser. Group 1 (control group) consisted of rabbit eyes with intact corneas. In group 2 corneas, intrastromal tunnels were formed, in group 3 - intrastromal pockets, and in group 4 - intrastromal tunnels with 2 intracorneal segments (ICS). In groups 5 and 6, intrastromal pockets, each supplemented with an intrastromal ring, were created at the depth of 62-72% and 80% of pachymetry readings from the 5.0-mm optical zone, respectively.

RESULTS

Higher voltage had to be applied to stretch the samples from group 2 as compared to those from groups 3 and 6. Distribution of the Young's modulus of the test corneas agreed with voltage distribution in the study groups.

CONCLUSION

IP was associated with greater reduction in corneal biomechanical stability as compared with IT. Ring implantation into an IP yielded a more pronounced increase in the strength properties of the cornea than ICS implantation into an IT. The result was also more favorable at greater depths of intrastromal ring implantation.

5-year follow-up of combined non-topography guided photorefractive keratectomy and corneal collagen cross linking for keratoconus

AIM

To evaluate the visual outcomes of simultaneous non-topography guided photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL) in eyes with keratoconus 5y after the procedure.

METHODS

Prospective, interventional, non-randomized, and non-controlled case series design was used. Sixty eyes of 30 patients (16 males and 14 females; age: 21-41y) with mild, non-progressive (stages 1-2) keratoconus were enrolled. Refraction, uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), flat and steep keratometry readings, and adverse events were evaluated preoperatively and postoperatively. Data were collected preoperatively and postoperatively at 3mo, 1, 2, 3, 4, and 5y follow-up visits after combined non-topography-guided PRK with CXL was performed. All patients had at least 5y of follow-up.

RESULTS

All study parameters showed a statistically significant improvement at 5y over baseline values. The mean follow-up time was 68.20±4.71mo (range: 60-106mo). Patients showed a significant improvement in UDVA from 1.24±0.79 logMAR prior to combined non-TG-PRK+CXL to 0.06±0.15 logMAR postoperatively at the time of their last follow-up visit. CDVA significantly increased from 0.06±0.19 logMAR preoperatively to 0.03±0.12 logMAR postoperatively. A significant decrease in the mean spherical equivalent (SE) refraction was observed from -2.28±1.8 to -0.79±0.93 diopters (D) (P<0.05), and the manifest sphere decreased from -1.62±1.23 to -0.27±0.21 D (P=0.001). The manifest cylinder significantly decreased from -1.73±0.86 to -0.29±0.34 D postoperatively (P=0.001). The mean steep keratometry was 45.13±1.32 vs 47.28±2.12 D preoperatively (P<0.05), and the preoperative mean steepest keratometry (Kmax) 48.6±3.1 was reduced significantly to 46.8±2.9 postoperatively (P<0.05).

CONCLUSION

Combined non-TG-PRK with 15min CXL is an effective and safe option for correcting mild refractive error and improving visual acuity in patients with mild stable keratoconus.

Collagen cross-linking as an adjunct for repair of corneal lacerations: a cadaveric study

OBJECTIVE

To determine the efficacy of collagen cross-linking (CXL) as an adjunct to suturing in the repair of corneal lacerations.

METHODS

A cadaveric study was undertaken in which a linear 5 mm corneal laceration was created in the central cornea of 20 eyes. The eyes were then randomized to receive 1 (n = 8), 2 (n = 8), or 3 (n = 4) standard corneal sutures. The burst pressure of the wound was then measured. All eyes in the 1- and 2-suture group then underwent standard CXL, with burst pressure repeated afterward.

RESULTS

The initial wound burst pressure in the 1-, 2-, and 3-suture groups was 54.9, 74.0, and 201.2 mm Hg, respectively. After CXL, wound burst pressure increased by a mean of 3.2 and 62.3 mm Hg in the 1- and 2-suture groups, respectively. This change was statistically significant in the 2-suture group (p = 0.017). After CXL, the 2-suture group still had a significantly lower burst pressure compared with the 3-suture group (p = 0.011).

CONCLUSIONS

The study highlights a potential novel application for CXL to strengthen corneal wounds. Provided that suture density is sufficient to appose the wound edges, CXL may result in short-term wound strengthening. This could potentially allow for decreased corneal suture density and a corresponding decrease in suture-related complications.

[Comparative analysis of corneal aberrations after intrastromal segments and MyoRing implantation using femtosecond laser in patients with keratoconus]

AIM

to comparatively analyze corneal aberrations after intrastromal corneal segments (ICS) and MyoRing implantation using femtosecond laser in patients with stage II-III keratoconus (KC) by Pentacam examination.

MATERIAL AND METHODS

We have operated on 135 patients (145 eyes) with stage II or III KC. Depending on surgical technique, all patients were divided into two groups. Group I consisted of patients with KC, who received optimized femtosecond laser-assisted MyoRing implantation, group II - of those, who received femtosecond laser-assisted ICS implantation. Depending on the stage of the disease, each group was further divided into two subgroups, for stage II and stage III KC, respectively. Before and after surgery, all patients underwent visometry, biomicroscopy, corneal topography, and corneal aberrations measurement under photopic and mesopic conditions on Pentacam. The follow-up period averaged 30 months (from 6 to 34 months).

RESULTS

In both groups corneal aberrations significantly decreased after surgery, which was confirmed by an improvement in parameters of refraction and keratometry readings.

CONCLUSION

Implantation of intrastromal MyoRings leads to a greater reduction in the total corneal aberration, higher-order aberrations under photopic and mesopic conditions, and spherical aberration under photopic conditions as compared to ICS in patients with stage III KC; a comparable reduction in the total corneal, higher-order, and spherical aberrations under photopic conditions as compared to ICS in patients with stage II KC; a comparable increase in spherical aberration under mesopic conditions as compared to ICS in patients with stage III KC.

Evaluation of possible relationship between COL4A4 gene polymorphisms and risk of keratoconus

PURPOSE

Keratoconus (KC) is a genetically heterogeneous corneal dystrophy with unknown etiology that causes loss of visual acuity. Evidence has shown that corneas from patients with KC contain reduced amounts of total collagen proteins, and collagen type IV has been suggested as a candidate gene in KC pathogenesis. This study aimed to evaluate the possible associations between collagen type IV alpha-4 chain (COL4A4) polymorphisms (rs2229813 G/A, M1327V and rs2228555 A/G, V1516V) and susceptibility to KC.

METHODS

A total of 262 Iranian subjects including 112 patients with KC and 150 healthy individuals as controls were recruited in this case-control study. Diagnosis was based on clinical examination, electronic refractometry, and keratometry. Genotyping for the COL4A4 rs2229813 and rs2228555 variants was executed using allele-specific polymerase chain reaction and Tetra-ARMS polymerase chain reaction, respectively.

RESULTS

A significant difference was found between the 2 groups regarding allelic and genotyping distribution of COL4A4 polymorphism at position rs2229813 G>A. The COL4A4 rs2229813 AA and GA+AA genotypes were risk factors for developing KC (odds ratio [OR] = 2.1, P = 0.036 and OR = 1.7, P = 0.042, for the AA and GA+AA genotypes, respectively). The COL4A4 rs2229813 A allele was also associated with an increased risk for KC (OR = 1.5, 95% confidence intervals: 1.1-2.2, P = 0.018). However, in our study, we found no association between COL4A4 rs2228555 polymorphism and the risk of KC.

CONCLUSIONS

We suggest that the COL4A4 rs2229813 AA and GA+AA genotypes as well as the A allele play roles as risk factors for developing KC in our population.

Association of Lysyl oxidase (LOX) Polymorphisms with the Risk of Keratoconus in an Iranian Population

BACKGROUND

Keratoconus is a connective tissue-related eye disease with unknown etiology that causes the loss of visual acuity. Lysyl oxidase (LOX) is an amine oxidase that catalyzes the covalent cross-link of collagens and elastin in the extracellular environment, thus determining the mechanical properties of connective tissue. The current study aimed to investigate the possible associations between two LOX polymorphisms, rs1800449 and rs2288393, and susceptibility to keratoconus.

METHODS

A total of 262 Iranian subjects including 112 patients with keratoconus and 150 healthy individuals as controls were recruited. Genotyping for the LOX variants was performed using allele-specific PCR.

RESULTS

A significant difference was found between two groups regarding allelic and genotyping distribution of LOX polymorphism at position rs1800449 G>A. The frequency of AA and GA + AA genotypes were increased in patients compared to controls (17% versus 8% and 62.5% versus 50%, respectively), showing a statistically significant difference (OR = 2.827, 95% CI: 1.251-6.391, p = 0.012). The A allele was associated with an increased risk for keratoconus, with the frequency of 39.9% and 29% in patients and controls, respectively (OR = 1.614, 95% CI: 1.119-2.326, p = 0.011). Furthermore, the haplotype analysis revealed that the rs1800449G/rs2288393C is a protective factor against keratoconus (OR = 0.425, 95% CI = 0.296-0.609, p = 0.001). Conversely, the +473A/rs2288393C (OR = 3.703, 95% CI = 2.230-6.149, p = 0.001) and +473G/rs2288393G (OR = 15.48, 95% CI = 3.805-63.03, p = 0.001) haplotypes were identified as risk factors for keratoconus.

CONCLUSION

Our study demonstrated that the LOX rs1800449 genotypes (AA and GA + AA) and allele (A) appears to confer risk for susceptibility to keratoconus.

Keratoconus: current perspectives

Keratoconus is characterized by progressive corneal protrusion and thinning, leading to irregular astigmatism and impairment in visual function. The etiology and pathogenesis of the condition are not fully understood. However, significant strides have been made in early clinical detection of the disease, as well as towards providing optimal optical and surgical correction for improving the quality of vision in affected patients. The past two decades, in particular, have seen exciting new developments promising to alter the natural history of keratoconus in a favorable way for the first time. This comprehensive review focuses on analyzing the role of advanced imaging techniques in the diagnosis and treatment of keratoconus and evaluating the evidence supporting or refuting the efficacy of therapeutic advances for keratoconus, such as newer contact lens designs, collagen crosslinking, deep anterior lamellar keratoplasty, intracorneal ring segments, photorefractive keratectomy, and phakic intraocular lenses.