[Bandage lamellar-optical keratoplasty for post-excimer laser keratectasia]

[Keratoconus: main lines of research]

Keratoconus (KC) research focuses on studying pathogenesis, advancing diagnostic techniques and methods of correction and treatment. The working hypothesis for KC etiopathogenesis is based on abnormalities in distribution of microelements in the cornea and its potential influence on the processes of stromal collagen disorganization. Improvement of early diagnosis of KC is associated with evaluation of microstructural changes in the cornea using computerized methods such as Scheimpflug camera and high-definition optical methods for visualization of initial signs of a pigment ring. The main optimization directions of KC contact correction are associated with increasing gas permeability of the material, improving lens design and methods of lens fitting. Customized fitting of gas-permeable scleral hard contact lenses with consideration of topographic features of the anterior corneal surface allows achieving stable lens positioning and preserving the tear gap between the lens and the cornea. Alternative methods of correcting the refraction component of KC are associated with surgical interventions involving increase in corneal volume in the paracentral area. Implantation of corneal ring segments should be considered as an alternative to correction of refractive errors in cases with unsatisfactory individual subjective tolerance and insufficient patient compliance with contact correction. Femtolaser-assisted implantation of intrastromal allotransplants along with a decrease in the degree of spherical and astigmatic components of refractive errors contribute to prevention of KC progression. Advancement of techniques of corneal collagen cross-linking for prevention of KC progression is aimed at reducing the risk of developing post-operative complications directly related to the extent of intraoperative deepithelization. Limiting corneal ectatic area by implantation of intrastromal allotransplants can be considered an alternative approach. Deep anterior lamellar keratoplasty and penetrating keratoplasty are the surgeries of choice in replacing altered corneal layers in KC. With regard to the modern trends in selective keratoplasty, selective replacement of the cornea in lamellar keratoplasty reduces the rate of injuries and the risk of tissue reaction.

[Opto-functional results in keratoconus patients after intrastromal keratoplasty]

Intrastromal keratoplasty with allograft implantation can stop the progression of keratoconus (KC) and improve visual acuity (VA). Although optimization of keratometric parameters and an increase in VA improve the quality of vision (QoV), there are other indicators that affect the QoV and the quality of life (QoL) of patients and require further study.

PURPOSE

Analysis of quantitative and qualitative characteristics of vision in patients with stage II and III keratoconus who underwent intrastromal allokeratoplasty.

MATERIAL AND METHODS

The study included 15 patients (15 eyes) with stage II-III KC (Amsler-Krumeich classification) aged 17 to 38 years old (28.8±6.2). All patients underwent intrastromal keratoplasty with implantation of an allograft in the form of a wide incomplete ring. The following parameters were assessed before and 6 months after surgery: distance VA with and without correction, near VA with and without correction, VA with glare effect, high-order aberrations (HOA), thickness of the tear film lipid layer, spatial contrast sensitivity (SCS) under photopic and mesopic conditions with light filters, reading speed.

RESULTS

VA without correction increased from 0.15 to 0.7; with correction from 0.35 to 0.7. The glare effect with varying degrees of illumination did not affect VA either before or after surgery. Statistically significant changes were observed when comparing the aberrations «coma», «spherical», «trefoil» before and after the intervention, they became inverted. The thickness of the tear film lipid layer did not change significantly when comparing pre- and postoperative data. The use of light filters (orange, yellow) did not lead to significant changes in the VA and SCS under photopic and mesopic conditions.

CONCLUSION

The use of a wide intrastromal allograft to correct deformity and stabilize the cornea in keratoconus improves the patients' quality of vision and visual performance.

[On the tactics for surgical treatment of keratoconus in significantly altered corneal thickness]

PURPOSE

To evaluate the clinical and functional outcomes of bandage therapeutic-optical keratoplasty (BTOK) surgery in patients with keratoconus (KC) and significant changes in corneal thickness.

MATERIAL AND METHODS

Surgical treatment was performed in 15 patients (15 eyes) with stage IV KC aged from 22 to 51 years (mean age - 32.61±7.94 years). The follow-up period lasted 3 years. All patients underwent BTOK surgery using an interlamellar graft with a thickness of 320 to 350 µm.

RESULTS

Uncorrected and best corrected visual acuity increased in all patients after BTOK surgery and did not change statistically significantly during the entire follow-up period (3 years), amounting to 0.47±0.12 and 0.53±0.13, respectively. Keratometric parameters also remained stable by that observation time point and amounted to: K_max - 53.01±2.30 D; K_min - 41.63±2.24 D; K_m - 47.32±1.91 D.

CONCLUSION

The BTOK surgery helps achieve long-term (3 years) visual, optical and strengthening outcomes in stage IV KC patients when the use of other known techniques (corneal collagen crosslinking, corneal segments) is technically impossible because of the risk of complications due to significantly thinned cornea (less than 400 µm).

[Changes in the quality of vision after intrastromal allokeratoplasty for keratoconus (clinical observation)]

Scleral lenses, corneal collagen crosslinking, corneal implants and deep anterior keratoplasty are used to correct deforming changes in the cornea at advanced stages of keratoconus, which improves the quality of vision (QoV). The article presents an analysis of changes in QoV in a 30-year-old patient with stage III keratoconus who underwent intracorneal implantation of an allograft with a width of 2.75 mm and thickness of 300 µm at a depth of 370 µm. The following parameters were measured before and 6 months after the procedure: uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), VA with glare, higher order aberrations (HOA), thickness of the lipid layer of the tear film, spatial contrast sensitivity, visual productivity. Observation results show that the K_max index decreased from 55.9 D to 48.0 D, K_min - from 39.8 D to 39.4 D, UCVA increased from 0.1 to 0.8 and BCVA - from 0.35 to 0.8. Thickness of the lipid layer of the tear film remained the same. The glare effect with different degrees of brightness did not affect visual acuity. Spatial contrast sensitivity in photopic conditions at medium frequencies increased from 19 to 37 dB, at high frequencies from - 0.5 to 22.5 dB, in mesopic conditions at medium frequencies from 11 to 28 dB, at high frequencies from - 0.5 to 12 dB. The «coma» and «spherical» aberrations decreased by 2 and 3 times, respectively, while «trefoil» increased by 3 times. Visual productivity increased by 36.8%. It may be concluded that the use of a wide intrastromal allograft in keratoconus improves the patient's visual quality and visual productivity. At the same time, the «vignetting» effect from the graft side is negligible in photopic conditions and is significant in mesopic conditions.

Ectasia After Corneal Refractive Surgery: A Systematic Review

INTRODUCTION

The incidence of ectasia following refractive surgery is unclear. This review sought to determine the worldwide rates of ectasia after photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) based on reports in the literature.

METHODS

A systematic review was conducted according to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Publications were identified by a search of eight electronic databases for relevant terms between 1984 and 2021. Patient characteristics and preoperative values including manifest refractive spherical refractive equivalent (MRSE), central corneal thickness (CCT), anterior keratometry, postoperative residual stromal bed (RSB), and percent tissue altered (PTA) were summarized. In addition, annual rates of each refractive surgery were determined, and incidence of post-refractive ectasia for each type was calculated using the number of ectatic eyes identified in the literature.

RESULTS

In total, 57 eyes (70 eyes including those with preoperative risk factors for ectasia) were identified to have post-PRK ectasia, while 1453 eyes (1681 eyes including risk factors) had post-LASIK ectasia, and 11 eyes (19 eyes including risk factors) had post-SMILE ectasia. Cases of refractive surgery performed annually were estimated as 283,920 for PRK, 1,608,880 for LASIK, and 96,750 for SMILE. Reported post-refractive ectasia in eyes without preoperative identifiable risk factors occurred with the following incidences: 20 per 100,000 eyes in PRK, 90 per 100,000 eyes in LASIK, and 11 per 100,000 eyes in SMILE. The rate of ectasia in LASIK was found to be 4.5 times higher than that of PRK.

CONCLUSION

Post-refractive ectasia occurs at lower rates in eyes undergoing PRK than LASIK. Although SMILE appears to have the lowest rate of ectasia, the number of cases already reported since its recent approval suggests that post-SMILE ectasia may become a concern. Considering that keratoconus is a spectrum of disease, pre-existing keratoconus may play a larger role in postoperative ectasia than previously accounted for in the literature.

[Comparative assessment of the quality of life of keratoconus patients before and after intrastromal keratoplasty]

Surgical treatment of keratectasia, in addition to its cessation, is aimed at increasing the acuity and quality of vision. This can also significantly affect patient's quality of life. The criteria for assessing the quality of life does not always consider the balance between quantitative indicators and subjective perception, which can depend on the psychological aspect of self-esteem.

Purpose - to perform comparative assessment of the quality of life of patients with keratoconus (KK) before and after intrastromal keratoplasty by a newly developed method using an original questionnaire.

MATERIAL AND METHODS

The study included 20 patients (14 men and 6 women, with mean age of 33 years, from 21 to 45 years old; 20 eyes) diagnosed with degree II-IV KK, with non-corrected visual acuity of 0.3 or lower. The original questionnaire with three blocks of questions about subjective assessment of the severity of discomfort associated with the disease, expectations of treatment results and its effectiveness was used to study the quality of life of KK patients who underwent surgery. The evaluation method used a five-point grading scale.

RESULTS

Despite the inability to objectively assess the result of treatment, patients can generally note the trend for improvement. Especially significant are the increase of visual acuity, improvement of general health, feeling of comfort and more optimistic view of one's future. Comparison of the expectations and treatment results has shown that some therapeutic effects are overestimated by the patients, while some others are underestimated. A priori, they overvalue the effects of treatment (actions associated with visual tasks - reading, writing), but at the same time undervalue the characteristics of overall personal and emotional state (except for spatial safety and comfort), i.e. the characteristics that determine the quality of life.

CONCLUSION

The aims of writing a valid and reliable questionnaire have been achieved partially, and its further development requires comparison of the obtained results with psychodiagnostic data, which would reveal the nature of psychological factors that form the quality of life perception in patients with various vision disorders.

[Results of confocal microscopy of the cornea after bandage therapeutic-optical keratoplasty in keratoconus]

Bandage therapeutic-optical keratoplasty (BTOK) is one of the modern methods of surgical treatment of keratoconus (KC) that allows to improve visual functions by changing keratotopographic and pachymetric parameters of the cornea in the zone of ectasia. Long-term results show that changes also affect the central part of the cornea, which tends to flatten.

PURPOSE

To compare the light confocal microscopy appearance of the cornea before and after BTOK surgery.

MATERIAL AND METHODS

We examined 15 patients (15 eyes) with progressive keratoconus (7 eyes with Amsler stage I KC and 8 eyes with Amsler stage III KC), who subsequently underwent BTOCK surgery. Using the Confoscan-4 confocal light microscope (Nidek, Japan), we studied the structure of central and paracentral cornea. The exact zone of interest was determined individually depending on the location of the graft.

RESULTS

In all cases, morphological changes in the cornea characteristic of the stage II and III KC were detected. Twelve months after the operation, there was an increase in the transparency of intercellular substance of the stroma with a clearer visualization of keratocyte nuclei in the optical zone as well as at the site of the graft. In the area of interface, tissue compaction in the form of diffuse fibrosis with local scar formation could be seen. Neither significant changes in the cell structure, nor a decrease in cell density were found in the central part of ectasia and the areas of clear visualization of the endothelium under the graft. Additional postoperative assessment of the level of corneal light scattering indicated a tendency towards restoration of stromal transparency and optical uniformity.

CONCLUSION

As a result of interlayer graft implantation in the zone of corneal ectasia, a tendency to structural improvement in its central and paracentral parts was revealed. Local fibrosis in the interface area can indirectly indicate biomechanical «strengthening» of this zone.