Photorefractive keratectomy after DMEK for corneal decompensation by phakic IOL

Purpose To provide the first description of photorefractive keratectomy (PRK) for the correction of mild residual refractive error after Descemet membrane endothelial keratoplasty (DMEK). Methods Case report. Results A 45 year-old woman presenting with phakic intraocular lens (PIOL)-related corneal decompensation underwent staged DMEK surgery following PIOL explantation and cataract surgery. Eighteen months after DMEK, uncorrected distance visual acuity (UDVA) was 20/60 and best-corrected visual acuity (BCVA) was 20/22, with a stable refraction. The patient requested refractive surgery to decrease spectacle dependance, and wavefront-optimized PRK was performed. At last follow-up observation thirty-three months after PRK (54 months after DMEK surgery), UDVA was 20/20, the cornea remained clear without signs of rejection or endothelial failure, and the endothelial cell loss rate was not accelerated after PRK. Conclusion Since long-term visual and refractive stability can be expected after DMEK, PRK may be a particular safe and effective approach for the correction of mild residual refractive errors after DMEK. However, we consider that surgeons must exercise caution when considering keratorefractive surgery in these eyes due to postoperative changes in corneal curvature and thickness, and further studies are encouraged.

Phacoemulsification and calculation of intraocular lenses in patients given keratorefractive surgery. Part 2

Effective rehabilitation of patients with cataracts who underwent keratorefractive surgeries requires that the optical power of the IOL be calculated correctly to avoid hyperopic error. The purpose of the 2nd part of the research (for the 1st part, see ROJ, 2021; 14 (2): 55–58) is to present the results of cataract phacoemulsification in patients subjected to keratorefractive surgery based on the author’s algorithm for calculating the optical power of the IOL. Material and methods. The algorithm used optical biometry with an IOL-Master device. The main technique of improving the accuracy of IOL calculation after keratorefractive operations has been to introduce amendments to standard IOL calculation formulas. This work proposes an alternative, which consists in using the Hoffer Q formula, as it is more consistent with changes in the anterior segment of the myopic eye after keratorefractive surgery than other basic. The main distinguishing feature of the Hoffer Q formula is that the corneal refraction is not converted into the radius of curvature but is applied directly as the optical power of a “thin lens”. Results. The empirical customized correction was +1.0 D with regard to the estimated planned postoperative refraction (for patients with initial myopia from -3 to -9 D). The use of the “thin lens” principle made it possible to extrapolate this formula and apply it after LASIK surgery and after radial keratotomy. Conclusion. The proposed technique of IOL calculation was implemented for cataract phacoemulsification in over 200 patients who underwent keratorefractive surgeries. No cases of hyperopic shift of postoperative refraction were noted. The deviation from the planned myopic refraction did not exceed 1.0 D.

Assessment of changes in the biomechanical properties of the cornea after FemtoLASIK surgery

Purpose. The aim of the study is to investigate the biomechanical properties of the cornea before and after FemtoLASIK in patients with myopia. Material and methods. 24 patients (42 eyes) underwent refractive vision correction using the FemtoLASIK method. The Oculus CORVIS ST ® device (Oculus, Germany) was used to assess the biomechanical properties of the cornea. Results. A statistically significant decrease in the rigidity and strength of the cornea was noted after keratorefractive surgery. Conclusion. Refractive surgery using FemtoLASIK technology leads to a decrease in the rigidity of the cornea, and therefore to a reduction in its framework properties. Key words: refractive surgery, FemtoLASIK, myopia, laser correction, biomechanical properties of the cornea, Oculus CORVIS ST ®.

Choosing the optimal method for preoperative risk assessment of dry eye syndrome development in patients with myopia

Aim. Comparative analysis of the effectiveness of keratotopography methods and classical Norn’s test in assessing the stability of the tear film (TF) in patients with myopia before photorefractive surgery. Methods. The study involved 26 patients. All of them were planned for keratorefractive surgery to correct myopic refraction and astigmatism. Their age averaged 32.5±14.5 years (18-47 years). The stability of pre-corneal tear film was assessed using computed keratotopography and Norn’s test - the tear film rupture time (TFRT) was determined. A standard questionnaire was also used to assess the severity of symptoms of dry eye syndrome (DES). A comparison was made of the indicators of tear film, stability obtained by the methods of keratotopography and Norn’s test, with their subsequent comparison with the data of the questionnaire. Results. In 17 patients (65.4 %), TFRT index corresponded to the age norm. In the remaining 9 people (34.6 %), indicators of tear film stability were reduced both by keratotopography (12±4 sec) and by Norn’s test (13.5± 4.5 sec), and there were also subjective signs of dry eye syndrome according to questionnaire data. The data turned out to be comparable. Conclusion. The incidence of impaired stability of the TF and subjective manifestations of DES among patients planned for keratorefractive surgery for myopia and myopic astigmatism was significant and, according to our data, made 34.6 %. To prevent complicated postoperative course of photorefractive surgery, it is necessary to assess the condition of the ocular surface immediately before refractive surgery, to identify the risk group for DES development. Key words: dry eye syndrome; tear film; keratotopography; Norn’s test; tear film rupture time.

Phacoemulsification and calculation of intraocular lenses in patients given keratorefractive surgery. Part 1

Rationale.Qualitative rehabilitation of patients with cataracts who had keratorefractive surgeries depends on phacoemulsification technology and correctly calculated optical power of the IOL. Purpose: present the author’s own approaches to the development of surgical tactics for treating patients with cataracts who underwent keratorefractive surgeries. Material and methods. The complicated character of cataract surgery performed after LASIK — deterioration of visualization due to the presence of an optical ablation zone and a transition zone (6–7 mm) — is successfully compensated by instillations of a dispersed viscoelastic (methylcellulose) onto the surface of the cornea. Another factor is the deepening of the anterior chamber in high myopia, which is uncomfortable for manipulation and may require a lowerlevel of irrigation (up to 60 mm Hg). The technology of surgery performed after radial keratotomy (RK) requires utmost attention to the prevention of surgical astigmatism that could emerge due to biomechanical instability of the cornea. To ensure such prevention, paracentesis is performed outside the zone of keratotomy scars, the main 2.2 mm incision is made after capsulorhexis in the sclerolimbal zone, and at theend of the operation, a subconjunctival injection is performed in the conjunctival zone of the knife keratom entrance for the tamponade ofthe outer part of the incision without suturing. These techniques made it possible to successfully perform more than 200 operations and achieve a favorable course of the postoperative period from the first day. Fast adaptation of the incision (1–2 days), uncomplicated course of the postoperative period and the absence of induced astigmatism are important advantages of this technology. Conclusion. The choice of surgical technology, taking into account the initial state of the eye after LASIK and RK surgeries, is an important task. Yet the main problem with which the doctor is faced after keratorefractive surgery is the difficulty of calculating the optical power of the IOL which must take into account the special needs of the patient with a particular refractive history, which will be reported in part 2 of the article.

Corneal topography and classical test in the diagnosis of dry eye syndrome in patients with myopia and myopic astigmatism before keratorefractive surgery

Purpose.To conduct a comparative analysis of the effectiveness of assessing the stability of the tear film using corneotopography and the classic Norn test in patients with myopia and myopic astigmatism before keratorefractive surgery. Material and methods. The study included 26 patients planned for keratorefractive surgery for myopia and myopic astigmatism, aged 18 to 47 years. 7 people there was a mild degree of myopia, in 14 people – medium degree, in 5 people – high degree. The average degree of corneal astigmatism was 2.25 diopters. The stability of the pre-corneal tear film was assessed using computed keratotopography and Norn's test – the tear film rupture time (TFRT) was deter- mined. A standard questionnaire was also used to assess the severity of symptoms of dry eye syndrome. A comparison was made of the indicators of the stability of the tear film obtained by the methods of corneotopography and the Norn's test, with their subsequent comparison with the data of the questionnaire. Results. In 17 patients (65.4%), the TFRT index corresponded to the age norm. In the remaining 9 people (34.6%), indicators of stability of the tear film were reduced both by corneotopography (12±4 sec) and by Norn's test (13.5±4.5 sec), and there were also subjective signs of dry eye syndrome according to data questionnaire. The data turned out to be comparable. Conclusions. 1. Among the total population of patients, 34.6% were persons with impaired tear film stability and subjective manifestations of dry eye syndrome. 2. Assessment of the stability of the tear film, determined using the method of corneal topography, showed a high degree of comparability with the results of Norn's test. A significant advantage of the keratotopography method is its non-invasiveness. 3. It is necessary to pay attention to the condition of the ocular surface and identify risk groups to avoid chronicity or aggravation of existing disorders. Key words: dry eye syndrome, tear film, keratotopography, Norn's test.

Logistic Regression Model Using Scheimpflug-Placido Cornea Topographer Parameters to Diagnose Keratoconus

Purpose. Diagnose keratoconus by establishing an effective logistic regression model from the data obtained with a Scheimpflug-Placido cornea topographer. Methods. Topographical parameters of 125 eyes of 70 patients diagnosed with keratoconus by clinical or topographical findings were compared with 120 eyes of 63 patients who were defined as keratorefractive surgery candidates. The receiver operating character (ROC) curve analysis was performed to determine the diagnostic ability of the topographic parameters. The data set of parameters with an AUROC (area under the ROC curve) value greater than 0.9 was analyzed with logistic regression analysis (LRA) to determine the most predictive model that could diagnose keratoconus. A logit formula of the model was built, and the logit values of every eye in the study were calculated according to this formula. Then, an ROC analysis of the logit values was done. Results. Baiocchi Calossi Versaci front index (BCVf) had the highest AUROC value (0.976) in the study. The LRA model, which had the highest prediction ability, had 97.5% accuracy, 96.8% sensitivity, and 99.2% specificity. The most significant parameters were found to be BCVf ( p = 0.001 ), BCVb (Baiocchi Calossi Versaci back) ( p = 0.002 ), posterior rf (apical radius of the flattest meridian of the aspherotoric surface in 4.5 mm diameter of the cornea) ( p = 0.005 ), central corneal thickness ( p = 0.072 ), and minimum corneal thickness ( p = 0.494 ). Conclusions. The LRA model can distinguish keratoconus corneas from normal ones with high accuracy without the need for complex computer algorithms.