Thin Corneas Research Articles

Сравнительный анализ результатов ускоренного кросслинкинга коллагена тонкой роговицы при первичном кератоконусе и ятрогенных кератэктазиях

Сравнительный анализ результатов ускоренного кросслинкинга коллагена тонкой роговицы при первичном кератоконусе и ятрогенных кератэктазиях

Corneal Cross-linking in Thin Corneas: 1-Year Results of Accelerated Contact Lens-Assisted Treatment of Keratoconus.

To evaluate the safety and efficacy of accelerated contact lens-assisted cross-linking (A-CACXL) for patients with keratoconus and thin corneas. This retrospective study included consecutive patients undergoing A-CACXL for progressive keratoconus from 2015 to 2017. Patients with a minimum corneal thickness of 400 µm or less after epithelium removal who underwent A-CACXL (9 mW/cm2 for 10 minutes, using iso-osmolar 0.1% riboflavin solution and a 90-µm thick, daily disposable bandage soft contact lens) with a follow-up time of 12 months or more were included. The main outcome measures were uncorrected (UDVA) and corrected (CDVA) distance visual acuity and minimum corneal thickness at the last visit. Progression (increase) and flattening (decrease) were defined as a change of 1.00 diopters (D) or greater in maximum keratometry or 1.50 D or greater in mean keratometry. Overall, 24 eyes of 24 patients were included with a follow-up time of 18.2 ± 6.3 months and a mean minimum corneal thickness, after epithelial debridement, of 353.13 µm. There was a significant improvement in UDVA (P = .009), maximum keratometry (P = .03), anterior steep keratometry (P = .04), anterior astigmatism (P = .02), and posterior astigmatism (P = .04) with no significant change in minimum corneal thickness (P = .11). There was a significant improvement in UDVA (0.90 ± 0.63 to 0.64 ± 0.47 logMAR, P = .009), maximum keratometry (61.20 ± 6.30 to 59.90 ± 5.70 D, P = .03), anterior steep keratometry (55.10 ± 3.90 to 54.50 ± 4.10 D, P = .04), anterior astigmatism (5.50 ± 2.40 to 4.60 ± 2.10 D, P = .02), and posterior astigmatism (0.90 ± 0.40 to 0.80 ± 0.40 D, P = .04) with no significant change in minimum corneal thickness (from 399.8 ± 30.7 to 391.0 ± 43.8 μm, P = .11). Flattening occurred in 45.8% (n = 11) and progression in 20.8% (n = 5). There were no serious adverse events. Persistent clinically significant stromal haze occurred in one case and completely resolved by 6 months. There was no significant change in endothelial cell density (P = .10). In patients with keratoconus and thin corneas, A-CACXL halted keratoconus progression in 80%, led to flattening in 45%, and significantly improved UDVA and keratometry values without any evidence of damage to the corneal endothelium or permanent adverse events. [J Refract Surg. 2019;35(10):642-648.].

Analysis of corneal biometry in a black South African population

Background: Corneal astigmatism and central corneal thickness are important clinical parameters for cataract surgery and glaucoma, respectively. There is very little research on the central corneal thickness and the prevalence and pattern of corneal astigmatism in black South Africans. Aim: The aim of this study was to analyse the corneal astigmatism and central corneal thickness of a large population of black South Africans awaiting cataract surgery. Setting: The study was conducted at St John Eye Hospital, Soweto, South Africa. Methods: This was a cross-sectional study of a database of adult black patients awaiting cataract surgery. Biometric data was captured using Sheimpflug Imaging (Nidek AL-Scan). Steep corneas (K readings of more than 48 D) or abnormally thin or thick corneas (central corneal thickness [CCT] 650 μ m) were excluded from the study. Results: A total of 3231 eyes of 1713 patients were included in this study. Patient ages ranged from 18 to 99 years with a median age of 67 years (interquartile range [IQR] 57–75 years). There were more females ( n = 1064) than males ( n = 649). The median central corneal thickness was 494 μ m (IQR 473 μ m–516 μ m). The median corneal astigmatism was 0.92 dioptres (IQR 0.55–1.43 dioptres). A large proportion (45%) of our study sample patients had 1 dioptre or more of corneal astigmatism. Conclusion: This analysis of corneal biometric data revealed that a large proportion of black South African patients awaiting cataract surgery have thin corneas and visually significant corneal astigmatism.

Corneal Biomechanics and Visual Field Progression in Eyes with Seemingly Well-Controlled Intraocular Pressure

To investigate the incidence and risk factors for glaucomatous visual field progression in eyes with well-controlled intraocular pressure (IOP). Prospective cohort. A total of 460 eyes of 334 patients with glaucoma under treatment. Study subjects had a mean follow-up of 4.3±0.8 years. Patients were classified as well controlled if all IOP measurements were less than 18 mmHg. Rates of visual field progression were calculated using ordinary least-squares linear regression of standard automated perimetry (SAP) mean deviation (MD) values over time. Progression was defined as a significantly negative MD slope (alpha= 0.05). Rates of SAP MD change; mean and peak IOP, and IOP fluctuation; and corneal biomechanics: corneal hysteresis (CH), central corneal thickness (CCT), and corneal index. Of the 179 eyes with well-controlled IOP, 42 (23.5%) demonstrated visual field progression. There was no significant difference between progressing and stable patients in baseline MD (-6.4±7.1 decibels [dB] vs.-6.0±6.2 dB; P= 0.346), mean IOP (11.7±2.0 mmHg vs. 12.1±2.3 mmHg; P= 0.405), IOP fluctuation (1.6±0.6 mmHg vs. 1.6±0.5 mmHg; P= 0.402), or peak IOP (14.3±1.9 mmHg vs. 14.6±2.1 mmHg; P= 0.926). Progressing eyes had significantly lower CH (8.6±1.3 mmHg vs. 9.4±1.6 mmHg; P= 0.014) and thinner CCT (515.1±33.1 μm vs. 531.1±42.4 μm; P= 0.018, respectively) compared with stable eyes. In the multivariate analysis, a 1 standard deviation lower corneal index, a summation of normalized versions of CH and CCT, resulted in a 68% higher risk of progression (odds ratio, 1.68; 95% confidence interval, 1.08-2.62; P= 0.021). Approximately one-quarter of eyes with well-controlled IOP may show visual field progression over time. Thin cornea and low CH are main risk factors.

To Study the Safety of Multi-dose Topical Anaesthetic Eye Drops One Month after Opening

Purpose: To determine the risk of ocular infections due to topical multi-dose anaesthetic eye drops in patients one month after opening the bottle. Study Design: Quasi experimental study. Place and duration of study: Department of Ophthalmology DHQ Teaching Hospital, Gujranwala from 22nd May 2018 to 22nd June 2018. Materials and Methods: In this study topical anaesthetic eye drops containing proparacaine hydrochloride 0.5% as main ingredient and benzalkonium choride as preservative (Alcaine�) were tested daily to see if any bacterial/fungal growth occurs in the bottle containing eye drops or not. Same bottle was used in patients presenting in outdoor and indoor departments. Samples taken from the bottle contents were cultured on different media to see growth of fungi or bacteria. Patients who already had keratitis, conjunctivitis, corneal opacities, thin corneas and having dry eyes which were prone to get infected were excluded from this study. Results: There were 60 patients included in our study and they were divided in two groups. Group A included those who presented in the outdoor department and group B comprised of those admitted for various operative procedures. There were 30 patients in each group. All patients were adults (18-60 years). After 1 month of daily culturing on agar plates, no micro-organism growth was seen in both groups. Conclusion: Topical anaesthetic eye drops can be used safely for 1 month in different patients after opening the bottle without any risk of causing infectious keratitis, conjunctivitis or endophthalmitis. Keywords: Proparacaine, Culture medium, Endophthalmitis.

The frequency of non-pathologically thin corneas in young healthy adults.

Purpose: Measurement of normal corneal thickness and corneal epithelial thickness is important in keratorefractive surgery, glaucoma, following extended contact lens wear, and in patients with corneal disease. Clinically, a central corneal thickness less than 500 µm is considered to be moderately-to-extremely thin. The purpose of this study was to compare biological differences in patients with clinically thin compared to normal corneal thickness values in healthy young adults using Fourier domain optical coherence tomography.Patients and methods: In total, 168 eyes from 84 patients aged 19–38 years were scanned using an Avanti optical coherence tomographer. To eliminate circadian effects on corneal thickness, all patients were scanned within a 4-hour window. Corneal thickness was measured across the central 6 mm of the cornea. Total central corneal thickness, corneal epithelial thickness, and corneal stromal thickness were compared between males and females and tested for correlations with age, use of systemic hormones, degree of myopia, and corneal curvature.Results: The average central corneal thickness for males and females was 540.5±32.0 μm and 525.2±33.0 μm, respectively (P=0.020). Thirty-eight eyes had corneal thickness measurements below 500 µm; 12% (6 eyes) from males and 28% (16 eyes) from females (P=0.008). All women with corneas below 500 μm were bilaterally thin. This finding differed for men. Corneal thinning was not associated with age, use of systemic hormones, or degree of myopia. Females had steeper keratometry (K) readings (P=0.01 for flat K, P=0.002 for steep K) than males. No differences in layer offset values between normal thickness corneas and thin corneas were evident, suggesting that the reduced thickness was not pathological.Conclusion: The results of this study indicate that a subpopulation of healthy young adults have non-pathologically thin corneas, well below 500 μm; and that these thinner corneas are more frequent in females. This underscores the importance of accurate corneal thickness measurements prior to keratorefractive surgery and when evaluating intraocular pressure in glaucoma.

Методика ультрафиолетового кросслинкинга в лечении прогрессирующего кератоконуса при «тонкой роговице»

Методика ультрафиолетового кросслинкинга в лечении прогрессирующего кератоконуса при «тонкой роговице»

Коррекция миопии высокой степени у пациентов с тонкой роговицей методом имплантации кольца MyoRing

Коррекция миопии высокой степени у пациентов с тонкой роговицей методом имплантации кольца MyoRing

Сравнительный анализ коррекции миопии высокой степени и сложного миопического астигматизма у пациентов с тонкой роговицей методом фемтолазерной интрастромальной имплантации кольца MyoRing и имплантации отрицательной факичной интраокулярной линзы

Сравнительный анализ коррекции миопии высокой степени и сложного миопического астигматизма у пациентов с тонкой роговицей методом фемтолазерной интрастромальной имплантации кольца MyoRing и имплантации отрицательной факичной интраокулярной линзы

Central Corneal Thickness and Its Association with Birth Parameters in Chinese Adolescents

ABSTRACT Purpose To examine the distribution and determinants of central corneal thickness (CCT) including birth weight and gestational age in a school-based samples of Grade 7 students in rural China. Methods 2346 (93.5%) grade 7 students with a mean age of 13.8 years participated in the study. CCT was measured for both eyes using the LenStar LS900. Information regarding birth weight and gestational age was retrieved from the participants’ delivery records. A linear regression model was established to examine the relationship of birth weight, gestational age and other factors with CCT. Results The mean CCT in this population was 534.7 µm and boys had a greater CCT compared with girls (P = .06). CCT was positively related to axial length (r = 0.056) while negatively related to anterior chamber depth (r = −0.076) and corneal power (r = −0.105) . In multivariate analyses, the cornea was 19.35µm thinner in individuals with low birth weight compared with those with normal. In addition, the cornea was 25.25µm thinner in prematurely born adolescents compared with full-term ones. The combined effect of birth weight and gestational age on CCT was not statistically significant (P for interaction = 0.12) Conclusions Low birth weight and small gestational age are associated with thinner corneas in adolescence. This disparity across groups with different levels of birth parameters should be taken into account by future studies investigating CCT as risk factors or diagnostic tests for glaucoma.

Application of optical coherence tomography and optical path length method for monitoring corneal thickness and refractive index change during corneal cross-linking.

Corneal cross-linking (CXL) using UVA irradiation with a riboflavin photosensitizer has emerged as a new treatment paradigm for corneal ectatic disorders. The thickness threshold for protection of intraocular structures has often been challenged with ongoing developments, and corneal thinning becomes an important safety concern, especially for patients with thin corneas. In this study with an ex vivo bovine eye model, we monitored corneal thinning and corneal refractive index changes using optical coherence tomography (OCT) integrated with an adaptation of the optical path length method. CXL experiments were performed based on the standard protocol that includes removal of the corneal epithelium to facilitate diffusion of riboflavin into the stroma. The corneal stromal thickness and group refractive index were measured by a 1310nm Fourier-domain OCT imaging system at three critical points of the procedure: immediately after epithelial removal, after 30min riboflavin instillation, and after 30min UVA irradiation with continuing instillation. We found that the refractive index of the bovine cornea changed significantly from epithelial removal to riboflavin instillation and UVA irradiation, increasing from 1.377±0.005 (mean±standard deviation) after de-epithelization to 1.387±0.003 after 30min instillation and 1.388±0.008 after subsequent irradiation. The corneas also underwent a considerable decrease (10%-20%) in stromal thickness with thinning of 95±29 μm (mean±standard deviation) after riboflavin instillation and a further decrease (∼5%) with thinning of 42±19 μm after UVA irradiation. Our study highlights the importance of corneal thickness monitoring during CXL, especially after riboflavin instillation when the decrease is the largest, to avoid delivering endothelial cytotoxic doses. An increase in refractive index heightens the concern for corneal thinning and the need for careful monitoring as a safety precaution.

Factors of Cataractogenesis in Laser Corneal Refractive Surgery

Purpose: to consider the main factors that stimulate cataractogenesis and the earlier development of cataracts after laser refractive surgery of the cornea. Patients and methods. The clinical material covers observations of the condition in more than 10 thousand eyes from 1 year to 20 years, after various laser refractive corneal operations (PRK, TransPRK, LASIK, FemtoLASIK). Results. Risk factors for cataractogenesis included high initial ametropia, accommodation disturbance, age, and increased external UV exposure. Clinical observations have shown that with laser correction of high degrees of ametropia, the number of cataractogenesis risk factors and their total value increased. Any laser refractive corneal surgery was accompanied by oxidative stress in all structures of the anterior eye and aseptic inflammatory response. The cornea thinning after refractive surgery increased the external UV load on the lens and created the conditions for the accumulation in it of an excessive amount of peroxide radicals. This was one of the important factors predisposing to the earlier development of cataracts. Conclusion. For clinically significant early cataract development after laser refractive corneal surgery, a combination of several cataractogenic factors is needed, such as the degree of severity of oxidative stress in the anterior eye tissue in the early postoperative period, cornea thinning, high corrective ametropia, lack of accommodation, and the patient age over 40 years old.

Corneal Safety and Stability in Cases of Small Incision Lenticule Extraction with Collagen Cross-Linking (SMILE Xtra).

Purpose To assess the safety and stability in cases of small incision lenticule extraction with collagen cross-linking (SMILE Xtra). Methods This study was a retrospective interventional comparative study that included 60 eyes of 30 patients divided equally into two groups: SMILE Xtra and SMILE alone. The inclusion criteria were patients >18 years of age, myopic error >6 D, thinner cornea <520 microns, and abnormal corneal topography. Outcome data were recorded including uncorrected distance visual acuity and corrected distance visual acuity (UDVA and CDVA), manifest refraction spherical equivalent (MRSE), central corneal thickness, average keratometry, endothelial cell density, corneal resistance factor (CRF), and corneal densitometry. The follow-up period was 24 months. Results There was a significant difference between the 2 groups regarding UDVA, CDVA, and MRSE at 1 month. In the SMILE Xtra group, 90% of eyes had postoperative UDVA of 20/20 and 97% had UDVA of 20/30 at 24 months. At 24 months, 26 eyes (87%) vs. 25 eyes (84%) were within ±0.50 D of attempted correction in SMILE Xtra and SMILE groups, respectively. Regarding stability, both groups showed improvement of MRSE at 1st month postoperatively and remained stable along the 24 months of follow-up. CRF and corneal densitometry were higher in the SMILE Xtra group along the whole follow-up period (p=0.001). Conclusion Combining corneal cross-linking with SMILE procedure (SMILE Xtra) is a promising tool to prevent ectasia in high-risk patients. It is a safe and simple procedure that can be offered to patients undergoing SMILE with risk for ectasia. Trial registration no: PACTR201810577524718.

Corneal Cross-Linking: The Science Beyond the Myths and Misconceptions.

There has been a recent explosion in the variety of techniques used to accomplish corneal cross-linking (CXL) for the treatment of ectatic corneal diseases. To understand the success or failure of various techniques, we review the physicochemical basis of corneal CXL and re-evaluate the current principles and long-standing conventional wisdom in the light of recent, compelling, and sometimes contradictory research. Two clinicians and a medicinal chemist developed a list of current key topics, controversies, and questions in the field of corneal CXL based on information from current literature, medical conferences, and discussions with international practitioners of CXL. Standard corneal CXL with removal of the corneal epithelium is a safe and efficacious procedure for the treatment of corneal ectasias. However, the necessity of epithelium removal is painful for patients, involves risk and requires significant recovery time. Attempts to move to transepithelial corneal CXL have been hindered by the lack of a coherent understanding of the physicochemistry of corneal CXL. Misconceptions about the applicability of the Bunsen-Roscoe law of reciprocity and the Lambert-Beer law in CXL hamper the ability to predict the effect of ultraviolet A energy during CXL. Improved understanding of CXL may also expand the treatment group for corneal ectasia to those with thinner corneas. Finally, it is essential to understand the role of oxygen in successful CXL. Improved understanding of the complex interactions of riboflavin, ultraviolet A energy and oxygen in corneal CXL may provide a successful route to transepithelial corneal CXL.

Effect of Riboflavin Solution With Hydroxypropyl Methylcellulose and Eyelid Speculum on Pachymetry Changes During Accelerated Collagen Crosslinking.

To assess corneal thickness changes with isotonic riboflavin (RF) solution with hydroxylpropyl methylcellulose in patients undergoing accelerated corneal collagen crosslinking (CXL) with and without an eyelid speculum. Fifty-two eyes of 48 patients with progressive keratoconus were enrolled in this study. The patients in this study were divided into 2 groups: in group 1 an eyelid speculum was removed during 20-minute RF (0.1%) + hydroxylpropyl methylcellulose (Mediocross M; Avedro Inc, Waltham, MA) instillation, and in group 2 the eyelid speculum was retained in place during the entire CXL procedure. All patients underwent accelerated CXL using continuous ultraviolet-A (UVA) light exposure at 9 mW/cm for 10 minutes; total energy dose was 5.4 J/cm. Intraoperative ultrasound pachymetry measurements were obtained before and after epithelial removal, after RF loading, and after UVA light exposure at 5 and 10 minutes. The preoperative pachymetric measurements decreased in both groups after the removal of epithelium [group 1 (n = 26): -25 μm, group 2 (n = 26): -31 μm, P = 0.234]. Although the thinnest pachymetry significantly increased after soaking in both group 1 (52.26 μm) and group 2 (27.88 μm, P < 0.001), closure of the eyelids during RF instillation further increased the pachymetry readings (P < 0.0001). The corneal thickness remained stable in both groups during UVA irradiation at 5 and 10 minutes (P > 0.05). Closure of the eyelids further induces corneal swelling that may offer an advantage to improve safety of the procedure particularly in thin corneas.

Differences in ocular biometrics and aqueous humour dynamics between Chinese and Caucasian adults

BackgroundGlaucoma prevalence and subtype profile vary across different racial and ethnic groups. This study provides a comparative evaluation of differences in aqueous humour dynamics (AHD) and ocular biometrics in healthy...

Central Corneal Thickness Variances Among Different Asian Ethnicities in Glaucoma and Nonglaucoma Patients

To compare the central corneal thickness (CCT) between different ethnicities and particularly Asian subethnic groups that may contribute to the different glaucoma diagnoses using the optical low-coherence reflectometry technique. A retrospective study of 6 years including 1512 eyes of 929 patients of the Beckman vision center, University of California, San Francisco from 2011 to 2017 had their biometric parameters, including CCT, measured with the Lenstar. Patients were categorized into African Americans, Caucasians, Hispanics, Pacific Islanders, and Asians. Asians were further subcategorized into Chinese, Vietnamese, Koreans, Filipinos, and Japanese. Among 1356 patients who had their CCT measured by Lenstar from 2011 to 2017, 1512 eyes of 929 patients were included. The study population included 462 Caucasians (52.96%), 60 African Americans (6.46%), 92 Hispanics (9.9%), 32 Pacific Islanders (3.44%), 130 Chinese (13.99%), 52 Filipinos (5.6%), 37 Vietnamese (3.98%), 34 Koreans (3.66%), and 30 Japanese (3.23%). African Americans had the thinnest CCT with a mean of 518.62±40.3 followed by Asians with a mean of 539.29±34.1. Among the Asian study sample, the Chinese had the thinnest CCT with a mean of 537.66±32.5. CCT was adjusted for age, sex, glaucoma diagnosis, diabetes status, and prostaglandin analogs use for >12 months. Optical low-coherence reflectometry is a widely used technology, which can measure CCT. Our study confirms that African Americans have the thinnest corneas followed by Asians. In the latter group, relatively thin CCT may partly explain their high rates of normal-tension glaucoma.

Modified Goldmann prism intraocular pressure measurement accuracy and correlation to corneal biomechanical metrics: multicentre randomised clinical trial

PurposeClinically evaluate intraocular pressure (IOP) measurements taken with a Goldmann applanation tonometer (GAT) prism and a modified surface Goldmann prism examining measurement differences correlated to central corneal thickness (CCT) and...

Correlation of Central Corneal Thickness and Keratometry with Refraction and Axial Length: A Prospective Analytic Study.

Introduction The correlation between corneal curvature and central corneal thickness (CCT), with ocular parameters like axial length and refraction, remains elusive. The various ocular biometric parameters are interdependent and their correlation varies with the population studied. A comprehensive study is required for a better understanding of the ocular biometric properties of Indian eyes.MethodologyThis is a prospective study done in 156 subjects. Subjects with clear lens and clear cornea were included in the study. Those with corneal opacity, cataract, pregnancy, and diabetes were excluded. Cycloplegic refraction, autokeratometry (Potex, ultrasonic auto keratometer), central corneal thickness (ultrasonic pachymeter), and axial length (Sonomed) were done in all subjects. Subjects were divided into two groups based on refraction, for an analysis of parameters. Group one included subjects with refraction of +3 diopters (D) to -2.99D and group two with subjects with > -3D refraction.ResultsWith an increasing axial length and myopic refraction, the corneal curvature tends to be steeper. The average CCT of subjects in group one and group two were 530.34 microns and 542.63 microns, respectively. Subjects with refraction more than 10 diopters or axial length more than 25 mm had a mean CCT of 525.25 microns. Subjects with myopic refraction between 3 diopters and 10 diopters had a mean CCT of 551.32 microns.ConclusionIncrease in corneal power is associated with increasing myopic refraction. Steeper corneal curvature is correlated with increasing axial length and thinner corneas. The mean CCT was 533.87 microns with a standard deviation (SD) of 40.02. Axial myopia is associated with an increase in corneal thickness. These ocular biometric findings have crucial implications in refractive surgeries.

Current concepts in crosslinking thin corneas.

Corneal cross-linking (CXL), introduced by Wollensak et al. in 2003, is a minimally invasive procedure to halt the progression of keratoconus. Conventional CXL is recommended in eyes with corneal thickness of at least 400 microns after de-epithelialization to prevent endothelial toxicity. However, most of the keratoconic corneas requiring CXL may not fulfill this preoperative inclusion criterion. Moderate-to-advanced cases are often found to have a pachymetry less than this threshold. There are various modifications to the conventional method to circumvent this issue of CXL thin corneas while avoiding the possible complications. This review is an update on the modifications of conventional CXL for thin corneas.