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Purpose: The objective of this study was to investigate the usefulness of four different algorithms to correct noncontact intraocular pressure measurement errors in keratoconus patients and normal individuals. Methods: Noncorrected intraocular pressure and corrected intraocular pressures were measured in one eye of 34 patients with keratoconus and 34 age- and gender-matched healthy controls using Corvis Scheimpflug Technology. The correlation of noncorrected intraocular pressure and corrected intraocular pressures with age, axial length, corneal shape, thickness, and biomechanics was calculated. Corrected intraocular pressures were compared with noncorrected intraocular pressure using paired t test and Bland-Altman plots (95% limits of agreement). Results: The noncorrected intraocular pressure correlated with corneal thickness and biomechanical parameters in both groups (all p≤0.047), and front and back mean keratometry in the keratoconus group (r=-0.39, p=0.02, and r=0.39, p=0.02, respectively). After adjustment with different intraocular pressure correction algorithms, biomechanically corrected intraocular pressure showed a minimal correlation with corneal features and a nonsignificant difference with noncorrected intraocular pressure in the healthy group (-0.1 ± 1.1 mmHg, p=0.58; 95% limits of agreement: -2.3 to 2.1 mmHg). Conclusions: Measuring intraocular pressure using noncontact tonometry and its corrected forms with a corneal thickness-based simple linear formula in patients with keratoconus is associated with many errors. Using more complex formulas that take into consideration more corneal stiffness parameters in addition to corneal thickness, such as biomechanically corrected intraocular pressure formula, may be more reliable and beneficial in this group of patients. RESUMO Objetivo: Investigar a utilidade de quatro algoritmos diferentes para corrigir erros de medição sem contato da pressão intraocular em pacientes saudáveis e com ceratocone. Métodos: A pressão intraocular não corrigida e as pressões intraoculares corrigidas foram medidas em um olho de 34 pacientes com ceratocone e 34 pacientes do grupo controle saudável pareados por idade e gênero usando a tecnologia Corvis Scheimpflug. Foi calculada a correlação da pressão intraocular não corrigida e das pressões intraoculares corrigidas com idade, comprimento axial e formato, espessura e biomecânica da córnea. As pressões intraoculares corrigidas foram comparadas com a pressão intraocular não corrigida usando o teste t pareado, e gráficos de Bland-Altman (limites de concordância de 95%). Resultados: A pressão intraocular não corrigida correlacionou-se com a espessura da córnea e com os parâmetros biomecânicos em ambos os grupos (todos p≤0,047) e a ceratometria média frontal e posterior no grupo com ceratocone (r=-0,39, p=0,02, r=0,39, p=0,02, respectivamente). Após o ajuste com diferentes algoritmos de correção da pressão intraocular, a pressão intraocular corrigida biomecanicamente revelou uma correlação mínima com as características da córnea e uma diferença não significativa com a pressão intraocular não corrigida no grupo saudável (-0,1 ± 1,1 mmHg, p=0,58; limites de concordância de 95%: -2,3 a 2,1 mmHg). Conclusões: A medição da pressão intraocular usando tonometria sem contato e suas formas corrigidas usando fórmulas lineares, simples, baseadas na espessura da córnea em pacientes com ceratocone estão associadas a muitos erros. O uso de fórmulas mais complexas que consideram mais parâmetros de rigidez da córnea além da espessura da córnea, como fórmula de pressão intraocular corrigida biomecanicamente, pode ser mais confiável e benéfico neste grupo de pacientes.

PURPOSE: To examine and compare corneal cellular and subbasal nerve (SBN) characteristics in post-laser-assisted in situ keratomileusis ectasia (PLE) corneas, normal post-laser-assisted in situ keratomileusis corneas (PLC), keratoconus (KC) corneas, and normal virgin corneas (NC). METHODS: In this cross-sectional comparative study, 18 PLE eyes of 11 patients, 18 PLC of 15 cases, 32 KC eyes of 32 patients, and 29 NC of 29 subjects were assessed using in vivo confocal microscopy. The density of the basal epithelial cell (BEC), anterior keratocyte, posterior keratocyte, and endothelial cell layers, as well as the characteristics of SBN fibers, was compared between the 4 groups. RESULTS: The density of the BEC and anterior and posterior keratocyte layers was significantly lower in KC compared with NC (-650 ± 190, P = 0.013; -181 ± 39, P < 0.001; and -36 ± 11, P = 0.021, respectively). However, there was no significant difference between PLE and PLC regarding these parameters (all Ps � 0.6). Mean SBN parameters, including central corneal nerve branch density, nerve fiber length, total branch density, and nerve fiber area, were significantly lower in KC compared with NC and in PLE compared with PLC (all Ps � 0.021). CONCLUSIONS: The pathophysiology of PLE seems to differ from KC. Apparent changes in the BEC and anterior and posterior keratocytes associated with KC were not observed in PLE. However, SBNs seem to be involved in both conditions.

Trabeculectomy is the most common surgical procedure for the management of glaucoma, which may significantly influence ocular biometry. Axial length and anterior chamber depth tend to decrease, while crystalline lens and choroidal thickness increase post-operatively. An increase in with-the-rule astigmatism is also observed after the procedure. Such biometric changes affect intraocular lens power calculation even years after the procedure. Non-contact biometric methods and postponing cataract surgery after trabeculectomy could reduce calculation errors associated with surgically induced alterations in ocular biometrics.

PURPOSE To compare biometric changes measured with contact and noncontact methods after mitomycin-C-augmented trabeculectomy. METHODS In this prospective study, 31 eyes from 31 glaucoma patients scheduled for primary trabeculectomy were enrolled. Biometric parameters including axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) were measured using contact ultrasound biometry (UD-6000 Ultrasonic A/B scanner biometer; Tomey Corporation, Nagoya, Japan) and a noncontact optical biometry device (Lenstar; Haag-Streit AG, Koeniz, Switzerland). Measurements were taken the day before trabeculectomy and then compared with measurements obtained 3 and 6 months after surgery. RESULTS The AL and ACD were significantly decreased at 3 and 6 months compared with baseline values taken with each biometry method. There was a significant increase in LT measured by the Lenstar device at the 3- and 6-month follow-up. At both the 3- and 6-month follow-up, the mean AL measurement reduction with the Lenstar device was significantly lower than that of the A-scan ultrasound measurements. The mean ACD changes between the two devices were not significantly different. CONCLUSIONS There is a small but significant decrease in the AL and ACD after trabeculectomy as measured with both the contact and noncontact methods. The amount of AL reduction measured is significantly smaller using the noncontact method, making it the preferable method for intraocular lens power calculation for patients who need cataract surgery combined with or after trabeculectomy. The LT measured by the Lenstar device increased significantly after the operation, which can be an early sign of the progression of cataractous changes after trabeculectomy.

This review article aimed to evaluate ocular biometric changes after trabeculectomy. The PubMed database was searched using the keywords "axial length" (AL), "anterior chamber depth" (ACD), "corneal astigmatism," "corneal topography" and "trabeculectomy." The extracted studies were categorized based on the evaluated parameters and the biometry method (contact and non-contact). Comparable studies with respect to their sample size were combined for statistical analysis. Twenty-five studies including 690 individuals which met the inclusion criteria were selected. After trabeculectomy, a significant and persistent AL reduction, with a range of 0.1-0.19 and 0.1-0.9 mm measured with contact and non-contact methods, respectively, was observed. With respect to topographic changes, 0.38-1.4 diopters (D) with-the-rule (WTR) astigmatism was induced postoperatively. All studies revealed ACD reduction immediately after surgery, which gradually deepened and approximated its preoperative levels on day 14. ACD reduction was not significant after that period in the majority of cases. In conclusion, changes in ACD is of small amount and of short period, thus it can be ignored; however, reported changes in AL and keratometry are of sufficient magnitude and can affect the refractive prediction of combined cataract surgery and trabeculectomy.

To compare surgical sequences of combined intracorneal ring segment (ICRS) implantation and corneal collagen cross-linking (CXL) in keratoconus and corneal ectasia in terms of visual, refractive, and keratometric outcomes.A comprehensive electronic search (in PubMed, Web of Science, Scopus, Embase, and Cochrane Library) was conducted in accordance with the PRISMA statement to find articles on combined ICRS implantation and CXL in keratoconus and corneal ectasia. The search period was from the inception of the database up to April 2017. Eligible articles were categorized into 3 surgical sequences (same day, ICRS first, and CXL first) and assessed qualitatively. Articles with 12 months of follow-up data after combined surgery were included in the meta-analysis.The initial search identified 120 related articles, of which 17 were included in the review after screening. The quality assessment showed that visual, refractive, and keratometric improvement was observed in all studies in all 3 groups of combined surgery. Meta-analysis on 6 studies that reported 12-month follow-up outcomes showed no significant differences between the 3 groups regarding uncorrected and best-corrected visual acuity and cylindrical refractive error. However, results with simultaneous surgery were superior to the CXL-first technique in terms of spherical refractive errors and flat-K (P = 0.011 and P = 0.0001, respectively) and to both CXL first and ICRS first in terms of steep-K (P = 0.002 and P = 0.007, respectively).Simultaneous ICRS implantation and CXL may provide better outcomes than staged techniques for improving the corneal shape.

Purpose To evaluate biometric changes after mitomycin C augmented trabeculectomy and their effect on intraocular lens (IOL) power calculation using different formulas. Methods In this prospective, interventional case series study, 34 eyes of 31 phakic glaucoma patients who were scheduled for primary trabeculectomy were enrolled. Using a noncontact biometry device (Lenstar, Haag-Streit AG, Koeniz, Switzerland), axial length (AL), mean corneal power, and IOL power were calculated with the Hoffer Q, Holladay, and SRK/T formulas 1 day before surgery and compared to those obtained 3 and 6 months after the operation. Bland-Altman plot was used to determine agreement between preoperative and postoperative IOL power values. Results The AL was significantly decreased at month 3 (-0.14 ± 0.13 mm) and month 6 (-0.14 ± 0.15 mm) as compared to baseline values (both p values Conclusions Despite significant changes in AL and corneal power after trabeculectomy, IOL power calculation remains unchanged; therefore adjustment of IOL power calculation after trabeculectomy seems unnecessary.