How long does the recovery of corneal sensitivity in different corneal regions take after LASEK?

AIM: To determine the corneal sensitivity recovery period after laser-assisted sub-epithelial keratectomy (LASEK) refractive surgery and investigate the effects of ablation depth on it. METHODS: In this study examinations were performed on 90 right eyes of 90 people (34 males and 56 females) with an age range of 20-35 and an average of 22.26±3.8 years old. A sensation of 5 corneal regions, including the center and 4 mid-peripheral regions, i.e., nasal, inferior, temporal, and superior, each at a distance of 2 mm from the center of the cornea were measured with a Cochet-Bonnet esthesiometer device in 3-time points including before LASEK, 1 and 3mo after the surgery, respectively. LASEK was performed on individuals with stabilized myopia of -1.00 to -7.00 diopters and astigmatism of less than 2.00 diopters. Furthermore, the individuals were divided into three groups regarding ablation depth. RESULTS: The highest level of corneal sensitivity before surgery was related to the center of the cornea (59.1±7.76), and the highest level of corneal sensitivity loss was also related to this region. The sensation of all measured corneal regions significantly reduced 1mo postoperatively and returned to their preoperative levels 3mo after surgery (mean of 5 corneal regions in levels of preoperation: 58.2±6.48, 1mo postoperation: 57.3±5.84, 3mo postoperation: 58.2±5.49; P<0.05). A significant relationship was found between ablation depth and corneal sensitivity changes in the center and temporal regions (P<0.05). CONCLUSION: Corneal sensitivity in myopia and low astigmatism decreases after LASEK and reaches the preoperative level within 3mo. The depth of ablation during surgery affected the recovery of corneal sensitivity.

Agreements' profile of Scheimpflug-based optical biometer with gold standard partial coherence interferometry.

AIM: To determine the agreement of ocular biometric indices including axial length, keratometric readings, anterior chamber depth, and horizontal corneal diameter between the Pentacam AXL and IOL Master 500. METHODS: The study was a large cross-sectional population-based study (Tehran Geriatric Eye Study) conducted from Jan 2019 to Jan 2020. A total of 160 clusters were randomly selected proportional to size (each cluster contained 20 individuals) from 22 strata of Tehran city. All people aged 60y and above were invited to participate in the study. For all participants, preliminary ocular examinations were performed including the measurement of uncorrected and best-corrected visual acuity, objective and subjective refraction, anterior and posterior segment examinations. All participants underwent an ocular biometry using the Pentacam AXL and IOL Master 500. RESULTS: The 95% limits of agreement (LoA) between the two devices were -0.13 to 0.19, -0.15 to 0.17, and -0.13 to 0.19 in normal, pseudophakic, and cataractous eyes, respectively. With increasing the axial length, the difference between the two devices significantly increased in all three groups of normal, pseudophakic, and cataractous eyes (P<0.001). The 95% LoAs between the two devices regarding the mean keratometry shows that the best LoAs were seen in cataractous (-0.33 to 0.81) and followed by normal eyes (-0.36 to 0.86) and the pseudophakic eyes (-0.48 to 0.90) had the widest LoA. The 95% LoAs for horizontal corneal diameter measurements were -0.08 to 0.86, -0.03 to 0.83, and -0.07 to 0.87 in normal, pseudophakic, and cataractous eyes, respectively. The 95% LoAs of anterior chamber depth measurements between the two devices was -0.39 to 0.19 and -0.37 to 0.13 in normal eyes and cataractous, respectively. CONCLUSION: The Pentacam AXL has excellent agreement with the gold standard, IOL Master 500 in measuring axial length. In eyes with cataracts, the difference between the two devices is more scattered. With the increasing of axial length, the difference between the two devices increased, which should be considered when using Pentacam AXL.

Comparison of Intraocular Lens Power Calculation between Standard Partial Coherence Interferometry-Based and Scheimpflug-Based Biometers: The Importance of Lens Constant Optimization.

Purpose: To compare the intraocular lens (IOLs) power calculated with Haigis, Hoffer Q, Holladay 1, and SRK/T formulas between the IOLs Master 500 and Pentacam AXL according to the lens status. Methods: In this cross-sectional study, sampling was done in subjects above 60 years living in Tehran using multi-stage cluster sampling. All participants underwent optometric examinations including the measurement of visual acuity and refraction as well as slit-lamp biomicroscopy to determine the lens status. Biometric measurements and IOLs power calculation were done using the IOL Master 500 and Pentacam AXL. The order of imaging modalities was random in subjects. IOL power calculation was done according to optimized ULIB constants for the Alcon SA60AT lens. The IOL power was calculated according to a target refraction of emmetropia in all subjects. Results: After applying the exclusion criteria, 1865 right eyes were analyzed. The mean IOL difference between the two devices was -0.33 ± 0.35, -0.38 ± 0.39, -0.41 ± 0.43, and -0.51 ± 0.43 according to the SRK/T, Holladay, Hoffer Q, and Haigis formulas, respectively. The Pentacam calculated larger IOL power values in all cases. The 95% limits of agreement (LoA) between the two devices for the above formulas were -1.01 to 0.35, -1.14 to 0.39, -1.25 to 0.43, and -1.35 to 0.33, respectively. The best LoA were observed in normal lenses for all formulas. The difference in the calculated IOL power between the two devices using the four formulas had a significant correlation with axial length, mean keratometry reading, and anterior chamber depth. According to the results of the four formulas, mean keratometry reading had the highest standardized regression coefficient in all formulas. Conclusion: Although the difference in the calculated IOL power between IOL Master 500 and Pentacam AXL is not significant clinically, the results of these two devices are not interchangeable due to the wide LoA, especially for the Haigis formula; therefore, it is necessary to optimize lens constants for the Pentacam.

Comparison of anterior segment parameters of the eye between type 2 diabetic with and without diabetic retinopathy and non-diabetic.

AIM: To compare anterior segment parameters between two groups of type 2 diabetic with and without diabetic retinopathy (DR) and non-diabetic elderly subjects based on hemoglobin A1c (HbA1c) levels and status of DR. METHODS: This study was conducted on 997 residents aged 60y or over in Tehran, Iran. Diabetic group had HbA1c level ≥6.4% with no other systemic problems. The non-diabetic participants had normal eye findings and no systemic diseases. K1, K2, mean K, Q-value, anterior, central, posterior, and total corneal densitometric findings, anterior chamber volume (ACV), anterior chamber depth (ACD), corneal volume (CV), and pachymetry were measured by Pentacam AXL. RESULTS: A total of 678 non-diabetic (39% male) and 319 diabetic (35% male) subjects with mean age of 66.31±5.23 and 67.22±4.96y were examined, respectively. No statistically significant difference was found in anterior segment parameters between non-diabetic and diabetic groups (all P>0.05). However, middle, posterior, and total corneal densitometric values were statistically different between two groups after controlling the effects of confounders (P=0.014, 0.007, and 0.042, respectively). Corneal densitometric values in all layers, ACD, and ACV were different between diabetic subjects with and without DR (all P<0.05). In the diabetic group, only corneal densitometric values had a negative relationship with fasting blood sugar (P<0.001). ACD and ACV had a negative correlation with HbA1c levels (all P<0.05, r=-0.129 and -0.146, respectively). However, the relationships were not observed after controlling the confounders (P=0.938, 0.466, respectively). CONCLUSION: Considering the higher densitometric values of the cornea and lower ACD and ACV in diabetic subjects with DR, it is suggested that the examiners should perform comprehensive retinal examinations when faced with such conditions.

The Repeatability of Axial Length Measurements Using a Scheimpflug-based System.

Purpose: To assess the repeatability of Pentacam AXL as a Scheimpflug-based system or measuring axial length according to the age, sex, lens type, axial length value, and type of cataract. Methods: The present study was conducted using multistage cluster sampling in Tehran, Iran. Ocular biometry was performed, using the Pentacam AXL, by an experienced optometrist on all the participants. The axial length (AL) measurements were taken thrice, with a gap of 10 minutes. To evaluate the repeatability, the intraclass correlation coefficient (ICC) and the repeatability coefficient (RC) were calculated. To determine the significant difference in the repeatability index among study variables, the tolerance index (TI) was calculated. Results: In this report, 897 eyes of 677 individuals aged between 20 and 91 years (mean ± SD: 64.90 ± 13.62 years) were reported. The ICC of the axial length measurements was 0.981 for all cases. Based on the within-subject standard deviation, the RC was 0.401. The ICC was 0.976 and 0.985 in men and women, respectively. The TI showed better RC of measurements among females. The ICC decreased from 0.999 in participants under 40 years to 0.973 in individuals over 60 years of age. The TI showed a decrease in RC with advancing age. The RC was worse in eyes with nuclear cataracts; the RC was also worse in the first quartile of the signal-to-noise ratio (SNR) compared to the other SNR quartiles. Conclusion: The Scheimpflug-based systemPentacam AXL had high repeatability in measuring axial length. Some variables such as male gender, older age, and nuclear cataract were associated with reduced repeatability of the measurements. A higher SNR was associated with better repeatability of the axial length measurements.

Does Long-Term Night Shift Work Cause Dry Eye in Hospital Nurses?

Purpose: To determine the long-term effects of night shift work on dry eye in hospital nurses. Methods: Each participant was evaluated four times, including at the beginning of the day shift (8 am), at the end of the day shift (2 pm), at the beginning of the night shift (8 pm), and at the end of the night shift (8 am), using the tear break-up time (TBUT) test and ocular surface disease index (OSDI) questionnaire. Results: The results showed significant differences in the TBUT and OSDI between the end of the day shift (2 pm) (10.26, 16.61) and the end of the night shift (8 am) (6.89, 38.59) relative to each other and relative to the beginning of the day and night shifts. As for the correlation between TBUT and OSDI, a significant correlation was found at all measurement times (correlation coefficient: -0.478, -0.707, -0.556, and -0.365, respectively) (p < 0.05). Conclusion: The results showed that the severity of dry eye increased after the night shift with variation over a 24-hr period. Moreover, a significant correlation was observed between TBUT and OSDI results at the beginning and at the end of the day and night shifts.

Dynamic Electrooculography Findings for Medial Rectus Myofascial Release in Esodeviation.

Purpose: To determine which mechanisms are operative in releasing the extraocular myofascial tissue in response to extraocular myofascial release (EOMR) and to evaluate the effect of EOMR on saccadic velocity and esodeviation angle in patients with convergence spasm. Methods: Fourteen patients with convergence spasm aged 20-35 participated in this research. The treatment included touching the medial rectus and its interrelated fascial tissue with the index finger pulp from over the eyelid for at least 300 s and applying very gentle and uniform pressure. We evaluated the saccadic velocity obtained from dynamic electrooculography (EOG) and the angle of deviation. The findings of dynamic EOG were used as a reliable quantitative method to assess eye movement function. Results: The amount of esodeviation decreased significantly at both far 2.39Δ, 95% confidence interval (CI) (1.27-3.52) (P = 0.002) and near 5.57Δ, 95% CI (4.67-6.47) (P = 0.001) after two sessions of EOMR in a week. There was no significant difference in saccadic velocities before and after treatment. Conclusion: In the short term, the EOMR only affects the static condition of the eye. Therefore, a significant improvement could be seen in the deviometric findings. However, the dynamic properties of the extraocular muscles did not improve and probably needed a more extended treatment period for acting the long-term mechanisms.

Correction methods for noncontact intraocular pressure measurement in patients with keratoconus and healthy individuals / Métodos de correção para medição sem contato da pressão intraocular em indivíduos normais e com ceratocone

ABSTRACT 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.

Repeatability of Corneal Densitometry Measurements using a Scheimpflug Camera in Healthy Normal Corneas.

Purpose: To determine the repeatability of corneal densitometry measured by the Scheimpflug imaging system. Methods: This cross-sectional study was conducted on photorefractive keratectomy candidates. One eye of each participant underwent imaging using Pentacam HR three times, 10 min apart. The repeatability of densitometry measurements was evaluated in four concentric annuli around the corneal apex and in different corneal depths. The repeatability of the measurements was evaluated using the intraclass correlation coefficient (ICC), repeatability coefficient (RC), and coefficient of variation (CV). The difference of repeatability between layers and zones was tested by tolerance index (TI). Results: Sixty eyes of sixty patients with a mean age of 27.76 ± 3.93 years were studied. Half of the participants were female (n = 30, 50%). ICC was above 0.9 in all corneal parts. The posterior layer and central zones showed the least variability of densitometry measurements considering the CV values. The RC was 2.06, 1.17, and 0.92 in anterior, central, and posterior layers, respectively. The RC was 0.88, 0.71, 1.51, and 4.56 in 0-2, 2-6, 6-10, and 10-12 mm circles, respectively. Only the reliability of densitometry in 10-12 mm annulus was statistically lower than the central zone (TI = 0.71). Conclusions: Corneal densitometry measurements provided by the Pentacam had good repeatability. The repeatability of densitometry measurements decreased from the center to the periphery (with an exception for 0-2 mm and 2-6 mm) and from the posterior to the anterior of the cornea. The reliability of the 10-12 mm zone was markedly less than other zones.

Correction methods for noncontact intraocular pressure measurement in patients with keratoconus and healthy individuals.

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.

Is retinal nerve fibre layer thickness correlated with visual function in individuals having optic neuritis?

CLINICAL RELEVANCE: The existence of a correlation between the results of paraclinical retinal imaging and clinical tests such as contrast sensitivity can reduce time and cost in diagnosing optic neuritis (ON). BACKGROUND: To demonstrate whether changes of peripapillary retinal nerve fibre layer (RNFL) thickness are correlated with the results of visual acuity, contrast sensitivity and colour vision in eyes with acute ON. METHODS: Thirty patients with acute ON, 23 females and seven males, who had no previous history of ON in neither eye, were examined. Inclusion criteria were: subjects had spherical refraction of less than ±5D, no prior ON or optic disc swelling, no history of amblyopia or colour blindness, and no history or ophthalmoscopic evidence of glaucoma, diabetic retinopathy, or maculopathies. Visual acuity, contrast sensitivity and colour vision were tested and optical coherence tomography was performed for all patients after complete ophthalmologic examinations including refraction, biomicroscopy, and funduscopy with a 90D lens by a neuro-ophthalmologist. RESULTS: Thirty patients who were 18-45 years old entered the study. There was an inverse correlation between contrast sensitivity and nasal (r = -0.430, p = 0.018), inferior (r = -0.503, p = 0.005) and mean (r = -0.510, p = 0.004) RNFL thickness. The multiple linear regression model, after adjustment for age and sex, showed a significant association between visual acuity and nasal RNFL thickness (coefficient = 0.025, p = 0.032). There was also a significant inverse correlation between contrast sensitivity and nasal (coefficient = -0.003, p = 0.036), inferior (coefficient = -0.006, p = 0.010) and mean (coefficient = -0.007, p = 0.012) RNFL thickness. No significant correlation was found between colour vision and RNFL thickness. CONCLUSION: Contrast sensitivity is more correlated with changes in RNFL thickness in comparison with visual acuity and colour vision. Contrast sensitivity measurement therefore can be used as one of the first assessments in patients with ON.

Effect of Short Versus Long-Term Steroid on Corneal Haze After Photorefractive Keratectomy: A Randomized, Double-Masked Clinical Trial.

PURPOSE: To compare the effect of duration of fluorometholone 0.1% treatment on corneal haze after photorefractive keratectomy (PRK) with mitomycin C (MMC) 0.02%. DESIGN: Prospective, randomized, double-blind, clinical trial. METHODS: Single-center clinical trial of 252 myopic PRK candidates (252 eyes) aged 21 to 40 years with a mean spherical equivalent (SE) of ≤ 6 diopters (D). Participants were randomized to receive one of the three corticosteroid regimens after PRK: Group A = 1 month followed by 2-month placebo; Group B = 2 months followed by 1-month placebo; and Group C = 3 months. The main outcome measures were corneal haze incidence, subjective SE, uncorrected distance visual acuity (UDVA), and corneal densitometry. RESULTS: The corneal haze incidence (Grade ≥ 1) at 12 months was 1.35% (1/74 eyes) in Group A and 0% in the other two groups. The mean anterior corneal densitometry (grayscale unit) was 21.19 ± 2.07, 21.09 ± 2.19, and 21.31 ± 2.21 in Groups A, B and C, respectively. The mean SE was 0 ± 0.09, 0 ± 0.11, and 0 ± 0.10, and UDVA (decimal) was 1 ± 0, 1 ± 0.01, and 1 ± 0 in Groups A, B and C, respectively. During 1-year follow-up, no statistically significant difference was observed in mean SE (P = .158), UDVA (P = .343), and anterior corneal densitometry (P = .109) at any stage between the study groups. CONCLUSIONS: Long-term topical corticosteroids are unnecessary following PRK with MMC for moderate myopia.

Distribution of near Point of Convergence, near Point of Accommodation, Accommodative Facility and Refractive Errors in a Rural Population Living in Northern Iran.

Purpose: To evaluate near point of convergence (NPC), near point of accommodation (NPA), and accommodative facility (AF) in order to determine their normative data in a rural population.Methods: The target population for this population-based, cross-sectional study was people living in rural areas. Each subject underwent extensive optometric and ophthalmic examinations, including the measurement of visual acuity, refraction, NPA, NPC, and AF.Results: The data of 1113 individuals was analyzed of whom 58.8% (n = 576) were women. The mean age of the participants was 15.26 ± 7.38 years (range: 6-30 years). The mean spherical equivalent of the subjects was 0.16 ± 0.63 D. The prevalence of myopia, hyperopia and astigmatism was 16.28% (13.97-18.58), 5.97% (4.49-7.44), 11.93% (9.91-13.95) in this study, respectively The mean and 95% confidence interval of NPC, NPA, and binocular accommodative facility (BAF) was 6.99 cm (6.84-7.15), 9.91 cm (9.71-10.11), and 9.84 cpm (9.63-10.06), respectively. A significant correlation was found between age and the parameters such that all evaluated parameters worsened significantly with age (P < .001).Conclusion: The results of the present study showed the normal ranges of NPA, NPC, and BAF in a 6-30 year-old population living in rural areas of northern Iran. These parameters changed significantly with age.

Predictor factors of prism effectiveness in young adults with convergence insufficiency.

Clinical relevance: The findings of this study can be useful in the process of patient selection as well as in optimising the prescription of the prism in patients with convergence insufficiency.Background: To determine the relationship between the demographic variables and baseline clinical characteristics with the prism effectiveness in young adults with convergence insufficiency.Methods: Sixty-four young adults with convergence insufficiency entered a randomised clinical trial and were randomly assigned to either treatment or placebo groups. For participants in the treatment group, the near optical correction containing base-in prism was determined based on the Sheard's criterion. Participants in the placebo group received near optical correction. After three months of using the assigned correction, the outcome examinations were performed.Results: In the univariate analysis, a remote near point of convergence, a higher baseline symptoms score, and a higher prescribed prism power showed a significant relationship with the increase in prism effectiveness. A significant inverse relationship was found between the near positive fusional vergence, vergence facility, and prism adaptation rate with the prism effectiveness. Based on the results of the multiple regression, the prism adaptation rate was the only independent predictor factor of prism effectiveness, so that the prism effectiveness increased by 0.60 for each per cent reduction in prism adaptation rate.Conclusion: Prism adaptation is the only independent predictive factor of prism effectiveness in young adults with convergence insufficiency. Based on the findings of the present study, it is recommended that careful assessment of prism adaptation be considered before considering prism prescription.

Dynamic corneal biomechanics in different cell layers: in keratoconus and normal eyes.

PURPOSE: This study aimed to determine the relationship between corneal cellular structures and biomechanical deformation parameters in keratoconic (KC) and healthy eyes. METHODS: In this prospective comparative study, 29 eyes of 29 KC patients were age- and gender-matched with 28 eyes of 28 healthy individuals using frequency matching. Corneal parameters examined included the density of basal epithelial cells, anterior keratocytes, posterior keratocytes and endothelial cells as assessed by in vivo corneal confocal microscopy (HRT III-RCM, Heidelberg Engineering, www.heidelbergengineering.com). Additionally, the coefficient of variation of endothelial cell size (CV) and the percentage of hexagonal endothelial cells (HEX%) were measured by specular microscopy (Konan NSP-9900, Konan Medical, www.konanmedical.com). Further, biomechanical deformation parameters were derived from Corvis Scheimpflug Technology (Corvis ST, Oculus, www.oculus.de). All cellular and biomechanical deformation parameters in KC and normal groups were compared, and the relationship between cellular and biomechanical parameters calculated. RESULTS: In the KC group, the highest concavity (HC) delta arc length and maximum delta arc length were associated with endothelial cell density (Beta = -0.39, p = 0.03 and Beta = -0.60, p Ë‚ 0.001, respectively). Furthermore, there was a significant association between HC deflection length and HEX% (Beta = -0.67, p = 0.001). In the normal group, HC delta arc length and HC deflection length were significantly associated with endothelial cell density (Beta = 0.46, p = 0.02; and Beta = -0.51, p = 0.01, respectively). HC time, HC deformation amplitude and applanation 1 delta arc length were associated with CV (Beta = 0.50, p = 0.01; Beta = 0.27, p = 0.009; and Beta = -0.57, p = 0.002, respectively). Applanation 1 and applanation 2 deformation amplitudes were associated with HEX% (Beta = -0.49, p = 0.005; and Beta = -0.46, p = 0.02). CONCLUSIONS: Biomechanical deformation parameters were significantly correlated with endothelial cell properties in both KC and normal groups, thereby indicating the importance of the integrity of endothelial cells to the biomechanical properties of both KC and normal corneas.

Comparison of ocular aberrations in three types of rigid gas permeable lenses in keratoconus patients.

Purpose: To determine the effect of different types of Rigid Gas Permeable (RGP) contact lenses on ocular aberrations in patients with keratoconus. Methods: Eighteen eyes of young patients with mild to moderate keratoconus were selected. General ocular examinations such as refraction, visual acuity, and ocular aberrations were performed. Three types of RGP contact lenses, i.e., Boston, Senso Select and Wohlk, were fitted using the cross over method. Repeated measures analysis of variance and Mauchly's test of sphericity were used to compare the average of residual high order aberrations and visual acuity after fitting each type of lens. Results: Vertical coma was -0.271 ± 0.37 µm before fitting and decreased to 0.081 ± 0.08 µm with Boston, 0.098 ± 0.08 µm with Senso Select and 0.124 ± 0.08 µm with Wohlk contact lens (P-value < 0.0001). The mean RMS (root mean square) for high order aberrations decreased from 0.526 ± 0.43 µm before fitting to 0.256 ± 0.09 µm with Boston, 0.263 ± 0.12 µm with Senso Select, and 0.304 ± 0.10 µm with Wohlk contact lens (P-value= 0.001). The mean RMS for low order aberrations decreased from 1.480 ± 0.78 µm before fitting to 0.703 ± 0.43 µm with Boston, 0.802 ± 0.39 µm with Senso Select, and 0.760 ± 0.45µm with Wohlk (P-value < 0.0001). Conclusion: Despite achieving optimal fit and good visual acuity with these different RGP lenses, in keratoconus patients, their performance is different in reducing ocular aberrations.

Corneal Scheimpflug Densitometry in Photorefractive Keratectomy Candidates.

PURPOSE: To describe the normative data of corneal densitometry in photorefractive Keratectomy (PRK) candidates by using a Scheimpflug camera. METHODS: Five hundred twenty-two eyes of 261 PRK candidates that underwent comprehensive optometric and ophthalmic examinations were enrolled in this study. Corneal densitometry values were obtained using a Scheimpflug camera (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany) and displayed in grayscale units (GSU). RESULTS: Of 261 participants, 187 (71.6%) were women. The mean age of the participants was 28.79 ± 5.02 years (range: 21-40 years). The mean entire corneal densitometry was 14.86 ± 2.37 GSU. According to corneal depth, maximum and minimum densitometry values were seen in the anterior (30.28 ± 7.42 GSU) and posterior (9.86 ± 2.08 GSU) layers, respectively (P < 0.001). Based on the annulus over the cornea, the highest and lowest densitometry values were seen in the 10- to 12-mm (21.31 ± 4.26 GSU) and 2- to 6-mm zones (13.26 ± 2.34 GSU), respectively. However, this difference was not seen after 35 years of age. Individuals aged 30 to 35 years showed higher corneal densitometry values compared with subjects aged 20 to 25 years old (P < 0.001). In generalized linear models, the corneal thickness was associated with the densitometry value in the central and posterior corneal layers. There were no significant differences in sex and refractive errors among participants. CONCLUSIONS: This study provided normal corneal densitometry data in PRK candidates. Corneal densitometry increased with age until 35 years of age and then decreased thereafter. This finding should be considered in patient selection for PRK and their postoperative examinations.

Visual Acuity Improvement in Adult Anisometropic Amblyopes After Active Vision Therapy.

PURPOSE: The aim of this study is to evaluate the effect of active vision therapy in adults with anisometropic amblyopia. METHODS: In this study, 20 adults with anisometropic amblyopia aged from 17-35 years old were treated for five sessions (one session per week) with vision therapy techniques which include accommodative rock, vergence rock, and saccadic training. Moreover, computerized vision therapy was performed by Optosys® software. Also, patients had been given a daily program for home training, including accommodative and vergence rock, and Optosys® software. Best corrected visual acuity (BCVA) was measured before and after treatment. RESULTS: Comparison of data using t-test showed that BCVA significantly improved after the vision therapy period. Initial BCVA (Log MAR) was 0.37±0.04 (mean±standard deviation) which improved to 0.14±0.03 after treatment. The correlation between initial BCVA and the amount of improvement showed that the worse the pre-treatment visual acuity was, the greater improvement that occurred. CONCLUSION: The improvement of visual acuity in adult anisometropic amblyopes showed that there are some degrees of plasticity in the visual system of amblyopic patients even in adulthood. Thus, therapists should give the chance of treatment to adult amblyopes.

Comparison of Corneal Higher-order Aberrations between Miniscleral and Hybrid Lenses in Keratoconus.

SIGNIFICANCE: Fitting specialty contact lenses (hybrid and miniscleral) can be a useful option in keratoconus patients to decrease higher-order aberrations (HOAs) and increase the quality of vision. PURPOSE: The aim of the present study was to compare corneal HOAs between miniscleral and hybrid lenses in keratoconus patients. METHODS: The target population of this study was 37 patients with bilateral keratoconus aged 20 to 35 years who were referred to a specialized contact lens clinic by a corneal specialist. Pre-fitting examinations included objective and subjective refraction, measurement of uncorrected and best spectacle-corrected visual acuity, and measurement of corneal HOAs. Lens fitting was performed in the next step. Finally, post-fitting measurements including contact lens-corrected visual acuity and corneal HOAs were performed. RESULTS: The root mean square of the total HOAs significantly decreased after fitting both miniscleral and hybrid lens designs. There was a significant change in the third-order vertical coma and spherical aberration after fitting the miniscleral lens. In the hybrid lens group, a significant change was found only in vertical coma after fitting. There was no significant difference in the post-fitting HOA change between the two groups. CONCLUSIONS: The results of this study showed the effectiveness of both miniscleral and hybrid lenses in decreasing HOAs in keratoconus patients. No significant difference was observed between these two lenses in this regard.

Low-contrast Pattern-reversal Visual Evoked Potential in Different Spatial Frequencies.

PURPOSE: To evaluate the pattern-reversal visual evoked potential (PRVEP) in low-contrast, spatial frequencies in time, frequency, and time-frequency domains. METHODS: PRVEP was performed in 31 normal eyes, according to the International Society of Electrophysiology of Vision (ISCEV) protocol. Test stimuli had checkerboard of 5% contrast with spatial frequencies of 1, 2, and 4 cycles per degree (cpd). For each VEP waveform, the time domain (TD) analysis, Fast Fourier Transform(FFT), and discrete wavelet transform (DWT) were performed using MATLAB software. The VEP component changes as a function of spatial frequency (SF) were compared among time, frequency, and time-frequency dimensions. RESULTS: As a consequence of increased SF, a significant attenuation of the P100 amplitude and prolongation of P100 latency were seen, while there was no significant difference in frequency components. In the wavelet domain, an increase in SF at a contrast level of 5% enhanced DWT coefficients. However, this increase had no meaningful effect on the 7P descriptor. CONCLUSION: At a low contrast level of 5%, SF-dependent changes in PRVEP parameters can be better identified with the TD and DWT approaches compared to the Fourier approach. However, specific visual processing may be seen with the wavelet transform.