[The cornea in high axial myopia]

Initial screening for occult congenital ectopia lentis based on ocular biological parameters in preschool children

BACKGROUND

This study aimed to identify an initial screening tool for congenital ectopia lentis (CEL) by comparing ocular biological parameters in children with myopia.

METHODS

A retrospective case-control study was conducted at one tertiary referral centre, from October 2020 to June 2022. Axial length (AL), corneal curvature (CC), refractive astigmatism (RA), corneal astigmatism (CA), internal astigmatism (IA), the difference between the axis of RA and CA [AXIS(RA-CA)], white-to-white corneal diameter (WTW), and axial length-corneal radius ratio (AL/CR) were compared in 28 eyes of CEL patients, and 60 eyes of myopic patients matched for age and refraction. The spherical equivalent of each eye was < -3.00 D. Area under the curve (AUC) of the receiver operating characteristic curves were calculated.

RESULTS

The differences in RA, AL, mean keratometry (Kmed), maximum keratometry (Kmax), minimum keratometry (Kmin), CA, IA, AXIS(RA-CA), WTW, and AL/CR between the CEL and myopic groups were statistically significant (p < 0.05; p < 0.001; p < 0.001; p < 0.001; p < 0.001; p < 0.05; p < 0.001; p < 0.001; p < 0.001; p < 0.001, respectively). In logistic regression analysis RA, IA, AXIS(RA-CA), and AL/CR were significantly associated with CEL (p < 0.05). AUCs for RA, IA, AXIS(RA-CA), and AL/CR were 0.694, 0.853, 0.814, and 0.960, respectively. AUCs for AL/CR in SE< -6.00 D subgroup was 0.970, and 0.990 in -6.00 D ≤ SE < -3.00 D group. An AL/CR < 3.024 was the optimal cut-off point differentiating the CEL and control groups (sensitivity, 92.9%; specificity, 88.30%).

CONCLUSIONS

A smaller AL/CR could identify CEL in children with myopia. An AL/CR cut-off value of 3.024 may be the most sensitive and specific parameter for the differential diagnosis of CEL in patients with mild to high myopia.

Effect of central corneal curvature on corneal material stiffness parameter acquired by dynamic corneal responses

The stress-strain index (SSI) is a measure of corneal material stiffness, which is obtained using the Corvis ST algorithm based on dynamic corneal response parameters. The reduced SSI corresponds to the longer axial length (AL). In a previous study, we found SSI increases as the corneal curvature flattens, whereas a flatter corneal curvature indicates a longer AL (emmetropia or myopia). Therefore, in this cross-sectional study, we aimed to address these contradictory findings. First, we characterized the features of SSI, curvature radius of the anterior corneal surface (CR), and AL and analyzed their correlation with advanced myopia. Next, we compared the relationship between AL and SSI after adjusting for the effect of CR. We found a significant positive correlation between SSI and CR, which contradicts the developmental law of axial myopia. Furthermore, after accounting for the effect of CR, we observed a stronger correlation between SSI and AL than that in the unadjusted model. In conclusion, CR is an independent influencing factor for SSI in addition to AL, which masked the decrease in SSI caused by prolonged AL in axial myopia.

The Distribution of Keratometry in a Population Based Study

Purpose

To determine the distribution of keratometry values in a wide age range of 6-90 years.

Methods

In this cross-sectional study, samples were selected from two villages in Iran using multi-stage random cluster sampling. After completing optometry and ophthalmic examinations for all cases, corneal imaging was done using Pentacam, and keratometry values were determined.

Results

Of the 3851 selected people, 3314 people participated in the study, and after applying the exclusion criteria, analyses were done on data from 2672 people. Mean age of the participants was 36.30 ± 18.51 years (from 6 to 90 years). Mean keratometry (mean-K) in flat and steep meridians was 42.98 (42.9-43.06) diopters (D) and 43.98 (43.91-44.07) D, respectively. Average of mean-K was 43.48 (43.41-43.56) D. Mean-K increased linearly up to the age of 70 years, and the cornea became slightly flat afterwards (coefficient = 0.01; P < 0.001). Mean-K was significantly higher in females (P < 0.001). Myopic cases had the highest mean-K (P < 0.001). The correlation of mean-K with age, gender, central corneal thickness, anterior chamber depth, pupil diameter, and spherical equivalent was investigated in a multiple regression model. Only older age and female gender showed a statistically significant association with mean-K. Overall, 31.62% (29.14-34.09) of the sample in this study had at least 1.0 D of corneal astigmatism.

Conclusions

This is one of the few studies worldwide that demonstrates changes in keratometry in a wide age range from childhood to old age. Results indicated that age and gender are variables associated with keratometry.

Relationship between Axial Length and Corneo-Scleral Topography: A Preliminary Study

The main objective of the current study was to investigate further the relationship of the overall length of the eye with a great variety of anterior segment parameters, including scleral geometry. A total of 64 eyes of 32 participants with ages from 12 to 52 years were included in this prospective non-randomized single-center study. All participants underwent a complete eye examination, including an analysis of corneo-scleral shape with a Fourier-domain profilometer. A strong negative correlation was found between axial length and temporal-nasal ocular sagittal height difference for different chord lengths. For the right eye, a consistent and stable linear model was obtained to predict the axial length from the spherical equivalent, the corneal diameter, the high-order aberrations root mean square, and the minimum sagittal height for 13- and 14-mm chord. For the left eye, a model was obtained to predict the axial length from the spherical equivalent and the mean corneal curvature, including other parameters such as corneal diameter or high-order aberrations, depending on the chord length, considered for estimating the sagittal height values. More studies with larger samples are needed to confirm these preliminary outcomes.

Anterior and Posterior Segment Manifestations of Pathological Myopia: A Clinical Study from Turkish Aegean Region

Background and Objective:

Myopia is one of the most prevalent vision conditions caused by a mismatch between the refractive power and axial length of the eyeball. High myopia may have a degenerative disorder, including cornea, sclera, choroid, optic disc, vitreous, macula, and peripheral retina. Although there are few studies regarding clinical features of pathological myopia, especially in the far-eastern countries where myopia is common, but are no comprehensive data in our region. This study was aimed to demonstrate both anterior and posterior ocular segment manifestations of pathological myopia.

Methods:

One hundred forty eyes of 82 patients who met the pathological myopia criteria were enrolled in this prospective study. Measurements of Central Corneal Thickness (CCT), endothelial cell parameters, Anterior Chamber Depth (ACD), Axial Length (AL) and Subfoveal Choroidal Thickness (SFCT) were performed in all patients. Presence of posterior segment pathologies such as peripapillary atrophy, tilted disc, Lacquer's crack, foveoschisis, myopic maculopathy, Choroidal Neovascularization (CNV), and peripheral retinal degeneration was recorded.

Results:

The mean age was 54.1 ± 14.2 years. 43 (52.4%) of the patients were female. One hundred patients (71.4%) were phakic and 40 (28.6%) were pseudophakic. The mean CCT, corneal endothelial cell density, ACD, AL, and SFCT were 548.91 ± 43.44 µm, 2335.89 ± 374.38 cells/mm2, 3.93 ± 0.79 mm, 28.75 ± 2.20 mm, and 94.56 ± 73.11 µm, respectively. Tilted disc, peripapillary atrophy and posterior staphyloma were detected in 89 (63.6%), 119 (85%) and 78 (55.7%) eyes, respectively. Normal fundus, tessellated fundus, diffuse chorioretinal atrophy, focal chorioretinal atrophy and macular atrophy were seen in 13 (9.3%), 59 (42%), 26 (18.6%), 14 (10%), and 28 (20%) eyes, respectively. Lacquer crack, CNV, and Fuchs spot were observed in 11 (7.9%), 39 (27.9%), and 47 (33.6%) eyes, respectively.

Conclusion:

This study reported clinical characteristics of eyes with pathological myopia in a retina specialty clinic at a tertiary referral center from the Turkish Aegean Region. Pathological myopia may affect both anterior and posterior ocular segments. However, posterior segment manifestations may be associated with lesions that threaten vision. Therefore, periodic follow-up in patients with pathological myopia is critical.