Retinal measurements using time domain OCT imaging before and after myopic Lasik

Retinal and Choroidal Changes Following Implantable Collamer Lens V4c Implantation in High Myopia Patients-A 1-Year Follow-Up Study

This prospective study aimed to evaluate the impact of Visian Implantable Collamer Lens (ICL) V4c implantation on retinal and choroidal morphology in patients with high myopia. A total of 97 eyes from 52 high myopic patients who underwent ICL V4c implantation were followed up for 12 months. Preoperative and postoperative evaluations included comprehensive ophthalmic assessments and enhanced depth imaging optical coherence tomography (EDI-OCT) to analyze changes in central retinal thickness (CRT), retinal volume (CRV), choroidal thickness (ChT), total choroidal area (TCA), luminal area (LA), and choroidal vascular index (CVI). Repeated measures mixed-effects models were used for comparing pre- and postoperative measurement variables and exploring relationships among age, axial length (AL), spherical equivalent refraction (SER), and postoperative retinal and choroidal changes, with statistical significance set at p < 0.05. Follow-up assessments were conducted at various time points, with participation rates ranging from 21% to 98%. Baseline characteristics showed a median age of 26.7 years, -10.14 diopters of SER, and an AL of 27.44 mm. Throughout the 12-month follow-up, CRT and 3.0 mm CRV consistently increased compared to the baseline, with statistically significant rises observed at postoperative day 1, week 1, and month 12. Most ChT measurements, including subfoveal ChT, declined over the 12 months, except at postoperative 6 months. Horizontal and vertical TCA and LA values significantly increased throughout the follow-up, except for month 6. After surgery, both horizontal and vertical CVI parameters exhibited an increase compared to the baseline, with some changes reaching statistical significance. Correlation analysis performed by repeated measures mixed-effects models showed that no relationship was found between age, AL, and SER and changes in postoperative retinal parameters and CVI parameters. However, postoperative changes in ChT and choroidal area parameters showed a negative correlation with AL and a positive correlation with SER. Our research demonstrated that ICL V4c implantation resulted in noteworthy alterations in retinal and choroidal morphology over a 1-year follow-up period. Moreover, in patients with high myopia, individuals with longer AL and higher degrees of myopia exhibited more pronounced postoperative changes in the choroid and retina. Further studies with extended follow-up durations are necessary to comprehensively understand the long-term effects of ICL implantation on retinal and choroidal morphology and function.

Effect of phakic collamer intraocular lens with a central hole on structural tests measurements of retinal nerve fiber layer and macula

AIM

To evaluate whether the Visian Implantable Collamer Lens with a central port (V4c ICL®; STAAR Surgical, Switzerland) affects the retinal nerve fibre layer (RNFL), macula and optic nerve head (ONH) measurements obtained by optical coherence tomography (OCT), and Heidelberg Retina Tomography (HRT).

METHODS

This prospective study included myopic patients undergoing V4c ICL® implantation. RNFL thickness, macular thickness, ganglion cell analysis (GCA) and ONH main parameters were evaluated with RTVue OCT (Optovue Inc., USA) and Cirrus-HD OCT (Carl Zeiss Meditec, USA). ONH variables were also analysed with HRT-3 (Heidelberg Engineering, Germany). All measurements were performed before and 1 week and 12 months after the surgery.

RESULTS

31 eyes of 31 patients (mean age 30.1 ± 5.5 years) were included. Comparing with preoperative values, no significant differences in average RNFL thickness were found with RTVue, while a slight increase (4.3 µm) was detected with Cirrus-HD (85.2 ± 10.3 µm, preoperatively) at 1-week postoperatively (89.5 ± 8.3 µm; p < 0.05). Those changes were not observed at the last follow-up visit (86.6 ± 8.6 µm; p = 0.41). Cirrus-HD detected that macular thickness was slightly higher 1 week after surgery, compared with the preoperative examination (3.4% increase; p = 0.04). That difference remained stable at the 12-month postoperative visit (p = 0.01). GCA showed no changes. The ONH analysis with Cirrus-HD determined that rim area (p = 0.03) as well as disc area (p = 0.04) significantly increased. HRT-3 found no significant changes affecting those variables.

CONCLUSIONS

The implantation of V4c ICL® did not induce a clinically significant impact on the results of the RNFL/ONH analysis with OCT and HRT.

Decreased Macular Retinal Thickness in Patients With Pterygium

Purpose

To explore alterations in macular retinal thickness (RT) and analyze correlation between macular RT and pterygium area, length in pterygium patients.

Methods

Totally 13 patients with pterygium (left eye) and 13 healthy controls (left eye) were recruited. OCTA was applied to scan each eye to generate three-dimensional images. Based on the Early Treatment Diabetic Retinopathy Study (ETDRS) method, each image was divided into nine subregions for the ETDRS: central (C); inner superior (IS); outer superior (OS); inner nasal (IN); outer nasal (ON); inner inferior (II); outer inferior (OI); inner temporal (IT); and outer temporal (OT). The macular RT in each subregion was measured. Furthermore, the correlation between RT and the area, length of pterygium was analyzed.

Results

The visual acuity of pterygium patient was different from that of the control (P < 0.05). Besides, decreased intraretinal thickness of the IN and ON, increased intraretinal thickness of OT, decreased extraretinal thickness of OT, IN, ON, OS, and decreased retinal full layer thickness of medial superior, OS, IN, ON, and II subregions in pterygium group were observed. There was a negative correlation between RT of the IN and ON subregions and the length of pterygium (r = -0.5803 and r = -0.6013, P = 0.0376 and P = 0.0297). The RT of IN subregion was negatively correlated with pterygium area (r = -0.5844, P = 0.0359). According to the receiver operating characteristic analysis, in the ON subregion, the areas under the curve of the inner retinal thickness, outer retinal thickness and the whole retinal thickness were 1.0 (95% CI: 1.0), 0.882 (95% CI: 0.715 and 0.963), and 1.0 (95% CI: 1.0). The smallest area under the curve of retinal thickness in OT subregion was 0.018 (95% CI: 0-0.059).

Conclusion

RT of pterygium patients was significantly decreased, and the main alterations occurred in the temporal side suggesting there might exist retinal structural alterations in pterygium.

The link between Keratoconus and posterior segment parameters: An updated, comprehensive review

Keratoconus (KCN) has been typically known as a disorder with effects limited to the cornea. Because of this viewpoint, less attention has been devoted to its effects on the posterior segment structures. We aimed to provide a comprehensive review of the literature to understand the potential link between KCN and posterior segment structures and their functions. It is clear from the extensive evidence in the literature that KCN can be associated with morphological and functional changes in different parts of the posterior segment. It is worth noting that anatomical changes have been not only noted in several layers of the retina but also in the optic nerve head and the choroid. Several mechanisms have been proposed to explain this observation, including incidents induced by oxidative stress in keratoconic corneas and retinal adaptions to the distorted image that lands on the retina. Consequently, when KCN has been diagnosed, it seems practical to consider assessing the retinal and choroidal profile using optical coherence tomography and potentially functional abnormalities through electrophysiology procedures.

Effects of SMILE Surgery on Intraocular Pressure, Central Corneal Thickness, Axial Length, Peripapillary Retinal Nerve Fiber Layer, and Macular Ganglion Cell Complex Thickness

Purpose. To evaluate the change in intraocular pressure (IOP), central corneal thickness (CCT), axial length, peripapillary retinal nerve fiber layer (RNFL) thickness, and macular ganglion cell complex (GCC) thickness after small incision lenticule extraction (SMILE) surgery. Methods. This prospective observational study was conducted in Espace Nouvelle Vision, Ophthalmological Clinic, Paris, France. Fifty eyes of 25 patients were enrolled in this study and underwent SMILE surgeries. IOP, central corneal thickness (CCT), axial length (AL), peripapillary RNFL thickness, and macular GCC thickness were measured before and at 3 months after SMILE. Results. The mean preoperative spherical equivalent was −3.15 ± 1.50 diopters (D), and the mean postoperative value was 0.15 ± 0.28 D. After SMILE surgery, IOP decreased from 15.03 ± 2.79 mmHg to 11.02 ± 2.73 mmHg and 10.02 ± 2.21 mmHg at 1 and 3 months, respectively ( $P<0.01$ for both comparisons). The mean decrease in measured IOP as a function of ablation depth was 0.065 ± 0.031 mmHg/μm. CCT decreased from 545.98 ± 26.61 μm to 478.40 ± 30.26 μm after SMILE surgery ( $P<0.01$ ). AL decreased from 24.80 ± 0.84 mm to 24.70 ± 0.83 mm ( $P<0.01$ ). There was no statistically significant change in mean peripapillary RNFL or mean GCC thickness after SMILE surgery. Conclusions. SMILE surgery modified IOP measurement, CCT, and AL but did not change peripapillary RNFL and macular GCC thicknesses. The postoperative drop in measured IOP might be explained by the decreased CCT. An accurate re-evaluation of AL should be performed before cataract surgery among post-SMILE patients.

Short-term changes in the anterior segment and retina after small incision lenticule extraction

Background

To analyse short-term changes in the anterior segment and retina after small incision lenticule extraction (SMILE).

Methods

Patients with myopia scheduled for SMILE were recruited from Ruijin Hospital, Shanghai, China. Basic patient information such as age, sex, and refractive errors was recorded. Ocular measurements were taken before surgery, and 1 day and 1 week after surgery; they included axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), white to white (WTW), pupil diameter (PD), macular thickness (MT), ganglion cell layer thickness (GCL), retinal nerve fiber layer thickness (RNFL), choroidal thickness (CT), macular vessel density, and optic disc vessel density.

Results

Sixty-one eyes of 31 patients were selected for this study. AL, CCT, ACD, and postoperative PD were significantly reduced (p < 0.05), while LT was thickened after surgery (p < 0.05). MT at the fovea decreased 1 day and 1 week after surgery (p < 0.05). GCL showed no significant changes after surgery. RNFL was unchanged 1 day after surgery, but the inferior sector was thickened 1 week after surgery. CT was thicker at the fovea 1 day after surgery and 1.0 mm from the fovea in the nasal sector 1 week after surgery. Macular vessel density was significantly decreased 1 day after surgery and most recovered in 1 week. Optic disc vessel density decreased at the peripapillary part 1 day after surgery and recovered after 1 week. ΔACD and ΔLT showed no significant correlation 1 day after surgery. ΔACD was negatively correlated with ΔLT and sphere 1 week after surgery (r = − 0.847, p < 0.000; r = − 0.398, p = 0.002). ΔLT was positively correlated with the sphere 1 week after surgery (r = 0.256, p = 0.048).

Conclusion

The anterior segment was the most affected, while the retina also underwent changes with regard to MT, RNFL, CT, macular vessel density, and peripapillary vessel density.

Should Pearson's correlation coefficient be avoided?

PURPOSE

To survey the use of Pearson's correlation coefficient (r) and related statistical methods in the ophthalmic literature, to consider the limitations of r, and to suggest suitable alternative methods of analysis.

RECENT FINDINGS

Searching Ophthalmic and Physiological Optics (OPO), Optometry and Vision Science (OVS), and Clinical and Experimental Optometry (CXO) online archives using correlation and Pearson's r as search terms resulted in 4057 and 281 hits respectively. Coefficient of determination, r square, or r squared received fewer hits (65, 8, and 22 hits respectively). The assumption that r follows a bivariate normal distribution was rarely encountered (3 hits) although several studies applied Spearman's rank correlation (70 hits). The intra-class correlation coefficient (ICC) was widely used (178 hits), but fewer hits were recorded for partial correlation (43 hits) and multiple correlation (13) hits. There was little evidence that the problem of sample size was addressed in correlation studies.

SUMMARY

Investigators should be alert to whether: (1) the relationship between two variables could be non-linear, (2) the data are bivariate normal, (3) r accounts for a significant proportion of the variance in Y, (4) outliers are present, the data are clustered, or have a restricted range, (5) the sample size is appropriate, and (6) a significant correlation indicates causality. In addition, the number of significant digits used to express r and the problems of multiple testing should be addressed. The problems and limitations of r suggest a more cautious approach regarding its use and the application of alternative methods where appropriate.

Retinal nerve fiber layer thickness after laser-assisted subepithelial keratomileusis and femtosecond LASIK: a prospective observational cohort study

Purpose

Based on the assumption that high levels of intraocular pressure (IOP) during femtosecond laser-assisted in situ keratomileusis (FS-LASIK) may compromise the retinal nerve fiber layer (RNFL), newer femtosecond platforms that operate without causing significant IOP elevation have been developed in recent years. However, this assumption has not been adequately tested. The aim of the current study was to evaluate possible changes in RFNL thickness in nonglaucomatous myopic patients undergoing FS-LASIK using the 60 KHz IntraLase^® device that significantly elevates the IOP for an appreciable period of time vs an advanced surface ablation technique (laser-assisted subepithelial keratomileusis, LASEK) that does not induce any IOP elevation.

Methods

This was a prospective, observational, controlled cohort study. One randomly selected eye of 114 consecutive eligible patients was analyzed. Inclusion criteria were myopia up to -6.00 diopters and astigmatism up to -2.00 diopters. As clinically indicated, 50 patients underwent LASEK and 64 underwent FS-LASIK. The RNFL thickness was determined with a spectral-domain optical coherence tomography device preoperatively and 3 months postoperatively by the same masked observer.

Results

There was no significant difference in preoperative refractive error, age, or sex between the groups. Preoperatively, central corneal thickness was significantly lower in the LASEK group (529.1±36.1 vs 562.4±31.6 µm, P=0.001). For the LASEK group, there was no significant difference between preoperative and postoperative RNFL thickness in the studied sectors (superior-temporal, temporal, inferior-temporal, average). For the FS-LASIK group, compared to preoperative RNFL measures, statistically significant thicker postoperative values were found for the average RNFL (mean difference: 0.67 µm, 0.7% increase, P=0.008) and the inferior-temporal sector (mean difference: 0.92 µm, 0.6% increase, P=0.02).

Conclusion

LASIK with a femtosecond platform that induces high intraoperative IOP did not cause RNFL thinning. The observed differences between preoperative and postoperative values are below the axial resolution limit of optical coherence tomography devices.

Analysis of Macular and Retinal Nerve Fiber Layer Thickness in Children with Refractory Amblyopia after Femtosecond Laser-assisted Laser In situ Keratomileusis: A Retrospective Study

Background:

Localized macular edema and retinal nerve fiber layer (RNFL) thinning have been reported shortly after laser in situ keratomileusis (LASIK) in adults. However, it is still unclear how LASIK affects the retina of children. This study aimed to investigate the macular retina and RNFL thickness in children with refractive amblyopia who underwent femtosecond laser-assisted LASIK (FS-LASIK).

Methods:

In this study, we included 56 eyes of 32 patients with refractive amblyopia who underwent FS-LASIK in our hospital from January 2012 to December 2016. Foveal (foveal center retinal, parafoveal retinal, and perifoveal), macular inner retinal (superior and inferior), and peripapillary RNFL thicknesses (superior, inferior, temporal, and nasal) were measured using Fourier-domain optical coherence tomography before surgery and 1 day, 3 days, and 1 week after surgery. We divided these patients into three groups based on their refractive error: High myopic group with 22 eyes (equivalent sphere, >6.00 D), mild myopic group with 19 eyes (equivalent sphere, 0–6.00 D), and hyperopic group with 15 eyes (equivalent sphere, >+0.50 D). We compared the macular retina and RNFL thickness before and after LASIK. A paired simple t-test was used for data analysis.

Results:

One week after surgery, the visual acuity for all 56 eyes of the 32 patients reached their preoperative best-corrected vision. Visual acuity improved two lines or better for 31% of the patients. The residual refractive errors in 89% of the patients were within ±0.5 D. In the high myopic group, the foveal center retinal and parafoveal retinal thicknesses were thicker 1 day and 3 days after surgery than before surgery (t = 2.689, P = 0.012; t = 2.383, P = 0.018, respectively); no significant difference was found 1 week after surgery (P > 0.05). The foveal center retinal and parafoveal retinal thicknesses were greater 1 day after surgery than they were before surgery (P = 0.000 and P = 0.005, respectively) in the mild myopic and hyperopic groups. No significant difference was found 3 days or 1 week after surgery (P > 0.05). In all three groups, no significant difference was found in the macular inner retinal or peripapillary RNFL thickness 1 day, 3 days, or 1 week after surgery (P > 0.05).

Conclusions:

The foveal center retinal edema after FS-LASIK is mild and reversible in children, that mostly occurred in the high myopic group with no effect on the visual acuity, and is always relieved within 1 week.

Considerations for refractive surgery in the glaucoma patient

PURPOSE OF REVIEW

Given the popularity of keratorefractive surgery, and an aging populous of patients who have undergone these procedures, there is an increasing need for updated management protocols. This is particularly relevant for patients with chronic progressive diseases such as glaucoma, due to the variety of related diagnostic and management challenges inherent to these diseases. Here, we will review the current literature to provide an update on the management of patients with glaucoma who are undergoing, or have had laser ablative refractive surgery. Preoperative testing and eligibility considerations, intraoperative factors, and postoperative observation and follow-up will be discussed.

RECENT FINDINGS

Intraoperative intraocular pressure (IOP) rise during flap creation is associated with low risk of acute complications, and furthermore do not appear to have significant long term effects. Modern technologies have improved our ability to determine accurate IOP after refractive surgery despite postoperative changes in corneal architecture. Furthermore, advances in structural imaging allow for earlier detection of even subtle glaucomatous nerve damage.

SUMMARY

Although glaucoma remains a relative contraindication to refractive surgery, it is a safe procedure for many patients with appropriate perioperative management and follow-up. Advancements in diagnostic modalities have allowed for earlier detection of glaucomatous disease, and subsequent earlier intervention when appropriate. Standardized diagnostic algorithms and rigorous perioperative assessment are critical to safe management of glaucoma patients undergoing refractive corneal surgery.

Assessment of Macular Parameter Changes in Patients with Keratoconus Using Optical Coherence Tomography

Keratoconus is typically diagnosed through changes at the anterior ocular surface. However, we wished to assess if macular parameter changes might also occur in these patients. We assessed posterior changes through the use of optical coherence tomography and compared to a nonkeratoconus patient group. All subjects underwent clinical examination including macular thickness measurements. The generalized estimation equation model was used to estimate the means and compare the differences in various measurements between keratoconus and nonkeratoconus patients. A total of 129 keratoconus eyes of 67 cases and 174 nonkeratoconus eyes of 87 controls were analysed. Keratoconus individuals presented with a significantly greater mean retinal thickness in the central fovea, inner, and outer macula compared to the nonkeratoconus group (p < 0.05). In addition, individuals presenting with the early signs of keratoconus had significantly greater inner and outer macular volume compared to the nonkeratoconus group (p < 0.05). This study indicates the retina appears to thicken at the fovea and macula and had increased macular volume in keratoconus individuals compared to nonkeratoconus individuals. Thus we posit that structural retinal changes exist in keratoconus eyes that are additional to those typically seen in the anterior segment.