Comparison of Different Measurement Tools and Dimensional Parameters of Pterygium to Investigate its Impact on Refractive Indices and Ocular Aberrations.

OBJECTIVES: The aim of this study was to compare different measurement tools and parameters, including a new computer-assisted image processing technique for the quantitative analysis of the percentage of pterygium on the corneal surface, horizontal/vertical lengths obtained using slitlamp beam and surgical compass. METHODS: A total of 21 pterygia of 17 patients were included in the study. The pterygia were measured by three different methods: a slitlamp beam, a surgical compass, and a new computer-assisted image processing method. Refractive indices and higher-order aberrations were analyzed in all cases. RESULTS: The new computer-assisted image processing technique revealed excellent intraclass correlation coefficients for intraobserver and interobserver reliability (0.999 and 0.995, respectively). However, horizontal and vertical lengths revealed more deviation between the measurements obtained with slitlamp beam and surgical compass. Although uncorrected visual acuity did not show any significant correlation between horizontal and vertical lengths of pterygia measured by either slitlamp beam or surgical compass, it was correlated with the digital pterygium ratio (rho, 0.462; P=0.035). All ocular aberration (total, higher-order, coma, trefoil, quatrefoil, spherical, and higher-order astigmatism) Root-mean-square values more strongly correlated with higher percentage values of pterygium that covers the cornea, measured by the new computer-assisted image processing technique. CONCLUSION: The percentage of pterygium covering the corneal surface seems to be more associated with the pterygium-related visual disturbances than with horizontal and vertical lengths measured by conventional techniques. Moreover, the new computer-assisted image processing technique can accurately and reliably measure the percentage extension of pterygium on cornea.

Change in Accommodation and Ocular Aberrations in Keratoconus Patients Fitted With Scleral Lenses.

PURPOSE: To evaluate the accommodative response to different accommodative stimulus and to determine the changes in ocular higher-order aberrations with accommodation in keratoconus patients fitted with mini scleral lenses. MATERIAL AND METHODS: The study included 15 keratoconus patients wearing mini scleral lenses (Misa Scleral Lens-Microlens, Arnhem, the Netherlands) and 15 keratoconus patients wearing rigid gas permeable lenses. Hartmannn Shack aberrometer (IRX-3; Imagine Eyes, Orsay, France) was used for the evaluation of accommodation. Accommodative responses to the accommodative stimulus ranging from 0.5 to 5.0 diopters (D) with intervals of 0.5 D were recorded. Spherical, coma, trefoil aberration, and root mean square (RMS) of total higher-order aberrations (HOAs, third to sixth orders) at baseline, at 2.5 D stimulus, and at 5 D stimulus were also recorded. RESULTS: Although accommodative response to accommodative stimulus of 0.5 to 2.5 D (with 0.5 D intervals) was similar in both groups, accommodative response to accommodative stimulus of 3.0 to 5.0 D was significantly lower in keratoconus group wearing mini scleral lenses. The coma, spherical, trefoil aberrations, and the RMS of total HOAs at baseline, at 2.5 D stimulus, and at 5 D stimulus were not significantly different between the groups. However, changes in the coma and trefoil aberrations and RMS of total HOA with 2.5 D and 5.0 D stimulus were significant only in the RGP group. CONCLUSIONS: Accommodative response to increasing accommodative stimulus was found to be impaired in keratoconus patients wearing mini scleral lenses.

Evaluation of corneal topographic changes and surgically induced astigmatism after transconjunctival 27-gauge microincision vitrectomy surgery.

PURPOSE: To evaluate the corneal topographic changes and postvitrectomy astigmatism after 27-gauge (g) microincision vitrectomy surgery (MIVS) by using Pentacam HR-Scheimpflug imaging system. METHODS: This prospective descriptive study included 30 eyes of 30 patients who underwent 27-g MIVS. All eyes underwent a Pentacam HR examination preoperatively and on the first week, first month and third month postoperatively. The power of the corneal astigmatism, mean keratometry (K m), K 1 and K 2 values and corneal asphericity (Q value) values for the both front and back surfaces of the cornea, index of surface variance (ISV), index of vertical asymmetry (IVA), index of height asymmetry (IHA), index of height decentration (IHD) and higher-order aberrations including coma, trefoil, spherical aberration, higher-order root-mean-square and total RMS were recorded. Additionally, the mean induced astigmatism was estimated by vector analysis. RESULTS: No statistically significant changes were observed in the mean power of corneal astigmatism, mean keratometry, K 1 and K 2 values, corneal asphericity values, ISV, IVA, IHA, IHD and higher-order aberrations on the first week, first month and third month after the operation. The mean surgically induced astigmatism was calculated as 0.23 ± 0.11 D on the first week, 0.19 ± 0.10 D on the first month and 0.19 ± 0.08 D on the third month postoperatively. CONCLUSION: Minor corneal surface and induced astigmatic changes are expected to result in rapid visual rehabilitation after pars plana vitrectomy with the 27-g MIVS system.

Corneal tomography and biomechanics in primary pterygium.

PURPOSE: To study the Scheimpflug's imaging and corneal biomechanics in primary pterygium. METHODS: A prospective observational study of 55 patients with unilateral primary nasal pterygium was done. The normal fellow eyes of patients with pterygium were taken as controls. Clinical parameters noted included visual acuity, values of corneal curvature by doing Scheimpflug imaging, wavefront aberrations in terms of higher and lower-order aberrations and corneal hysteresis (CH) as well as corneal resistance factor (CRF) values by using ocular response analyzer. RESULTS: Of the total 55 patients, mean age was 43.0 + 11.4 years (range: 20-72 years). Mean LogMar uncorrected visual acuity in pterygium eyes and control eyes was 0.21 + 0.20 and 0.12 + 0.15, respectively (p = 0.016). On Scheimpflug imaging the mean anterior corneal curvature values (Ka1/Ka2 D) were 41.09 + 3.38/44.33 + 2.29 in pterygium eyes, 43.13 + 1.79/43.98 + 2.17 in control eyes (p < 0.0005) and mean posterior corneal curvature (Kp1/Kp2 D) values were 6.14 + 0.39/6.53 + 0.43 in pterygium eyes and 6.13 + 0.28/6.46 + 0.47 in control eyes (p > 0.05). Analysis of corneal aberrations showed significantly higher corneal wavefront aberrations in pterygium eyes. Highest correlation of corneal astigmatism was noted with corneal area encroached by pterygium (ρ = 0.540 for LOA and 0.553 for HOA) and distance from pupillary center (ρ = 0.531 for LOA and 0.564 for HOA). Corneal biomechanical parameters including CH and CRF were found to be lower in the pterygium eyes, though not statistically significant (p value 0.60 and 0.59, respectively). CONCLUSION: Pterygium leads to deterioration of visual performance not only by causing refractive and topographic changes but also by causing a significant increase in corneal wavefront aberrations.

Effect of Iris registration on visual outcome in wavefront-guided LASEK for myopic astigmatism.

PURPOSE: This study aimed to investigate the effect of iris registration (IR) on visual outcomes in wavefront-guided LASEK for myopic astigmatism. METHODS: The retrospective chart review was performed for wavefront-guided LASEK using VISX Star S4 in patients with myopic astigmatism (cylinder ≥ 1.00 diopter[D]). Eyes were divided into IR group (LASEK with IR at the time of surgery) and Non-IR group (LASEK without IR system + failed-IR engagement during LASEK). Visual acuity (VA), astigmatism, higher-order aberration (HOA), and contrast sensitivity were assessed preoperatively and 3 months postoperatively. The IR and Non-IR groups were subcategorized depending on the spherical equivalent (lower myopia ≤-5.00 D vs. higher myopia >-5.00 D) for the comparison of HOA changes. RESULTS: Postoperative uncorrected VAs showed no differences between IR (n = 30) and Non-IR (n = 46). In astigmatic vector analyses, no differences were noted in the mean magnitude of error and the mean angle of error between two groups. There were no differences in postoperative total HOA, spherical aberration (SA), coma, and trefoil between the groups, either. The total HOA and SA increased in both groups, while coma increased only in Non-IR. In higher myopia, ΔRMS of coma was smaller in IR. Preoperative and postoperative total HOA were linearly correlated in Non-IR, but not for IR. Contrast sensitivity of 12 cycles per degree improved in both groups. CONCLUSION: IR had similar outcomes to conventional trackers in wavefront-guided LASEK, with less tendency of inducing coma, especially in higher myopia.

Characteristics of higher-order aberrations and anterior segment tomography in patients with pathologic myopia.

PURPOSE: To investigate prospectively the characteristics in the higher-order aberrations and anterior segment tomography in patients with pathologic myopia. METHODS: One hundred and twelve consecutive highly myopic patients (mean age 43.4 ± 9.3 years, spherical equivalent of refractive error ≥8 D and an axial length ≥26.5 mm) were studied. Thirty-seven emmetropic individuals (mean age 37.0 ± 14.5 years, spherical equivalent of refractive error ≤ ±1 D) were analyzed as controls. The ocular and cornea higher-order aberrations were measured using a Hartmann-Shack wavefront sensor (KR-1W; Topcon Corporation, Tokyo, Japan). The crystalline lens rise, the angle-to-angle, and the white-to-white values were measured using anterior segment OCT (SS-1000; Tomey Corporation, Nagoya, Japan). The mean curvature of the anterior corneal surface, the thickness at the thinnest central corneal point, the location of the central corneal point, the corneal volume, the anterior chamber volume, and the anterior chamber depth were measured using the Pentacam HR (Oculus, Inc., Wetzlar, Germany). RESULTS: The ocular total higher-order aberration for 4-mm pupil, the ocular spherical aberrations, and internal spherical aberration for 6-mm pupil were significantly higher in highly myopic eyes than in the emmetropic controls. The crystalline lens rise was significantly smaller in highly myopic eyes than in the emmetropic controls. The anterior chamber depth and the anterior chamber volume were significantly larger in highly myopic eyes than in the emmetropic controls. CONCLUSION: Highly myopic eyes had higher-order aberrations than emmetropic eyes because of the increasing internal aberrations.

Corneal Higher-Order Aberrations of the Anterior Surface, Posterior Surface, and Total Cornea After SMILE, FS-LASIK, and FLEx Surgeries.

OBJECTIVES: To investigate the corneal higher-order aberrations (HOAs) of the anterior surface, posterior surface, and total cornea after small incision lenticule extraction (SMILE) and compare the results using femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and femtosecond laser lenticule extraction (FLEx). METHODS: This study included 160 eyes in total; 73 eyes underwent SMILE, 52 eyes underwent FS-LASIK, and 35 eyes underwent FLEx surgery. Corneal HOAs of the anterior surface, posterior surface, and total cornea were evaluated using a Scheimpflug camera over 6-mm diameter preoperatively and 3 months postoperatively. RESULTS: The anterior and total corneal HOAs significantly increased after SMILE, FS-LASIK, and FLEx surgeries, especially the spherical aberration and coma, whereas most posterior corneal HOAs remained unchanged. The SMILE procedure induced significantly lower anterior corneal and total corneal spherical aberration and third to eighth HOAs compared with FLEx surgery (P<0.01). FLEx surgery induced higher posterior corneal coma than SMILE (P=0.013) and FS-LASIK (P<0.001) surgeries. CONCLUSIONS: SMILE, FS-LASIK, and FLEx surgeries mainly induced coma and spherical aberrations in the anterior surface and total cornea. The SMILE procedure induced less spherical aberration of the anterior cornea and total cornea than FLEx surgery. The posterior corneal spherical aberration significantly increased after FS-LASIK surgery. The SMILE procedure seems to have fewer effects on posterior corneal coma compared with the FLEx procedure.

Real-Time Measurement of Dynamic Changes of Anterior Segment Biometry and Wavefront Aberrations During Accommodation.

OBJECTIVES: To analyze the dynamic relationship between ocular geometrical structure and high-order aberrations (HOAs) in teal-time during accommodation of human eye. METHODS: A custom-built spectral domain optical coherence tomography (OCT) system with high-speed and ultra-long scan depth was used to image the anterior segment, whereas a Shack-Hartmann wavefront sensor was used to detect the whole-eye aberration. A Badal optometer with switched visual targets was integrated with this system to induce 0 and 3.00 D accommodative stimuli. Three young adult subjects were measured and the structural parameters of anterior segment were measured from OCT images and accommodative response and HOAs were calculated and exponentially fitted in real time during the accommodation. RESULTS: The dynamic process from nonaccommodation to 3.00 D accommodation results in reduced pupil diameter, shallower anterior chamber depth, and increased crystalline lens thickness. After an accommodative active time, the RMS of the HOAs changes sharply when an accommodative stimulus is introduced and then tends to be stable. The accommodative response time and velocity are characterized by fitted parameters. The individual differences of changing in HOAs between subjects can be explained by the different sign and changing tendency of certain terms of aberration coefficients in form of Zernike polynomials during the accommodation. CONCLUSIONS: Based on the integrated ocular measurement platform including OCT system and wavefront sensor, our research demonstrated how the morphology of the human anterior segment affect the aberration in real time during accommodation. The dynamic relationship between them helps us to deeply understand the mechanism of accommodation.

Corneal reshaping and wavefront aberrations during overnight orthokeratology.

PURPOSE: To investigate changes of corneal thickness at the vertical and horizontal meridians and of wavefront aberrations (WA) over a 30-day period of overnight myopia orthokeratology (OK) lens wear. METHODS: Sixteen subjects (11 women, 5 men, 26.3±3.2 years) were enrolled and fitted for OK lenses. Long scan depth optical coherence tomography was used to measure corneal thickness profiles at both horizontal and vertical meridians at baseline and on days 1, 7, and 30 days. Corneal and ocular WA of a 6-mm pupil were measured and the root-mean-square (RMS) of the astigmatism, coma, spherical aberration (SA), and total higher-order aberrations (HOAs) were determined. RESULTS: During the 30-day period, the central cornea thinned in the horizontal and vertical meridians, whereas corneal thickening occurred in the temporal, nasal, and inferior mid-peripheries. In contrast, the cornea thinned in the mid-peripheral superior. There were significant increases in RMS for astigmatism, SA, coma, and positive horizontal coma during the study period. After OK, there were significant positive correlations between the midperipheral-central thickness change difference and the changes in corneal and ocular RMS of total HOAs and SA (r range: 0.281 to 0.492, P<0.05). Only the change of corneal coma RMS was correlated with midperipheral-central thickness change difference (r=0.270, P<0.05). The change in corneal horizontal coma was correlated with the temporal-nasal thickness change difference (r=-0.289, P<0.05). CONCLUSIONS: Overnight OK caused unique changes in corneal thickness profiles at the vertical and horizontal meridians and increased corneal and ocular HOAs related to corneal reshaping.

Comparison of the Distribution of Lenticule Decentration Following SMILE by Pupil Center or Tear Film Mark Centration.

PURPOSE: To investigate lenticule decentration following small incision lenticule extraction (SMILE) via the pupil center or tear film mark centration method and compare induction of corneal higher order aberrations (HOAs) between the two methods. METHODS: This study analyzed decentration values obtained from tangential topography difference maps of 100 eyes (100 patients) undergoing SMILE with the pupil center (n = 50) or tear film mark (n = 50) centration method. Total HOAs and component aberrations were measured preoperatively and 6 months postoperatively. Relationships between the magnitudes of decentration and induced corneal HOAs were assessed. RESULTS: Both vertical and total decentered displacement were significantly different (P < .001) between the two centration groups. A significant relationship between the preoperative pupillary offset and decentration was noted in the pupil center group (P < .001), but not in the tear film mark group (P = .530). Significantly greater induction of total HOAs, coma, and vertical coma (all P < .001), as well as horizontal coma (P = .001) and spherical aberration (P = .023), were observed in the pupil center group. Association between the total decentered displacement and induced total HOAs (P < .001), as well as all other significantly increased phenomena, was also significant in the pupil center group. Differences in decentered displacement and induced corneal HOAs were significant for preoperative pupillary offset (angle kappa) greater than 200 µm, but not for angle kappa less than 200 µm. CONCLUSIONS: SMILE with tear film mark centration can yield improved treatment centration and less induction of total HOAs, coma, and spherical aberrations. [J Refract Surg. 2020;36(4):239-246.].

Two-year observation of posterior corneal elevations after small incision lenticule extraction (SMILE) for myopia higher than -10 dioptres.

AIM: To investigate the change in posterior corneal elevations (PCEs) of eyes with extremely high myopia 2 years after small incision lenticule extraction (SMILE). METHODS: We evaluated 39 eyes of 39 patients with spherical equivalent higher than -10.00 dioptres (D). Using a Scheimpflug camera (Pentacam), we measured change in PCEs at 1 day, 3 months, 6 months and 2 years after SMILE. Another 34 eyes of 34 patients who underwent femtosecond laser-assisted in situ keratomileusis (FS-LASIK) were examined before, at 1 day and long-term after surgery as the control group. For each eye, elevations at central, thinnest, maximal points and 24 other predetermined points were measured. RESULTS: No significant forward displacements of PCEs were observed in both surgeries. The maximal but not significant forward displacement occurred around 3-6 months following SMILE, and all returned to original levels 6 months postoperatively except superior area. The peripheral area tended to displace backward, while the central area tended forwardly. In both procedures, elevations along horizontal meridians, inferior and temporal hemispheres were significantly higher than those along vertical meridians, superior and nasal hemispheres, respectively (p<0.05). Elevation on the 4 mm, 6 mm diameters at 1 day and on the 6 mm diameter and temporal hemisphere at long-term follow-up postoperatively were significantly higher in FS-LASIK than SMILE (p<0.05). Change in elevations on the 6 mm diameter circle correlated with residual bed thickness (p=0.047). CONCLUSIONS: SMILE is a safe way to correct for myopia higher than -10 D, with PCEs remaining stable 2 years after surgery.

Corneal thickness association with ocular and corneal high-order aberrations.

PURPOSE: To investigate the association among central corneal thickness, peripheral corneal thickness (PCT), and wavefront aberrations in the anterior cornea, posterior cornea and the whole eye in myopia. METHODS: Sixty-four eyes of 64 myopic subjects were evaluated with a Pentacam rotating Scheimpflug camera (Oculus, Inc., WA) corneal topographer for: (1) wavefront aberrations from the anterior and posterior corneal surface, (2) corneal thickness (central and peripheral), and (3) with a wavefront aberration-supported cornea ablation wavefront analyzer (Wavescan, Visx, Inc., Santa Clara, CA) for wavefront aberrations generated in the whole eye. Relationships between the wavefront aberrations and corneal thickness were analyzed. RESULTS: The mean age of subjects was 34.75 +/- 10.08 years. The central corneal thickness was 550.5 +/- 28.459 microm. The mean peripheral thickness was 629.9 +/- 32.1 microm. Central and PCTs were not significantly correlated with corneal or ocular high-order aberrations. Intraocular pressure was significantly correlated with ocular trefoil (r = -0.307, P=0.001). CONCLUSIONS: Central and PCT were not significantly associated with either anterior or posterior corneal Zernike aberrations; in addition, no association with the whole ocular wavefront aberrations was found.

Quantitative Analysis of Objective Forward Scattering and Its Relevant Factors in Eyes with Cataract.

This study was aimed to quantitatively assess objective forward scattering and its relevant factors in eyes having cataract. Our study comprised 192 eyes of 192 patients (mean age, 71.3 ± 9.2 (standard deviation) years) who have cataract formation for surgical consultation. We determined uncorrected and corrected distance visual acuities (UDVA and CDVA), manifest refraction, the grade of nuclear sclerosis, objective scattering index (OSI) with the OQAS II (Visiometrics, Spain), log(s) with the C-Quant (Oculus, Germany), and ocular higher-order aberrations (HOAs) using the wavefront sensor (KR-1W, Topcon, Japan). The mean OSI was 5.11 ± 3.19 (0.90 to 20.90). We found explanatory variables relevant to the OSI to be, logMAR CDVA (p < 0.0001, partial regression coefficient B = 5.917) and log(s) (p = 0.0006, B = 0.911) (adjusted R2 = 0.333), in order of influence. No significant correlation was found with other clinical factors such as gender, age, manifest refraction, UDVA, ocular HOAs, or nuclear sclerosis. Eyes with worse CDVA and higher log(s) are more predisposed to show higher OSI in cataractous eyes. It is suggested that objective forward scattering was associated, not only with CDVA, but also with subjective forward scattering, in cataractous subjects.

Corneal Irregular Astigmatism and Curvature Changes After Small Incision Lenticule Extraction: Three-Year Follow-Up.

PURPOSE: To evaluate the long-term changes in anterior and posterior corneal irregular astigmatism and curvatures after small incision lenticule extraction (SMILE). METHODS: Fifty eyes of 28 patients underwent SMILE for myopic astigmatism. All procedures were performed using the VisuMax® femtosecond laser. A Scheimpflug camera was used for preoperative and 3-year postoperative tomography. Anterior and posterior corneal Fourier parameters (spherical component, regular astigmatism, asymmetry, and irregularity) and curvature data were evaluated and compared within 2 subgroups according to the magnitude of the refractive correction (low myopia group: spherical equivalent (SEQ) ≥ -6 D; high myopia group: (SEQ) < -6 D). Associations between all studied parameters were examined. RESULTS: Three years postoperatively, an increase in anterior corneal curvatures and Fourier parameters was detected and the results were strongly correlated with the preoperative SEQ, lenticule thickness, and volume. At the posterior cornea, the flattest radius, corneal astigmatism, spherical component, regular astigmatism, and irregularity decreased only in the high myopia group. A correlation was found between changes in posterior astigmatism and changes in anterior radii (R = 0.349, P = 0.014), SEQ (R = 0.396, P = 0.0049), and lenticule thickness (R = -0.414, P = 0.0031). Moreover, changes in posterior corneal irregularity correlated with the changes in anterior and posterior radii (R = -0.3, P = 0.034, and R = 0.449, P = 0.0012, respectively), changes in preoperative SEQ (R = 0.284, P = 0.0477), and lenticule thickness (R = -0.311, P = 0.0298). CONCLUSIONS: Three years after SMILE, there was a reduction of posterior astigmatism in high refractive corrections. This could result in undercorrection in high refractive treatments. Total irregularities increased despite the compensatory effect of the posterior corneal surface.

Evaluation of Anterior and Posterior Corneal Irregularity After Descemet Membrane Endothelial Keratoplasty.

PURPOSE: To investigate the changes in anterior and posterior corneal irregularity after Descemet membrane endothelial keratoplasty (DMEK). METHODS: This retrospective study included 27 eyes of 23 patients who underwent DMEK and 27 eyes of age-matched healthy controls. Corneal irregularity indexes, surface regularity of height (SR_H), and higher-order aberrations were evaluated in 4- and 6-mm diameters of the cornea, preoperatively and postoperatively, using anterior segment optical coherence tomography. RESULTS: The best spectacle-corrected visual acuity (logarithm of the minimum angle of resolution) improved from 1.01 ± 0.54 preoperatively to 0.08 ± 0.11 at 6 months postoperatively. Anterior SR_H was significantly lower at 6 months postoperatively [from 1.86 ± 0.73 to 1.20 ± 0.34 (P < 0.01) (4-mm) and from 2.29 ± 0.62 to 1.64 ± 0.42 (P < 0.01) (6-mm)]. Posterior SR_H showed a significant decrease from 6.87 ± 4.19 to 2.18 ± 0.51 (4-mm) and from 5.21 ± 2.60 to 2.44 ± 0.38 (6-mm) at 6 months postoperatively (P < 0.001). The SR_H was positively correlated with best spectacle-corrected visual acuity (anterior 4 mm: R = 0.524; anterior 6 mm: R = 0.477; posterior 4 mm: R = 0.655; posterior 6 mm: R = 0.655, P < 0.001) and with higher-order aberrations for 4-mm and 6-mm diameters (R = 0.511 and R = 0.325, P < 0.001, respectively). CONCLUSIONS: The SR_H reflects corneal irregularity and is correlated with the visual outcome after DMEK, which may be very helpful to corneal surgeons as an index indicating the severity before DMEK, and the quality of visual function after DMEK.

Additional Intrastromal Corneal Ring Segments in Keratoconus.

PURPOSE: To evaluate the outcome of additional KeraRing (Mediphacos, Belo Horizonte, Brazil) implantation in patients with keratoconus with previously implanted INTACS (Addition Technology Inc, Fremont, CA) segments. METHODS: The KeraRing was implanted in 5 eyes of 3 patients with keratoconus without removal of previous intrastromal corneal ring segments. Tunnels were created manually. Snellen uncorrected distance visual acuity (UDVA), corrected distance visual acuity, refractive and keratometric values, and higher-order aberrations were recorded before and after KeraRing implantation. RESULTS: UDVA, corrected distance visual acuity, subjective refraction, and keratometric values were improved in 4/5 of cases and remained stable during a median follow-up of 36 months. UDVA improved from 20/200 and 20/100 to 20/100 and 20/40 in the right and left eyes of patient 1, respectively, and from 20/200 to 20/40 in both eyes of patient 2. The reduction in mean keratometric value was 2.1 and 4.4 D in the right and left eyes of patient 1, and 1.4 and 1.9 D in the right and left eyes of patient 2, respectively. In patient 3, UDVA (20/100) and mean keratometric value (52.4) remained unchanged after second intrastromal corneal ring segment implantation. Total higher-order aberrations were improved in all cases. No intraoperative or postoperative complication was observed. However, one of the cases reported glare under scotopic conditions. CONCLUSIONS: KeraRing implantation in properly selected eyes with previously implanted INTACS could enhance final visual and refractive outcomes.

Persistence of the Cone on the Posterior Corneal Surface Affecting Corneal Aberration Changes After Intracorneal Ring Segment Implantation in Patients With Keratoconus.

PURPOSE: To analyze the changes in anterior and posterior corneal surfaces and aberrations in patients who underwent intracorneal ring segment (ICRS) implantation for the treatment of keratoconus. METHODS: Eighty-nine eyes of 59 patients with keratoconus who underwent ICRS implantation were analyzed. All eyes were evaluated using a tomography system combining a Placido disc and Scheimpflug photography before and at least 6 months after surgery. Total, anterior, and posterior corneal aberrations, anterior and posterior sagittal and tangential anterior and posterior curve analysis, keratometry (K), minimum corneal thickness, and anterior chamber depth were analyzed before and after surgery. RESULTS: Flattening with a decrease in the cone shape on the anterior corneal surface and steepening in the paracentral area with persistence of cone appearance on the posterior corneal surface were noted in all cases after ICRS implantation. The total corneal higher-order aberrations (HOAs) significantly decreased from 1.09 ± 0.43 to 0.71 ± 0.32 µm, and anterior corneal HOAs significantly decreased from 0.98 ± 0.46 to 0.81 ± 0.37 µm, whereas the posterior corneal HOAs increased from 0.53 ± 0.29 to 0.66 ± 0.25 µm after ICRS implantation (P < 0.05). There was a significant decrease in anterior maximum keratometry, but there was a significant increase in posterior maximum keratometry after ICRS implantation (P < 0.05). CONCLUSIONS: The cone shape persists on the posterior corneal surface despite its correction on the anterior corneal surface, leading to a decrease in anterior corneal aberrations and an increase in posterior corneal aberrations after ICRS implantation in eyes with keratoconus.

Visual Outcomes and Aberrometric Changes With Topography-Guided Photorefractive Keratectomy Treatment of Irregular Astigmatism After Penetrating Keratoplasty.

PURPOSE: To evaluate the visual acuity and keratometric and aberrometric changes in patients with corneal transplants (PKP), who underwent topography-guided photorefractive keratectomy (TG-PRK) with mitomycin C (MMC). METHODS: In this case study, 15 patients with spherical equivalents ranging from -11.00 to -0.25 diopters (D) who underwent penetrating corneal transplantation and had irregular astigmatism ranging from -7.5 to -2.0 D underwent TG-PRK with MMC. Corneal topography and wavefront of all patients were measured preoperatively and 12 months postoperatively. RESULTS: Twelve months after TG-PRK with MMC, 46% of eyes achieved a best spectacle-corrected visual acuity (BSCVA) of 20/20 compared with 1 eye preoperatively (P = 0.0221, χ test). The BSCVA did not improve in 1 patient and increased by 1 line or more in all others. Astigmatism decreased significantly (P = 0.003) from 5.10 ± 0.4 D to 3.37 ± 0.06 D, the corneal best-fit sphere increased and keratometry measurements flattened significantly (P = 0.0001 for both comparisons), and the corneal total root mean square aberrations and trefoil decreased significantly (P = 0.0077 and P = 0.0054, respectively) from 9.11 ± 2.56 µm to 7.58 ± 3.15 µm and 2.00 ± 1.2 to 1.38 ± 0.27 µm, respectively, as measured by wavefront aberrometry. CONCLUSIONS: Twelve months postoperatively, the BSCVA improved significantly, the lines of vision increased, and astigmatism, corneal best-fit sphere, mean keratometry, corneal thickness, corneal root mean square total, and corneal spherical aberrations decreased. TG-PRK with MMC is a good alternative for correcting post-PKP cases with irregular astigmatism with elevated higher-order aberrations.

Corneal Tomographic Changes After UV Cross-Linking for Corneal Ectasia (1-Year Results).

PURPOSE: To evaluate changes in maximum keratometry (Kmax), corneal higher-order aberrations (HOAs), and densitometry (backscattered light) up to 1 year after UV cross-linking and their possible relation with changes in the visual outcome. METHODS: Retrospective cohort study on 18 eyes of 16 patients, who underwent UV cross-linking after the Dresden protocol for progressive keratoconus or ectasia after laser-assisted in situ keratomileusis. Corrected distance visual acuity (CDVA), Scheimpflug-based corneal tomography, mean image brightness (corneal densitometry) from the anterior 120 µm of the midcornea, and posterior 60 µm of the central 6 mm of the cornea, and HOAs were evaluated. RESULTS: Kmax at 1 month (59.7 ± 6.0D) after UV cross-linking resembled preoperative Kmax (59.3 ± 6.4D, P = 0.368), decreased until 3 months postoperatively (58.3 ± 6.3D, P = 0.002), and stabilized thereafter (P > 0.227). All postoperative corneal densitometry values were higher than preoperative values in all measured depths (P < 0.05). One-month anterior and total corneal HOAs (4.28 ± 1.64 µm and 3.87 ± 1.62 µm, respectively) resembled preoperative values (4.10 ± 1.70 µm and 3.67 ± 1.62 µm, respectively; P > 0.221) and then decreased until 12 months postoperatively (3.86 ± 1.84 µm and 3.40 ± 1.80 µm, respectively; P < 0.005). Thinnest point thickness decreased from before (442 ± 25 µm) to 3 months postoperatively (427 ± 25 µm, P < 0.001), with no difference at 12 months postoperatively compared with preoperative values (437 ± 29 µm, P = 0.149). CDVA and endothelial cell density remained unchanged (P > 0.345 and P > 0.257, respectively). No relations were found between CDVA and the evaluated parameters (P > 0.05). CONCLUSIONS: One year after UV cross-linking, the observation of stable CDVA and thinnest point thickness, together with reduced Kmax suggests no ectasia progression within the study period in these cases. Although HOAs showed a trend toward improvement, corneal densitometry remained elevated.

Refractive Changes Induced by Spherical Aberration in Laser Correction Procedures: An Adaptive Optics Study.

PURPOSE: To study the effect on vision of induced negative and positive spherical aberration within the range of laser vision correction procedures. METHODS: In 10 eyes (mean age: 35.8 years) under cyclopegic conditions, spherical aberration values from -0.75 to +0.75 µm in 0.25-µm steps were induced by an adaptive optics system. Astigmatism and spherical refraction were corrected, whereas the other natural aberrations remained untouched. Visual acuity, depth of focus defined as the interval of vision for which the target was still perceived acceptable, contrast sensitivity, and change in spherical refraction associated with the variation in pupil diameter from 6 to 2.5 mm were measured. RESULTS: A refractive change of 1.60 D/µm of induced spherical aberration was obtained. Emmetropic eyes became myopic when positive spherical aberration was induced and hyperopic when negative spherical aberration was induced (R2 = 81%). There were weak correlations between spherical aberration and visual acuity or depth of focus (R2 = 2% and 3%, respectively). Contrast sensitivity worsened with the increment of spherical aberration (R2 = 59%). When pupil size decreased, emmetropic eyes became hyperopic when preexisting spherical aberration was positive and myopic when spherical aberration was negative, with an average refractive change of 0.60 D/µm of spherical aberration (R2 = 54%). CONCLUSIONS: An inverse linear correlation exists between the refractive state of the eye and spherical aberration induced within the range of laser vision correction. Small values of spherical aberration do not worsen visual acuity or depth of focus, but positive spherical aberration may induce night myopia. In addition, the changes in spherical refraction when the pupil constricts may worsen near vision when positive spherical aberration is induced or improve it when spherical aberration is negative. [J Refract Surg. 2017;33(7):470-474.].