Content development for a new item-bank for measuring multifocal contact lens performance.

BACKGROUND: Presbyopia is an age-related condition that causes a decreased ability to focus on nearby objects. Multifocal contact lenses are commonly used to address this issue. However, there seems to be a notable dissatisfaction among multifocal contact lens wearers. The absence of a reliable instrument to measure the patient's perspective, despite the widespread use of this method, highlights the need for further research in this area. OBJECTIVE: The objective of this study is to develop an item-bank integrating all domains necessary to assess the patient's perspective on multifocal contact lens performance, offering a comprehensive measure. The item-bank will ensure a high level of content validity, be self-administered, and will initially be available in Spanish. The aim of this tool is to serve as a valuable resource for research and optometric clinics, facilitating the follow-up of patients with presbyopia who wear multifocal contact lenses or those who are newly starting to use them. METHODOLOGY: The MCL-PRO item bank, followed a systematic and step-wise inductive approach to gather information, following the recommendations outlined in the COSMIN guidelines and similar studies. The process involved the following steps: (1) Literature review and relevant existing items identification (2) Social media review, (3) Semi-structured focus groups, (4) performing qualitative analysis, (5) refining and revising the items, and (6) generating the content of the item bank. RESULTS: A total of 575 items were included in the item-bank hosted under 8 different domains that were found to be important for presbyopic population: visual symptoms (213), activity limitation (111), ocular symptoms (135), convenience (36), emotional well-being (33), general symptoms (16), cognitive issues (21) and economic issues (10). CONCLUSION: The item-bank created has followed standardised methodology for its development and encloses all the aspects for MCL performance evaluation from patients perspective.

Forward-scattered and backward-scattered light in moderate keratoconus.

INTRODUCTION: To evaluate the backscattered light, objective scatter index (OSI) and retinal straylight in patients with moderate keratoconus and healthy control subjects. METHODS: A prospective observational study was developed with 33 patients in the moderate-keratoconus group (KC) and 34 in the non-keratoconus group (NKC). Corneal densitometry was obtained using Scheimpflug corneal tomography and measurements were expressed in grayscale units (GSU) over four zones within a 12.00 mm diameter around the corneal apex. A straylight meter was used to determine the amount of intraocular straylight under scotopic conditions, and the straylight parameter (LOG(s)) and test duration were recorded. The Optical Quality Analysis System based on the double-pass technique determined the OSI value. RESULTS: Significant differences were observed between the KC and NKC groups for corneal densitometry (except in the 6-10 mm zone), OSI and retinal straylight. A moderate and significant correlation was found between OSI and retinal straylight LOG(s) (r = 0.52, p = 0.002). Weaker and non-significant correlations were found between corneal densitometry and the other parameters analysed (i.e., OSI, retinal straylight LOG(s) and retinal straylight times). CONCLUSIONS: Backscattered light, retinal straylight and the OSI show clear differences between healthy eyes and those with moderate KC. The changes present in the stages of KC evaluated in the current study (stages II and III according to the Amsler-Krumeich classification) might alter the scattering of the light entering the eye.

Effect of defocus combined with rotation on the optical performance of trifocal toric IOLs.

PURPOSE: To objectively analyze the optical quality of the FineVision Toric intraocular lens (IOL) with two cylinder powers when different combinations of rotations and residual refractive errors are induced. METHODS: This study assessed the FineVision Toric IOL with two different cylinder powers: 1.5 and 3.0 diopters (D). Three different rotation positions were considered: centered, 5° and 10° rotated. An optical bench (PMTF) was used for optical analysis. The optical quality of the IOLs was calculated by the modulation transfer function (MTF) at five different focal points (0.0, 0.25, 0.50, 0.75, and 1.00 D). RESULTS: The MTF averaged value of the reference situation was 38.58 and 37.74 for 1.5 and 3.0 D of cylinder, respectively. For the 1.5 D cylinder, the combination of 5° of rotation with a defocus of 0.25, 0.50, 0.75, and 1.0 D induced a decrease on the MTF of 12.39, 19.94, 23.43, 24.23 units, respectively. When induced rotation was 10°, the MTF decrease was 17.26, 23.40, 24.33, 24.48 units, respectively. For the 3.0 D cylinder, the combination of 5° with 0.25, 0.50, 0.75, and 1.0 D of defocus, induced a decrease on the MTF of 12.51, 18.97, 22.36, 22.48 units, respectively. When induced rotation was 10°, the MTF decrease was: 18.42, 21.57, 23.08, and 23.61 units, respectively. CONCLUSION: For both FineVision Toric IOLs there is a certain optical tolerance to rotations up to 5° or residual refractive errors up to 0.25 D. Situations over these limits and their combination would affect the visual quality of patients implanted with these trifocal toric IOLs.

Changes in Optical Quality Induced by Tilt and Decentration of a Trifocal IOL and a Novel Extended Depth of Focus IOL in Eyes With Corneal Myopic Ablations.

PURPOSE: To assess the effect of decentration and tilt combined with prior myopic ablations on the optical performance of a trifocal intraocular lens (IOL) and a novel IOL with an extended depth of focus (EDOF) design. METHODS: The XACT Mono-EDOF ME4 (Santen Pharmaceutical Co Ltd) and the trifocal FineVision (PhysIOL) IOLs were analyzed with and without simulated previous myopic ablations. The optical quality of the IOLs was evaluated with the PMTF optical bench (LAMBDA-X). The through-focus modulation transfer function (MTF) curves were recorded. Measurements were done for three situations: centered, 0.4 mm decentered, and 4 degrees tilted. RESULTS: The trifocal IOL showed three peaks of vision and the EDOF IOL showed a far distance peak with intermediate addition. When decentration or tilt were induced, the trifocal IOL showed negligible changes but the EDOF IOL showed a -0.50 diopters (D) shift of the overall curve. With simulated myopic ablation, the trifocal IOL showed a -0.50 D shift of the curve. When tilt or decentration were also induced, the better optical results were found at -1.00 D. With myopic ablations, the EDOF IOL showed a -0.50 D shift of the optical quality and when decentration or tilt were then induced, negative shifts over -1.00 D were found. CONCLUSIONS: The trifocal IOL was less affected by mis-alignments. When myopic ablations were induced, both lenses decreased their optical quality and the effects of misalignments were higher. In patients who have undergone corneal myopic ablation procedures, proper alignment of the implanted IOL and obtaining effective emmetropia becomes even more critical. [J Refract Surg. 2021;37(8):532-537.].

Optical tolerance to rotation of trifocal toric intraocular lenses as a function of the cylinder power.

BACKGROUND: The aim was to assess the impact of 5- and 10-degree rotations in the optical quality of a trifocal toric intraocular lens with different amounts of cylinder. METHODS: Two Physiol Toric intraocular lenses with 1.5 and 3.0 D of cylinder were analysed in three different positions: centred, 5 and 10 degrees rotated. The optical quality of the intraocular lenses was evaluated with the PMTF optical bench through specific perpendicular targets. The analysis was performed by the through-focus modulation transfer function curves and the modulation transfer function corresponding to distance vision (0 D of vergence). RESULTS: For a centred situation, the through-focus modulation transfer function curves of both intraocular lenses showed the classical three peaks corresponding to the powers of the two principal meridians of the intraocular lenses. When 5 and 10 degrees of rotation were induced, the three peaks were attenuated in both cases. The case with the intraocular lens with 3.0 D of cylinder and 10 degrees of rotation showed the worst optical quality and a significant loss of trifocality. The modulation transfer function values obtained for distance vision also showed the worst optical quality for the intraocular lens with 3.0 D of cylinder and 10 degrees of rotation. CONCLUSION: Rotations over 5 degrees decreased the optical quality of trifocal toric intraocular lenses, being this reduction moderate from 5 to 10 degrees for low levels of cylinder (≤1.5 D). For mid-high levels of cylinder (≥3.0 D), rotations over 5 degrees cause a significant loss of optical quality at all object distances.

Optical Performance of a Trifocal IOL and a Novel Extended Depth of Focus IOL Combined With Different Corneal Profiles.

PURPOSE: To assess the effect of prior myopic ablations on the optical performance of a trifocal diffractive intraocular lens (IOL) and a novel extended depth of focus (EDOF) diffractive design. METHODS: The novel XACT Mono-EDOF ME4 diffractive IOL (Santen Pharmaceutical) and the trifocal diffractive FineVision IOL (PhysIOL) were analyzed standing alone and combined with a simulated myopic corneal ablation. The optical quality of the IOLs in both situations was evaluated with the PMTF optical bench (LAMBDA-X). The through-focus modulation transfer function (MTF) curves and the MTF at three different focal points (+0.50, 0.00, and -0.50 diopters [D]) were recorded. RESULTS: The through-focus MTF curves showed three differentiated peaks for the trifocal IOL and two overlapped peaks for the EDOF IOL. The presence of simulated myopic corneal ablations induces a -0.50 D shift on the overall through-focus curves and softens the multifocal properties of both lenses by decreasing the variations through focus of the MTF. For the analysis of the lenses standing alone, the highest MTF values were obtained for an object vergence of 0.00 D. For a simulated myopic corneal ablation, both IOLs showed better optical quality results at -0.50 D. CONCLUSIONS: The trifocal IOL provides better optical quality at far and near distances when analyzed alone. The EDOF IOL optical properties are more stable when a myopic ablation is introduced. Preoperative calculations of both lenses should consider that prior myopic corneal ablations induce a -0.50 D shift on their far peak quality. [J Refract Surg. 2020;36(7):435-441.].

Effects of Blink Rate on Tear Film Optical Quality Dynamics with Different Soft Contact Lenses.

OBJECTIVE: The aim of this study was to investigate tear film optical quality dynamics for four types of silicone hydrogel contact lenses (SHCLs) for daily wear over a 15-day period and for different blink rate (BR) patterns. METHODS: A prospective randomized, double-blind, cross-over pilot study including four SHCLs (A: lotrafilcon B (Air Optix plus HydraGlyde, Alcon Laboratories); B: samfilcon A (Ultra, Bausch & Lomb); C: comfilcon A (Biofinity, CooperVision); and D: filcom V3 (Blu:gen, Mark'Ennovy)). Serial measurements of Objective Scatter Index (OSI) using the HD Analyzer (Visiometrics S.L., Terrassa, Spain) were taken at different blinking patterns: blinking every 2.5 seconds (high BRs) and every 9 seconds (low BRs). They were performed during the first visit before CL insertion (baseline), after 20 minutes of CL wear (Day 1), and during the last visit after 8 hours of CL wear on day 15 of use (Day 15). RESULTS: Normal young healthy subjects were recruited and fitted with the four lenses. For low BRs, the mean OSI value increased over time for all CLs and the slope of the curve also increased for all CLs, except for CL D. However, for high BRs, the mean OSI value increased only for CLs B and C and the slope of the curve did not change over time for any of them. CONCLUSIONS: These results suggest that the tear film optical quality dynamics after wearing SCHLs for 15 days seems to undergo a slight deterioration only for lowest BR.

Comparison of the impact of nesofilcon A hydrogel contact lens on the ocular surface and the comfort of presbyopic and non-presbyopic wearers.

AIM: To assess and compare the impact of a daily disposable contact lens (CL) with high water content on the ocular surface and comfort of the presbyopic and non-presbyopic population after one day of use. METHODS: Totally 20 presbyopes and 30 non-presbyopes non-contact wearers were fitted with nesofilcon A CLs. CL thickness was measured to assess material stability during daily wear, and ocular surface parameters were also assessed. Optical quality was analyzed for all cases. In addition, CL comfort was rated. RESULTS: No significant differences were found in CL thickness, tear film osmolarity, average tear break-up time, bulbar redness, central corneal thickness, corneal volume, root-mean-square of higher-order aberrations (RMS of HOAs) and vertical and horizontal coma, either as a function of the group or time of use. A significant decrease in tear meniscus height and first break-up of the tear film was found in the presbyopic group (P=0.038; P=0.007 respectively). A decrease in spherical aberration coefficient was found after CL insertion (P=0.031 monofocal CL; P=0.023 low addition multifocal CL; P=0.016 high addition multifocal CL). Multifocal CL were thicker than monofocal CL (P=0.045). Comparison between groups showed more discomfort in presbyopes than non-presbyopes (P=0.003). CONCLUSION: This study evidence that the behavior of the daily disposable CL with high water content seems to be stable during the day of use. Ocular parameters measured during wear show that CL behavior is the same for presbyopes and non-presbyopes, being more uncomfortable for presbyopes.

Repeatability of Noninvasive Keratograph 5M Measurements Associated With Contact Lens Wear.

OBJECTIVE: To assess the intrarater repeatability of the measurements of tear meniscus height (TMH), noninvasive keratograph tear break-up time (NIKBUTs), and ocular redness measurements obtained with the Keratograph 5M (K5M) in a sample of soft silicone hydrogel contact lens (CL) wearers over 15 days. METHODS: Prospective study over two consecutive weeks. Three measurements of TMH, NIKBUTs (NIKBUT first and NIKBUT average), and ocular redness were obtained in different sessions; the first day (baseline, at 8 hr of wear, and after lens removal) and the last day of wear-15th day (at 8 hr of wear and after lens removal). The repeatability of measurements were assessed by two intraclass correlation coefficient (ICC) forms; single measurement [ICC (2,1)] and multiple measurements (k=3) [ICC (2, k)]. RESULTS: Sixty-four eyes were analyzed. The repeatability of baseline TMH [ICC (2,1) greater than 0.90; coefficient of repeatability (CR)=0.06 mm] and after and during CL wear [ICC (2,k) greater than 0.90; CR≤0.07 mm] were excellent. The repeatability of baseline NIKBUT average [ICC (2,k)=0.89 (0.82-0.93); CR=6.07 sec] was maintained after CL removal but was poorer during CL wear. The repeatability of baseline NIKBUT first [ICC (2,k) =0.80 (0.69-0.87); CR=8.74 sec] was maintained after CL removal and during CL wear at moderate-good level. CONCLUSIONS: Intrarater repeatability of TMH, NIKBUTs, and ocular redness performed by K5M after CL wear remains stable when three measurements are performed. However, intrarater repeatability during CL wear decreased only for NIKBUT average and was not affected by time of use (15 days).

Randomized crossover trial of silicone hydrogel contact lenses.

PURPOSE: The aim of the current study is to assess, using new technologies, the interaction of four monthly silicone hydrogel contact lenses on the ocular surface and the comfort over 15 days of use. METHODS: Prospective cross-over, randomized and double-masked study including four materials (lotrafilcon-B, samfilcon-A , comfilcon-A and filcom-V3). Clinical examination was performed in the following order: tear meniscus height, first break-up of the tear film, the average time of all tear film breakup incidents, bulbar redness, limbal redness (Keratograph 5M ,Oculus, Germany); central corneal thickness (Pentacam, Oculus, Germany), thermography values (FLIR A325; FLIR Systems Inc., USA), and slit-lamp evaluations, including ocular surface staining. Finally, subjective comfort was obtained from Contact Lens Dry Eye Questionnaire-8. RESULTS: The impact of contact lens wear on the ocular surface didn't show statistically significant changes over time except for corneal and conjunctival staining grades on day 15 compared to day 1 for the comfilcon A group (P = .003 and P = .01, respectively). Contact lens stability and impact on the ocular surface during contact lens wear didn't show statistically significant changes over time except in the case of the comfilcon A material with respect to the irritation item (P = .01). CONCLUSIONS: These results suggest that the impact of monthly silicone hydrogel contact lens materials on the ocular surface after and during contact lens wear, contact lens stability over time, and subjective comfort did not reveal any significant changes over 15 days of use for any of the materials.

Long-term changes in straylight induced by corneal refractive therapy: a pilot study.

PURPOSE: To assess long-term intraocular straylight changes induced by corneal refractive therapy (CRT) and to determine whether these changes persist after cessation of CRT lens wear. METHODS: A single-center, prospective, longitudinal study was performed in 22 subjects (group 1) undergoing overnight corneal refractive therapy for 1 year. Ten right eyes of 10 subjects (group 2) with emmetropia served as controls. In each subject, high contrast visual acuity (HCVA), manifest refraction and intraocular straylight were determined at several time points during treatment and 1 month after discontinuing treatment. Straylight was measured using the van den Berg straylight meter (third generation). EDTRS charts (logMAR units) were used to assess HCVA. For both groups, only data for the right eyes were analyzed. RESULTS: Straylight (mean ± standard deviation) significantly fell from baseline (0.98 ± 0.13) to values recorded after 1 month (0.88 ± 0.13, p=0.011), 3 months (0.88 ± 0.13, p=0.004), 6 months (0.88 ± 0.13, p=0.000) and 12 months (0.76 ± 0.12, p=0.003) of treatment. One month after discontinuing CRT lens wear, straylight was still significantly lower than baseline (0.89 ± 0.13, p=0.003). No correlations were observed between intraocular straylight and HCVA. CONCLUSIONS: Good refractive outcomes and reductions in straylight were observed in response to corneal refractive therapy for myopia. The reduction in straylight observed after discontinuing CRT warrents further investigation.

Anterior segment changes produced in response to long-term overnight orthokeratology.

PURPOSE: To evaluate the effect of overnight orthokeratology (OK) on anterior chamber depth (ACD), posterior radius of corneal curvature (PRCC) and axial length (AL) over one year. METHODS: In this prospective longitudinal study, measurements were made in 34 right eyes of 34 subjects at baseline, 15 days, 1 and 12 months after starting OK treatment. ACD and PRCC measurements were obtained using a Pentacam system and AL was measured using an IOL-Master. ACD and PRCC were measured along the horizontal and vertical meridians at 1 mm intervals. These measurements were expressed as the distance from the center in the nasal (N), temporal (T), superior (S) and inferior (I) directions. RESULTS: A significant reduction in ACD was observed in both meridians during treatment. PRCC flattened significantly in the (T) direction after 15 d (1 mm, p < 0.05), at the corneal center after 15 d (p < 0.01), in the (T) direction after 1 month (1 mm, p < 0.05), in the (S) direction after 12 months (1 mm p < 0.05), in the (N) direction after 12 months (1 mm p < 0.05), in the (N) and (T) directions after 12 months (3 mm, p < 0.05) and in the (T) direction after 12 months (4 mm p < 0.05), at the corneal center after 12 months (p < 0.01). AL was significantly reduced during treatment (p < 0.05). CONCLUSIONS: A long period of OK reduces ACD and AL and changes PRCC.

Recovery evaluation of induced changes in higher order aberrations from the anterior surface of the cornea for different pupil sizes after cessation of corneal refractive therapy.

PURPOSE: To assess corneal aberration changes induced by corneal refractive therapy (CRT) for different pupil sizes and to examine the recovery after cessation of contact lens wear. METHODS: A single-center, prospective, and longitudinal study was performed. Thirty-four subjects who underwent CRT for 1 year were included. High-contrast corrected distance visual acuity (CDVA), manifest refraction, and corneal topography were determined during the treatment and 1 month after the discontinuation of the treatment. Corneal aberrations were calculated using the Vol-CT 6.89 software. Corneal spherical aberration, Z(4,0), and root mean square values (RMS) for coma-like, trefoil, tetrafoil, and higher order aberrations (HOAs) were estimated for different pupil sizes (3-, 4-, 5-, 6-, and 7-mm diameters). Early Treatment Diabetic Retinopathy Study charts were used to measure CDVA. RESULTS: The CRT treatment induced a statistically significant increase of all aberrations studied for all pupil diameters. RMS values for coma-like, trefoil, and tetrafoil aberrations and HOAs after cessation of contact lens wear were not statistically significantly different for any of the different pupil diameters studied at baseline. However, Z(4,0) significantly increased from baseline to 1 month after discontinuation of the CRT lens wear for 5-, 6-, and 7-mm diameter pupils. CONCLUSIONS: Our results suggest that CRT is a treatment completely reversible at 1 month after cessation of contact lens wear in terms of CDVA, refractive error, and RMS of coma-like aberrations and HOAs for all pupil sizes. However, for spherical aberration, 1 month is not enough to recover to the baseline level.

Long-term changes in corneal morphology induced by overnight orthokeratology.

PURPOSE: To assess long-term morphological and biometric corneal changes produced by overnight orthokeratology and to examine their recovery after cessation of contact lens wear. METHODS: Prospective, single-center, longitudinal trial. Fifteen right eyes with low to moderate myopia underwent overnight orthokeratology for 1 year. The central cornea was examined using a confocal microscope and changes determined in visual acuity, refractive error and corneal topography. Cell counts were performed using both the confocal microscope's software and the image analysis software of the USA Health Institute. All measurements were made during orthokeratology treatment and 1 month after discontinuing treatment. RESULTS: No significant changes in endothelial cell density were observed over time but polymegethism increased significantly and baseline values were not recovered (p < 0.01). Stromal cell density remained unchanged though numbers of activated keratocytes increased during the study and returned to baseline when lens wear ceased. Basal epithelium cell densities significantly fell (p < 0.01) and epithelial wing and superficial cells showed enhanced visibility (p < 0.05). Superficial cells increased in height and width; this width increase being significant after 1 year of orthokeratology (p < 0.01). All epithelial cell changes returned to baseline. Corneal thickness, Bowman layer thickness, subbasal plexus thickness and epithelial thickness were reduced in the central cornea but the stroma was thickened. Of these changes, the decrease in epithelium thickness reached statistical significance (p < 0.01) and baseline values were not recovered. CONCLUSION: Overnight orthokeratology induces structural and optical changes particularly in the central corneal epithelium during myopia treatment. If confirmed, the irreversible changes detected indicate a need for further investigation.

Straylight and contrast sensitivity after corneal refractive therapy.

PURPOSE: To compare intraocular straylight and contrast sensitivity determined before corneal refractive therapy and after 15 days and 1 month of treatment. METHODS: A single-center, prospective, and longitudinal study was performed in 30 subjects undergoing corneal refractive therapy. In each subject, high-contrast visual acuity (HCVA), low-contrast visual acuity (LCVA), straylight, and contrast sensitivity were determined at baseline and after 15 days and 1 month after the treatment. Straylight was measured using the van den Berg straylight meter (third generation). Contrast sensitivity was determined under both photopic and mesopic conditions using the VCTS 6500 instrument (Vision Contrast Test System). EDTRS charts (logMAR units) were used to measure HCVA and LCVA. RESULTS: Straylight (mean ± standard deviation) significantly fell from baseline (0.94 ± 0.14) to the values recorded at 1 month (0.85 ± 0.11, p = 0.009). Photopic contrast sensitivity remained stable yet mesopic contrast sensitivity measured at high spatial frequencies was significantly reduced. No correlations between intraocular straylight and contrast sensitivity, HCVA, or LCVA were observed 15 days and 1 month after corneal refractive therapy. CONCLUSIONS: Our findings suggest improved intraocular straylight readings 1 month after starting the treatment, although the changes observed in straylight could not be related to changes in mesopic and photopic contrast sensitivity or HCVA and LCVA. Mesopic contrast sensitivity was more affected by the treatment intervention than photopic contrast sensitivity.

Short-term effects of overnight orthokeratology on corneal cell morphology and corneal thickness.

PURPOSE: To examine the morphological and biometric corneal changes produced over periods of 15 days and 1 month after overnight orthokeratology (OK). METHODS: Prospective, single-center, longitudinal trial. Twenty-seven right eyes of 27 subjects (group 1) with low to moderate myopia wore OK lenses for 1 month. Ten right eyes of 10 subjects (group 2) with emmetropia to low myopia who did not wear any type of contact lens served as controls. Corneal morphometric measurements were obtained in vivo using a confocal microscope to examine the central and midperipheral cornea. Thickness measurements in the peripheral cornea were obtained by optical coherence tomography. Changes in visual acuity, refractive error, and corneal topography were also analyzed. RESULTS: No significant changes in either endothelial cell or stromal cell density were observed after 1 month of OK. Basal epithelial cells were, however, significantly reduced (P < 0.01), and epithelial wing and superficial cells showed enhanced visibility (P < 0.05). Superficial cells increased in height and width, the width increase after 1 month being significant (P < 0.01). Epithelial thickness was significantly reduced in the central cornea and 2 mm around the center. Corneal pachymetry increased significantly in the band from 5 to 10 mm from the corneal apex (P < 0.01). CONCLUSIONS: OK lenses for myopia induce significant structural and optical changes particularly in the central epithelium after 15 days or 1 month of wear. The central corneal epithelium responds to OK wear by undergoing significant epithelial cell shape and size alterations with no effects, however, on the cells of the corneal endothelium or the corneal stroma. Peripheral corneal thickness increased with respect to baseline values. These findings suggest that the corneal epithelium is the principal structure affected by the mechanical forces exerted by the OK lenses.

Intraocular straylight and contrast sensitivity (1/2) and 6 months after laser in situ keratomileusis.

OBJECTIVES: To compare intraocular straylight and contrast sensitivity determined before and 15 days and 6 months after laser keratomileusis. METHODS: A single-centre, prospective, longitudinal randomized trial was performed on 20 subjects undergoing refractive surgery. In each subject, best spectacle-corrected visual acuity (BSCVA) and straylight and contrast sensitivity were determined preoperatively (on the day of refractive surgery) and then after laser in situ keratomileusis (LASIK) surgery in the 15-day and 6-month follow-up visits. Straylight was measured using the van den Berg straylight meter (third generation). Contrast sensitivity was determined under photopic and mesopic conditions using the VCTS 6500 (Vision Contrast Test System). BSCVA was measured using Early Treatment Diabetic Retinopathy Study charts (LogMAR units). All measurements were obtained over time and compared. RESULTS: Straylight values (mean +/- SD) were 0.99 +/- 0.03, 0.88 +/- 0.03, and 0.93 +/- 0.03 before and (1/2) and 6 months after LASIK surgery. These values significantly fell from preoperative levels to those recorded 15 days after LASIK (P = 0.03) although values at 6 months failed to differ from baseline (P>0.05). Photopic and mesopic contrast sensitivity measured at several spatial frequencies remained stable. No correlations between contrast sensitivity or BSCVA and intraocular straylight were observed 15 days and 6 months after LASIK. CONCLUSIONS: Intraocular straylight was reduced 15 days after surgery although by 6 months values returned to preoperative levels. These changes in straylight values could not be related to changes in mesopic and photopic contrast sensitivity or BSCVA during the follow-up period.

Intraocular straylight and corneal morphology six months after LASIK.

PURPOSE: To assess the relationship between changes in human corneal morphology and intraocular straylight produced over time after laser in situ keratomileusis (LASIK). METHODS: Thirty subjects who underwent LASIK surgery were enrolled in this single-center, prospective and longitudinal trial. Twenty-five eyes were included in the study. A scanning, slit white light confocal microscope using a ConfoScan 4 equipped with 40x front lenses and a sensor called "z-ring" was used to examine structural changes in a cornea. Endothelial and stromal cellular count was randomized and masked at observer. Straylight was determined using the van den Berg straylight meter (third generation). All measurements were obtained over time and compared. RESULTS: No significant differences were detected in the endothelial layer. Anterior keratocyte density was lower at the time points of 15 days and 6 months after refractive surgery (p < 0.01, analysis of variance) than the presurgery value, although densities at 6 months failed to differ with Wilcoxon matched-pairs signed rank test. Posterior keratocyte density was reduced at 15 days post-surgery but had recovered slightly at 6 months (p < 0.05) with analysis of variance and Wilcoxon matched-pairs signed rank test. Intraocular straylight measurements improved after surgery with significant differences observed when presurgery values were compared to those recorded 15 days or 6 months after LASIK (p < 0.01) with analysis of variance being adjusted by the Kruskal-Wallis test. However, straylight value at 6 months failed to differ with Wilcoxon matched-pairs signed rank test. Correlation was detected between diminished anterior keratocyte density and increased intraocular straylight both at 15 days (r = -0.50, p < 0.05) and 6 months (r = -0.53, p < 0.05). CONCLUSION: Patients with anterior corneal cell density reduced as a consequence of LASIK, showed augmented intraocular straylight. This correlation warrants further research with larger samples.

Relationship between anterior corneal asphericity and refractive variables.

BACKGROUND: The anterior corneal surface is closely modelled by a conic section that is fully described by asphericity (Q) and the apical radius of curvature. Computerized corneal topographers have allowed for more accurate and complete descriptions of corneal shape. Our objective was to compare anterior corneal asphericity (Q) values determined for different corneal diameters in eyes of different refractive state. METHODS: Q-values were determined in 118 eyes of 118 subjects using both a videokeratoscope (Atlas Mastervue, Humphrey Instruments-Zeiss) and Vol-CT 6.89 software (Sarver & Associates Inc.), which estimates Q-values for several corneal diameters (3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 7.0 mm and 8.0 mm) using topographic data obtained with the instrument. For comparisons, Q-values were stratified three ways: by refractive error (myopic, emmetropic or hyperopic eyes), corneal power (low, intermediate and high) and corneal astigmatism (low, intermediate and high). RESULTS: Mean corneal asphericity was -0.35 +/- 0.03, differing significantly from reported data (Student's t-test). Asphericities determined using both methods did not vary significantly with regard to refractive error or corneal power, but did differ among the corneal astigmatism groups (p < 0.01). A trend was observed towards more negative Q-values with increasing corneal diameter, but differences in corneal asphericity according to corneal diameter were only significant in the astigmatism group (p < 0.01). CONCLUSION: Q-values varied according to the refractive properties examined. However, the relationship between refractive state and corneal asphericity was found to be determined more by the geometric properties of the eye (corneal power and axial length) than by manifest refraction.