Abstract Keratoconus is the most common primary ectasia. It usually occurs in the second decade of life and affects both genders and all ethnicities. The estimated prevalence in the general population is 54 per 100,000. Ocular signs and symptoms vary depending on disease severity. Early forms normally go unnoticed unless corneal topography is performed. Disease progression is manifested with a loss of visual acuity which cannot be compensated for with spectacles. Corneal thinning frequently precedes ectasia. In moderate and advance cases, a hemosiderin arc or circle line, known as Fleischer's ring , is frequently seen around the cone base. Vogt's striaes , which are fine vertical lines produced by Descemet's membrane compression, is another characteristic sign. Most patients eventually develop corneal scarring. Munson's sign , a V-shape deformation of the lower eyelid in downward position; Rizzuti's sign , a bright reflection from the nasal area of the limbus when light is directed to the limbus temporal area; and breakages in Descemet's membrane causing acute stromal oedema, known as hydrops, are observed in advanced stages. Classifications based on morphology, disease evolution, ocular signs and index-based systems of keratoconus have been proposed. Theories into the genetic, biomechanical and biochemical causes of keratoconus have been suggested. Management varies depending on disease severity. Incipient cases are managed with spectacles, mild to moderate cases with contact lenses and severe cases can be treated with keratoplasty. This article provides a review on the definition, epidemiology, clinical features, classification, histopathology, aetiology and pathogenesis, and management and treatment strategies for keratoconus.
Abstract Scleral contact lenses (ScCL) have gained renewed interest during the last decade. Originally, they were primarily used for severely compromised eyes. Corneal ectasia and exposure conditions were the primary indications. However, the indication range of ScCL in contact lens practices seems to be expanding, and it now increasingly includes less severe and even non-compromised eyes, too. All lenses that partly or entirely rest on the sclera are included under the name ScCL in this paper; although the Scleral Lens Education Society recommends further classification. When a lens partly rests on the cornea (centrally or peripherally) and partly on the sclera, it is called a corneo-scleral lens. A lens that rests entirely on the sclera is classified as a scleral lens (up to 25 mm in diameter maximum). When there is full bearing on the sclera, further distinctions of the scleral lens group include mini-scleral and large-scleral lenses. This manuscript presents a review of the current applications of different ScCL (all types), their fitting methods, and their clinical outcomes including potential adverse events. Adverse events with these lenses are rare, but the clinician needs to be aware of them to avoid further damage in eyes that often are already compromised. The use of scleral lenses for non-pathological eyes is discussed in this paper.
Abstract Purpose To compare corneal hysteresis (CH) and corneal resistance factor (CRF) between eyes treated with small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (femto-LASIK). Setting Beyoğlu Eye Training and Research Hospital. Design Prospective comparative case series. Methods Sixty eyes from 30 patients with bilateral myopia or myopic astigmatism were studied. Inclusion criteria were spherical equivalent of subjective manifest refraction (SE) <10 diopters (D) and a difference ≤0.50 D between the SEs of both eyes. One eye of each patient was treated with SMILE, and the fellow eye underwent femto-LASIK. Randomization was performed using a sealed envelope system. The main outcome measures were CH and CRF measured preoperatively and postoperatively (1 and 6 months). Results Preoperative SE was similar in both groups ( p = 0.852). CH and CRF values were reduced postoperatively in both groups compared to their corresponding preoperative values ( p < 0.001). At the 6-month follow-up visit, the mean CH values in the SMILE and femto-LASIK groups were 8.95 ± 1.47 and 9.02 ± 1.27, respectively ( p = 0.852), and the mean CRF values were 7.77 ± 1.37 and 8.07 ± 1.26, respectively ( p = 0.380). Conclusion CH and CRF decreased after SMILE. There were no differences between SMILE and femto-LASIK treatments in postoperative CH or CRF values.
Abstract Objective To report the 6 months results of a large prospective study on Descemet membrane endothelial keratoplasty (DMEK) for management of corneal endothelial disorders. Methods DMEK was performed in 300 consecutive eyes with Fuchs endothelial dystrophy, bullous keratopathy or previous corneal transplant failure. Best spectacle corrected visual acuity (BSCVA), refractive outcome and endothelial cell density (ECD) were evaluated before and at 1, 3, and 6 months after surgery. Intra- and postoperative complications were documented. Results At 6 months, 98% of eyes reached a BCVA of ≥20/40 (≥0.5), 79% ≥20/25 (≥0.8), 46% ≥20/20 (≥1.0), and 14% ≥20/18 (≥1.2) ( n = 221). The pre- to 6 months postoperative spherical equivalent (SE) showed a +0.33D (±1.08D) hyperopic shift ( P = 0.0000). Refractive stability was shown at 3 months after DMEK, i.e. no significant change in SE ( P = 0.0822) or refractive cylinder ( P = 0.6182) at 3 versus 6 months follow-up. Donor ECD showed a decrease from 2561 (±198) cells/mm2 before, to 1674 (±518) cells/mm2 at 6 months after surgery ( n = 251) ( P = 0.0000). The main complication was (partial) graft detachment occurring in 31 eyes (10%). Secondary ocular hypertension was seen in 13 eyes (6%): 6 induced by air-bubble dislocation posterior to the iris and 4 induced by steroids. Secondary cataract requiring phaco-emulsification developed in 3 out of 63 (5%) phakic eyes. Conclusions DMEK may provide a refractively neutral near complete, rapid visual rehabilitation with ECDs similar to earlier endothelial keratoplasty techniques. This combined with a relatively low complication rate, would indicate that DMEK is a safe and effective treatment for corneal endothelial disorders.
Highlights • Review of complications and fit challenges associated with scleral contact lenses. • There is a low incidence of threatening infectious events reported. • Hypoxia effects and inflammatory reactions are typically controllable. • Midday fog, conjunctival prolapse, and epithelial bogging are common complications.
To examine the time course of the reduction in central corneal clearance and horizontal and vertical lens translation (decentration) during miniscleral contact lens wear and the theoretical influence upon the optics of the post-lens tear layer. Repeated high-resolution OCT images were captured over an 8 h period of miniscleral contact lens wear (using a rotationally symmetric 16.5 mm diameter lens) in 15 young, healthy participants with normal corneae. Central corneal clearance and lens decentration were derived from OCT images using semi-automated image processing techniques. Central corneal clearance decreased exponentially over time, reducing by 76 ± 8 μm over 8 h. Fifty percent of this reduction occurred within 45 min of lens wear and seventy-five percent within 2 h, with thinning of the post-lens tear layer plateauing 4 h after lens insertion. Lens translation exhibited a similar pattern of change (0.18 ± 0.04 mm temporal and 0.20 ± 0.09 mm inferior decentration) stabilising 1.5–2 h after insertion. The change in the lens fit over time resulted in a small reduction in the power of the post-lens tear layer (−0.12 ± 0.01 D) and induced a prismatic effect of 0.01 ± 0.16 Δ base out and 0.50 ± 0.19 Δ base down relative to the pupil centre. For the miniscleral contact lens studied, horizontal and vertical lens decentration followed an exponential decay over 8 h that plateaued approximately 2 h after lens insertion, while central post-lens tear layer thinning plateaued after 4 h of lens wear.
Abstract Background/Purpose Although scleral contact lenses are prescribed with increasing frequency, little is known about their long-term effects on ocular physiology. The main goal of this paper is to predict values of oxygen transmissibility of scleral lens systems by applying the concept of resistors in series to parameters characteristic of current scleral lenses. A second aim is to find the maximal lens and post-lens tear layer thickness combinations above which hypoxia-induced corneal swelling would be found. Methods Theoretical calculations were used to predict the oxygen transmissibility of scleral lens systems, considering several material permeabilities ( Dk s 100–170), varying lens thicknesses (250–500 μm), the known tear permeability ( Dk of 80) and expected post-lens tear layer thicknesses (100–400 μm). The Holden–Mertz Dk / t criteria of 24 Fatt units for the central cornea and the Harvitt–Bonanno criteria of 35 Fatt units for the limbal area were used as reference points. Results Our calculations of oxygen transmissibility, with varying tear layer and lens thicknesses, ranged from 10 to 36.7 at the scleral lens centers and from 17.4 to 62.6 at the peripheries. Our calculations of maximum central lens thicknesses show a practical range of 250–495 μm, in conjunction with a post-lens tear layer thickness of 100–250 μm. Conclusion Our computations show that most modern scleral lenses, with recommended fitting techniques, should lead to some level of hypoxia-induced corneal swelling. Recommendations are made to minimize hypoxia-induced corneal swelling: highest Dk available (>150) lens with a maximal central thickness of 250 μm and fitted with a clearance that does not exceed 200 μm.
Highlights • Posterior corneal elevation (PCE) changes and corneal biomechanical parameters were evaluated for SMILE and FS-LASIK. • PCE change in FS-LASIK was greater than SMILE at 12 months post-operation. • CH and CRF were reduced for both procedures at 6 and 12 months, FS-LASIK demonstrated a greater reduction in CRF than SMILE. • PCE was moderately correlated with CH and CRF change, indicating an increase in PCE with greater reduction in CH and CRF.
The purpose of this study was to evaluate the shape of the anterior sclera by measuring the sagittal height and corneoscleral transition angles in the four cardinal and four oblique segments of the eye. In this study, 78 normal eyes of 39 subjects were evaluated. The sagittal height, corneoscleral angle and scleral angle were measured at three chord lengths (10.0 mm, 12.8 mm and 15.0 mm) in all eight segments of the anterior eye using optical coherence tomography (Zeiss Visante AS-OCT). Scleral toricity was calculated for each eye, defined as the greatest sagittal height difference found between two perpendicular meridians. At a 12.8 mm chord length, the shape of the anterior eye was found to be nearly rotationally symmetric, and at a chord of 15.0 mm the shape became more asymmetric. The average sagittal heights of the eight segments at a 12.8 mm chord ranged from 2890 μm to 2940 μm; at a 15.0 mm chord they ranged from 3680 μm to 3790 μm. The average scleral angles at a 15.0 mm chord ranged from 35.17° to 38.82°. Significant differences between opposing segments were found in the sagittal height and scleral angle measurements at a chord of 15.0 mm (sagittal height p ≤ 0.0021; scleral angle p ≤ 0.0105). The nasal measurements revealed flatter scleral angles and concave corneoscleral transitions, whereas temporal scleral angles were steeper, with tangential or convex corneoscleral transitions. These findings are important to consider when designing and fitting contact lenses that rest beyond the boundaries of the limbus, such as scleral lenses.
Abstract Aim To analyse repeatability of subjective grading and objective assessment in non-contact infra-red meibography. Methods Meibography photographs of 24 subjects (female 14; mean age = 46; range = 19–69 years, upper-lid images = 12, lower-lid images = 12) were classified in two sessions by three experienced observers (OI, OII, OIII). Relative area or portion affected by meibomian glands (MG) loss was classified applying three different grading scales in randomized order: a four-grade scale (4S) (degree 0 = no partial glands; 1 = 75% partial glands), a pictorial five-grade scale (5S) (degree 0 = no meibomian gland loss (MGL); 1 = 75% MGL) and objectively by a 100-grade scale (DA) applying ImageJ software. Results Observed MG loss ranged from 0% to 69%. Intra-observer agreement of the 5S (OI: κ = 0.80, p < 0.001; OII: κ = 0.40, p = 0.009; OIII κ = 0.81, p < 0.001) was better than of the 4S (OI: κ = 0.79, p < 0.001; OII: κ = 0.15, p = 0.342; OIII κ = 0.50, p = 0.0071). Intra-observer agreement of OI and OIII (±0.88 (95% confidence interval), ±1.305) was better than of OII (±2.21) in 4S and 5S (±0.99, ±2.00 and ±0.91; OI, OII and OIII, respectively) while it was relatively similar in DA (±18, ±17 and ±17). Inter-observer agreement was better in DA (OI–OII: ±13, OI–OII: ±19, OII–OIII: ±26) than in 4S (OI–OII: ±1.76; OI–OIII: ±1.29 and OII–OIII: ±1.31) or 5S (OI–OII: ±1.49; OI–OIII: ±0.91 and OII–OIII: ±1.20). Conclusion Intra-observer and inter-observer agreement was better in computerized grading followed by the subjective five-grade scale and four-grade scale.
Abstract Purpose Myopia is a global public health issue; however, no information exists as to how potential myopia retardation strategies are being adopted globally. Methods A self-administrated, internet-based questionnaire was distributed in six languages, through professional bodies to eye care practitioners globally. The questions examined: awareness of increasing myopia prevalence, perceived efficacy and adoption of available strategies, and reasons for not adopting specific strategies. Results Of the 971 respondents, concern was higher (median 9/10) in Asia than in any other continent (7/10, p < 0.001) and they considered themselves more active in implementing myopia control strategies (8/10) than Australasia and Europe (7/10), with North (4/10) and South America (5/10) being least proactive (p < 0.001). Orthokeratology was perceived to be the most effective method of myopia control, followed by increased time outdoors and pharmaceutical approaches, with under-correction and single vision spectacles felt to be the least effective (p < 0.05). Although significant intra-regional differences existed, overall most practitioners 67.5 (±37.8)% prescribed single vision spectacles or contact lenses as the primary mode of correction for myopic patients. The main justifications for their reluctance to prescribe alternatives to single vision refractive corrections were increased cost (35.6%), inadequate information (33.3%) and the unpredictability of outcomes (28.2%). Conclusions Regardless of practitioners’ awareness of the efficacy of myopia control techniques, the vast majority still prescribe single vision interventions to young myopes. In view of the increasing prevalence of myopia and existing evidence for interventions to slow myopia progression, clear guidelines for myopia management need to be established.
Highlights • Schirmer's test was abnormal in 33% symptomatic computer users at baseline. • Tear film break up time was abnormal in 55% symptomatic computer users at baseline. • Dry eye symptoms scores improve after dietary intervention with omega 3 fatty acids for 3 months. • Omega 3 fatty acids decrease tear evaporation rates. • Conjunctival goblet cell density increases after omega 3 fatty acid treatment.
Abstract Purpose To compare postoperative visual acuity and higher-order aberrations (HOAs) after femtosecond lenticule extraction (FLEX) and after small-incision lenticule extraction (SMILE). Methods Medical records of refractive lenticule extraction patients were retrospectively reviewed. Twenty patients were treated with FLEX. A comparable group of 20 SMILE patients were retrospectively identified. Only one eye of each patient was randomly chosen for the study. Visual acuity, subjective manifest refraction and corneal topography before and 6 months after the surgery were analyzed for both groups. Total HOAs, spherical aberrations, coma and trefoil were calculated from topography data over the 4- and 6-mm-diameter central corneal zone. Results The mean preoperative SE was −4.03 ± 1.61 in the SMILE group and −4.46 ± 1.61 in the FLEX group. One year after surgery, the mean SE was −0.33 ± 0.25 in the SMILE group and −0.31 ± 0.41 in the FLEX group ( p = 0.86). In the SMILE group a greater number of eyes were within ±0.50 D of the target refraction (95% versus 75%); however, the difference was not statistically significant ( p = 0.18). Furthermore, 80% of FLEX eyes and 95% of SMILE eyes had an uncorrected distance visual acuity of 20/25 or better ( p = 0.34). Total HOAs, spherical aberration, coma and trefoil increased postoperatively in both groups. However, there was no statistically significant difference between the groups preoperatively and postoperatively. Conclusion FLEX and SMILE result in comparable refractive results. In addition, corneal aberrations induced by different techniques of lenticule extraction seemed similar to each other.
Abstract Proteins are a key component in body fluids and adhere to most biomaterials within seconds of their exposure. The tear film consists of more than 400 different proteins, ranging in size from 10 to 2360 kDa, with a net charge of pH 1–11. Protein deposition rates on poly-2-hydroxyethyl methacrylate (pHEMA) and silicone hydrogel soft contact lenses have been determined using a number of ex vivo and in vitro experiments. Ionic, high water pHEMA-based lenses attract the highest amount of tear film protein (1300 μg/lens), due to an electrostatic attraction between the material and positively charged lysozyme. All other types of pHEMA-based lenses deposit typically less than 100 μg/lens. Silicone hydrogel lenses attract less protein than pHEMA-based materials, with <10 μg/lens for non-ionic and up to 34 μg/lens for ionic materials. Despite the low protein rates on silicone hydrogel lenses, the percentage of denatured protein is typically higher than that seen on pHEMA-based lenses. Newer approaches incorporating phosphorylcholine, polyethers or hyaluronic acid into potential contact lens materials result in reduced protein deposition rates compared to current lens materials.
Abstract Only about 5% of drugs administrated by eye drops are bioavailable, and currently eye drops account for more than 90% of all ophthalmic formulations. The bioavailability of ophthalmic drugs can be improved by a soft contact lens-based ophthalmic drug delivery system. Several polymeric hydrogels have been investigated for soft contact lens-based ophthalmic drug delivery systems: (i) polymeric hydrogels for conventional contact lens to absorb and release ophthalmic drugs; (ii) polymeric hydrogels for piggyback contact lens combining with a drug plate or drug solution; (iii) surface-modified polymeric hydrogels to immobilize drugs on the surface of contact lenses; (iv) polymeric hydrogels for inclusion of drugs in a colloidal structure dispersed in the lens; (v) ion ligand-containing polymeric hydrogels; (vi) molecularly imprinted polymeric hydrogels which provide the contact lens with a high affinity and selectivity for a given drug. Polymeric hydrogels for these contact lens-based ophthalmic drug delivery systems, their advantages and drawbacks are critically analyzed in this review.
Highlights • Retention rate for CL neophytes was 74% (sphere 78%, toric 73%, multifocal 57%). • A high proportion of those lapsing did so during the first two months of wear (47%). • Handling and comfort were key performance reasons for new wearers lapsing. • Visual problems were the key reason new toric and multifocal wearers discontinued. • In a third of cases, the reasons for discontinuation were unknown. • For 71% of dropouts, no alternative lens or management strategy had been tried. • Factors associated with retention rate include lens power, material and type, and purchase frequency.
To quantify the effect of short-term miniscleral contact lens wear on the anterior eye surface of healthy eyes, including cornea, corneo-scleral junction and sclero-conjuctival area. Twelve healthy subjects (29.9 ± 5.7 years) wore a highly gas-permeable miniscleral contact lens of 16.5 mm diameter during a 5-hour period. Corneo-scleral height profilometry was captured before, immediately following lens removal and 3 h after lens removal. Topography based corneo-scleral limbal radius estimates were derived from height measurements. In addition, elevation differences in corneal and scleral region were calculated with custom-written software. Sclero-conjuctival flattening within different sectors was analysed. Short-term miniscleral lens wear significantly modifies the anterior eye surface. Significant limbal radius increment (mean ± standard deviation) of 146 ± 80 μm, (p 0.004) and flattening of −122 ± 90 μm in the sclero-conjuctival area, ( << 0.001) were observed immediately following lens removal. These changes did not recede to baseline levels 3 h after lens removal. The greatest anterior eye surface flattening was observed in the superior sector. No statistically significant corneal shape change was observed immediately following lens removal or during the recovery period. Short-term miniscleral contact lens wear in healthy eyes does not produce significant corneal shape changes measured with profilometry but alters sclero-conjuctival topography. In addition, sclero-conjuctival flattening was not uniformly distributed across the anterior eye.
Abstract A contaminated contact lens case can act as a reservoir for microorganisms that could potentially compromise contact lens wear and lead to sight threatening adverse events. The rate, level and profile of microbial contamination in lens cases, compliance and other risk factors associated with lens case contamination, and the challenges currently faced in this field are discussed. The rate of lens case contamination is commonly over 50%. Coagulase-negative Staphylococcus, Bacillus spp., Pseudomonas aeruginosa and Serratia marcescens are frequently recovered from lens cases. In addition, we provide suggestions regarding how to clean contact lens cases and improve lens wearers’ compliance as well as future lens case design for reducing lens case contamination. This review highlights the challenges in reducing the level of microbial contamination which require an industry wide approach.
Abstract Aim To determine the validity and reliability of the measurement of corneal curvature and non-invasive tear break-up time (NITBUT) measures using the Oculus Keratograph. Method One hundred eyes of 100 patients had their corneal curvature assessed with the Keratograph and the Nidek ARKT TonorefII. NITBUT was then measured objectively with the Keratograph with Tear Film Scan software and subjectively with the Keeler Tearscope. The Keratograph measurements of corneal curvature and NITBUT were repeated to test reliability. The ocular sensitivity disease index questionnaire was completed to quantify ocular comfort. Results The Keratograph consistently measured significantly flatter corneal curvatures than the ARKT (MSE difference: +1.83 ± 0.44 D ), but was repeatable ( p > 0.05). Keratograph NITBUT measurements were significantly lower than observation using the Tearscope (by 12.35 ± 7.45 s; p < 0.001) and decreased on subsequent measurement (by −1.64 ± 6.03 s; p < 0.01). The Keratograph measures the first time the tears break up anywhere on the cornea with 63% of subjects having NITBUTs <5 s and a further 22% having readings between 5 and 10 s. The Tearscope results were found to correlate better with the patients symptoms ( r = −0.32) compared to the Keratograph ( r = −0.19). Conclusions The Keratograph requires a calibration off-set to be comparable to other keratometry devices. Its current software detects very early tear film changes, recording significantly lower NITBUT values than conventional subjective assessment. Adjustments to instrumentation software have the potential to enhance the value of Keratograph objective measures in clinical practice.
Abstract Purpose A detailed evaluation of the corneo-scleral-profile (CSP) is of particular relevance in soft and scleral lenses fitting. The aim of this study was to use optical coherence tomography (OCT) to analyse the profile of the limbal sclera and to evaluate the relationship between central corneal radii, corneal eccentricity and scleral radii. Methods Using OCT (Optos OCT/SLO; Dunfermline, Scotland, UK) the limbal scleral radii (SR) of 30 subjects (11 M, 19F; mean age 23.8 ± 2.0SD years) were measured in eight meridians 45° apart. Central corneal radii (CR) and corneal eccentricity (CE) were evaluated using the Oculus Keratograph 4 (Oculus, Wetzlar, Germany). Differences between SR in the meridians and the associations between SR and corneal topography were assessed. Results Median SR measured along 45° (58.0; interquartile range, 46.8–84.8 mm) was significantly (p < 0.001) flatter than along 0° (30.7; 24.5–44.3 mm), 135° (28.4; 24.9–30.9 mm), 180° (23.40; 21.3–25.4 mm), 225° (25.8; 22.4–32.4 mm), 270° (28.8; 25.3–33.1 mm), 315° (30.0; 25.0–36.9 mm), and 90° (37.1; 29.1–43.4 mm). In addition, the nasal SR along 0° were significant flatter than the temporal SR along 180° (p < 0.001). Central corneal radius in the flat meridian (7.83 ± 0.26 mm) and in the steep meridian (7.65 ± 0.26 mm) did not correlate with SR (p = 0.186 to 0.998). There was no statistically significant correlation between corneal eccentricity and scleral radii in each meridian (p = 0.422). Conclusions With the OCT device used in this study it was possible to measure scleral radii in eight different meridians. Scleral radii are independent of corneal topography and may provide additional data useful in fitting soft and scleral contact lenses.