Resistance of plastic ophthalmic lenses: the effect of base curve on different materials during static load testing.

PURPOSE: This study was designated to evaluate, through a static load test, the influence of lens base curve on the fracture resistance of three common plastic materials. METHODS: A JJ Lloyd load cell machine was used to test the fracture resistance of -4.00 D spherical lenses. The samples had a nominal center thickness of 2.0 mm and a base curve distributed in one of five groups (+0.50, +2.50, +4.50, +6.50, and +8.50 D). The lenses were manufactured in CR39, polycarbonate, and TL16, a high refractive index plastic (n = 1.599). RESULTS: The lens base curve influenced fracture resistance for all materials. For these materials, resistance increased as the base curve varied from +0.50 to +8.50 D. The resistance of CR39, TL16, and polycarbonate lenses was found to be linearly dependent on lens base curve. The effect is stronger for polycarbonate. Fracture resistance was higher for TL16 than for CR39, and polycarbonate was much more resistant to breakage than the two other materials. CONCLUSIONS: For a given power, the fracture resistance of an ophthalmic lens is reduced when its base curve has a low value. Consequently, the flattening of ophthalmic lenses for cosmetic purposes is not recommended as far as fracture resistance is concerned.     

THE COMPARATIVE PERFORMANCE OF EYE PROTECTOR MATERIALS

Impact resistance data, obtained from drop-tower and ballistic experiments, is presented for (a) spectacle lens materials and (b) other protective materials. It is shown that 3 mm thick toughened glass spectacle lenses have a higher impact resistance (7.6 metres per second) than allyl resin of 3 mm (6.6 m/s) and 2 mm (5.0 m/s) thick nesses when tested with the 25.4 mm (one inch) steel ball. In ballistic tests with a 3.2 mm (¹/₈ inch) steel ball, however, the position is reversed, the fracture velocities being 29 m/s for 3 mm thick glass and 88 m/s and 63 m/s respectively for 3 mm and 2 mm thick allyl resin. Comparable figures for untoughened and laminated glass and for polymethyl methacrylate are also given. The impact resistance of other protective devices, determined by similar ballistic tests, is also reported. Clip-on configurations have velocities ranging from 58 m/s to more than 310 m/s; polycarbonate goggles of 294 m/s; and cellulose acetate, in face-shield form, has about twice the impact resistance (192 m/s) of the same material made up in goggle form (111 m/s). The paper concludes with a short discussion on suitable materials for occupational eye protection.     

Spectacle-induced ocular trauma: an unusual mechanism

PURPOSE: To report an unusual, spectacle-related injury. METHODS: A 16-year-old boy wearing spectacles with polycarbonate lenses presented with an unusual, spectacle-related injury. Impact with the ball during a ball sport (cricket) led to extreme torsion of the frame with resultant direct blunt trauma to the right eye by the spectacle arm. On examination, the patient had a 10 x 10-mm area of conjunctivalized scleral dehiscence superiorly in Zones 2 and 3, with uveal prolapse. Superior retinal detachment was also noted. RESULTS: Patient underwent wound repair with a scleral patch graft with transscleral cryotherapy and sulfur hexafluoride injection. CONCLUSION: Although increased impact resistance of newer spectacle lens materials is assumed to reduce the incidence of ocular trauma, such unusual mechanisms may still lead to severe ocular trauma. We report this case to highlight an unusual mechanism of spectacle injury, hitherto unreported, and to show the continued need for use of eye protection while wearing spectacles.     

The effect of multiple antireflective coatings and center thickness on resistance of polycarbonate spectacle lenses to penetration by pointed missiles.

PURPOSE: Previous work has shown that the impact resistance to blunt missiles is affected by coatings applied to either CR-39 or polycarbonate lenses. We investigated the effects of multiple antireflection (minimum angle of resolution [MAR]) coatings on the resistance of polycarbonate lenses to puncture on impact by sharp, high-speed missiles. METHODS: Four groups of surfaced plano polycarbonate lenses were investigated. Two groups had a scratch-resistant (SR) coating applied to both surfaces. One of these groups had a 2-mm center thickness and the other had a 3-mm center thickness. The other two groups of 2-mm and 3-mm thick lenses had a MAR coating applied over the SR coating. The lenses were impacted by a missile consisting of an industrial sewing machine needle mounted in a cylindrical aluminum carrier. RESULTS: The sharp missiles were able to pierce the lenses at speeds between 29.6 m/s and 46.2 m/s. Impact resistance was lowest for the thinner lenses and lenses with a MAR coating. The effect of the MAR and lens thickness was subadditive. CONCLUSIONS: We have confirmed previous observations that polycarbonate lenses are more susceptible to penetration by sharp, high-speed missiles than blunt missiles. We have also found that reducing lens center thickness and applying a MAR coating further reduces the penetration resistance. Therefore, the use of 2-mm center thickness and MAR-coated polycarbonate lenses should be discouraged for industrial eye protectors where sharp missile hazards are possible.     

Ballistic impact resistance of selected organic ophthalmic lenses

Purpose: The aim was to assess the impact resistance of coated and uncoated mid‐index spectacle lens materials using the ballistic impact test. Methods: Nominally plano lenses of each material in three thicknesses were obtained. The lenses were flat edged to a 50 mm diameter. Each lens was impacted by a 6.35 mm steel ball. Impact velocities were selected using the Zippy Estimation by Sequential Testing protocol to determine the threshold fracture impact velocity. Results: Threshold fracture impact velocity generally increased with thickness; however, there was a wide variation in performance among the various lens materials at each thickness. In all but two instances, the differences in impact velocity at each thickness of lens material were significant. Comparison of the data for CR39 and Hoya Phoenix with the results of earlier studies showed that the lens mounting is a significant factor. The fracture velocities found in the present study were significantly lower than the fracture velocities found when the lens edge is restrained in the mounting. A scratch resistant coating reduced the impact resistance of CR39. The effect of the antireflection coating on the fracture velocity depended on the nature of the base scratch‐resistant coating. Conclusions: Mid‐index lens materials of the same thickness show widely varying levels of impact resistance under the ballistic test. Impact resistance increases non‐linearly with centre thickness. The lens mounting might affect the results of the ballistic impact test. The presence of ‘cushion coatings’ might enhance impact resistance.     

Intraocular lens power calculation in children

With improving surgical technique and equipment, the acceptable age for placing an intraocular lens in infants and children is becoming younger. The tools for predicting intraocular lens power have not necessarily kept up, as current theoretical and regression intraocular lens power prediction formulas are largely based on adult eyes at axial lengths, anterior chamber depth, and keratometric values much different than those seen in infants. In addition, the adult eye has matured and is no longer growing, whereas the eyes of infants and children may continue to note changes in axial length, keratometric values, and possibly optical characteristics. Another source of error in intraocular lens power selection that is more likely to occur in pediatric patients than in adult patients is inaccuracy in measurement of axial length or keratometric power. A review of current tools and considerations for intraocular lens power prediction in infants and children is presented.     

Schutzbrille

Several activities in the occupational environment or in leisure time implicate an increased risk of eye injuries. Many injuries could be prevented by wearing adequate eye protection devices; however, the selection of appropriate eye protection devices requires considerations of different attributes in order to achieve a maximum of protection efficiency. This article provides an overview on the three basic types of eye protection device, introduces the classification regarding optical and protective properties and gives some additional advice on the selection of protective eyewear beyond the current standard regulations.     

Sports eyewear protective standards

Eye injuries sustained during sport comprise up to 20 per cent of all injuries to the eye serious enough for medical attention to be sought. The prevalence of eye injuries in sport is not easily assessed due to lack of authoritative participation rates, so most studies report total numbers in a time period. The evidence on the proportion of all ocular injuries that are from sport is reviewed. The relative frequencies in different sports are compared in a qualitative manner and the sports with greater numbers of ocular injuries are detailed. In common with occupational injuries to the eye, most sports eye injuries are considered preventable. The hierarchy of action for occupational risk is detailed and adapted to use in a sports scenario. All the available international, regional and national standards on sports eye protection are detailed and their provisions compared. The major function of the standards is to provide adequate protection against the hazard of the sport concerned. These are detailed and compared as a function of energy transfer. Eye protection must not introduce additional or secondary hazards (for instance, fracturing into sharp fragments on impact) and not introduce features that would deter the wearing of eye protection (for instance, restricting field of view to impede playing the sport). The provisions of the standards intended to limit secondary hazards are detailed and compared. The need for future work in standards writing and the activities of the International Standardization Organization in sports eye protection are detailed.     

Shotgun eye injuries. Ocular risk and eye protection efficacy.

BACKGROUND: Little is known about the efficacy of shotgun eye protection. Shotguns can easily propel pellets with enough energy to penetrate the human eye, and a large percentage of shotgun eye injuries occur during shotgun sports such as hunting, trap, skeet, and sporting clays. Many of these injuries are preventable with proper eye protection. Although it is known that polycarbonate is the best lens material for shotgun eye protection, there has been no research that addresses the vision protective system design and its influence on eye protection. METHODS: A field study was performed during which shotshells were fired at 1:1 scale photographs of human faces to determine the risk of ocular trauma. The protective efficacy of three types of polycarbonate protective eye wear (standard industrial safety glasses with snap-on side shields, wrap-around racket sport glasses, and three-piece glasses with integral side shields) was tested by firing shotshells at them at various distances. Both frontal and side protection was evaluated. RESULTS: Results showed that the eye is at a high risk (55% to 100%) of being hit with shot pellets at ranges of 15 to 40 yards. It also was determined that the protective eye wear will give good frontal eye protection from shotgun pellets but integral side shields and a headband are necessary to obtain adequate side protection. CONCLUSION: These findings, coupled with the poor visual prognosis of ocular shotgun injuries, indicate that polycarbonate protective eye wear with integral side shields and headbands should be worn by all involved with shotgun sports.     

Effect of multiple antireflection coatings on impact resistance of Hoya Phoenix spectacle lenses

Purpose: To investigate how the impact resistance of Hoya Phoenix spectacle lenses is affected by centre thickness and the application of a multilayer antireflection (MAR) coating. Methods: Four groups of plano lenses were tested: dress thickness with scratch resistant (SR) coating on both surfaces, dress thickness with SR and MAR, industrial thickness with SR and industrial thickness with SR and MAR. Lenses were edged to a clear circular aperture of 50 mm with a 0.5 mm hidden bevel and mounted in a specially‐designed lens support. A pneumatic gun was used to propel a 6.35 mm steel ball at the centre of each lens. Impact speed was varied using the ZEST protocol to determine the threshold breakage speed. Results: The threshold breakage speeds of the dress and industrial thickness SR lenses were 55.1 and 63.2 m/s, respectively and the corresponding threshold breakage speeds for SR‐MAR lenses were 50.1 and 54.7 m/s. All comparisons were statistically significant using Student's t‐test with a rejection level of p < 0.005. Unlike polycarbonate lenses, dress thickness Phoenix lenses do not display ‘oilcanning’ deformation on high energy impact and therefore are less likely to be dislodged from their mountings. Conclusions: We found that the mean impact resistance of the Phoenix lenses was greater than the level required of eye protector lenses by the standards AS/NZS 1337:1992, ANSI Z87.1‐2003 and CSA Z94.3‐02. Similar to CR39 and polycarbonate, the application of MAR to Phoenix lenses reduces their impact resistance, however, they provide an acceptable level of impact protection in industrial settings, where there is little danger of exposure to pointed or sharp‐edged high‐speed missiles.     

虹膜夹型人工晶状体植入治疗外伤术后无晶状体眼

目的:探讨虹膜夹型人工晶状体(verisyse)植入治疗外伤术后无晶状体眼的术后视功能及并发症,以期为外伤术后无晶状体眼的术式选择、手术方法提供一些临床依据。方法:回顾2006-08/2008-07来本院住院的外伤术后无晶状体眼患者42例43眼随机纳入试验组和对照组,以虹膜夹型人工晶状体植入作为试验组,晶状体悬吊作为对照组。作术后视力、角膜内皮及并发症的比较。结果:试验组所有病例术中1次固定成功,术后裸眼视力均较术前提高,最佳矫正视力均达到或接近术前最佳矫正视力。术后少数患者出现一过性高眼压、人工晶状体光学面倾斜、偏斜、脱位、眩光等并发症,所有病例中均未出现玻璃体积血、脉络膜脱离等并发症。两组术后视力、角膜内皮细胞及并发症差异无统计学意义。结论:虹膜夹型人工晶状体植入治疗外伤术后无晶状体眼具有操作简单及安全的优点。适合于无后囊、前房深浅正常及角膜内皮正常的病例。     

人工骨片在眼球萎缩时的美容作用

目的探讨人工骨片眶内植入术在轻中度眼球萎缩时的美容作用。方法中度眼球萎缩11例（11眼）行人工骨片眶内植入术，术后3周配戴美容性角膜接触镜，随访半年，观察其效果。结果睑裂高度，眼睑饱满度及眼球活动度与健眼均十分相似，容貌显著改善，外观满意。结论人工骨片眶内植入术用于轻中度眼球萎缩，可获得良好的美容效果。     

TFOS DEWS II Management and Therapy Report

The members of the Management and Therapy Subcommittee undertook an evidence-based review of current dry eye therapies and management options. Management options reviewed in detail included treatments for tear insufficiency and lid abnormalities, as well as anti-inflammatory medications, surgical approaches, dietary modifications, environmental considerations and complementary therapies. Following this extensive review it became clear that many of the treatments available for the management of dry eye disease lack the necessary Level 1 evidence to support their recommendation, often due to a lack of appropriate masking, randomization or controls and in some cases due to issues with selection bias or inadequate sample size.Reflecting on all available evidence, a staged management algorithm was derived that presents a step-wise approach to implementing the various management and therapeutic options according to disease severity. While this exercise indicated that differentiating between aqueous-deficient and evaporative dry eye disease was critical in selecting the most appropriate management strategy, it also highlighted challenges, based on the limited evidence currently available, in predicting relative benefits of specific management options, in managing the two dry eye disease subtypes.Further evidence is required to support the introduction, and continued use, of many of the treatment options currently available to manage dry eye disease, as well as to inform appropriate treatment starting points and understand treatment specificity in relation to dry eye disease subtype.     

Development of the optical surfaces of the kitten eye

In the intact post-natal kitten eye, an extensive vascular network severely limits optical quality. We have used scanning electron microscopy to find the locations of this network, to examine all optical surfaces of the eye, and to trace changes with age. Standard preparative procedures were used to view anterior and posterior surfaces of the cornea and lens of 11-, 16-, and 25-day-old kittens and an adult. No significant differences with age are found for the cornea. The vascular network that engulfs the anterior, lateral, and posterior lens is very prominent at 11 days but substantially reduced at 16 days. The anterior surface seems to clear first, and by the 25th day the network is gone although some debris remains. The period of absorption of the vascular system coincides with a marked improvement in optical quality.     

Contact lenses and the cornea: age and length of wear.

During a monitoring study related to photorefractive keratectomy, objective tests with the Oqual (a device that can be attached to the slit-lamp) were made of the image forming quality of treated, central, and untreated peripheral regions of the cornea. In a significant number of cases the untreated part was optically inferior to the treated part. Observations on 183 patients implicated prior contact lens wear: patients who had worn hard or gas permeable lenses scored less well than those wearing soft ones or none at all. The effects of age and length of wear were analysed. With one exception, corneal quality did not correlate with age or with length of contact lens wear either for the total sample (A) or for those aged 40 years and less (B). In A, all contact lens wearers scored less well than those who had never worn any. In B, whose eye lenses were most probably more transparent than those of the older group (A-B), those who had worn hard or gas permeable lenses scored significantly less than soft contact lens wearers or those who had never worn any. Although visual acuity is unimpaired, the optical capacity of the affected peripheral corneal regions appears to be permanently degraded, and the observation may have a potential bearing--for example, on the choice of contact lens types selected for cosmetic reasons.     

Sharp cutoff filters in intraocular lenses optimize the balance between light reception and light protection

PURPOSE: To facilitate the selection of the spectral filter in intraocular lenses (IOLs). SETTING: Department of Ophthalmology, University Medical Center Utrecht, Utrecht, The Netherlands. METHODS: The spectral transmission of commercially available IOLs was measured, and information from manufacturer data sheets and the literature was gathered. Illumination with sunlight filtered by the natural eye media (aged 20 and 70 years) and artificial eye media resulted in calculated values for the blue-light damage and the signals from the sensory systems (rods, cones, melatonin suppression, and melanopsin). Results were presented as log differences with respect to the 20-year-old human lens. A single rating value for each lens was calculated to facilitate the selection. RESULTS: The 70-year-old lens showed a reduction in blue-light damage of 0.45 log units compared to the 20-year-old lens, although a similar reduction occurred in the signal from the short-wave-sensitive cones. Intraocular lenses showed a range of nearly 1 log unit in blue-light damage protection. A change in dioptric power in blue-filtering IOLs, with a corresponding change in thickness, strongly influenced behavior. Dioptric power was less of a factor in IOLs with sharp cutoff filters. CONCLUSIONS: Blue-filtering IOLs sometimes showed density spectra very different from those of the natural lens; however, their filtering generally caused only mild sensory losses. Nearly none of the IOLs offered an optimum tradeoff between protection and signal reduction. Sharp cutoff filtering near 445 nm provided better performance, removing limitations in optical design.