ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Purpose. Previous work on rabbits has demonstrated a four-fold increase in tear evaporation when the tear lipid layer is removed. However, in vitro work has suggested that the lipid layer does not play a role in retarding evaporation of the aqueous layer. The importance of the lipid layer in human tear film stability and evaporation was determined in the current study by measurement of these parameters in the same individuals. Methods. The left eyes of 161 normal and dry eye subjects (72 males, 89 females), with an age range of 13 to 85 years, were examined. Tear evaporation was derived from the vapor pressure gradient measured with a modified Servomed evaporimeter. Lipid layer structure and noninvasive break-up time (NIBUT) were assessed clinically, by specular reflection, with the Keeler Tearscope. Lipid layer structure was categorized into marmoreal (open and closed meshwork), flow, amorphous, and colored fringe (normal and abnormal) patterns. These observed patterns reflect lipid layer thickness. Ambient temperature and relative humidity remained fairly constant throughout the experiment. Results. Tear evaporation rate was found to vary significantly with different lipid layer patterns. Eyes with no visible lipid layer, or exhibiting an abnormal colored fringe pattern (with clumping of lipid amidst areas of little or no lipid cover), demonstrated a significantly higher rate of evaporation of the tear film (p<0.001). There were no significant differences amongst the remainder of the patterns. The NIBUT was also found to vary significantly with lipid layer pattern (p<0.001), with the absent or abnormal colored fringe lipid patterns exhibiting the poorest stability. Conclusions. Where the human lipid layer is absent, or is not confluent, and the tear film is unstable, tear evaporation is increased four-fold. However, where there is a stable, intact lipid layer, regardless of lipid thickness, tear evaporation is retarded.

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Background. Second generation corneal topography-based contact lens software programs attempt to fit the cornea based on topographical information rather than simulated keratometry and nomogram-based fits. The EyeSys System 2000 Pro-Fit software (Version 3.1) was clinically evaluated for efficiency in fitting rigid gas permeable (RGP) lenses on 22 normal subjects. Methods. Balanced manifest refractions, slitlamp examinations, keratometry, computerized topographic analysis and lens fitting, and manual diagnostic RGP fitting were performed on all patients. The topographically fit eyes were compared to corresponding eyes which were manually fit with diagnostic trial lenses. Lens parameters for the topographically fit eye were chosen after an optimal fluorescein pattern was achieved by either accepting the initially recommended Pro-Fit lens or a modification. Final lens parameters were based on clinical performance. Lenses were reordered when there was a need for base curve changes of 0.1 mm or more, power alterations of ±0.50 D or more, or for any alteration in diameter, optic zone, or edge lift. Results. Both manual and topographically fit groups achieved 17/22 (77%) eyes successfully fit without any subsequent lens modifications. Time records for the manually fit group averaged 16.5 min, whereas the topographically fit group averaged 8.0 min. Conclusions. This study reports a 51.4% reduction in chair time when using a topographically based contact lens software program while achieving the same clinical results as in traditional diagnostic RGP fitting, suggesting increased efficiency in fitting RGPs to normal eyes.

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

This study compared the compensatory response to hyperopic defocus imposed on chicks in two different ways: (1) with —10 D spectacle lenses, and (2) with piano hard contact lens. The hyperopia seen with the contact lenses in situ was a consequence of their flat profile relative to the chick cornea, resulting in a negative fluid lens of approximately 16 D at day 2 and 9 D by day 10. This decrease with age reflects the corneal flattening that accompanies normal eye growth. By optically neutralizing the cornea, the contact lenses also had two other important effects: (1) a reduction in refractive astigmatism to almost negligible levels, and (2) a reduction in accommodative gain. The latter effect reflects the loss of the corneal component of the chick's accommodation and was estimated to be of the order of 40 to 57%, based on measurements made using topically applied nicotine to stimulate accommodation. Thus any estimate of the imposed hyperopic defocus based on accommodative effort required to overcome such errors will be too large. Chicks wearing either lens type on a continuous basis from hatching to 10 days only partially compensated for the imposed hyperopia through an increase in vitreous chamber growth. However, the effects were smaller in the spectacle lens group (e.g., a mean myopic shift of -4.1 ± 2.3 D compared to -6.3 ± 2.4 D for the contact lens group at day 10), although both groups experienced similar amounts of hyperopic defocus around day 10 (effective power of —10 D spectacle lens: —9.4 D). The changes seen in the spectacle lens group thus represent poorer compensation, i.e., 44 vs. 71 % of the imposed error. However, overcompensation is the predicted effect, if any, of the accommodative deficit imposed on the contact lens group, and this was not seen. That compensation, albeit incomplete, occurred with the contact lens as well as the spectacle lens, suggests that neither accommodation nor astigmatism are fundamental cues for emmetropization as modeled here.

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Purpose. The number of children exposed to cocaine in utero each year is increasing. Recent reports suggest significant visual anomalies in infants prenatally exposed to cocaine. The purpose of this retrospective study was to determine if children exposed prenatally to cocaine were at a greater risk for visual abnormalities, such as strabismus and significant refractive errors. Methods. This pilot study was conducted at two sites, an outpatient clinic and a hospital-based practice. Consecutive files from January to July, 1993, of 79 children (aged 4 months to 94 months), who were identified by case history or meconium analysis information as being exposed to cocaine in utero, were reviewed. Fifty-five children met the inclusion criteria for the study. In addition, a control group of 100 pediatric patients were randomly selected from the pediatric patients seen at the outpatient clinical site. Results. Of the 30 children from the Illinois Eye Institute (IEI) and the 25 children from The Children's Hospital (TCH), spherical refractive errors in the right eye ranged from +6.50 to —12.50 D. The median refractive errors were +0.75 and +0.50 D, respectively. No statistical difference was found in spherical refractive error, astigmatism, or anisometropia between the cocaine-exposed cohorts and the control group (N=100). Strabismus was found in 15/55 (27%) of the children in the cocaine-exposed group. There was a statistically significant difference in the prevalence of strabismus between the cocaine-exposed group and the control group. Further analysis revealed that full birthweight (>2500 g) children prenatally exposed to cocaine were at a greater risk for strabismus as compared to the full birthweight control group. Ocular abnormalities were rare, but included optic nerve atrophy and retinopathy of prematurity. Conclusions. These data suggest cocaine exposure during pregnancy may place a child at risk for conditions that may negatively impact the visual system, specifically strabismus.

ISSN:1040-5488    

出版商:OVID    

年代:1997

数据来源: OVID