Oxygen tension beneath piggyback contact lenses and clinical outcomes of users.

PURPOSE: Patients with keratoconus sometimes wear a rigid contact lens as a piggyback over a countersunk soft one. This geometry restricts movement of the rigid lens over the central cornea and may also reduce corneal oxygenation. This aim of this study was to estimate the equivalent oxygen percentage beneath such lenses and to review the clinical records of users to determine their success rate. METHODS: The right eyes of four normal subjects were covered for 5 minutes with a combination of rigid gas permeable (Boston ES or 7 [Polymer Technology Corp., Rochester, NY]) and soft (Acuvue [Johnson & Johnson, Jacksonville, FL], Keraflex [KF] 3 or 5 [Blanchard, Sherbrooke, QC, Canada]) contact lenses. After removal of the lenses, oxygen tension was measured with a Clark electrode. In order to determine whether measurements of oxygen tension were supported by clinical data, the clinical files of 11 patients fitted with KF 5-Boston ES piggyback lenses were reviewed for the presence of corneal edema. RESULTS: Mean relative equivalent oxygen percentage ranged from 6.9% to 11.2% beneath the following lens combinations: KF 3-Boston ES; KF 3-Boston 7; KF 5-Boston ES; KF 5-Boston 7; Acuvue-Boston ES; and Acuvue-Boston 7. Of the ten patients followed after dispensing, none had any sign of corneal edema. Nine had worn their contact lenses for periods up to 6 years. CONCLUSIONS: Based on the measured equivalent oxygen percentage and on the absence of corneal edema in patients, the combination of countersunk KF 5 with Boston ES lenses provides enough oxygen to fulfill corneal needs in oxygen during daily wear.

Isolation and characterization of cytochrome c from the marine copepod Tigriopus californicus.

Mitochondrial energy production requires complex interactions among proteins encoded in both the nuclear and mitochondrial genomes. The intergenomic coevolution of interacting gene products has been previously suggested based on interspecific comparisons of cytochrome c (encoded by the nuclear CYC gene) and cytochrome c oxidase (partly encoded in the mitochondrial DNA by the COX1, COX2 and COX3 genes). In the intertidal copepod, Tigriopus californicus, non-synonymous substitutions in the COX1 gene have previously been found in interpopulation comparisons. In order to determine if CYC also shows interpopulation variation, this gene was isolated from a cDNA library using a degenerate primer/polymerase chain reaction approach. Characterization of a cDNA sequence and 25 genomic DNA sequences derived from four T. californicus populations yielded the following results: (1) the T. californicus CYC gene is interrupted by an intron that occurs at the same position as the intron found in vertebrate CYC genes; (2) there is extensive sequence variation within both the coding region and intron of this gene and the vast majority of this variation occurs between sequences drawn from geographically distinct populations; (3) the coding sequence variation includes a minimum of five amino acid replacement substitutions; (4) segregation of length variants among offspring in an interpopulation cross revealed genotypic ratios consistent with the proposed allelic nature of the CYC variants. These results demonstrate that the requisite genetic variation required for intergenomic coevolution exists in the CYC-COX system in T. californicus.

Discontinuation of contact lens wear: a survey.

Discontinuation from contact lens wear has been cited as a contributing factor to the lack of growth of the contact lens market in North America. To determine the reasons and extent of abandonment from contact lens wear among patients from optometric practices, 4415 questionnaires were randomly mailed to patients from 16 practices in Quebec, Canada, and were returned as anonymous responses to the Centre for Contact Lens Research in Waterloo. Thirty-three percent (n = 1444) of the surveys were returned. After 5 +/- 6 years of lens wear, 34% of patients had discontinued lens wear at least once. Of the patients who discontinued, 77% resumed wear and 48% of those discontinued a second time. Those who had discontinued were fitted at an older age (by approximately 2 years), were in the professional/health care/management occupation sector, and had a slightly lower myopic prescription. Before discontinuation, the wearing time of this group was approximately 1 day/week less than those continuing to wear lenses. Of the patients who had discontinued, 49% had been refitted at least once, and the primary reason for refitting was discomfort. The primary reasons for abandonment were discomfort, dryness, and red eyes. Improved comfort and relief of dryness were the primary factors that would improve contact lens wear for the group that had discontinued. Practitioners may be able to target specific patient groups with remedial measures to improve contact lens-wearing success.

In situ Rates of Fertilization Among Broadcast Spawning Gorgonian Corals.

Fertilization rates among marine benthic taxa have implicitly been assumed to be uniformly high in most analyses of life history evolution, but in situ fertilization rates during natural spawning events are rarely measured. Fertilization rates of the Caribbean gorgonians Plexaura kuna and Pseudoplexaura porosa were measured at a site in the San Blas Islands, Panama, by collecting eggs downstream of colonies during synchronous spawning events during the summer months in the years 1988-1994. Eggs collected by divers were incubated, and the proportion of eggs that developed was determined. Proportions of eggs developing suggest fertilization rates that vary from 0% to 100%. Monthly means ranged from 0% to 60.4%. Failure of gametes to develop can be attributed to sperm limitation, as eggs collected during spawning had higher fertilization rates if incubated with an excess of sperm. Plexaura kuna fertilization rates were highest during the July spawning events. Fertilization of Plexaura kuna eggs was usually lower during the first two nights of the 4-6 night spawning event. The proportion of eggs being fertilized when collected from a given place and time was highly variable, with one peak in the frequency distribution at or below 20% fertilization, and a second group of samples with greater fertilization rates. High variance in fertilization rates is evident at all levels of analysis: between replicate samples, times within nights, and among nights and months. This variance can be attributed to a combination of the effects of heterogeneity in the water column as gametes are diluted, spawning behavior of the gorgonians, and the current regime. Fertilization rates are often low and may represent a limiting step in recruitment during some years. Low fertilization rates may also be an important component of the life history evolution of these species.

Growth Rates and Growth Strategy in a Clonal Marine Invertebrate, the Caribbean Octocoral Briareum asbestinum.

Colony form directly effects colony reproductive output among colonial benthic invertebrates. The relationship between reproductive effort, colony form, and growth rate in colonies of the Caribbean octocoral Briareum asbestinum were examined by measuring the growth rates of 118 tagged colonies on Pinnacles and House Reef in the San Blas Islands, Panama. Colony growth rates, individual branch growth rates, and branch addition rates were measured over six month intervals from July 1986 to July 1988. Colonies grew at a net rate of 16.6 cm/year and added 1.2 branches/year. Individual branch measurements yielded a net rate of growth of 2.02 cm/year/branch. Positive growth rates, which provide a measure of minimum potential growth, were 71.3 cm/year, and 8.7 branches/year for colonies and 6.21 cm/year for individual branches. Net growth rates and branch addition rates were 76 and 85% less than potential growth rates indicating large losses to fragmentation and predation. Calculated mean longevity of individual colonies (ramets) is short (10.6 years), given observed rates of growth and loss. However, since fragmented branches can reattach and initiate new colonies, losses due to fragmentation contribute to the asexual expansion of the genet. In July 1987, 783 branches on the tagged colonies were individually mapped in order to characterize the relationship between branch size and the number of bifurcations (tips), and growth rates. The best predictor of growth rate was the number of tips per branch (r2 = 0.46; P < .0001). No relationship was found between branch growth and branch size, consequently branch growth per unit length decreased as branch size increased. The independence of branch growth and size may reflect the diversion of energy away from growth toward reproduction. As a consequence of this pattern, bifurcating growth forms will, on a colony basis, grow more rapidly and amass more reproductive tissue than simple linear extension. However, the short longevity of ramets of Briareum asbestinum limits the advantage to be gained from accumulating reproductive tissue by rapid branch bifurcation.