Evaluation of different recording parameters to establish a standard for flash electroretinography in rodents. (25/407)

Different electrodes and stimulus protocols commonly used for electroretinography in rodent eyes were compared for convenience of use, degree of damage to corneal epithelium, and for magnitude of amplitude, reproducibility, left versus right eye accuracy, and reliability of recorded parameters of the flash electroretinogram (ERG). Adult C57BL/6 pigmented mice and albino Wistar rats were used to determine scotopic ERGs in response to Ganzfeld or strobe-light stimulation and light-adapted (photopic) ERGs recorded from both eyes at the same time. Test-retest data were used for statistical analyses to compare a monopolar gold-wire contact lens electrode (CLE), a cotton-wick silver-silver chloride electrode (CSCE), a DTL fiber electrode (DTLE), and a circular stainless steel wire electrode (SSE). Corneas were evaluated for abrasion after ERG recordings using fluorescein staining and also for the time taken, ease of insertion, and re-insertions required for the different electrodes. Compared to CSCE, DTLE, and SSE, the ERG potentials recorded by CLE had significantly larger scotopic amplitudes and oscillatory potentials under strobe or Ganzfeld stimulation and for light-adapted ERG b-wave amplitudes in both mice and rats. In analyzing test-retest data of scotopic ERG a-wave and b-wave amplitudes, the intraclass correlation coefficient showed the best agreement for the CLE (range 0.61-0.94) compared to the SSE (0.13-0.77), DTLE (0.02-0.69), and CSCE (0.12-0.51). In mice and rats, logistic regression analyses revealed significant correlations for amplitudes of most scotopic ERG parameters between contralateral eyes obtained with CLE and for some ERG components recorded by SSE. When comparing ERG amplitudes for stimulation by strobe or Ganzfeld, the difference was least with the CLE compared to DTLE, CSCE, or SSE. The time taken to insert the four different electrodes was greatest for the CLE in both mice and rats. The extent of corneal abrasion resulting from electrode use in mice was largest for the SSE followed by the CLE. However, in rats there was almost no corneal damage after ERG recordings with the CLE. Because of the stability of eye contact, the CLE allows ERGs to be determined over a longer recording session. Recording of scotopic and photopic (light-adapted) ERGs in rodents with monopolar gold-wire contact lens electrodes provides greater amplitudes and higher reproducibility when compared to other commonly used corneal electrodes. These electrodes are significantly better overall than others that were evaluated and should be considered for a standard protocol to monitor retinal function in rodent eyes.  (+info)

Anomalies of binocular function in patients with longstanding asymmetric keratoconus. (26/407)

AIMS: To study binocular function in patients with longstanding asymmetric keratoconus. METHODS: In 20 adult patients with longstanding asymmetric keratoconus managed with a scleral contact lens a full clinical and orthoptic assessment was performed with and without the scleral contact lens in the poorer eye. RESULTS: All 20 patients had a corrected acuity of at least 6/9 in their better eye. With the scleral lens in situ the acuity of the poorer eye ranged from 6/6 to 6/60 and without the lens from 6/18 to hand movements. Patients were aged from 18 to 68 years and had worn a scleral contact lens for between 3 and 106 months. Without the contact lens in their poorer eye all patients had a small exotropia and all showed suppression, with the exception of one patient who had a right hypertropia with diplopia. With the scleral lens in situ 12 patients had an exophoria or esophoria, six a microexotropia, and two a manifest exotropia with suppression. CONCLUSIONS: Binocular function breaks down in some adult patients with longstanding asymmetric keratoconus. This is probably caused by longstanding unilateral visual deprivation. There are similarities to the breakdown of binocular function seen in some patients with a longstanding dense unilateral adult onset cataract who can develop intractable diplopia following cataract surgery.  (+info)

Phospholipase A(2) in rabbit tears: a host defense against Staphylococcus aureus. (27/407)

PURPOSE: This study analyzed rabbit tears for anti-staphylococcal activity, the role of phospholipase A(2) (PLA2) in this reaction, and the ability of enzyme inhibitors to promote bacterial survival. METHODS: Contact lenses with Staphylococcus aureus were applied to scarified rabbit eyes. The colony-forming units (CFU) per cornea or lens were determined and pathology was scored by slit-lamp examination (SLE). The bactericidal activity was measured by incubating bacteria with rabbit tears or PLA2 at 33 degrees or 37 degrees C. Radiolabeled S. aureus was incubated with PLA2 or tears to quantify the release of a membrane component that was identified by thin-layer chromatography. Inhibitors of these reactions were also analyzed. RESULTS: Application of Staphylococcus, on contact lenses, to rabbit corneas resulted in bacterial killing and limited inflammation. Incubation of tears and bacteria (1:1; v/v) in tryptic soy broth at 33 degrees C decreased CFU approximately 4 logs. Tears (> or =30 microl) or PLA2 (> or =30 U) incubated with bacteria in phosphate-buffered saline were bactericidal. PLA2 (> or =0.2 U) or tears (> or =2 microl) cleaved bacterial membranes, liberating arachidonic acid. Spermidine or tetracaine inhibited cleavage of bacterial membranes by tears or PLA2 and spermidine promoted bacterial survival and growth in tears. Tears (60 microl) killed >99% of the bacterial inoculum, whereas bacteria incubated in tears plus spermidine approximately doubled in number. CONCLUSIONS: PLA2 in rabbit tears kills Staphylococcus by hydrolyzing bacterial membranes to release arachidonic acid. Spermidine and tetracaine inhibited PLA2 activity and spermidine protected Staphylococcus from PLA2 in rabbit tears.  (+info)

Proliferation rate of rabbit corneal epithelium during overnight rigid contact lens wear. (28/407)

PURPOSE: To examine cell proliferation of the normal corneal epithelium and during extended rigid gas-permeable (RGP) lens wear. METHODS: Twenty-three New Zealand White rabbits were fitted unilaterally with either a low oxygen transmissible (Dk/t) or hyper-Dk/t RGP lens, with the other eye serving as a control. The rabbits were injected with 5-bromo-2-deoxyuridine (BrdU) 24-hours later and killed at three time points: 1, 3, and 7 days after injection. Corneas were processed for immunocytochemistry, and sequential digital images were taken from the superior limbus to the central epithelium with an epifluorescence microscope. The total number of BrdU-labeled cell pairs was quantified. RESULTS: The limbus in normal corneas was significantly less populated with BrdU-labeled cells than the central and peripheral epithelium (P < 0.05). The peripheral epithelium adjacent to the limbus was marked by a peak of labeled cells (P < 0.05). Both types of RGP lenses produced an increase in BrdU labeling in the limbus and a dramatic decrease in the central epithelium (80% for low Dk/t, 37% for hyper Dk/t). At day 3 and 7 after BrdU injection, the low-Dk/t lens continued to show decreased BrdU labeling centrally, whereas the limbus remained increased. Hyper-Dk/t lens wear however, showed persistent limbal elevation but equivalent numbers of BrdU-labeled cells centrally at days 3 and 7, compared with control corneas. Keratocytes unexpectedly showed BrdU labeling during RGP lens wear. CONCLUSIONS: Limbus, peripheral, and central epithelium were characterized by different proliferation rates in the normal rabbit cornea. RGP lens wear significantly altered the homeostatic proliferation pattern of the epithelium with the low-Dk/t lens having the most dramatic effect. RGP contact lens wear appears to stimulate proliferation of keratocytes.  (+info)

Staphylococcus corneal virulence in a new topical model of infection. (29/407)

PURPOSE: To develop a topical inoculation model of Staphylococcus aureus keratitis in which scarification, contact lenses, and spermidine are used to inhibit the host defenses and to investigate the role of alpha-toxin in this infection. METHODS: An alpha-toxin-positive parent strain (8325-4), its isogenic alpha-toxin-negative mutant (DU1090), and a genetically rescued form of the mutant (DU1090/pDU1212) were bound to rabbit-specific contact lenses, treated with spermidine (50 mM), and applied to scarified rabbit corneas. Eyes were treated topically with spermidine before and after lens application. Eyes were graded for disease by slit lamp examination (SLE) every 6 hours until 24 hours PI (PI), and erosion diameters were measured. Histopathologic changes and colony forming units (CFUs) of bacteria were determined. RESULTS: Spermidine treatment and inoculation of eyes with Staphylococcus on contact lenses resulted in significant increases in both CFUs per cornea (P = 0.0041) and SLE score (P or= 0.1959) multilog increase in CFUs over the inoculum at 24 hours PI. The alpha-toxin-producing strains, 8325-4 and DU1090/pDU1212, caused significantly more disease than the alpha-toxin-deficient mutant DU1090 at 24 hours PI (P +info)

Scedosporium prolificans keratouveitis in association with a contact lens retained intraocularly over a long term. (30/407)

Scedosporium prolificans is a soil saprophyte that is associated with a large variety of infectious processes and with respiratory colonization in immunocompetent and immunocompromised patients. We report the first described case of S. prolificans keratouveitis associated with the intraocular long-term retention of a contact lens in a 76-year-old female patient.  (+info)

Contact lens related corneal infections. (31/407)

This article describes microbial keratitis, infection of the cornea by micro-organisms. Contact lens wear is a predisposing factor for the development of microbial keratitis. Micro-organisms probably adhere to the contact lens, transfer from the contact lens to a damaged or compromised corneal epithelial surface, penetrate into the deeper layers of the cornea and produce corneal damage. Host responses to the invading micro-organisms, while designed to protect the eye, can often exacerbate the situation and the resulting microbial keratitis can lead to permanent blindness. The microbial, biochemical and immunological aspects of MK will be described in detail.  (+info)

Characteristics and functional outcomes of 130 patients with keratoconus attending a specialist contact lens clinic. (32/407)

AIMS: To evaluate the demographic profile, management and functional outcomes of patients with keratoconus attending the contact lens clinic of a tertiary ophthalmic referral centre over a one year period. METHODS: A retrospective cohort analysis was conducted by reviewing the computerised hospital records of 130 patients attending The Western Eye Hospital contact lens department over the period 1st Jan 1999 to 31st Dec 1999. Data on age, gender, referral pattern, visual acuity, contact lens fitting, degree of visual success, and some information on penetrating keratoplasty were obtained. RESULTS: 16.4% of all patients attending the Contact Lens clinic had keratoconus. The mean age at referral was 28.6 years and the mean age of keratoconus during the study period was 34.9 years. There was a predominance of male patients. Optometrists formed 72.2% of the referrals, and had prescribed some form of refractive correction in 70% of patients (two-thirds contact lenses) prior to hospital assessment. Of the 130 patients seen in the department during the study period, the post-referral management included bilateral contact lens fitting for 102 patients (78.5%), monocular contact lens fitting for 24 patients (18.5%) and no intervention in four patients (3%). The types of contact lenses used included PMMA lenses (2.7%), rigid gas permeable lenses (96.1%) of the spherical, elliptical and special cone lens designs, Keratosoft or Softperm lenses (0.8%) and scleral lenses (0.4%). Eleven eyes of eight patients had received penetrating keratoplasty (PK) prior to hospital assessment, of whom seven eyes needed post-surgical contact lens fitting. The main reasons for PK were contact lens intolerance (83%), frequent contact lens displacement (8.5%) and unsatisfactory visual acuity despite good contact lens fit (8.5%). Sixty-five per cent of patients were able to wear their contact lenses for more than 12 hours a day. With contact lens wear, 87% of patients had a visual acuity of 6/9 or better and 59% of eyes had improved visual acuity of 0.6 logMAR or more. CONCLUSION: Optometrists were the main source of referral for keratoconus patients to the Hospital Eye Service (HES). The mean age at referral was 28.6 years, with a predominance of male patients. Blurred vision formed the main presenting visual symptom on initial hospital assessment; subsequently, more than two-thirds of patients required bilateral contact lenses. Rigid gas permeable contact lenses remain the mainstay treatment for advanced keratoconus, with various designs enabling a large proportion of patients to attain improved visual acuity.  (+info)