Involvement of pigment epithelium-derived factor, docosahexaenoic acid and neuroprotectin D1 in corneal inflammation and nerve integrity after refractive surgery

Alterations in corneal innervations result in impaired corneal sensation, severe dry eye and damage to the epithelium that may in turn lead to corneal ulcers, melting and perforation. These alterations can occur after refractive surgery. We have discovered that pigment epithelium-derived factor (PEDF) plus docosahexaenoic acid (DHA or the docosanoid bioactive neuroprotectin D1 (NPD1)) induces nerve regeneration after corneal surgery that damages the stromal nerves. We found that PEDF is released from corneal epithelial cells after injury, and when DHA is provided to the cells it stimulates the biosynthesis of NPD1 by an autocrine mechanism. The combination of PEDF plus DHA also decreased the production of leukotriene B4 (LTB4), a neutrophil chemotactic factor, thereby decreasing the inflammation induced after corneal damage. These studies suggest that PEDF plus DHA and its derivative NPD1 hold promise as a future treatment to restore a healthy cornea after nerve damage.

Electrophysiological properties and chemosensitivity of acutely dissociated trigeminal somata innervating the cornea

Adult rat sensory trigeminal ganglion neurons innervating the cornea (cTGNs) were isolated and identified following retrograde dye labeling with FM1-43. Using standard whole-cell patch clamp recording techniques, cTGNs could be subdivided by their action potential (AP) duration. Fast cTGNs had AP durations <1 ms (40%) while slow cTGNs had AP durations >1 ms and an inflection on the repolarization phase of the AP. With the exception of membrane input resistance, the passive membrane properties of fast cTGNs were different from those of slow cTGNs (capacitance: 61+/-4.5 pF vs. 42+/-2.6 pF, resting membrane potential: -59+/-0.7 mV vs. -53+/-0.9 mV, for fast and slow cTGNs respectively). Active membrane properties also differed between fast and slow cTGNs. Slow cTGNs had a higher AP threshold (-25+/-1.6 mV vs. -38+/-0.8 mV), a larger rheobase (14+/-1.9 pA/pF vs. 6.8+/-1.0 pA/pF), and a smaller AP undershoot (-56+/-1.7 mV vs. -67+/-2.5 mV). The AP overshoot, however was similar between the two types of neurons (46+/-3.1 mV vs. 48+/-4 mV). Slow cTGNs were depolarized by capsaicin (1 microM, 80%) and 60% of their APs were blocked by tetrodotoxin (TTX) (100 nM). Fast cTGNs were unaffected by capsaicin and 100% of their APs were blocked by TTX. Similarly, cTGNs were also heterogeneous with respect to their responses to exogenous ATP and 5-HT. The current work shows that cTGNs have distinctive electrophysiological properties and chemosensitivity profiles. These characteristics may mirror the distinct properties of corneal sensory nerve terminals. The availability of isolated identified cTGNs constitutes a tractable model system to investigate the biophysical and pharmacological properties of corneal sensory nerve terminals.

Effects of glaucoma medications on corneal endothelium, keratocytes, and subbasal nerves among participants in the ocular hypertension treatment study

PURPOSE

To compare subbasal corneal nerve and keratocyte density and endothelial characteristics of ocular hypertensive patients treated with medications or observation.

METHODS

Participants in the Ocular Hypertensive Treatment Study (OHTS) randomized at Mayo Clinic to medication or observation were evaluated with specular microscopy annually for 6 years. Confocal microscopy was performed 78 to 108 months after enrollment. Subbasal nerve density was calculated by manual tracing and digital image analysis. Keratocyte density was determined by manual counting methods. Data were compared using a t test and a rank sum test.

RESULTS

After 6 years, corneal endothelial cell density, percent hexagonal cells, and coefficient of variation of cell area for the observation (n = 21) and medication groups (n = 26) were similar (2415 +/- 300 vs. 2331 +/- 239 cells/mm; 63% +/- 11% vs. 65% +/- 10%; and 0.32 +/- 0.07 vs. 0.30 +/- 0.06, respectively). Of 38 participants undergoing confocal examination, the medication group (n = 19) had fewer nerves (3.8 +/- 2.1 vs. 5.9 +/- 2.0 nerves/frame; P = 0.02) and a lower nerve density (5643 +/- 2861 vs. 9314 +/- 3743 mum/mm; P = 0.007) than the observation patients (n = 10). An additional 9 patients in the observation group, who began medication before confocal scanning, had intermediate nerve densities. Full-thickness keratocyte density was similar, with 22,257 +/- 2419 and 23,430 +/- 3285 cell/mm in the observation and medication groups, respectively.

CONCLUSIONS

Chronic administration of glaucoma medications causes a decrease in the number and density of corneal subbasal nerve fiber bundles but does not affect keratocyte density or corneal endothelial characteristics.

Use of nerve growth factor to treat congenital neurotrophic corneal ulceration

PURPOSE

This study was designed to assess the efficacy of nerve growth factor in the treatment of neurotrophic corneal ulceration in a child with bilateral congenital corneal anesthesia secondary to trigeminal insufficiency.

METHODS

A 5-month-old child presented to the casualty department with a 2-week history of red eyes and right corneal ulceration. Slit-lamp examination showed a central defect in the right corneal epithelium with underlying stromal opacification, only mild conjunctival inflammation with slight decreased tear production, and otherwise apparently normal eyes. Initially this was investigated as an infected ulcer and treated for several weeks as herpetic ulceration with no beneficial effect. Further clinical examination demonstrated bilateral decreased corneal sensation along with decreased facial sensation in keeping with congenital trigeminal nerve insufficiency. Investigation with magnetic resonance imaging showed no obvious abnormality. Conservative treatment with lubricants resulted in progressive right corneal stromal loss, and no healing occurred in the left corneal ulcer. Bilateral large lateral tarsorrhaphies were performed. Despite this, the left corneal ulcer demonstrated no improvement and increasing stromal opacification was noted. Topical nerve growth factor (NGF) was then used to treat the left cornea and resulted in epithelial healing within 1 week. Treatment was continued for a further 10 days after epithelial healing. Despite conventional treatment on 3 separate occasions, further epithelial breakdown occurred. Topical NGF treatment resulted in a rapid improvement and healing of the epithelial defect.'At present, the patient is receiving a 6-month continuous treatment plan of NGF.

RESULTS

Persistent epithelial defects (PED) secondary to neurotrophic ulceration have responded to topical NGF on 3 separate occasions during a 2-year period. The corneal epithelium now remains intact, and the cornea has no vascularization; however, mild anterior stromal opacification has gradually increased despite prolonged NGF treatment.

CONCLUSION

NGF seems to represent a safe and efficacious treatment option to restore the integrity of corneal epithelium in which there is congenital corneal anesthesia because of trigeminal insufficiency. However, this treatment alone is insufficient to prevent progressive anterior stromal opacification.

Changes in mechanical, chemical, and thermal sensitivity of the cornea after topical application of nonsteroidal anti-inflammatory drugs

PURPOSE

In addition to their well-known anti-inflammatory actions, some of the nonsteroidal anti-inflammatory drugs (NSAIDs) appear to have an analgesic effect. In human subjects, the changes in threshold and intensity of sensations evoked by mechanical, chemical, and thermal stimulation of the cornea induced by topical administration of two commercial NSAIDs, diclofenac sodium (Voltaren; Novartis, Basel, Switzerland) and flurbiprofen (Ocuflur; Allergan, Irvine, CA), were studied.

METHODS

Corneal sensitivity was measured in 10 young, healthy subjects with a gas esthesiometer. Chemical (10%-70% CO2 in air), mechanical (0-264 mL/min), and thermal (corneal temperature changes between -4.5 degrees C and +3 degrees C around the normal value) stimuli were applied to the center of the cornea. The intensity and perceived magnitude of the psychophysical attributes of the evoked sensation were scored at the end of the pulse in a 10-cm, continuous visual analog scale (VAS). The threshold was expressed as the stimulus intensity that evoked a VAS score >0.5. Sensitivity was measured in both eyes of each subject on two separate days, one without treatment and the other 30 minutes after topical application of 0.03% flurbiprofen (seven subjects) or 0.1% diclofenac sodium (six subjects).

RESULTS

Diclofenac attenuated significantly all the sensation parameters evoked by high-intensity mechanical, chemical, and thermal stimuli. Flurbiprofen produced a slight reduction of the sensations evoked by mechanical and chemical stimulation that became significant only for the irritation caused by chemical stimuli of maximum intensity (70% CO2). None of the drugs modified significantly the detection threshold of the different stimuli.

CONCLUSIONS

Flurbiprofen had a very limited effect on sensations evoked by corneal stimulation, whereas diclofenac reduced the intensity of sensations evoked by stimuli of different modality, suggesting a mild local anesthetic effect of this drug on all types of corneal sensory fibers. Such anesthetic action could explain the analgesic effect that has been reported after topical application of diclofenac in inflamed human eyes.

[Long acting analogue of somatostatin (Octreotide) for treatment of patients with neurochorioretinitis due to ocular sarcoidosis who failed corticosteroids therapy]

Neurochorioretinitis due to the course of ocular sarcoidosis is relatively rare case. It usually responds well to conventional treatment with corticosteroids. We want to present the patient effectively treated with long acting analogue of somatostatin (Octreotide), who failed to respond to previous corticosteroids treatment.

Sensations evoked by selective mechanical, chemical, and thermal stimulation of the conjunctiva and cornea

PURPOSE

To study the sensations evoked by selective mechanical, chemical, and thermal stimulation of the conjunctiva and compare them with those elicited by similar stimulation of the cornea.

METHODS

Six young subjects participated in the study. Using a gas esthesiometer, selective mechanical (air puffs at flows from 0 to 264 ml/min), chemical (0--80% CO(2) in air), and thermal (air at temperatures from -10 degrees C to +80 degrees C) stimulation was performed on the center of the cornea and on the temporal conjunctiva. The intensity, degree of irritation, stinging and burning pain components, and thermal characteristics of the evoked sensation were evaluated after each stimulus in separate, 10-cm continuous visual analogue scales (VASs). The ability of the subjects to identify the quality of the stimulus applied to the cornea and the conjunctiva was also studied.

RESULTS

The subjective intensity and thermal components (cooling or warming) of the sensation reported after mechanical, chemical, and heat stimulation were similar in the conjunctiva and cornea, although lower VAS scores were always reported in the conjunctiva for the irritation and the stinging and burning pain components. In the cornea, stimulation with low temperatures was perceived as a cooling sensation with an irritative component. In the conjunctiva, cooling was perceived as a purely cold sensation. Subjects showed similar discrimination capability in the cornea and the conjunctiva for the various types of stimuli.

CONCLUSIONS

Sensations evoked in the cornea by selective mechanical, chemical, and heat and cold stimulation always presented an irritation component. In the conjunctiva, stimuli of the same intensity are always perceived as less irritating than in the cornea. Cold and other non-noxious subqualities of sensation can be evoked in the conjunctiva.

Topical treatment with nerve growth factor for neurotrophic keratitis

OBJECTIVE

To evaluate the efficacy of nerve growth factor (NGF) in patients with neurotrophic keratitis.

DESIGN

Prospective, noncomparative, interventional case series.

PARTICIPANTS

Forty-five eyes of 43 consecutive patients with moderate (stage 2, n = 17) to severe (stage 3, n = 28) neurotrophic keratitis unresponsive to other nonsurgical therapies.

METHODS

After a 10-day washout with preservative-free artificial tears, 45 eyes with neurotrophic keratitis received murine NGF (200 microg/ml) every 2 hours for 2 days followed by one drop six times daily until the ulcer healed. A maintenance dose of one drop NGF (100 microg/ml) was administered four times daily for the 2 weeks subsequent to ulcer healing.

MAIN OUTCOME MEASURES

Size and depth of the ulcer or the epithelial defect, corneal sensitivity, best corrected visual acuity, side effects, and relapse of the disease in the follow-up period.

RESULTS

All patients had a complete resolution of the persistent epithelial defect (with or without an ulcer) after 12 days to 6 weeks of treatment with NGF. Patients affected by both stages of the disease demonstrated both improved corneal sensitivity and visual acuity (P<0.001). No significant differences were observed in the time to complete corneal healing between stage 2 and stage 3 patients. Hyperemia and ocular and periocular pain were side effects reported during the first days of treatment. No relapse of the disease was observed during the follow-up period, with the exception of three patients with trigeminal nerve resection, who required a single retreatment.

CONCLUSIONS

Nerve growth factor eye drops improved corneal sensitivity and promoted corneal epithelial healing in both moderate and severe neurotrophic keratitis. Although performed in an uncontrolled and nonrandomized series of patients, this therapy shows promise for the restoration of ocular surface integrity and visual function in neurotrophic corneal disease.

Effects of oleoresin capsicum pepper spray on human corneal morphology and sensitivity

PURPOSE

To examine the potential harmful effects on corneal structure, innervation, and sensitivity of a spray containing the neurotoxin capsaicin (oleoresin capsicum, OC).

METHODS

Ten police officers who volunteered for the study were exposed to OC. Clinical signs were assessed. Corneal sensitivity was measured using a Cochet-Bonnet or a noncontact esthesiometer that provides separate measurements of mechanical, chemical, and thermal sensitivity. Tear fluid nerve growth factor (NGF) was measured. Corneal cell layers and subbasal nerves were examined by in vivo confocal microscopy. The subjects were examined before application and 30 minutes, 1 day, 1 week, and 1 month after OC exposure.

RESULTS

OC spray produced occasional areas of focal epithelial cell damage that healed within 1 day. Each eye showed conjunctival hyperemia and in two subjects, mild chemosis. All except one eye had unchanged best corrected visual acuity (BCVA). A transient decrease (day 1) of mechanical sensitivity was observed with the Cochet-Bonnet esthesiometer. With the gas esthesiometer, mechanical sensitivity remained below normal values for 7 days. Chemical sensitivity to CO2 was high for as much as 1 day and decreased below normal 1 week later, whereas sensitivity to cold was unaffected. Two subjects had measurable tear NGF that increased after exposure. Basal epithelial cell morphology suggested temporary corneal epithelial swelling, whereas keratocytes, endothelial cells, and subbasal nerves remained unchanged.

CONCLUSIONS

Although OC causes immediate changes in mechanical and chemical sensitivity that may persist for a week, a single exposure to OC appears harmless to corneal tissues. The changes are possibly associated with damage of corneal nerve terminals of mainly unmyelinated polymodal nociceptor fibers.

Measurement of corneal sensitivity to mechanical and chemical stimulation with a CO2 esthesiometer

PURPOSE

To develop an instrument to measure corneal sensitivity. Mechanical stimulation was performed with increasing air flow. Chemical stimulation consisted of local pH decreases induced by a mixture of air and CO2 at different concentrations.

METHODS

Air and 98.5% CO2 were mixed with an electronic, proportional-direction control valve to obtain gas mixtures from 0% to 80% CO2. The regulated outflow of gas was carried to a probe mounted on a slit lamp holder, where it was warmed and its CO2 concentration monitored. An electronic valve directed gas pulses of controlled duration to the cornea. Corneal stimulation was performed in 17 young human subjects. The intensity of the experienced sensation was recorded in a continuous visual analog scale (VAS). To obtain threshold values and intensity-response curves, 3-second pulses were applied. For mechanical stimulation, air pulses of increasing flow were used. For chemical stimulation, gas mixtures of increasing CO2 concentration at subthreshold flow and CO2 in stepped increases of 5% was applied.

RESULTS

Mechanical and chemical stimulation of the cornea evoked a brief sensation of irritation. Mechanical threshold (flow values) varied among subjects but were reproducible within each subject and were higher with warmed air. The magnitude of the sensation increased proportionally to the flow of air. The mean chemical stimulation threshold (CO2 concentration) was 25% +/- 3%. Increases in CO2 concentration from 10% to 80% augmented proportionally the intensity of the evoked sensation.

CONCLUSIONS

The gas esthesiometer, which combines variable air flow and CO2 concentrations, permits application to the cornea of mechanical stimuli of controlled force and pH reductions of increasing magnitude. This instrument may be useful in a separate exploration of mechanical and chemical sensitivity of the cornea in human subjects.

Effects of calcium antagonists in the treatment of ophthalmic postherpetic neuralgia

Postherpetic neuralgia is one of the most common, but also one of the most difficult conditions to treat. This condition mainly involves trigeminal, intercostal and sciatic nerves and the brachial plexus area. It mostly appears in patients older than 60 years. Although pain is a transient condition, the pain of postherpeutic neuralgia may become intractable, disabling an may decrease the quality of the patient's life. We studied 30 patients affected by ophthalmic postherpetic neuralgia, appearing, some months after fronto-orbital cutaneous eruption. All patients received nicardipine retard, decreasing gradually, 40 mg/day for 2 weeks. The monitoring of pain was performed using the visual analogue score of Scott-Huskissonn. The results show an improvement in 'pain relief'.

[Suppressive effect of carbon dioxide on excitation of the cold receptors of the nasal cavity of the cat]

The impulse activity of afferent fibers was studied in n. ethmoidalis. While the room air was being sucked in through the nasal cavity to choanes, marked excitation of cold receptors of the nasal cavity walls occurred. In the air current from the choanes to the nostrils, the activity of the receptors was depressed. Insufflation through the nasal cavity of the mixtures of CO2 (1, 3, 6%) with air also depressed the activity of cold receptors. The degree of the depression depended on the concentration of CO2. The cold receptors of nasal cavity like the lung stretch receptors, have the features of chemoreceptors. Their activity is depressed with physiological concentrations of CO2 in the air.

The effects of external ocular irritation on intraocular pressure

Riot control agents (tear gases) cause intense eye irritation and reflex squeezing of the eyes. The intraocular pressure under these circumstances is unknown but animal and human studies of ocular irritation and forces acting upon the eye indicate a transient increase in intraocular pressure which is not necessarily detrimental to vision.