Tear production after unilateral removal of the main lacrimal gland in squirrel monkeys.

OBJECTIVE: To study the effects of lacrimal gland removal on basal and reflex tear production and on the ocular surface in the squirrel monkey. METHODS: Unilateral main lacrimal gland removal in 6 squirrel monkeys was followed by Schirmer testing, slit-lamp examination with fluorescein, and collection of basal and reflex (stimulated) tears for analysis of tear protein spectra between 0 and 20 kd, as well as histological evaluation. RESULTS: Schirmer test results showed an 80% decrease in basal tears and a 90% decrease in reflex tears during week 1, and a 32.2% and 33.3% decrease, respectively, at week 20 after surgery, compared with the contralateral control side. However, no gross abnormalities or fluorescein staining were seen in 5 of the 6 monkeys, and the conjunctival surfaces remained normal. The main and accessory lacrimal glands appeared to secrete similar types of proteins. No histological changes were seen in corneal, conjunctival, or eyelid tissues 20 weeks after surgery. CONCLUSIONS: Tears from accessory lacrimal glands were sufficient to maintain a stable tear layer on the cornea, suggesting that so-called basal tear flow is made up of fluid from both main and accessory lacrimal glands and that decreased tear production by the main lacrimal gland is not a causative factor in keratoconjunctivitis sicca. CLINICAL RELEVANCE: This study shows that total removal of the main lacrimal gland does not in itself lead to keratoconjunctivitis sicca. However, the nature of neural control of the accessory glands is not yet clear.

[Comparative study of tears protein composition in patients after photorefractive keratectomy and laser specialized keratomileusis]. / Sravnitel'noe issledovanie belkovogo sostava slezy patsientov posle fotorefraktsionnoi keratoéktomii i lazernogo spetsializirovannogo keratomileza.

Changes in the protein spectrum of the lacrimal fluid, resultant from refraction ocular surgery (photorefraction keratectomy, PRK, and laser specialized keratomileusis, LASIK) were evaluated. Lacrimal fluid was collected before operation and in various terms after it in 28 patients (48 eyes) subjected to PRK and in 34 patients (59 eyes) subjected to LASIK. Biochemical analysis of the lacrimal fluid was performed on a mass spectrometer. After PRK the greatest changes in the protein spectrum occurred immediately after the operation before reepithelialization. Changes after LASIK were negligible. Refraction laser operations cause changes in the protein composition of tears, LASIK being more physiological than PRK from viewpoint of intactness of the protein composition of tears.

Detection of substance P in human tears by laser desorption mass spectrometry and immunoassay.

PURPOSE: To determine whether substance P is present in human tears. METHODS: Tear samples (1-2 microliters) were collected from one eye of each of 12 subjects. Two of the eyes had dry eye syndrome, two wore contact lenses and had dry eye syndrome, and eight were normal. Five of the eight normal eyes were scheduled to undergo excimer laser refractive surgery, and tears were collected from these eyes before and after surgery. Tear samples were analyzed by laser desorption mass spectrometry. Pooled samples from one individual were subjected to enzyme-linked immunoabsorbent assay. RESULTS: Laser desorption mass spectra of the 18 tear samples displayed well defined peaks with mass to charge (m/z) ratios ranging from 1343.7 to 1355.9 and/or 1356.9 to 1364.7, corresponding to an average m/z of 1349.8 +/- 1.13 for protonated substance P and 1361.2 +/- 0.54 for oxidized substance P obtained from 14 mass spectra of standards formulated with substance P concentrations ranging from 10(-4) M to 10(-12) M. As confirmation, an enzyme-linked immunoabsorbent assay performed twice on pooled tears from one eye detected substance P in both replicates at a concentration of 125 pg/ml (9.26 x 10(-11) M). CONCLUSIONS: These findings demonstrate that substance P is a component of tears obtained from normal eyes of men and women ranging in age from 26 to 60 years, from eyes fitted with contact lenses, from eyes with dry eye syndrome, and from eyes 1 and 2 days after excimer laser refractive surgery. Whether the concentration of substance P in tears varies with sex, age, or eye condition, the source of substance P in tears, and its role in tears remains to be discovered.

Diclofenac sodium attenuates neural activity after photorefractive keratectomy in rabbits.

BACKGROUND: Photorefractive keratectomy for treating myopia has been associated with severe postoperative pain. The purpose of the present study was to investigate, in a rabbit model, the early effects of laser ablation on the physiology of the sensory nerves of the cornea. METHODS: Neurophysiologic monitoring of the corneal nerves was carried out 4 to 6 hours after 5-mm diameter, circular PRK ablations with a central depth of 85 microns. The effect of topical 0.1%, 0.25%, and 0.5% diclofenac sodium on the physiologic response to chemical and mechanical stimulation was evaluated. Corneas were prepared for anatomic studies of corneal innervation. RESULTS: Heightened neural activity was observed in the corneal nerves after ablation, and exaggerated responses to sensory stimulation with hypertonic sodium chloride solutions were recorded. Diclofenac sodium at 0.1% decreased the response to 0.5 M NaCl and 0.7 M NaCl to 67 +/- 9% and 68 +/- 7% (mean +/- standard error) of the control response. Mechanically sensitive nerves were more resistant to diclofenac; 0.1% diclofenac had no effect, but 0.25% diclofenac reduced the response significantly (P < 0.05). Anatomic observations showed that the ablation extended through the neural plexus. By 72 hours, long neurites tipped with growth cones had advanced into the injured region, indicating the initiation of neural regeneration. CONCLUSIONS: Diclofenac sodium was effective in attenuating neural activity in the cornea after excimer laser ablation. The action of this agent was shown to be different from that of a topical anesthetic, which rapidly and totally inhibited the response to all forms of stimulation.

Clinical analysis of excimer laser photorefractive keratectomy using a multiple zone technique for severe myopia.

PURPOSE: In an investigational procedure, excimer laser photorefractive keratectomy for severe myopia was performed at three clinical trial centers to determine the effectiveness of the multiple zone technique. METHODS: A VisX Model Twenty/Twenty excimer laser (VisX, Santa Clara, California) was used to perform photorefractive keratectomy on 14 severely myopic eyes (-10.37 to -24.5 diopters) of 12 patients by using a multiple zone technique. Postoperative follow-up ranged from six months to two years; retreatments were performed on four patients, with a follow-up of at least nine months. RESULTS: At six months postoperatively, before retreatment, three of the 14 eyes were within 2 diopters and seven of the 14 eyes were within 4 diopters of attempted correction. Regression of effect to more severe myopia was worse in five eyes treated with nitrogen gas blowing. Retreatments also demonstrated considerable myopic regression. Three patients had loss of two or more lines of best-corrected visual acuity, and these patients also had moderate or severe levels of haze. CONCLUSION: Excimer laser photorefractive keratectomy for severe myopia using a multiple zone technique is associated with considerable regression, haze, and loss of best-corrected visual actuity, especially when performed in association with nitrogen gas blowing.

Central photorefractive keratectomy for myopia. Partially sighted and normally sighted eyes.

Ten partially sighted and 19 normally sighted eyes underwent excimer laser photorefractive keratectomy for the correction of myopia. Nine of the partially sighted and 17 of the normally sighted eyes had 12 months of follow-up. Epithelial healing was complete in all eyes by day 6. None of the eyes had recurrent erosions, infections, or other medical complications. An increase in corneal haze after surgery was followed by a slow trend toward clearing. Average uncorrected visual acuity in the 7 normally sighted eyes with attempted corrections of 5 diopters (D) or less was 20/40 from month 2 on; the eyes with greater than 5 D attempted corrections had an average of 20/80--at month 2, which declined to 20/200--by month 6. Best spectacle-corrected visual acuity was within +/- 1 Snellen line of preoperative values in 14 of the normally sighted eyes, improved 2 or more lines in 2 eyes, and worsened two or more lines in two eyes. Hard contact lens overcorrection restored all of the two-line loss in 1 eye and 1 line of the 3-line loss in the other. Refraction and keratometry indicated corneal flattening without induced astigmatism.

Myopic excimer laser photorefractive keratectomy: an analysis of clinical correlations.

In this study, we examined the correlations among various factors that may affect the results of central photorefractive keratectomy for myopia. Data analyzed from our studies of blind, partially sighted, and normally sighted eyes included patient age, attempted correction, time to re-epithelialization, postoperative corneal clarity, refraction (relative spherical equivalent), and uncorrected visual acuity. We found that larger attempted corrections resulted in less accurate refractions and poorer uncorrected visual acuity. Older patients tended to have better results than younger patients, regardless of the amount of attempted correction. The relationship between the amount of attempted correction and corneal clarity was weak. There was a statistical correlation between corneal clarity scores and uncorrected visual acuity, but the range of corneal clarity scores was small and even the highest scores were probably not in the range that interfered with vision, so the relationship was probably not causal. The rate of epithelial healing did not appear to affect either refractive or visual results, and was not affected by patient age. These findings may be useful in guiding future efforts to improve the results of this new surgical procedure for the correction of refractive error.

Evaluation of an opacity lensometer for determining corneal clarity following excimer laser photoablation.

The appearance of haze in the central cornea following photoablation with a 193 nm excimer laser is an important factor in the postoperative course of this procedure. Data from 37 human eyes treated with photorefractive keratectomy, 4 eyes treated with phototherapeutic keratectomy, and 5 untreated eyes were used to evaluate the ability of a commercially available opacity lensometer to provide an objective measure of corneal clarity. We found that the opacity lensometer was able to detect light scattered from the cornea but was not sufficiently sensitive to distinguish reliably among excimer-treated eyes with degrees of corneal haze evaluated as clear, trace, or 1+ by slit-lamp microscope examination. In untreated, clear corneas, the values obtained with the opacity lensometer in eyes measured with and without a clear contact lens were within one unit of each other for any given eye, but values from eye to eye varied over a range of six units. In a test simulating different amounts of corneal haze using contact lenses evenly coated with nail polish enamel, the log-transformed opacity lensometer values varied directly with percent light scattering as determined by spectrophotometry. These results suggest that the opacity lensometer measurements are reliable and reproducible, but that in the human cornea something is being measured by the opacity lensometer that is not taken into account in clinical slit-lamp microscope evaluation. Overall, it appears that, in its present form, this instrument is not useful to measure corneal clarity after excimer laser photoablation.

Central photorefractive keratectomy for myopia. The blind eye study.

Prior to undertaking a study in sighted human eyes, we performed photorefractive keratectomy with the 193-nm excimer laser for the correction of myopia in nine legally blind eyes to evaluate safety, efficacy, predictability, and stability. In most cases, reepithelialization was complete by 5 days after surgery; no recurrent erosions were seen. By the end of the 6-month study, all of the corneas had a 0 or 1+ clarity score, on a scale of 0 (clear) to 5+ (opaque). Keratometry and pachometry demonstrated stable flattening of the corneas. One month after surgery, changes in refraction evaluated by retinoscopy showed fair predictability, with no significant increase in refractive or keratometric astigmatism, followed by some regression of effect by the end of the study, possibly caused by anatomical remodeling. The amount of regression appeared to be directly related to the amount of correction intended, suggesting that this effect would not be clinically important in the treatment of mild to moderate myopia.