Efficacy of topical nerve growth factor treatment in dogs affected by dry eye

Background: Preliminary data show that nerve growth factor (NGF) may improve tear production in humans. We evaluated the efficacy of topical NGF treatment in dogs who developed dry eye after the excision of the third eyelid lacrimal gland. Methods: English Bulldogs (2- to 6-year-old males and females) that had undergone the surgical removal of the prolapsed lacrimal gland of the third eyelid in both eyes at the age of 3-6 months developed chronic keratoconjunctivitis sicca associated with a decrease of Schirmer tear test I values after at least 1 year. One eye, randomly selected, of each dog was treated twice daily with 100 mul of NGF ointment for 1 month, while the fellow eye was used as control and treated with the ointment vehicle only. At baseline and after 1 month of NGF treatment the following examinations were performed: corneal evaluation by slit lamp, fluorescein staining, Schirmer tear test I, tear ferning test, corneal esthesiometry by cotton swab and conjunctival impression cytology. Results: Topical application of NGF caused a significant improvement of all the evaluated parameters compared with baseline values. In contrast, in the control eyes there was no significant difference between the values measured before and after treatment. In particular, after NGF treatment superficial punctate keratopathy was resolved, corneal haze was reduced from stage 4 to stage 2 and Schirmer test values increased (17.2+/-1.7 mm/min vs 4.5+/-1.3 mm/min; p<0.05), as did the tear mucous component (as demonstrated by ferning test: 2.0+/-0.0 vs 4.0+/-0.0; p<0.05); conjunctival impression cytology evaluation demonstrated the presence of numerous mucous filaments and a significant increase in conjunctival goblet cell density (102.7+/-68.3 vs. 18.2+/-14.3 cell x field; p<0.05). Topical NGF treatment improved corneal sensitivity in two of three eyes. Conclusions: This open study suggests that topical application of NGF may enhance the production and functional characteristics in tear film, with an improvement of ocular surface signs in dogs with surgically induced dry eye. These results suggest the possibility of performing further, larger, controlled studies.