Current understanding of sensitivity and sensation experienced across the ocular surface remains limited. This project explored the regional variation of corneal sensitivity and transducer function, interaction of sensory and autonomic nerves in the lacrimal functional unit, and the ocular surface sensitivity in Dry Eye and with silicone hydrogel (SH) lens wear. Experiments were undertaken, using Belmonte esthesiometer to deliver pneumatic mechanical, chemical and thermal stimuli and Cochet-Bonnet esthesiometer for tactile stimuli, to the cornea and conjunctiva. Psychophysical methods were used to determine the thresholds of stimulus detection, and the magnitude of sensations to suprathreshold stimulation was estimated assuming Steven’s power law. Additionally, tear secretion in response to corneal sensory input was determined by tear meniscus height measured using Optical Coherence Tomography. Sensitivity to pneumatic cool and mechanical stimuli varied slightly across the cornea while chemical sensitivity was not different between regions. The transducer function was also similar between central and peripheral cornea but different between stimulus modalities. In comparison, the reflex tearing response to suprathreshold stimuli was greater with central corneal stimulation. Also, corneal and conjunctival hypersensitivity was found in the dry eye symptomatic group, and it appeared to be associated with symptom severity, tear film stability and corneal epitheliopathy. Refitting with SH lenses after an initial no-lens interval led to increased conjunctival pneumatic mechanical sensitivity, while corneal tactile sensitivity showed a decrease. In addition, corneal staining induced by certain lens-solution combination appeared to be accompanied by increased corneal and conjunctival sensitivity. In conclusion, the position-invariant corneal sensitivity to pneumatic mechanical, chemical and thermal stimuli suggests that the distribution of human corneal sensory fibres may be more homogeneous than previously hypothesised. The mechanisms mediating the sensory aspect of corneal nociception may be similar across the cornea, while, perhaps due to the importance of the visual axis, the tear reflex response to central and peripheral cornea seems to be driven by different neural circuitry, perhaps at the higher levels of the sensory processing pathway. It appears that alteration in sensory processing of the ocular surface occurs in Dry Eye and accompanies SH lens-solution-induced corneal staining. This altered sensitivity seems to be more prominent in the conjunctiva than in the cornea.

Current understanding of sensitivity and sensation experienced across the ocular surface remains limited. This project explored the regional variation of corneal sensitivity and transducer function, interaction of sensory and autonomic nerves in the lacrimal functional unit, and the ocular surface sensitivity in Dry Eye and with silicone hydrogel (SH) lens wear. Experiments were undertaken, using Belmonte esthesiometer to deliver pneumatic mechanical, chemical and thermal stimuli and Cochet-Bonnet esthesiometer for tactile stimuli, to the cornea and conjunctiva. Psychophysical methods were used to determine the thresholds of stimulus detection, and the magnitude of sensations to suprathreshold stimulation was estimated assuming Steven’s power law. Additionally, tear secretion in response to corneal sensory input was determined by tear meniscus height measured using Optical Coherence Tomography. Sensitivity to pneumatic cool and mechanical stimuli varied slightly across the cornea while chemical sensitivity was not different between regions. The transducer function was also similar between central and peripheral cornea but different between stimulus modalities. In comparison, the reflex tearing response to suprathreshold stimuli was greater with central corneal stimulation. Also, corneal and conjunctival hypersensitivity was found in the dry eye symptomatic group, and it appeared to be associated with symptom severity, tear film stability and corneal epitheliopathy. Refitting with SH lenses after an initial no-lens interval led to increased conjunctival pneumatic mechanical sensitivity, while corneal tactile sensitivity showed a decrease. In addition, corneal staining induced by certain lens-solution combination appeared to be accompanied by increased corneal and conjunctival sensitivity. In conclusion, the position-invariant corneal sensitivity to pneumatic mechanical, chemical and thermal stimuli suggests that the distribution of human corneal sensory fibres may be more homogeneous than previously hypothesised. The mechanisms mediating the sensory aspect of corneal nociception may be similar across the cornea, while, perhaps due to the importance of the visual axis, the tear reflex response to central and peripheral cornea seems to be driven by different neural circuitry, perhaps at the higher levels of the sensory processing pathway. It appears that alteration in sensory processing of the ocular surface occurs in Dry Eye and accompanies SH lens-solution-induced corneal staining. This altered sensitivity seems to be more prominent in the conjunctiva than in the cornea.

Made available in DSpace on 2014-07-29T15:13:52Z (GMT). No. of bitstreams: 1 Tese2008_Andreia_Vitor.pdf: 720178 bytes, checksum: 3c6505b8992ec266a19192cbb8d7619a (MD5) Previous issue date: 2009-09-26 / Corneal anesthesia is required in order to evaluate the intraocular pressure (IOP) and eyelid blockades may also be necessary, using local anesthetic agents in horses. The aim of this study was to evaluate the IOP and the corneal touch threshold (CTT) at the central area of the cornea, after eyelid blockades with anesthetic 0.75% ropivacaine, 0.75% levobupivacaine and 2% lidocaine. Nine adult female animals of undefined breed horses, which received 2.0 ml of anesthetic for supraorbitary blockade and 2.5 ml for auriculopalpebral blockagde. All animals were anesthetized with the three anesthetic drugs, with an interval period of seven days between drugs, performing a Latin square 3x3x3. The IOP and CTT were measured before and 10, 20, 40, 60, 80 and 100 minutes after the blockades. The PIO was maintained within the limits considered normal in all three anesthetic drug groups evaluated. After 10 minutes, there was significantly CTT values decrease for all three anesthetics. The recovery time of CTT was higher in 30 the animals anesthetized with lidocaine than those anesthetized with levobupivacaine and ropivacaine / Os agentes anestésicos locais possuem ampla utilização e aplicação na oftalmologia de grandes animais, uma vez que os eqüinos e os bovinos apresentam o músculo orbicular potente, exercendo vigoroso fechamento das pálpebras na presença de dor ou pela simples tentativa de manipulação pelo examinador. Sendo assim, os bloqueios palpebrais são requeridos desde a realização de exame clínico oftálmico de rotina a procedimentos cirúrgicos locais em cavalos. Nesse estudo, foram avaliados os efeitos de soluções anestésicas a base de cloridrato de ropivacaína a 0,75%, cloridrato de levobupivacaína a 0,75% e cloridrato de lidocaína a 2% na pressão intraocular (PIO), no limiar de sensibilidade ao toque corneal (LSTC), na produção lacrimal e na movimentação e sensibilidade palpebral em nove eqüinos, adultos, fêmeas, submetidas ao bloqueio auriculopalpebral e supraorbitário. A PIO e o LSTC foram mensurados antes e aos 10, 20, 40, 60, 80 e 100 minutos após os bloqueios palpebrais. Foi possível observar que a ropivacaína a 0,75% e a levobupivacaína a 0,75% acarretam em diminuição da pressão intra-ocular quando se comparada com a lidocaína a 2%, porém com flutuações dentro da faixa de PIO considerada normal para eqüinos. Verificou-se também que a ropivacaína e levobupivacaína diminuem de forma significativa LSTC, da área central da córnea, e o mantém em níveis que proporcionam anestesia corneal por até 100 minutos. A produção lacrimal foi mensurada utilizando-se o Teste Lacrimal de Schirmer 1 (STT-1) e Teste de Schirmer 2 (STT-2) antes dos bloqueios e o STT foi mensurado aos 20, 60 e 100 minutos após os bloqueios anestésicos palpebrais. Foi observado que valores de STT nos bloqueios palpebrais com ropivacaína a 0,75%, levobupivacaína a 0,75% e lidocaína a 2% foram significativamente maiores quando comparados ao STT-2 e que não houve diferença significativa entre STT-1 e STT, após bloqueio anestésico do auriculopalpebral e supra-orbitário, não sendo observadas também diferenças da produção lacrimal relativamente aos diferentes fármacos anestésicos. A movimentação e a sensibilidade palpebrais foram avaliadas utilizando os testes neurológicos de reflexos de ameaça e palpebrais Foi possível concluir que, a ropivacaína a 0,75% e a levobupivacaína a 0,75% promoveram semelhantes bloqueios motor e sensitivo, enquanto que, a lidocaína 2% determinou um rápido retorno da movimentação e da sensibilidade palpebral em cavalos submetidos aos bloqueios do supraorbitário e auriculopalpebral