By measuring and comparing the corneal biomechanical parameters of normal people, patients with allergic conjunctivitis, keratoconus, whether allergic conjunctivitis causes changes in corneal biomechanics can be explored, and sensitive mechanical indicators of allergic conjunctivitis can be identified. Furthermore, through rubbing frequency, ocular allergic symptom scores and physical sign scores observation, corneal morphological parameters, corneal epithelial thickness, tear inflammatory cytokines levels, and conjunctival microvascular parameters measurements, related factors affecting corneal biomechanics in patients with allergic conjunctivitis can be identified. Otherwise, by comparing corneal biomechanical changes in vernal keratoconjunctivitis before and after drug treatment, biomechanical change tendency during treatment can be clarified.

The current study involves 3 parts. The first part aims to explore whether allergic conjunctivitis causes changes in corneal biomechanics and to identify sensitive mechanical indicators of allergic conjunctivitis. This part is a cross-sectional study. Four groups are included: normal group, vernal keratoconjunctivitis (VKC) group, seasonal allergic conjunctivitis (SAC) group and keratoconus (KC) group, with 25 eyes in each group (in normal group one eye is randomly selected , and in VKC group, SAC group and KC group the more severe one is selected). Patients in all groups meet inclusion criteria and voluntarily join this study with informed consents. Medical history is collected, including basic information, allergic history and course of disease. Corneal biomechanics is measured by Corvis ST. The difference of corneal biomechanics among groups is analyzed to determine corneal biomechanical changes of AC and to find sensitive mechanical indicators of AC.

The second part aims to identify related factors affecting corneal biomechanics in patients with allergic conjunctivitis. This part is also a cross-sectional study. Four groups are included: normal group, VKC group, SAC group and KC group, with 25 eyes in each group. Medical history is collected, including basic information, allergic history and course of disease. Eye rubbing frequency, ocular allergic symptom scores and physical sign scores are measured and recorded in VKC group and SAC group. Corneal biomechanics measured by Corvis ST, corneal morphological parameters measured by Pentacam, corneal epithelial thickness measured by Optovue OCT, tear cytokine levels measured by Milliplex kit and conjunctival microvascular parameters measured by functional slit lamp are performed in all patients. Correlation analysis of corneal biomechanical parameters and other measurement indicators in VKC group and SAC group is performed to determine the relevant influencing factors of corneal biomechanics in AC.

The third part aims to determine corneal biomechanical change tendency during treatment in VKC. This part is a prospective case-control study. 25 patients with 25 eyes (the more severe eye is selected) are included. Medical history is collected, including basic information, allergic history and course of disease. Eye rubbing frequency, ocular allergic symptom scores and physical sign scores are measured and recorded in VKC group and SAC group. Corneal biomechanics measured by Corvis ST, corneal morphological parameters measured by Pentacam, corneal epithelial thickness measured by Optovue OCT, tear cytokine levels measured by Milliplex kit and conjunctival microvascular parameters measured by functional slit lamp are performed in all patients before drug treatment. And all the patients adopt a unified medication regimen. The same ophthalmological examinations are performed again after 3 month medication. Based on the analysis of the difference between the two measurements before and after the drug treatment, corneal biomechanical change tendency during treatment in VKC is clarified and the potential mechanical parameter needed to be monitored during follow-up is identified. The specific therapeutic regimen is as follows: 0.1% tacrolimus eye drops four times daily; 0.1% flumirone eye drops twice daily; azelastine hydrochloride eye drops four times daily; hyaluronic acid sodium eye drops four times daily. After 1M, 0.1% flumilone eye drops is replaced with 0.02% flumirone eye drops twice daily, and the rest of the medication remaines unchanged.

Normal group

Inclusion Criteria:

1. No abnormalities are found by slit lamp and Pentacam.
2. Diopters: diopter of spherical: -6.0D~+3.0D, diopter of cylinder: -2.0D~+2.0D, spherical equivalent: -6.0D~+3.0D
3. Best corrected visual acuity ≥ 1.0

Exclusion Criteria:

1. Patients diagnosed with other eye diseases other than refractive error.
2. With a history of eye surgery or trauma.
3. With systemic diseases such as immune diseases and connective tissue diseases.
4. With a family history of keratoconus and glaucoma.
5. Wear soft contact lens within 2 weeks or rigid contact lens within 1 month.

SAC group

Inclusion Criteria:

1. Symptoms: Itching, foreign body sensation, increased discharge in conjunctival sac. And children may mainly show an increase in blinking frequency.
2. Signs: conjunctival hyperemia, swelling, tarsal papillae.
3. Medical history: seasonal onset
4. Diopters: diopter of spherical: -6.0D~+3.0D, diopter of cylinder: -2.0D~+2.0D, spherical equivalent: -6.0D~+3.0D
5. Best corrected visual acuity ≥ 0.8

Exclusion Criteria:

1. Corneal scar.
2. Other active inflammatory diseases of the eye.
3. With a history of eye surgery or trauma.
4. With systemic diseases such as immune diseases and connective tissue diseases.
5. Wear soft contact lens within 2 weeks or rigid contact lens within 1 month.
6. Unable to fixate and cooperate.

VKC group

Inclusion Criteria:

1. Symptoms: Itching, foreign body sensation, increased discharge in conjunctival sac. And children may mainly show an increase in blinking frequency.
2. Signs: giant papillae on the upper tarsal conjunctiva and gelatinous infiltration of the limbus.
3. Diopters: diopter of spherical: -6.0D~+3.0D, diopter of cylinder: -2.0D~+2.0D, spherical equivalent: -6.0D~+3.0D
4. Best corrected visual acuity ≥ 0.8

Exclusion Criteria:

The same as SAC group.

Keratoconus group

Inclusion Criteria:

1. With a history of myopia and astigmatism
2. Best corrected visual acuity <1.0
3. At least 1 positive sign of the following is found by slit lamp examination: thinning of the corneal stroma, a cone-shaped ectatic protrusion of the cornea, Fleischer ring and Vogt striae.
4. Typical signs of corneal topography: central corneal power value of the anterior surface >47D, central inferior/superior dioptric asymmetry >3D (within 3mm), central dioptric asymmetry between two eyes >1D.

Exclusion Criteria:

The same as SAC group.

The patients of Zhongshan ophthalmic center and healthy volunteers recruited.