Conjunctival Ultraviolet Autofluorescence & Sun Exposure

Abhirami E, M. Optom

Assistant Professor, Karpagam Faculty of Medical Science and Research, Coimbatore, India

Ultraviolet Radiation and Ocular Health

Sun exposure is a major preventable risk factor for many ocular diseases. ⁽¹⁾ Sunlight is a part of the electromagnetic radiation emitted by the sun, which consists of visible light, ultraviolet light, infrared, radio waves, X-rays, and gamma rays which are arranged based on wavelength. Ultraviolet radiation (UVR) is a form of electromagnetic radiation which is not visible to human eyes. The wavelength of UV ranges from 10 to 400 nanometres (nm). UVR can be classified into three types as UV-A, UV-B, UV-C based on the wavelength. As the wavelength decreases, the amount of energy produced will be more, thus increased UVR exposure can lead to sun burn, melanoma etc (Table 1). ⁽²⁾

Ultraviolet Radiation (UVR) has higher energy compared to visible light. Intense UVR exposure can cause direct damage to cells. UVR is highly absorbed in the anterior part of the eye, this absorption will depend upon the tissue regards, age of the person and the amount of wavelength of UV received. Children are more vulnerable to UVR induced ocular damage due to the increased pupil size. ⁽³⁾ Around 80% of an individual’s lifetime UV exposure is attained before 18 years of age. ⁽⁴⁾ 2- 5% of UVR is received by the age of 8 to 10 years which can reach the retina, this will get reduce to 1-2% by the age of 25 years. Only a small amount of UVR (≤ 1%) will reaches the retina, because the UVR ranges from 300 to 400 nm wavelength is blocked by crystalline lens and less than 300 nm is blocked by cornea. ⁽⁴⁾

Table 1: Different UV spectral regions with wavelength and its ocular effects. ⁽⁵⁾

Conjunctival Ultraviolet Autofluorescence and Sun Exposure

Sun light induced ocular disease occurs years before the clinical manifestation. Disease such as pinguecula and pterygium occurs in later stages of life.⁽⁵⁾ Early detection can be helpful in preventing many diseases to avoid vision and ocular health related complications. ⁽⁵⁾ Conjunctival Ultraviolet Autofluorescence (CUVAF) is a method of detecting conjunctival cell damage due to excessive sun exposure. ⁽⁶⁾ CUVAF areas of damage can be obtained from ultraviolet autofluorescence photography.

Cells have molecules that can be excited by the absorption of light energy from lower wavelength and emitting light energy at a higher wavelength. The excited state of a molecule cannot be sustained for a higher time, that can result in the emission of light energy, which is otherwise known as fluorescence. When this emission occurs from excitation of internal cellular components is called auto-fluorescence, which is an inherent property of cells. ⁽⁷⁾ Due to UVR exposure, autofluorescence of UV light can occur in isolated areas of the conjunctiva, which can lead to cellular changes. ^(8,9)

In initial times UVAF photography was used to identify sun exposure related skin problems. UVAF photography system was developed from Wood’s lamp.⁽⁹⁾ CUVAF photography system consists of a good quality camera system attached with UV filters with transmittance range 300 to 400 nm and peak 375 nm wavelength which could transfer UV light that can excite the conjunctival tissue. The principle behind the CUVAF photography system is that UV filters will emit UV and the camera will capture the autofluorescence. Elastin and collagen which is present in the conjunctival tissue will get damaged due to the excessive sun exposure, by the exposure of an excitatory light source the damaged tissues will emit fluorescence. This autofluorescence of damaged conjunctival tissue can be captured using CUVAF techniques and area can be measured to identify the extent of damage. Conjunctival areas of UV damage identified using CUVAF photography can be outlined, and area of damage can be measured using software like ImageJ. Total CUVAF area in mm² for an individual can be calculated by adding the nasal and temporal areas of both eyes. ^(9,10) The camera with an appropriate flash system can be kept in a fixed position to ensure the consistency of the image. CUVAF images should be captured in a dim illuminated room to avoid reflections.

Conclusion

CUVAF is a valuable tool which should be included in every eye clinic and eye screening camps to assess sun light induced ocular diseases. CUVAF plays an important role in prevention of UV induced ocular diseases like pterygium and pinguecula associated with sun exposure even before the clinical manifestation of ocular symptoms. It can be also helpful in future studies concentrating on UV and ocular effects.

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