본 연구에서는 소프트콘택트렌즈의 재질이나 착색여부에 따라 눈물막 안정성에 미치는 영향을 알아보고 렌즈 착용시간 경과에 따른 눈물막 안정성의 변화를 착용자의 눈물량으로 나누어 분석하였다.
본 연구의 목적에 동의하고 안질환 및 안과적 수술경험이 없으며 소프트콘택트렌즈 착용이 가능한, 각막 난시량이 ?0.75D 이하의 근시나 정시를 가진 20대 120안을 대상으로 하였다. 정상안과 건성안, 렌즈착용 경험군과 미경험군, 렌즈착용 경험여부에 따른 정상안과 건성안을 분류하여 렌즈착용 30분 후와 6시간 후에 비침입성 눈물막파괴시간, 렌즈 중심안정위치, 눈물막 깨짐 시작부위, 순목횟수를 측정하고 자·타각적 증상을 비교하였으며 눈물막 안정성에 영향을 미치는 요인을 분석하였다.
눈물량에 따라 눈물막 안정성을 비교하였을 때, 렌즈재질과 관계없이 정상안과 건성안 모두 렌즈착용 시간이 경과함에 따라 눈물량이 감소하였으며, 정상안의 경우 건성안에 비해 눈물량이 많아 감소비는 더 높게 나타났다. 렌즈중심안정위치 비교 시에는 정상안에 비해 건성안에서의 렌즈중심 이탈이 높게 나타났으며, 투명렌즈에 비해 써클렌즈에서 그 정도가 높게 나타났으나, 렌즈착용 시간이 경과함에 따라 정상안과 건성안 모두 렌즈움직임이 동공 중심으로 안정적인 것을 확인하였다. 또한 건성안의 경우 눈물량이 적어 렌즈의 중심안정위치 변화가 크지 않았다. 눈물막 깨짐 시작부위의 비교에서는 정상안과 건성안 모두 코방향보다는 귀방향, 상방보다는 하방, 중심부보다는 주변부에서 눈물막 깨짐 시작 비율이 높았으며, 중심부와 주변부에서는 확연한 차이를 나타내었다. 반면, 단위면적 당 눈물막 깨짐 개수를 측정하였을 때에는 중심부에서도 주변부에서와 유사한 눈물막 깨짐 개수가 측정되었으나, 재질에 따라 눈물막 깨짐 개수의 차이가 나타나는 것을 확인할 수 있었다. 순목횟수의 변화는 자·타각적 증상과 밀접한 관련이 있는 것으로 나타났는데 정상안에 비해 건성안에서의 순목횟수가 높게 측정되었고, 투명렌즈 착용에 비해 써클렌즈 착용 시 순목횟수가 높게 측정되었으며 자·타각적 증상의 점수와도 상관관계가 높은 것으로 나타났다. 또한 착용시간이 경과함에 따라 순목횟수도 증가하였는데, 렌즈착용 미경험군의 건성안에서 순목횟수가 가장 높게 나타났다.
렌즈착용 경험 여부에 따른 눈물막 안정성을 비교하였을 때, 렌즈재질과 관계없이 렌즈착용 시간이 경과함에 따라 눈물량이 감소하였으며 렌즈착용 경험군과 미경험군 모두 써클렌즈에 비해 투명렌즈에서 눈물량의 감소비가 높은 것을 확인하였다. 렌즈중심안정위치는 경험군에 비해 미경험군에서 중심이탈이 높게 나타났으나 착용시간이 경과함에 따라 렌즈가 동공 중심으로 이동하여 안정적인 것을 확인하였다. 이 결과로 착용시간이 증가함에 따라 눈물량은 감소하였지만 렌즈중심안정위치에 영향을 미치는 것을 알 수 있었다. 눈물막 깨짐 시작 비율의 비교에서 경험군과 미경험군 모두 코방향보다는 귀방향에서, 상방보다는 하방에서, 중심부보다는 주변부에서 눈물막 깨짐 시작 비율이 높게 나타났으나 렌즈착용 경험 유무에 크게 영향을 받지 않는 것으로 생각되었다. 착용시간이 경과함에 따라 경험군에 비해 미경험군이 써클렌즈 착용 시 투명렌즈에 비해 주변부에서의 눈물막 깨짐 시작 비율이 높게 나타났다. 반면, 중심부와 주변부에서 눈물막 깨짐 시작 비율의 가장 큰 차이를 나타내었으나 단위면적 당 눈물막 깨짐 개수의 비교에서는 주변부보다는 중심부에서 눈물막 깨짐 개수가 높게 측정되었으며, 렌즈재질에 따라 경험군과 미경험군 간의 눈물막 깨짐의 부위가 다르게 나타났다. 순목횟수의 비교에서는 착용시간 경과에 따라 경험군에 비해 미경험군에서의 순목횟수가 증가비가 높았으며 투명렌즈와 써클렌즈 간의 차이는 미미하게 나타났다. 이는 자·타각적 증상과도 관련이 있었으며 렌즈재질이나 착색여부에 따라 다소 차이를 보였으나 대체로 경험군에 비해 미경험군에서 자·타각적 증상의 총점이 높았다.
렌즈착용 경험 여부에 따라 착용군과 미경험군으로 나누고 다시 각 군을 정상안과 건성안으로 나누어 눈물막 안정성을 비교하였을 때, 렌즈착용 미경험군의 건성안에서 hilafilcon B 및 nelfilcon A 재질의 써클렌즈 착용 시 NIBUT의 값이 가장 낮게 측정되었던 반면, 착용시간이 경과함에 따라 경험군의 정상안에서 hilafilcon B 및 nelfilcon A 재질의 투명렌즈 착용 시 NIBUT의 값의 감소가 가장 크게 나타났다. 렌즈중심안정위치는 착용시간이 증가함에 따라 동공 중심쪽으로 위치하였으며, 렌즈착용 경험군은 정상안과 건성안 모두 hilafilcon B 재질의 투명렌즈 착용 시 가장 안정적으로 나타났다. 따라서 착용시간의 증가는 눈물량에 영향을 미치며 이에 따라 렌즈중심안정위치가 영향을 받는 것을 알 수 있었다. 눈물막 깨짐 시작 비율은 렌즈착용 경험여부에 관계없이 정상안과 건성안 모두 hilafilcon B 재질의 투명 및 써클렌즈 착용 시 코방향보다는 귀방향에서, 상방보다는 하방에서 눈물막 깨짐 시작이 높게 나타났으며 중심부와 주변부의 비교에서는 주변부에서 눈물막 깨짐 시작 비율이 차이가 높게 나타났으며 투명렌즈와 써클렌즈 간에는 미미한 차이를 나타내었다. 단위면적 당 눈물막깨짐 개수의 측정에서는 착용여부에 관계없이 정상안보다는 건성안에서의 눈물막 깨짐 개수가 높게 측정되었으며 착용시간이 경과함에 따라 주변부와 중심부 모두 눈물막 깨짐 개수가 증가하는 것을 알 수 있었다. Nelfilcon A 재질 렌즈착용 시에도 hilafilcon B 재질 렌즈착용 시와 유사하게 코방향보다는 귀방향에서, 상방보다는 하방에서 눈물막 깨짐 시작 비율이 높게 나타났으며 중심부와 주변부의 비교에서는 렌즈착용 경험군과 미경험군 모두 정상안에 비해 건성안에서 눈물막 깨짐 시작 비율이 높게 나타났다. 단위면적 당 눈물막 깨짐 개수의 비교에서는 경험군과 미경험군 모두 건성안에서 nelfilcon A 재질의 써클렌즈 착용 시 눈물막 깨짐 개수가 가장 높게 측정되었으나 경험군의 건성안에서는 주변부보다 중심부의 눈물막 깨짐 개수가 많게 측정되었고, 미경험군의 건성안에서는 중심부보다 주변부에서 눈물막 깨짐 개수가 더 많은 것을 확인하였으며, 두 렌즈간의 차이로 볼 때 같은 고함수, 비이온성 렌즈라 하더라도 렌즈재질에 따라 눈물막 깨짐 개수가 다르게 나타나는 것을 알 수 있었다. 순목횟수와 자·타각적 증상은 hilafilcon B 및 nelfilcon A 재질의 렌즈 모두 렌즈착용 미경험군의 건성안에서 가장 높게 나타났으며, 투명렌즈에 비해 써클렌즈 착용 시 순목이 높게 나타나는 것을 확인하였고, 자·타각적 증상의 비교에서는 렌즈착용 경험 여부와는 관계없이 정상안에 비해 건성안에서 증상이 높은 것을 알 수 있었다.
본 연구에서는 렌즈착용 시 건성안 뿐만 아니라 정상안에서도 착용초기에는 눈물량이 감소되어 각막에서 렌즈중심안정위치가 불안정해지며 렌즈의 중심이탈로 착용감이 저하되고, 그로 인한 불편함으로 순목횟수가 증가되는 것을 알 수 있었으며, 렌즈착용 시간 경과에 따른 눈물량의 감소는 렌즈표면에 요철이 확인된 써클렌즈 뿐만 아니라 균일한 표면을 가진 투명렌즈에서도 부위별 눈물막 깨짐 시작 비율에 변화를 유발하는 것을 확인함으로써 눈물막 안정성에 영향이 있음을 밝혔다. 동일재질의 투명 및 써클렌즈라 하더라도 착용자의 눈물량과 착용시간을 고려하여 눈물막 안정성 감소에 최소한의 영향을 미치며 시력의 질을 높일 수 있는 콘택트렌즈 설계의 개발이 필요할 것으로 생각된다. 또한 콘택트렌즈 초기 착용자나 눈물량이 부족한 건성안에서 렌즈착용 시에는 렌즈재질과 종류에 따라 정상안이나 기착용자와는 다른 눈물막 안정성을 보일 수 있으므로 콘택트렌즈 착용에 따른 가이드라인의 구체적인 사항을 제안하는 바이다.

This study was performed to investigate the effect of lens materials or pigmentation of soft contact lenses on tear film stability and analyze changes in tear film stability divided by the wearer’s tear volume according to the time of lens wearing.
One hundred and twenty eyes with myopia having the corneal astigmatism lower than ?0.75D or emmetropia in their 20s, who agreed with the purpose of the study, were free from any ocular disease and ophthalmic surgery experience, able to wear soft contact lenses were chosen as the subjects. They were classified into normal eyes and dry eyes, into experienced wearers and unexperienced wearers, and into normal eyes and dry eyes according to the experience of lens wearing, and their non-invasive tear film break up time (NIBUT), lens centration, the first appearing area of tear film break-up and blink rate were measured after 30 minutes abd 6 hours of lens wearing and the objective/subjective symptoms were compared. The factors affecting their tear film stability were further analyzed.
In a comparison of tear film stability according to tear volume, tear volume decreased in both normal eyes and dry eyes with the increase of lens wearing time regardless of the lens materials, and the ratio of reduction was higher in normal eyes than in dry eyes because of more initial tear volume in normal eyes. When comparing lens centration, more lens decentration was shown in dry eyes and in circle lens wear compared with it in normal eyes and in clear lens wear however, lens movement was stable to the direction of the pupil center in both normal eyes and dry eyes with the increase of lens wearing time. In addition, little change in lens centration was observed in dry eyes because of less tear volume. In a comparison of the first appearing area of tear film break-up, in both normal eyes and dry eyes, the first appearing ratio of tear film break-up was higher in the temporal area than in the nasal area, in the lower area than in the upper area, in the peripheral area than in the central area. There was a statistically significant difference between the center area and the peripheral area. On the other hand, the number of tear film break-up in the central area was similar to that in the peripheral area when measuring the number of tear film break-up per unit area however, there was a difference in the number of tear film break-up according to the lens materials. It turned out a change in blink rate was closely related to objective/subjective symptoms since the higher blink rate was measured in dry eyes than in normal eyes, and in circle lens wear than in clear lens wear. The high correlation between blink rate and the scores of objective/subjective symptoms was confirmed. In addition, the blink rate was increased with the increase of lens wearing time, and it was the highest in dry eyes of unexperienced wearers.
In a comparison of tear film stability according to the experience of lens wearing, tear volume was decreased with the increase of lens wearing time regardless of the lens materials. It was also found that the reduction ratio of tear volume was higher in clear lens wear than circle lens wear in both experienced and unexperienced wearers. As for lens centration, higher lens decentration was shown in unexperienced wearers than in experienced wearers however, the lenses moved toward the pupil center with the increase of lens wearing time and became stable. As a result, with the increase of lens wearing time, tear volume declined however, lens centration tended to be stable. In a comparison of the first appearing ratio of tear film break-up, a higher starting ratio of tear film break-up in the temporal area than in the nasal area, in the lower area than in the upper area and in peripheral area than in center area in both the experience group and the inexperienced group however, it was assumed that it was not greatly affected by the experience of lens wearing. With the increase of lens wearing time, a higher starting ratio of tear film break-up in the peripheral area was observed in the unexperienced wearers compared with the experienced wearers when wearing circle lenses compared with clear lenses. In contrast, there was the biggest difference in the starting ratio of tear film break-up between the center area and the peripheral area however, in a comparison of the number of tear film break-up per unit area, the higher number of tear film break-up was measured in the center area than in the peripheral area. There was a difference in tear film break-up area according to the lens material between the experienced and the unexperienced wearers. In a comparison of blink rate, with the increase of lens wearing time, the increase rate of blink rate was higher in the unexperienced wearers than in the experienced wearers, and there was a negligible difference between clear lenses wear and circle lenses wear. It showed the correlation with objective/ subjective symptoms, and there was somewhat difference according to lens materials or pigmentation of the lenses however, the total score of objective/ subjective symptoms was usually higher in the unexperienced wearers than in the experienced wearers.
The subjects were divided into the experienced and the unexperienced wearers according to the experience of lens wearing, and then each group was further divided into normal eyes and dry eyes. When tear film stability was compared, the lowest NIBUT value was measured in dry eyes of the unexperienced wearers when they wore circle lenses made of hilafilcon B and nelfilcon A, while with the increase of lens wearing time, the highest decline in NIBUT value was shown in normal eyes of the experienced wearers when they wore the clear lenses made of hilafilcon B and nelfilcon A. As for lens centration, the lenses moved toward the pupil center with the increase of lens wearing time, and it was most stable when wearing the clear lenses made of hilafilcon B in both in normal eyes and dry eyes of the experienced wearers. Thus, it was found that the increase of the lens wearing time affected tear volume, and lens centration was accordingly affected by that. As for the starting ratio of tear film break-up, the first appearing of tear film break-up was higher in temporal area than in nasal area, in lower area than in upper area, in both normal eyes and dry eyes in wearing clear and circle lenses made of hilafilcon B regardless of the experience of lens wearing, while the difference in the starting ratio of tear film break-up was higher in the peripheral area in a comparison between center area and peripheral area. There was slight difference between clear lenses wear and circle lenses wear. In a measurement of the number of tear film break-up per unit area, the higher number of tear film break-up was measured in dry eyes than in normal eyes regardless of lens wearing, and it was found that the number of tear film break-up increased in both peripheral area and center area with the increase of lens wearing time. Also, when wearing lenses made of nelfilcon A, the starting ratio of tear film break-up was higher in temporal area than in nasal area, and in lower area than in upper area like wearing lenses made of hilafilcon B, while in a comparison between center area and peripheral area, both the experienced and the unexperienced wearers had higher starting ratio of tear film break-up in dry eyes than in normal eyes. In a comparison of the number of tear film break-up per unit area, the highest number of tear film break-up was measured in dry eyes of both the experienced and the unexperienced wearers when they wore circle lenses made of nelfilcon A, while the higher number of tear film break-up was observed in center area than in peripheral area. There was more tear film break-up in the peripheral area than in the center area in dry eyes of the unexperienced wearers. In addition, from the difference between the two lenses, the number of tear film break-up differed depending on the lens materials, even high water content and nonionic lenses in same FDA group. The highest blink rate and objective/subjective symptoms were shown in dry eyes of the unexperienced wearers for both lenses made of hilafilcon B and nelfilcon A, and the blink was higher when they wore circle lens compared with clear lenses. In addition, in a comparison of the objective/subjective symptoms, the symptoms were higher in dry eyes than in normal eyes regardless of the experience of lens wearing.
From the results, it was found that tear volume declines in normal eyes as well as dry eyes in early phase of lens wearing, and it made lens centration on the cornea unstable, resulting in the increased blink rate induced by lens decentration, a cause of discomfort. In addition, a decline in tear volume with the increase of lens wearing time had an impact on tear film stability since it induced a change in the starting ratio of tear film break-up by area in clear lenses with even surface as well as circle lenses with uneven surface. It suggests that it would be necessary to develop a contact lens design that has the minimum impact on a decline of tear film stability and increase the visual quality, considering the wearer’s tear volume and the lens wearing time even when wearing clear and circle lenses made of the same materials. In addition, the new lens wearers or the dry eyes lacking tear volume may show different tear film stability from normal eyes or the experienced wearers according the materials and the kind of contact lens thus, this study suggests concrete matters for guidelines of wearing contact lenses.