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Patients who complain of poor visual function after LASIK may have unstable tear film, which affects the smoothness of the ocular surface and disturbs vision. With the help of the functional visual acuity meter, clinicians can assess functional vision over 60 seconds and then address any instability of the tear film if necessary.
"Unstable tear film is the key to the pathogenesis of dry eye [in these patients] and can be the target for treatment of the symptoms and the visual disturbances," said Dr. Tsubota, professor and chairman of ophthalmology, Keio University School of Medicine, Tokyo.
Patients suspected of having unstable tear film can be evaluated using the functional visual acuity meter (FVAM, Nidek), a device developed and later updated by Dr. Tsubota and colleagues. The original device required that patients keep their eyes open for 10 seconds during the visual acuity test, which was impossible for some patients. With the updated FVAM, visual acuity is measured over 60 seconds with patients blinking as often as needed. Patients sit in front of a computer display and respond to the Snellen chart. When a correct answer is given, the Snellen chart will decrease in size and the visual acuity is measured. If a wrong answer is given, the Snellen chart is enlarged and visual acuity measured.
"But after punctal occlusion, the visual acuity stabilized," said Dr. Tsubota. "The fluorescein staining was gone. The functional visual acuity increased to 0.9 in the right eye and 1.0 in the left eye. So, not only are the symptoms gone, but this patient enjoyed increased functional visual acuity with the punctal plugs. In fact, the corneal topography improved."
Dr. Tsubota opted for punctal occlusion to stabilize the tear film. Although the irregular astigmatism could not be treated because of the DLK, the functional visual acuity did improve to 0.5 with punctal occlusion. "The patient was happier with the better functional visual acuity and a TFBUT improvement from 1 second to 10 seconds," he said.
Cataract patients also have experienced unstable tear film, affecting their functional visual acuity, he continued. Dr. Tsubota said he saw a 72-year-old female patient who had undergone cataract surgery the day before. Although her UCVA was 1.0, she complained of poor functional visual acuity and a foreign body sensation. Examination of the ocular surface revealed unstable tear film and poor functional vision. With punctal occlusion, there was an increase of tear meniscus, improved tear film, and better functional vision, he said.
"Tears are a very important nutrient supply and are necessary for maintenance of the ocular surface," explained Dr. Tsu bota. "So far, the most effective treatment [for dry eye] is punctal occlusion."
He recommended both upper and lower punctal occlusion to help the accumulation of a small amount of tears on the ocular surface, which has been shown to provide a "remarkable result." He also suggested using artificial tears without preservatives.
"It is very important for the surgeon to pay attention to the stability of the tear film to ensure quality of vision, especially after refractive surgery," he concluded.