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Purpose: To investigate the rapid alterations in value and fluctuation of ocular wavefront aberrations during the interblink interval. Methods: Forty-two volunteers were examined with a WASCA Wavefront Analyzer (Carl Zeiss Meditec AG) using modified software. For each subject, 150 images (about 6 frames/second) were registered during an inter-blink period. The outcome measures were spherical and cylindrical refraction and root-mean-square (RMS) values for spherical, coma, and total higher order aberrations. Fifth order polynomials were fitted to the data and the fluctuation trends of the parameters were determined. We calculated the prevalence of the trends with an early local minimum (type 1). The tear production status (Schirmer test) and tear film break-up time (BUT) were also measured. Results: Fluctuation trends with an early minimum (type 1) were significantly more frequent than trends with an early local maximum (type 2) for total higher order aberrations RMS ( P =.036). The incidence of type 1 fluctuation trends was significantly greater for coma and total higher order aberrations RMS ( P =.041 and P =.003, respectively) in subjects with normal results in the BUT or Schirmer test than in those with abnormal results. In the normal subjects, the first minimum of type 1 RMS fluctuation trends occurred, on average, between 3.8 and 5.1 seconds after blink. Conclusions: We suggest that wavefront aberrations can be measured most accurately at the time after blink when they exhibit a decreased degree of dispersion. We recommend that a snapshot of wavefront measurements be made 3 to 5 seconds after blink. [ J Refract Surg. 2009;25:59–68.]

In most parts of the world, the Schirmer test (ST) is still the main test used by optometrists for the assessment of tear adequacy in the screening of potential contact lens wearers and as an aid in the diagnosis of "dry" eye. We tested the reliability of a 1-min ST in nine normal Hong Kong-Chinese (HK-Chinese) subjects during five to seven visits over a period of 2 weeks. For 4 of the subjects, the test consistently measured 0 mm/1 min, and 68% of the test results were less than 6 mm/1 min, a value suggested as the lower limit for normal asymptomatic eyes. The results obtained were inconsistent and it is concluded that the ST is unreliable and of little clinical value in this population.

In Reply. —I appreciate Dr Lambert's concern for data analysis. While I did not go into detail regarding the diagnosis of conjunctivitis sicca in my nine cases, I stated that all had Schirmer test values of less than 10 mm of wetting in five minutes. I also referred to their subjective symptoms and their response to a tear substitute. Were this the central theme of my study, I would have included such aspects as tear osmolarity and lactoferrin content studies recently reported by Farris 1,2 with rose bengal stain, lysozyme content, and electrophoresis (older criteria), which Dr Lamberts does not mention. From his own article, to which he does allude, I might also include the dimensions and qualities of the tear strip as visualized at the slit lamp. Yet the latter, as described by the authors themselves, are even more subjective and variable than are the Schirmer test readings. With

To the Editor.— Decreased lacrimation is not usually regarded as a feature of amyotrophic lateral sclerosis. In the course of treating ten such patients over the last two years, decreasedlacrimation as measured by the Schirmer test was observed. Since this is a devastating disease of unknown etiology, it is to be hoped that decreased lacrimation will be confirmed by others and explored as a new lead. The Schirmer tear test is performed by placing the tip of a strip of filter paper on the conjunctiva of the lower lid at the juncture of the outer and middle third of the lid. The patient closes his eyes lightly and after five minutes the length of filter paper wet by tears is recorded. Less than 15 mm of wetting is regarded as evidence of decreased tear production. Normal eyes can wet the entire 35-mm length in less than five minutes.

To the Editor.— In recent years there has been an increase in the number of persons seeking medical attention with the chief complaint of "itchy-burning eyes." Typically, the patient complains of smarting, burning, itching, excessive tearing, and redness of the eyes. On examination, the ophthalmologist frequently finds little objective physical evidence of ocular irritation. The usual signs of conjunctival inflammation, including congestion of vessels, follicle formation, papillae, and discharge are not found. Rarely, there is minimal conjunctival (either bulbar or palpebral) injection. The Schirmer test is negative and there is no demonstrable hypersensitivity to cosmetics or drugs as indicated by the presence of an eosinophilia. The authors reviewed and abstracted 50 cases of patients presenting to the Jules Stein Eye Institute clinic with these symptoms. Following is a summary of findings from these patients. Of the 50 patients, 49 were women and one was a man. Forty-six had consulted ophthalmologists

X-linked hypohidrotic ectodermal dyplasia (XLHED) is the most common form of ectodermal dysplasia. It often presents with ocular symptoms, already in early childhood. Multiple ophthalmological tests are available, but in early childhood only tests of lower invasiveness can be applied. We have evaluated tear film tests and ocular surface staining as screening methods in pediatric patients with signs of ectodermal dysplasia. These tests may also be used in adults with confirmed XLHED to determine the severity of ocular surface disease. Twelve children and 14 adults with XLHED were subjected to a panel of tests including the ocular surface disease index (OSDI), non-invasive measurement of tear film break-up time (NIBUT), osmolarity, Schirmer test, lissamine green staining, fluorescein staining, meibography and infrared thermography. Sensitivity and specificity were determined for single tests and selected test combinations. For adults with XLHED, OSDI, NIBUT and osmolarity were the best single routine tests (sensitivity between 84.6% and 85.7%; specificity of 100%). Their combination increased the sensitivity to 92.8%. Meibography yielded optimal results (100% sensitivity and specificity). Infrared thermography revealed a typical pattern for XLHED. In children with XLHED, NIBUT or OSDI were the most convincing single tests (sensitivity of 90.9% and 83.3%, respectively; specificity of 100% each), combination of which increased the sensitivity to 100%. More invasive tests such as meibography and infrared thermography led to good results if they were tolerated. Tear film tests can help to establish an early diagnosis in individuals with suspected XLHED, even before genetic test results are available. Meibomian gland disorder and resulting hyperevaporative dry eye are typical features of XLHED. Once the diagnosis is made, tear film tests are an important instrument to establish an effective therapy of dry eye disease.