Short-term comparative study of the effects of preserved and unpreserved topical levofloxacin on the human ocular surface

Assessment of Consistency in Assignment of Severe (Grade 3) Squamous Metaplasia to Human Bulbar Conjunctiva Impression Cytology Cell Samples

Nucleus-to-cytoplasm (N:C) characteristics of published images of human bulbar conjunctival cells designated as showing severe (grade 3) squamous metaplasia were retrospectively assessed. From publications over a 40-year period, measurements were made from images of cell and nucleus size (based on areas and dimensions) and four different calculations were made for nucleo-cytoplasmic (N:C) ratios. From 54 published images, the mean nucleus-to-cytoplasm area ratio (NU/CYT AREA ratio) was 0.145 +/- 0.077 (range 0.052 to 0.346), compared to two different reference set values of 0.069 +/- 0.017 and 0.080 +/- 0.021. Similarly, a nucleus-to-cytoplasm length ratio (as LNLONG) was 0.308 +/- 0.080 (range 0.191 to 0.475) compared to reference values of 0.226 +/- 0.032 and 0.236 +/- 0.034. Similar differences in reference values were obtained using two other N:C ratio calculations. A wide range of values was found for morphometric N:C indices from published images, especially those without a scale bar, indicating a high incidence of inconsistent grading assignments. Overall, only about 30% of the published images showed morphological features consistent with severe squamous metaplasia (i.e., with the rest neither enlarged nor showing substantially changed N:C ratios) with no substantial pictorial evidence indicating that cells from the human bulbar conjunctiva have pyknotic nuclei. Current evidence indicates that grade 3 squamous metaplasia cells should be substantially enlarged.

Goblet cells of the normal human bulbar conjunctiva and their assessment by impression cytology sampling

Goblet cells of the conjunctiva are the main source of mucus for the ocular surface. The objectives of this review are to consider the goblet cells as assessed by various histological, cytological and electron microscopy methods, and to assess the consistency of published reports (over more than 25 years) of goblet cell density (GCD) from impression cytology specimens from nominally healthy human subjects. Reported GCD values have been notably variable, with a range from 24 to 2226 cells/mm² for average values. Data analysis suggests that a high density of goblet cells should be expected for the healthy human conjunctiva, with a tendency toward higher values in samples taken from normally covered locations (inferior and superior bulbar conjunctiva) of the open eye (at 973 +/- 789 cells/ mm²) than in samples taken from exposed (interpalpebral) locations (at 427 +/- 376 cells/mm²). No obvious change in GCD was found with respect to age, perhaps because the variability of the data did not allow detection of any age-related decline in GCD. Analyses of published data from 33 other sources indicated a trend for GCD to be lower than normal across a spectrum of ocular surface diseases.

Sampling area selection for the assessment of goblet cell density from conjunctival impression cytology specimens

PURPOSE

To assess the impact of using different sampling areas (fields of view) on the reliability of goblet cell density (GCD) estimates from conjunctival impression cytology (CIC) specimens from healthy individuals.

METHODS

The CIC specimens were collected from the exposed nasal bulbar conjunctiva of 5 adult subjects (average age, 23 years) onto Biopore (Millicell) membranes and stained with Giemsa. A region from each of the specimens that contained abundant goblet cells was examined by light microscopy using a ×40 magnification objective lens, ×20 and ×10 lenses, the images were enlarged, and the goblet cells were marked and counted. The GCD values per square millimeter were calculated and then the impact of counting between 10 to many and 10 to few goblet cells assessed.

RESULTS

The mean GCD estimates at ×400 magnification, ×200, and ×100 were 950 ± 226, 620 ± 154 and 471 ± 158 cells per square millimeter, respectively; these values were statistically different (P<0.05). The GCD estimates could change by as much as ±31.6%, ±12.2%, and ±4.2% for differences of ±10 cells counted per image.

CONCLUSIONS

As a result of variability in goblet cell distribution across CIC specimens, the estimates of GCD can be expected to be different according to the sampling area used for goblet cell counts. Furthermore, the use of a small sampling area (high power field of view) is likely to result in an unacceptably large uncertainty (variability) in the GCD estimates.