Tuesday, April 15, 2008

Study: Sensitivity and dryness

Here's one for everybody with that classic "menthol" sensation:

Conjunctival and corneal pneumatic sensitivity is associated with signs and symptoms of ocular dryness.
Situ P, Simpson T, Fonn D, Jones LW.
Invest Ophthalmol Vis Sci. 2008 Apr 4 [Epub ahead of print]

Purpose: To investigate the relationships between dry eye symptoms, corneal and conjunctival sensitivity to pneumatic stimulation, tear film stability and clinical ocular surface characteristics in symptomatic and asymptomatic subjects.

Methods: 97 subjects were enrolled and grouped by a questionnaire based single score for symptom of ocular dryness (none to trace= "non-dry", mild to severe= "symptomatic"); 43 were symptomatic and 54 were non-dry. Corneal (K) and conjunctival (C) sensitivity were measured using a computer controlled Belmonte pneumatic (room temperature) stimulus. Symptoms were assessed using Ocular Surface Disease Index (OSDI). Ocular surface staining with fluorescein (FL) and Lissamine Green (LG), non-invasive tear film break-up time (NIBUT), and the Phenol Red Thread test (PRT) were assessed.

Results: The symptomatic group showed lower K and C thresholds (p0.01), greater corneal FL staining and conjunctival LG staining, and shorter NIBUT than the non-dry eye group (all others p0.05). OSDI scores were higher in the symptomatic group (p0.001). K and C thresholds, NIBUT were inversely correlated with OSDI scores and corneal and conjunctival staining (all p0.05). K and C threshold and NIBUT (all p0.01) were positively correlated. Stepwise multiple regression analysis showed that ocular surface sensitivity and NIBUT were significant predictors of OSDI scores.

Conclusion: Ocular irritation assessed using OSDI is associated with ocular surface hyperesthesia to cooling, corneal epitheliopathy and tear film instability. Although cause and effect are unclear, our analysis shows that altered corneal and conjunctival sensory processing and tear film attributes are essential aspects of what characterizes dry eye.

Report: UV implicated in lasik dry eye?

This is remarkable. I've seen a lot of studies trying to pin down the cause(s) of dry eye after LASIK and it has surprised me how, over time, they're still finding more possible mechanisms. When I come across something this obvious (in a sense) newly discovered it's downright disturbing. Kudos to Dr. Barraquer for taking the time to study this.

OSN Supersite, April 7th
UV protection during LASIK lowers dry eye incidence, surgeon says

Dry eye after LASIK may result from ultraviolet light exposure from the excimer laser itself, according to a speaker here, and UV protection during the excimer laser ablation can lower the incidence of post-LASIK dry eye occurrence by 70%....

"In our clinical surgical experience, we have never seen such a syndrome after penetrating grafts, after lamellar grafts, after ... keratomileusis," she said. "What is the difference then between LASIK ... and grafts or refractive procedures before excimer? Well, the most obvious answer is the excimer laser."

Dr. Barraquer hypothesized that the UV light in the laser interacts with oxygen, producing ozone, and "every pulse is associated with an equal area of collateral damage" to the eye.

In order to test her theory, she conducted a randomized, controlled, open label clinical trial in which she performed LASIK on 300 eyes: 150 with the standard procedure and 150 with her protective procedure....

"With the protected technique you have almost 70% less possibility of getting dry eye syndrome and ... females have three times more possibility of having dry eye syndrome" when they receive the standard treatment, she said.

Abstract: Dry eye diagnosis

Dry eye diagnosis.
Khanal S, Tomlinson A, McFadyen A, Diaper C, Ramaesh K.
Invest Ophthalmol Vis Sci. 2008 Apr;49(4):1407-14

PURPOSE: To determine the most effective objective tests, applied singly or in combination in the diagnosis of dry eye disease. METHODS: Two groups of subjects-41 with dry eye and 32 with no ocular surface disease-had symptoms, tear film quality, evaporation, tear turnover rate (TTR), volume and osmolarity, and meibomian gland dropout score assessed.

RESULTS: The subjects with dry eye had TTR, tear evaporation, and osmolarity significantly different from that of healthy normal subjects. Cutoff values between the groups were determined from distribution curves for each aspect of tear physiology, and the effectiveness of the cutoff was determined from receiver operator characteristic (ROC) curves. Values of 12%/min for TTR, 33 g/m(-2)/h for evaporation, and 317 mOsmol/L for osmolarity were found to give sensitivities, specificities, and overall accuracies of 80%, 72%, and 77%; 51%, 96%, and 67%; and 78, 78%, and 79%, respectively when applied singly as diagnostic criteria in dry eye. In combination, they yielded sensitivities, specificities, and overall accuracy of 100%, 66%, and 86% (in parallel) and 38%, 100%, and 63% (in series), respectively. Discriminant function analysis incorporating these three factors in an equation allowed diagnosis with a sensitivity of 93%, specificity of 88%, and overall accuracy of 89%.

CONCLUSIONS: Tear osmolarity is the best single test for the diagnosis of dry eye, whereas a battery of tests employing a weighted comparison of TTR, evaporation, and osmolarity measurements derived from discriminant function analysis is the most effective.

Study: If it's bad for mice...

For those not inclined to take seriously the role of humidity in dry eye symptoms... or for those whose employers (!) don't, have a look at this study. They built an environmental model to illustrate the role of environment on the eye surface in mice.

See highlighted text in the abstract for what happened to the mice subjected to 15% humidity with airflow for six weeks. I know, too many polysyllabic words but trust me it's bad. And many of you are working in office environments that aren't all that much better than this.

What to do? Put a flea in the ear of the HR people... don some moisture chambers... get a humidifier... get vents redirected... check DryEyeTalk for more tips, especially about computer use.

A murine model of dry eye induced by an intelligently controlled environmental system.
Chen W, Zhang X, Zhang J, Chen J, Wang S, Wang Q, Qu J.
Invest Ophthalmol Vis Sci. 2008 Apr;49(4):1386-91.

PURPOSE: To establish a novel murine model of dry eye using an intelligently controlled environmental system (ICES).

METHODS: Thirty BALB/c mice aged 4 to 6 weeks were housed in the ICES in which the relative humidity, airflow, and temperature were maintained at 15.3% +/- 3% (mean +/- SD), 2.1 +/- 0.2 m/s, and 21 degrees to 23 degrees C, respectively, for 42 days. Thirty mice of similar age and housed in a normal environment were controls (relative humidity, 60%-80%; no airflow; temperature, 21 degrees -23 degrees C). The ocular surfaces of the animals in both groups were analyzed before and 3, 7, 14, 28, and 42 days after the experiment for aqueous tear production, corneal barrier function, conjunctival morphology, and goblet cell density. The level of apoptosis on the ocular surface also was assessed using active caspase-3 at 42 days.

RESULTS: A low-humidity environment was maintained constantly by the ICES. Animals in this environment had decreased aqueous tear production, increased corneal fluorescein staining, and marked thinning and accelerated desquamation of the apical corneal epithelium compared with control eyes. Squamous metaplasia of the conjunctival epithelium with decreased goblet cell density also developed in the animals housed in the ICES. Active caspase-3 was highly expressed on the ocular surfaces of the animals housed in the ICES at 42 days.

CONCLUSIONS: The biological and morphologic changes of dry eye induced by ICES in mice are similar to those in humans. This dry eye environment appears to upregulate apoptosis on the ocular surface.

Abstract: Use of digital cameras in corneal damage assessment

Documentation of corneal epithelial defects with fluorescein-enhanced digital fundus camera photography.
Dean SJ, Novitskaya ES, Moore TC, Moore JE, Sharma A.
Clin Experiment Ophthalmol. 2008 Mar;36(2):113-8

The advent of digital photography in the ophthalmic setting has provided not only a means of documenting pathology, but with instantaneous results, it is possible to aid clinical diagnosis and management. This study was designed to demonstrate the ability to image corneal epithelial lesions stained with fluorescein, with a digital fundus camera set on fluorescein angiography settings. The contrast of this technique demonstrated both gross and subtle corneal epithelial lesions better than traditional methods. The results obtained demonstrated the high sensitivity and high contrast images this technique can facilitate in every ophthalmic practice equipped with a fundus camera with digital fluorescein angiography capability.

Study: Dry eye risks for diabetics after cataract surgery

Looks like a straightforward study indicating diabetics are at distinctly higher risk for dry eye after cat surgery than people without diabetes.

Changes of tear film and tear secretion after phacoemulsification in diabetic patients.
Liu X, Gu YS, Xu YS.
J Zhejiang Univ Sci B. 2008 Apr;9(4):324-8

Objective: To evaluate tear film stability and tear secretion in patients with diabetes after phacoemulsification. Methods: Twenty-five diabetic cataract patients and 20 age-matched non-diabetic cataract patients as control underwent phacoemulsification. Tear film break-up time (TFBUT), Schirmer I test (SIT), corneal fluorescein staining, and dry eye symptoms were measured pre- and postoperatively. Results: Diabetics had a decreased preoperative TFBUT and SIT. TFBUT was reduced on Day 1 and recovered on Day 180 postoperatively in both groups. SIT was increased after phacoemulsification, but returned to preoperative levels by Day 180 in non-diabetics, whereas it was lower than preoperative level in diabetics. Positive corneal fluorescein staining was elevated in both groups, and returned to preoperative levels only in controls. Dry eye symptoms were similar to fluorescein staining in both groups. Conclusion: Tear secretion was reduced in diabetic cataract patients after phacoemulsification, which worsened dry eye symptoms and predisposed those patients to ocular damage.