Manuscript Review

Validation of grading scales for contact lens complications

Efron N, Morgan PB, Katsara SS Ophthal Physiol Opt. 2001, 21: 17 - 29.

Clinical grading scales provide a means by which practitioners can assess the severity and evaluate the progression of complications associated with contact lens wear. A number of authors (1,2,3) have described the use of scales for grading adverse responses such as corneal staining, conjunctival/bulbar redness and contact lens-associated papillary conjunctivitis (CLPC).

Macropunctate Corneal Staining (CCLRU Grade Type 2) Click on image to magnify	Patch Corneal Staining (CCLRU Grade Type 4) Click on image to magnify

In clinical research and practice it is common to use subjective ratings of the degree of severity and change of clinical conditions that commonly occur. Many authors have described the need for a grading system to possess high reliability and also the power to discriminate accurately. Such scales should be capable of being administered quickly and simply.

Chong et. al. (4) examined the repeatability of discrete and continuous anterior segment grading scales. They suggest that grading scales that are coarse generally allow less sensitivity in the detection of meaningful clinical changes and point out that practitioners often overcome this limitation by adopting half-point scales, or by assigning plus and minus symbols next to an integer scale. They also suggest that by increasing the number of intervals to make the grading scale finer may reduce the degree of concordance between repeated measurements of the same clinical event (5). Finer scales have the advantage of being more sensitive to detect clinical difference (5).

This review examines a paper that describes the features of a number of different grading systems for use during contact lens wear (6).

The authors examined four illustrative contact lens grading scales and described them as the 'Efron', 'Annunziato', 'CCLRU' and 'Vistakon' systems. The images depicted in the Efron and Annunziato systems were painted by the ophthalmic artists Terry Tarrant and Monte Lay respectively, whereas those images represented in the CCLRU and Vistakon scales were developed from a collection of clinical photographs.

The aim of the study was to validate the four grading systems by way of documenting differences in their grading precision and reliability and to offer advice to practitioners of the expected performance of each system in a clinical setting. The authors chose the three complications that are common to each of the grading scales i.e. corneal staining, ocular redness and papillary conjunctivitis. Thirty images presented on a computer monitor of each of the complications were independently graded by 13 optometrists to the nearest 0.1 grading unit using each of the four systems. This same test was repeated some two weeks later using a different randomised sequence.

This study attempted to define the precision and reliability of the clinical grading techniques. Precision is defined as the closeness of agreement between independent test results obtained under specific conditions whereas reliability is the ability of the grader to give similar results time after time. The authors posed two questions:

• 'Do some observers grade significantly higher or lower than other observers?'
  
• 'How consistently can an observer judge a given non-varying condition on two occasions?'

The result of this study demonstrated that there are differences in the use of the four grading systems with respect to precision. Such differences need to be taken into account when comparing grading scores obtained using the different scales. This study also indicates that there are significant differences in grading precision between observers. The authors suggest using a correction factor to normalise the grading scores. The use of a training program to standardize the clinicians will also increase the degree of concordance between observers using such grading scales.

The overall reliability result was 0.63 grading scale units, giving 95% confidence limits of ± 1.23 grading scale units. The authors suggest that a change or difference in severity of greater than 1.2 grading scale units, when detected using any of the four systems investigated in the study, can be taken to be both clinically and statistically significant. It is important to remember that this study was conducted using untrained observers. This reinforces the need for all clinicians participating in research studies to undergo a rigorous training program to understand the application and implementation of any type of grading scale.

The study indicated that all four grading scale systems are validated for clinical use however the authors offer the following advice:

• Clinicians are advised to consistently use the same grading system
• Practitioners should develop an awareness of their own grading reliability

Grading scales offer the clinician the most effective way of monitoring the health of an eye wearing a contact lens. They allow for an accurate means of detecting change that can occur during lens use and provide the practitioner with the necessary information to intervene to minimize the risk of a chronic adverse reaction to the contact lens. Ideally, prior to contact lens wear, the baseline data for a range of clinical variables should be collected and then monitored throughout the course of the study or clinical assessment period.


References

1. Løfstrøm T, Andersen JS, Kruse A (1998). Tarsal abnormalities: a new grading system. Contact Lens Assoc Ophthalmol J. 24: 210 - 215.

2. Mackinven J, McGuinness CL, Pascal E, Woods R (2001). Clinical grading of the upper palpebral conjunctiva of non-contact lens wearers. Optom Vis Sci. 78: 13 - 18.

3. McMonnies CW, Chapman-Davies A (1987). Assessment of conjunctival hyperaemia in contact lens wearers. Part 1. Am J Optom Physiol Opt. 64: 246 - 250.

4. Chong T, Simpson T, Fonn, D (2000). The repeatability of discrete and continuous anterior segment grading scales. Optom Vis Sci. 77: 244 - 251.

5. Bailey IL, Bullimore MA, Raasch TW, Taylor HR (1991). Clinical grading and the effects of scaling. Invest Ophthalmol Vis Sci. 32: 422 - 432.

6. Efron N, Morgan PB, Katsara SS (2001). Validation of grading scales for contact lens complications. Ophthal Physiol Opt. 21: 17 - 29.