14.8 Photographic Screening

The gold standard for photographically detecting DR is seven-field stereoscopic fundus photography covering 65–75 degrees of the fundus. This method is costly, not liked by patients because of its higher flash intensity than digital imaging and need for more photographs, and impractical for screening

purposes; it is used in research protocols rather than clinical care.3,5,28,29,36 There are many strate-

gies for photoscreening, making comparison of different techniques difficult. Several of the strategies that have undergone pilot trials follow:

1.Mydriatic fundus photography with various

numbers of fields (2, 3, 5, 6) and various degrees captured per field (30, 45, 60).36,61,9,24,28,42,48

2.Nonmydriatic 45 degree fundus photography with various numbers of fields (1, 2, 4).3,21,61,62,63,64,11

3.Staged screening comprised of stage single-field nonmydriatic photography followed by singlefield mydriatic photography for ungradable images with stage 1 efforts followed by slitlamp biomicroscopy by an ophthalmologist for ungradable images with stage 1 and 2 efforts.

4.Single-field nonmydriatic fundus photography for patients < 50 years old and single-field mydriatic fundus photography for patients 50 years old.

5.For type 2 diabetics, three-field 45 degree nonmydriatic fundus photographs with dilation as needed to obtain satisfactory image quality. For

type 1 diabetics, five-field 45-degree mydriatic fundus photographs.26

An understanding of the trade-offs incurred by different strategies compared to seven-field imaging is helpful in choosing a preferred method of photoscreening. Underascertainment of DR by methodologies using fewer than seven fields has been estimated to range from 5 to 15%.65 Using TIFF and JPEG compressed images, digital images are associated with 86–92% and 72–74% sensitivity, respectively, compared to using color slides.36 Approximately 27% of cases of PDR and 8–15% of all DR lesions occur outside the area photographed with single-field 45 degree nonmydriatic photography.39 Over time and after weighing these relative drawbacks, the trend has been toward single-image screening methods (Table 14.2). Adding more fields adds to the cost, increases the probability of poor quality images and

leads to extra referrals for ophthalmic examination without sufficient compensatory improvement in case finding.66

The settings for screening have varied, but include university diabetes clinics, private practice offices, hospital endocrinology clinics, nursing homes, com-

munity health clinics, and mobile units in vans.3,21,36,42,66–68 Methods of notifying the target

population that screening will occur may be important.27 In some models multimedia advertisement of screening is used, whereas in others there is no advertising, but only routine use of a modality in the course

of diabetic, nonophthalmic care.11 The assessment of screening techniques may need to take into account the social environment. A successful screening approach in an urban environment with tertiary care medical centers may differ from the approach adapted to a rural environment with few eye care professionals.24 Screening for certain subgroups of the population, while a laudable goal, has proven impractical. For example, in nursing homes, the relatively high proportion of subjects who are unable to cooperate or undergo treatment even if amenable disease is discovered has rendered the cost per case too high.42

Technical and practical issues arise in photographic screening. Because the photographs are taken by ancillary staff in a general clinic, training is important in recognizing unusable images and repeating photography until a usable image can be obtained. With training, such staff perform as well as ophthalmic photographers in producing gradable images.36 Staff must be trained on the importance of physiologic mydriasis in a darkened room, and feedback on photographic quality is necessary to reduce the number of artifacts that degrade image quality. Photography of the second eye may need to be delayed for a time after the first eye photograph to allow for spontaneous redilation. It seems to be necessary to photograph both eyes and not one. A strategy of photographing only one eye results in a 9% rate of false negatives.62 Although DR is usually

a symmetric condition, it is asymmetric often enough that both eyes need to be screened.62,73

Many have worried that nonstereoscopic photographic screening methods will miss DME, yet the presence of hard lipid exudates within 1 disk diameter of the center of the macula is >90% sensitive in detecting DME, and lipid can be sensitively detected with nonstereoscopic fundus photography.36 Moreover, most of the cases of DME without lipid exudates are recommended for referral based on other screening criteria.36

Film-based photographic screening methods are now a chapter in history, not a viable method.68 Digital methods allow for the possibility of machine-based interpretation, teleophthalmic interpretation, and more rapid turnaround in interpretation compared to film-based systems.5 Who should interpret the digital fundus images remains controversial, but it appears that nonophthalmologists can perform well. With 40 h of training by an ophthalmologist, grading of fundus photographs by endocrinologists matched the gold standard results of consensus gradings by two experienced ophthalmologists in detecting DR.24 Various systems have

used technicians, opticians, nurse practitioners, internists, and optometrists for grading.9,47,74

14.9 Nonmydriatic Photography

The reported rates of ungradable images using a nonmydriatic camera range from 4 to 34%.11,21,30,68,75

These cameras are easy to use; training to a reasonable standard of proficiency can be attained within 1 h. Level of training in ophthalmic photography does not seem to influence image quality much, a favorable attribute for consideration in screening programs.76 Higher rates of ungradable images lead to higher rates of referral for dilated eye examinations by eye care professionals because of doubt by the photography graders regarding adequacy of the image to exclude the risk of missing referable retinopathy. This is seen by different subgroups in the care team as a positive or a negative. Where numbers of professionals are high relative to the proportion of patients to be seen, a higher rate of referral is seen as a positive. Where numbers of professionals are low relative to the number of patients to be seen, a higher rate of referral is seen as a negative and has led to adoption of mydriatic screening over nonmydriatic screening as a response.24 In Singapore, where national photographic screening for DR by trained family practitioners using a 45 degree fundus photograph obtained with a nonmydriatic camera has been in place since the early 1990s, only 38% of the patients referred actually had DR, reflecting a much poorer specificity for the technique in practice than under idealized study conditions.77 Similarly, in Gloucestershire, UK, the actual percentages of patients referred based on screening who, in fact, had no DR on actual clinical examination varied from 47.8 to 56.7% over the first 4 years of implementing a systematic screening program.78 It is recognized that most screening tests perform less well in real-world settings than in

settings based on a study design.55 In a study from Colorado, USA, family physicians reading nonmydriatic 45 degree fundus photographs failed to refer 10.2% of patients deemed needing a referral to an ophthalmologist by a secondary image grader who was an ophthalmologist.21 Nonmydriatic photography often requires placing the patient in a darkened room for a time and has been found to lengthen the screening process compared to a mydriatic screening procedure.24 There are metrics of fundus image quality other than percentage of ungradable images, such as grades of image quality and ability to detect referable DR, and all such metrics are beneficially influenced by mydriasis and negatively influenced by nonmydriasis.24 The perils of nonmydriatic fundus photography missing sight-threatening peripheral neovascular fronds have been documented, but despite admonitions that general practitioners become better direct ophthalmoscopists, the statistical evidence favors nonmydriatic photography over nonmydriatic ophthalmoscopy for detecting referable retinopathy.30

14.10 Mydriatic Photography

There are several objections raised whenever mydriatic methods of screening are considered. The first is that narrow angle glaucoma attacks may be triggered. The risk is low and has been estimated to be 1 in 7,000 examinations or lower.47,79 The second is that patients will object and refuse screening under these conditions. When mild mydriatic agents such as tropicamide 1% are used and only a single dose is given, patient acceptance has been high.24 The ability to drive after mydriasis is a third objection, particularly in those over 55 years of age. Somewhat counterintuitively, pharmacologic dilation has been reported to speed screening for DR compared to nonmydriatic screening.24 The choice of the mydriatic used may be important. Patient acceptance of moderate mydriasis achieved with tropicamide 1% was reported to be good.24 Mydriatic screening methods are particularly useful in older patients with more miotic pupils. Mydriatic photography as a backup when nonmydriatic photography gives poor images can reduce the rate of ungradable images to <1%.21

14.11Risk Factors for Ungradable Photographs

In nonmydriatic photoscreening, increasing the number of fields imaged above two increases the number of cases deemed to have poor quality sets of images requiring referral.66 The rate of ungradable photo-

graphs decreases if mydriatic photoscreening is used rather than nonmydriatic photoscreening.24,61,75 In 12

studies using nonmydriatic photography, the median

and the range of ungradable photographs were 18.3%

and 4.0–42.3%, respectively.24,75,61,5,68,11,21,47,63,71,64

By comparison, among six studies using mydriatic photography, the median and the range of ungradable

photographs were 3.7% and <1–5%, respectively.24,75,61,21,47,9 Increasing age is associated with

an increasing rate of ungradable photographs whether by nonmydriatic or mydriatic photographic technique, because of both an increasing effect of

cataract and a decreasing pupillary diameter alone or after pharmacologic mydriasis.5,24,61,71,75 There is

a floor for the percentage of ungradable photographs. In the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR), in which mydriasis and professional ophthalmic photographers were used in a population-based study, 1.5% of participants had ungradable photographs.17

14.12 Number of Photographic Fields

Whether a greater number of photographic fields are associated with a higher rate of detection of referable retinopathy at a reasonable price of more time, expense, and increased patient dissatisfaction with bright flashes is controversial.28 Some studies suggest that more fields increase the rates of referable retinopathy. Others suggest that no clinically important gains are made by this provision.61 The trend in the literature seems to be that single-field photography predominates based on adequate performance and simplicity.

14.13 Criteria for Referral

The criteria for referral for a complete, dilated eye examination by an ophthalmologist are not identical across studies. All screening methodologies