|Year : 1989 | Volume
| Issue : 3 | Page : 112-117
A simple accurate method of cataract classification Cataract I
YR Sharma, RB Vajpayee, R Bhatnagar, Madan Mohan, RV Azad, Mukesh Kumar, Ram Nath
R. P. Centre for Oph. Sciences, ARMS, Ansari Nagar, New Delhi - 110 029, India
Y R Sharma
R. P. Centre for Oph. Sciences, ARMS, Ansari Nagar, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
A simple and accurate system of cataract classification using slit lamp and direct ophthalmoscope is reported. Lens opacities are classified into cortical (anterior and posterior), nuclear and posterior sub-capsular and each sub-type of opacity is graded, extent and density wise, using both slit lamp and direct ophthalmoscope. A circle representing enface view of opacity divided into 100 equal parts is used in calculating the area of each opacity. This classification takes into account both the area and depth of opacity in arriving at the total extent of sub-type of each opacity. For density determination, we do not recommend the use of a resolution target projection ophthalmoscope. Intra-observer and inter-observer variability studies using this classification system indicated that the classification system is fairly reliable.
Keywords: Cataract classification : opacity extent and density; Medical therapy of cataracts
|How to cite this article:|
Sharma Y R, Vajpayee R B, Bhatnagar R, Mohan M, Azad R V, Kumar M, Nath R. A simple accurate method of cataract classification Cataract I. Indian J Ophthalmol 1989;37:112-7
|How to cite this URL:|
Sharma Y R, Vajpayee R B, Bhatnagar R, Mohan M, Azad R V, Kumar M, Nath R. A simple accurate method of cataract classification Cataract I. Indian J Ophthalmol [serial online] 1989 [cited 2020 May 28];37:112-7. Available from: http://www.ijo.in/text.asp?1989/37/3/112/26072
| Introduction|| |
Clinical and epidemiologic research into aetiology of cataracts has been limited by the lack of an objective, reproducible and standard method for detecting and grading the severity of cataracts in vivo . Various methods used in cataract studies include an ophthalmic loupe with focal illumination , direct ophthalmoscopy with undilated pupils ,, standard protocols with slit lamp examination with dilated pupil , slit lamp classification based on morphology and location of opacity  and various schemes based on slit lamp examination and cataract maturity, hand sketches and diagrams ,. Such examination methods have been found to exhibit high intra and inter observer variability . Some simple classification protocols have been reported with high intra observer agreement  but such gross classification systems are clearly unsuitable for precise epidemiological and clinical cataract studies , Photo-documentation using slit lamp photography , slit lamp photography using Sheimpflug principle ,,, retroillumination lens photography using fundus camera or specifically designed photographic systems have been suggested to be more reliable but they require a complex set up and are more expensive ,,. Sparrow, Bron, Brown et al reported a cataract classification scheme using the slit lamp . They also used a resolution target projection ophthalmoscope initially designed by Cotlier .
We wished to conduct studies on the aetiology and medical management of cataracts at our institution. Reported herein is the clinical classification designed for these purposes based on slit lamp and direct ophthalmoscopic examination. Our aim was to develop a simple and accurate classification system which adequately described and classified any given lens opacity and was fairly easy to learn by anyone experienced in the use of a slit-lamp microscope and direct ophthalmoscope.
| Material and methods|| |
The cataracts are classified into cortical (anterior and posterior), nuclear and posterior sub-capsular (PSC). If only one type of cataract is present, the cataract is classified as pure type. In the presence of more than one type of opacity, the cataract is classified as a mixed cataract. In the mixed cataract group, an attempt is made to identify the predominant type of opacity. The predominance of the opacity is assessed by the extent of the opacity - not by the effect, the opacity may have on the visual acuity. Lens examination is done with a maximally dilated pupil (about 8 mm). Patients in whom the pupils do not dilate maximally or in whom pupillary dilation is contra-indicated are excluded from the study.
| The proforma|| |
A standard pro forma on a full page sheet has been made (Fin 1).
This is used for detailed cataract classification. In longitudinal studies, the same proforma is used at each follow up without referral to previous records. The details of the proforma are as follows : The equatorial diameter of the lens in adult life is 9 mm . The sagittal diameter is 3.5-4 mm 22sub , or 4-5 mm 24 in adults. Of this approximately two third is the nucleus and one third is represented by the anterior and posterior cortex. The enface view of the lens representing a circle is divided into one hundred equal parts.
This is done by dividing the circle into ten sectors by use of chords passing through the centre and spaced at 36° apart from each other. Each sector between any two chords represents 10 per cent area of the circle. Each of these sectors is further divided into ten equal parts by drawing concentric circles of proper diameter. Appropriate diameter for each circle is determined by the formula: i d r = r d /i0. As the circles divide the segments of 10 percent of lens area into equal parts, each part would be equal to 10 percent of 10 percent i.e. 1 percent of the original area. So a segment between each two chords represents 10 percent and each circular area between the segments represents 1 percent of the area. Any given lens opacity is directly and accurately read. This system is applied using both slit lamp and direct ophthalmoscope on a maximally dilated pupil. The individual type of lens opacity is classified using a slit lamp. Direct, focal, diffuse and retro-illumination are used in classifying and grading cataracts. A cataract is defined as any definite lens opacity irrespective of any effect on visual acuity. For all three primary cataract types i.e. cortical (anterior and posterior separately), nuclear and posterior subcapsular cataracts the extent and density of the opacity is graded. For determining the extent of the opacity, the percentage of area covered by the opacity and its depth are taken into consideration. In the case of PSC cataracts, only the percentage area is computed which represents the extent of the opacity; the depth of the opacity is not considered.
The density is determined for each type of opacity on a scale of 0 to 3 +. The density is graded for each subtype of opacity using the slit lamp beam and graded by the effect it has on the visibility of immediately retro situated lens area or vitreous as the case may be. Ophthalmoscopically the extent is judged by distant direct ophthalmoscopy in a darkened room at one foot and density is determined on a scale of 0 to 3 +, depending on the clarity of visibility of major fundus landmarks usually a large vessel as seen through the opacity. We have also used resolution target projection ophthalmoscope for grading the density in about 200 patients.
| The cortical cataracts|| |
Two circles equally divided into 100 equal areas are used in drawing the opacities as seen in the anterior and posterior lens cortex. The percentage of area covered by the opacity is studied using direct focal, diffuse and retroillumination and is drawn on the diagrams. No special colours are used as each subtype of opacity is drawn separately. The thickness of the opacity is studied using a narrow beam and the approximate percentage drawn accordingly on a half circle representing cortical thickness.
This circle is further divided into five equal areas to facilitate thickness measurement of the cortical opacities. Area between two lines covers twenty percent thickness. Radial lines divide the cortical thickness diagram into 18 equal areas thus each segment represents about five percent of the cortical area. If the opacity is of uniform thickness, a single depth drawing indicating depth, suffices. When the cortical opacity is large or the opacities are multiple this facilitates calculation of the extent of opacity. The extent of opacity is calculated by multiplying the percentage area covered by the opacity with the cortical thickness involved in the opacity. This divided by 100 gives the extent of opacity. The density is determined for each opacity separately when there are multiple opacities.
Opacity in enface view is drawn as seen. Area covered is directly read from the number of one percent areas covered. For example, an opacity as seen in [Figure - 4] represents 40 percent area. One advantage of this system is that this eliminates the "impression" factor in gauging the area of opacity. In [Figure - 5] the central opacity represents only a ten percent area. Without the representation on equally divided areas such an opacity might be judged to be greater than what it actually is. Similarly, the outer hypothetical opacity might be under or over judged, but because it covers forty equal areas it covers 40 percent of the area. Similarly, in [Figure - 6] opacities A & C represent a 10 percent area and opacity B represents only a 6 percent area. Without the "equal areas" diagram the area of such opacities can be considerably under or over valued. In judging the thickness of cortical opacities, the thickness of cortex involved in the opacity is drawn using a thin slit beam. In case of large opacities because thickness can vary in different areas of the opacity multiple representations of different areas can be made. For example, in [Figure - 7], opacity A is uniform and covers 10 percent of the thickness. Opacity B is of variable thickness. In a 10 percent area, it involves 100 percent thickness, but in a 10 percent area the thickness of the opacity is only 40 percent. In C and E the opacity [Figure - 7] involves 100 percent thickness while in D 10 percent of the opacity area involves 40 percent thickness and the remaining 5 percent of opacity involves 20 percent thickness. In calculating the extent of the cortical opacity, the area percentage of opacity is multiplied by the thickness percentage and this divided by 100 represents the extent of the opacity.
| Nuclear cataract|| |
The equatorial diameter of the lens at birth is 6 - 6.5 mm and in adult life it is 9 mm . The diameter at birth represents the adult nucleus diameter . This definition excludes infantile and adult nucleus zones. Therefore, the diameter of the adult nucleus must exceed 6 -6.5 mm and we arbitrarily chose to omit the outer two circles in calculating the nuclear opacities. This leaves 80 equal circles. [Figure - 1] : Nuclear cataract). Nuclear opacity is drawn as seen by the slit lamp and the percentage area covered is arrived at by multiplying with 1.25 the number of one percentage areas covered by the opacity. For calculating the percentage depth of opacity five equal circles representing 20 percent of nucleus were drawn. Since the surfaces of various lens zones are not strictly concentric and since the fibres are thickened in the region of the equator, the further they are from the centre, the more elliptical their course becomes . Lines were drawn connecting the points where vertical and horizontal axis bisected the circles [Figure - 8] This scheme while not strictly accurate, was adopted as practical in estimating nucleus thickness. However, because of the peculiar nature of nuclear opacity, it is pertinent to assess the percentage depth of nuclear opacity and this can be done by assessing the percentage involvement in axial region. Area in each circle represents 20 percent nuclear area. The extent of opacity is calculated by multiplying the area covered by the opacity multiplied by percentage depth and dividing by whichever of the two is larger. The density of nuclear opacity is determined by clarity of visibility of the posterior cortex and posterior capsule on a scale of 0 to 3 +.
The thickness of the nucleus as seen to be involved in opacification out of the total nuclear thickness is drawn. Each of the squares in the diagram represents 20 percent thickness [Figure - 8]. The thickness of the opacity in [Figure - 9] represents 20 percent involvement but without the aid of the diagram it might be interpreted to represent much less than that. What is peculiar to nuclear opacity is that the depth of opacity is very important in determining the extent of the opacity. Often the whole area of the nucleus seems to be involved in the opacity but depth determination gives the true picture. This is the reason that in computing the extent of nuclear opacity, percentage enface multiplied by depth percentage involvement is divided by larger of the two which is invariably the area percentage. Because of the central location and two sided dimension of a nuclear opacity from the central point of the lens makes division of a nuclear opacity from the central point of the lens makes division by 100 to arrive at the extent of opacity, as in case of cortical opacities, impracticable.
| P s c cataracts|| |
The opacity studied by slit lamp is drawn on the diagram. The depth is not considered. The number of equal 1 percent areas covered by the opacity give the extent of opacity. The density is determined by using a beam and studying the clarity of visibility of the vitreous on the scale of 0 to 3 +.
| Mixed cataracts|| |
In mixed cataracts, the examiner has to judge the extent of opacity and its effect on density individually and more experience is needed in avoiding obvious error of attributing density effect to the wrong opacity.
| Ophthalmoscopic classification|| |
After completion of slit lamp examination, the over all percentage of lens area affected is studied by distant direct ophthalmoscopy carried out at one foot. It indicates the net effect, the opacities are having on lens transparency in an enlace profile. The diagram of opacities area is drawn on the standard diagram of 100 equal parts and directly read. The density is studied by passing the ophthalmoscope light through the opacity and observing some major fundus landmarks. The density grading is done on a scale of 0 to 3+. For estimating density with a resolution target projection ophthalmoscope, light is projected on the retina through the opacity and the examiner reads directly the smallest target he can resolve. Resolution target projection ophthalmoscope - In 200 patients Welch-Allyn ophthalmoscope with Air Force E Chart as described by Cotlier, Zuckerman and Cicchetti  was used for grading the density of opacity. Data analysis revealed too great a variability in grading all types of opacities. Its further use in studies on medical therapy of cataracts was thus not contemplated any further.
| Observer variability|| |
We conducted studies to assess the reliability of our classification system. Four qualified ophthalmologists with varying experience in the present classification system and cataract classification in general participated in the study. Twenty cataract patients were examined on four different occasions by each observer in a masked fashion. Excellent intra and interobserver agreement was found amongst all observers in classifying sub-types of cataracts (weighted kappa .85 to .95) using slit lamp. Intraobserver agreement in classifying the extent of opacity was fair (Weighted Kappa .60 to .65). The greatest intraobserver variability was noted in classifying the opacity ophthalmoscopically. Intraobserver Weighted Kappa value for the extent of opacity was .50 to .60 (fair) and for density it was .65 to .70 (good).
| The follow up|| |
The photograph of different lens opacities were obtained using Nikon zoom anterior segment slit lamp camera and Zeiss photo slit lamp. During follow up in longitudinal studies, the same steps of examination are repeated on a separate sheet without referring to previous records. The best corrected visual acuity is recorded at each follow up.
| Discussion|| |
Simple grading systems used in classifying cataracts using only ophthalmic loupe and direct ophthalmoscope with undilated pupil , or slit lamp classification system grading immature non tumescent, immature tumescent, mature and hypermature cataracts  clearly would be inadequate for exact epidemiological studies or for studies on medical therapy of cataracts . Photodocumentation system are available ,,, but they are expensive and not always practical. The classification system presented herein uses slit lamp and direct ophthalmoscope. Each major sub-type of opacity is graded extent wise and density wise using a slit lamp and also ophthalmically. The importance of classifying lens opacities anatomically has been stressed ,. Our classification system recognises this and is applicable in any set up where slit lamp and direct ophthalmoscope are available. Because the enlace lens area has been divided into 100 equal parts, it is felt that this lessens the error in calculating the extent of opacity. The inclusion of depth of opacity in assessing the extent of opacity increases the accuracy. This would be specially useful in longitudinal studies, especially the studies on medical therapy on cataracts. In addition, the assessment of density of the opacity yields additional information and it is understandable that density assessment can be as important as the extent of opacity and, it is also conceivable that some drugs may affect only the density or the extent. The inclusion of direct ophthalmoscopic assessment gives the overall effect of the opacity or of multiple opacities on the lens and yields additional information. We do not recommend the use of resolution target projection ophthalmoscope. Our results with it were grossly inconsistent and multiple factors such as the location of opacity, the fundus pigmentation, the fundus pattern and the age of the patient are the variables which seemed responsible. Only in younger individuals (less than 30 years) could the targets be clearly read. In older patients with nuclear sclerosis having normal vision the resolution obtained was grossly variable. Clearly more data from different centres will clarify the use of resolution target projection ophthalmoscope in grading the cataract severity.
The intraobserver and interobserver variability studies indicated that for qualified ophthalmologists using this classification system intraobserver and interobserver agreement in classifying opacities using slit lamp and ophthalmoscope was fairly good to excellent. Intraobserver weighted Kappa value for extent as well as density was satisfactory. Interobserver agreement was also fairly good. Important in longitudinal studies, interobserver variability is more important than intraobserver variability. Since in our studies we found a high intra and interobserver agreement in grading the various classification parameters, we consider our classification adequate for assessing the effect of medical intervention in cataract studies. Interobserver variability in such studies is more important than intraobserver variability because cataract patients put on any medical therapy will be examined repeatedly by the different investigators. The Nikon zoom camera and Zeiss photo slit lamp photographs were not satisfactory in quantitating the opacities or the progression. We have conducted and completed studies on the medical therapy of cataracts using this classification scheme. Systemic Aspirin, systemic vitamin E and topical glutathione and topical sulindac eye drops have been used for these studies. The methodology used and results of these studies will be reported separately.
| Acknowledgement|| |
The support of ICMR, India is gratefully acknowledged. During part of this study, Dr. Sharma was appointed by ICMR in the supernumerary research cadre scheme at Dr. R. P. Centre. We very deeply acknowledge the help of Mr. Sunil Kumar Goyal of Indian Institute of Technology, New Delhi.
We thank all the residents who refered their patients to the cataract cell.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9]