|Year : 1954 | Volume
| Issue : 1 | Page : 1-14
Early diagnosis of trachoma, clinical and laboratory
Tulsi Das, MS Nirankari, MR Chaddah
Department of Ophthalmology, Medical College, Amritsar, India
Department of Ophthalmology, Medical College, Amritsar
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Das T, Nirankari M S, Chaddah M R. Early diagnosis of trachoma, clinical and laboratory. Indian J Ophthalmol 1954;2:1-14
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Das T, Nirankari M S, Chaddah M R. Early diagnosis of trachoma, clinical and laboratory. Indian J Ophthalmol [serial online] 1954 [cited 2021 Feb 25];2:1-14. Available from: https://www.ijo.in/text.asp?1954/2/1/1/33588
According to Mac Callan (1936) trachoma afflicts the eyes of at least 50 per cent. of the total world population. It is a serious problem in Northern India, especially in the Punjab, Rajasthan and Uttar Pradesh. It has a decreasing incidence in India as we proceed towards the south and this may be due to the importation of trachoma by the Muhammadans from Central Asia and their carrying it on with them as they conquered various parts of Northern India. Their penetration being the least in the south conforms with the lowest incidence of trachoma in Madras and Southern India. Trachoma is responsible for 60 per cent, of the preventible blindness in the Punjab. It produces a lot of morbidity in the eye in addition to total or partial blindness.
The various phases of the problem which are studied in our department are : -
(1) Epidemilogy. (2) Aetiology. (3) Diagnosis-clinical and laboratory. (4) Treatment.
This paper deals with the early clinical and laboratory diagnosis of trachoma and is first of a series of papers to be published on trachoma.
| Details of Study|| |
For this study 500 patients were examined. They were taken from three kinds of subjects : policemen, students and patients attending public hospitals to represent a fair section of the social status of the population.
Out of the 500, Group I consisted of 119 policemen who were kept in the hospital for one month, Group II of 200 boarders of Sacred Heart and Alexandra Schools, Group III of 100 day scholars of S. S. High School and Group IV of 81 random cases of trachoma picked up from the outpatients department of Ram Lal Eye Hospital. Groups 11 and III come under the age of maximum incidence and taken from schools of different status would give a fair idea of the general dissemination of the disease in the population.
In all the four groups a thorough clinical examination was done and conjunctival smears were taken from the upper and lower conjunctival fornices. Groups I and II were submitted to controlled treatment with Terramycin eye ointment 0.5% in one eye and various other drugs in the fellow eye, whereas Group I was subjected to a study of the histopathological sections of the conjunctiva from both the upper and lower fornices.
Age groups and social status of these patients are given in [Table - 1],[Table - 2] and incidence of inclusion bodies in these patients is given in [Table - 3],[Table - 4],[Table - 5].
Four features were unusual and outstanding.
- Almost the maximum incidence of disease is reached below the age of 10.
- The lower fornix is equally, if not more revealing in the clinical and
- The percentage of inclusions found in a smear is heavy at all ages and in all classes of people. (Average 66% ).
- Inclusion bodies can be found even in the second and third stages of laboratory diagnosis of trachoma.
trachoma in quite a large percentage of cases. They are, however, not so numerous and not so easily found as in the first stage.
In various books of ophthalmology great emphasis has been laid on the early start of trachoma in the superior fornix and the involvement of the lower fornix is either ignored or lightly dismissed. Even Mac Callan (1936) 2 the noted authority on trachoma, stresses the importance of examination of the upper tarsal conjunctiva. According to our observations involvement of the conjunctiva of the upper tarsal plate is a comparatively late phenomenon as compared with the lower fornix, and this fact needs a strong emphasis. The usual diagnosis of trachoma is established in this country by the eversion of the upper lid and examination of the upper tarsal conjunctiva and fornix, which is a comparatively uncomfortable procedure. It was mainly to find some easier method of examination for an early diagnosis that this study was concentrated on the lower fornix and our labours have produced some interesting results. Our study has revealed that diagnosis of trachoma from the examination of the lower fornix is possible at so early a stage that there is great likelihood of its resolution or cure. Pulling the lower lid down and asking the patient to look up exposes the lower fornix where the early manifestations of the disease can be studied in the fornix and the adjoining bulbar conjunctiva.
This simple procedure does away with the irksome method of double-everting the lid to expose the superior fornix and incidentally soiling the fingers.
Thus in the early diagnosis of trachoma the examination of the lower fornix has many advantages over that of the upper fornix.
- It favours a very early diagnosis, that is in the stage when trachoma is most vulnerable.
- The exposure of fornix is very easy, and clean.
- The study of the bulbar conjunctiva as continuation of the lower fornix is possible and gives an important clue as to its early infiltration and extension of the opalescence (see below) towards the cornea as the conjunctiva is thinnest in the lower fornix.
- The lower bulbar conjunctiva is easily studied along with the two types of vessels (conjunctival and anterior ciliary).
- Since adenoid tissue is less dense in the lower than in the upper fornix and as the epithelium is only 2 to 3 layers thick in the lower as against 4 to 5 layers in the upper fornix the early changes in the conjunctival epithelium and the sub-epithelial infiltration are more obvious and can be more easily detected, in the lower fornix.
| Clinical Stages|| |
The following clinical stages of trachoma are described. They are highly suggestive of trachoma in countries where it is a rare disease and are almost sure signs where trachoma is commonly present. It may be emphasised here that early diagnosis of trachoma cannot be made without the use of a magnifying loupe (x 10).
Slitlamp examination was not found to be of any special value in the early diagnosis. The only advantage is that we get a more magnified view of what is seen with the loupe. For clinical examination, a magnifying loupe can easily replace the slitlamp.
The infiltration of the transparent conjunctiva with lymphocytes being very superficial in this stage, i.e. only in the epithelial and sub-epithelial layers, the lower fornix shows a superficial bright opalescence, patchy or diffuse in disposition. The blood vessels are dilated and brighter red in colour and more tortuous than normal with various anastomosing vessels standing out more prominently. The bright red colour of the blood vessels is rather enhanced and not dimmed on seeing through the delicate diaphanous veil of opalescence. The bulbar conjunctival vessels are more dilated, red and tortuous. The anterior ciliary or deeper bulbar vessels have a fine veil of nebulous clouds in front of them. They can still be seen and traced to their termination in the sclera. This veil is the continuation of the fornical opalescence and extends upwards to various degrees in the bulbar conjunctiva depending upon the duration of the disease [Figure - 1].
The lower tarsal conjunctiva in this stage may show red dots and white spots, in the centre or no change at all.
The upper fornix and tarsal conjunctiva show red dots of two types-fine dots like grains of red sand (early) and glomerular or vesicular type, marked at the upper edge of the tarsal plate (late). Conjunctival vessels are slightly more prominent. At the canthi small portions of the superior fornix are seen and they may show early infiltration in the form of a very superficial opalescence just like in the lower fornix spread out in a very small area. The superior fornix shows the same changes as the inferior fornix. These changes although more prominent are less differentiated as the epithelium and the adenoid tissue layers are denser in the upper fornix.
The infiltration of the bulbar conjunctiva starts both in the upper and lower reflections of the fornical conjunctiva on to the sclera. It proceeds gradually towards the limbus and thus takes some time to reach it.
Pannus cannot be seen in every case at this stage even with a slitlamp and corneal microscope. When present it just extends a millimetre or so into the superficial layers of the cornea making the corneal epithelium look cloudy. This infiltration is accompanied by the downward continuation of the superficial conjunctival vessels. This is quite an insiduous process usually producing no symptoms and is liable to be missed unless especially looked for.
This stage may be called the prefolicular stage.
STAGE II A. (EARLY)
In the lower fornix the vessels start becoming less visible due to heavy infiltration of the conjunctiva covering the vessels. The details of the vessels begin to disappear fast. At places they can be still visible through the infiltrated epithelium. The bright superficial opalescence characteristic of stage I almost disappears. The whole appearance is as if the conjunctiva has lost its smoothness and its surface is shaggy as the ruffled skin surface of a recently shorn lamb. Whenever papillary hypertrophy is marked one gets, instead of a smooth surface, red granules giving a fine strawberry appearance. The appearance is as if numerous fine grains of red sand are standing out from underneath the surface. Examination of the lower bulbar conjunctiva shows that the opalescence in front of the deeper vessels is more advanced towards the limbus. There is a thin veil in front of the superficial vessels [Figure - 2].
Clinical picture of the upper tarsal and fornical conjunctiva is almost similar to that of the lower except that papillary hypertrophy is more marked in the upper.
Pannus is present in almost every case and can be easily seen with a corneal loupe.
STAGE II B (LATE)
No individual vessel can be made out in the lower fornix and the appearance is that of red and dirty yellow colour intermixed irregularly, not conforming to any pattern whatsoever, like the shaggy and dirty wooly skin of a recently shorn lamb as mentioned before. In some cases individual vessels can be seen [Figure - 3]. There are discrete, small slightly raised, bluish or yellowish white follicles standing out between the vessels.
The usual change in the Indian patients is diffuse follicular infiltration rather than discrete follicle formation as reported by various authors. In children however, the adenoid tissue being more prominent than in adults, formation of discrete follicles is more in evidence. The infiltration in the lower bulbar conjunctiva spreads in front of the deeper vessels, where it can be clinically seen by contrast with the adjoining conjunctiva, right upto the limbus and may infiltrate the superficial layers of the corneal epithelium.
Similar changes are noticed in the upper tarsal and fornical conjunctiva. Pannus is more advanced and can be easily seen even without using a corneal loupe.
From hereon trachomatous changes become more prominent in the upper conjunctiva. The scarring starts in the lower fornix almost simultaneously with the upper but is less prominent than in the upper because of its more delicate structure. The scars are thinner finer and confined usually to the fornix [Figure - 4]. This produces gradual shrinkage and obliteration of the lower fornix. Entropion is less common in the lower lid as the scars are finer, more delicate and far away from the subtarsal sulcus. Since the tarsal plate is smaller in size and less infiltrated it is less deformed.
The upper palpebral conjunctiva and fornix show dense scarring with mapping out into islands of still red, congested and infiltrated conjunctiva in between the scars. Scarring does not show easily at canthi. At a later date the scar formation becomes more prominent in the subtarsal sulcus but more often remains as irregular linear criss-crossings or star patterns irregularly arranged. Vessels are no longer discernible in any part of the conjunctiva. When scarring is complete, which is a long drawn out process and in some cases may not be completed at all in the life time of a patient, the conjunctiva presents an atrophic whitish appearance with loss of details of vessels and markings of Meibomian glands which can be seen through a normal, thin uninvolved conjunctiva. Pannus gets regressive and consists of thin and obliterated vessels and superficial opacities.
STAGE IV. (STAGE OF COMPLICATIONS AND SEQUELAE)
The diagnosis is apparent and various manifestations are entropion and trichiasis, sinuous border, pseudoptosis, blepharitis, ectropion. obliteration of the fornices, strangulation of the Krause's glands, lagophthalmos, xerophthalmia, Herbert's pits, corneal ulcers, infection of the canaliculi and lacrymal sac.
A common feature of this stage is irregular pigmentation of the conjunctiva linearly along and close to the sulcus subtarsalis.
A brief resume of the stages as found in the lower fornix is given below:
- Bright superficial opalescence in front of the vessels in the tarsal conjunctiva, fornix and bulbar conjunctiva, seen more easily in the lower fornix than in the upper,
- Dilated tortuous conjunctival vessels bright red in colour.
- Red dots - both fine sandy and vesicular or glomerular.
STAGE II. (EARLY)
- Deeper infiltration with rather opaque conjunctiva.
- Details of the vessels disappearing.
- Typical shaggy appearance becoming prominent.
- Superficial opalescence of the bulbar conjunctiva spreads further towards the limbus but as adenoid tissue is less dense, the opalescence remains superficial.
- Red dots interspersed with white spots.
STAGE II. (LATE)
- Diffuse deep infiltration completely hiding the details of the vessels or discrete follicular formation, particularly in children.
- Well marked characteristic (almost pathognomic) shaggy appearance.
- Disappearance of red dots.
- The superficial opalescence reaches almost the limbus and may be evident as a low grade type of corneal vascularization and infiltration (pannus).
Beginning of very fine criss-crossing of scarring in the fornix with separation into islands of vascularized follicles as raised reddish white areas.
Complete loss of all details of vessels and follicles. Conjunctiva presents a smooth atrophic bluish white appearance. It becomes shrunken and adherent to the underlying tissues.
Sequelx of trachoma present in varying degrees of severity.
| Laboratory Diagnosis|| |
Microscopical Examination of Conjunctival Smears
It is a valuable aid in the early diagnosis when inclusions can be demonstrated in about 80 per cent. of the cases, specially in children. It is almost a proof positive of trachoma when supported by clinical signs. This early diagnosis is most essential as the disease is most vulnerable at this stage and there are ample chances of its cure without harmful cicatrisation which is productive of innumerable sequelae.
The method of staining adopted by us is as follows:-
After anaesthetizing the conjunctival sac with l drop of 1 % anethaine, the fornices are exposed with the help of a lid retractor. The edge of the lid retractor is pressed on the skin of the lifted upper lid just above the tarsal plate and the upper fornix is thus exposed. Mucus in the fornix is wiped off with a cotton swab soaked in 2% sodium bicarbonate solution. The epithelium is scraped with one edge of a cover slip. The secret of success lies in scraping the surface with a single gentle stroke without any bleeding. In summer, the edge of the cover slip is wetted with a 2 sodium carbonate solution so as to prevent drying of the cells. The material thus collected is evenly spread over a clean glass slide like a blood film. The smear is dried in air and fixed in absolute alcohol for 5 minutes. The fixed preparation is immersed in dilute Giemsa stain (1 in 10) contained in a staining trough for 15 to 20 minutes. The Giemsa stain should not be older than a week or ten days. After this the slide is washed with distilled water. A few drops of pure acetone are put on the slide for 5 to 10 seconds so as to wash away the pigment granules. The slide is again washed with distilled water, dried and examined with an oil-immersion lens. Cytoplasm of epithelial cells stains very light blue and the nuclei reddish violet. This simple technique was adopted after trying the various methods given in the literature recommended by various workers in the field.
It must be stated here that the search for inclusion bodies is time-consuming, and sometimes only two or three inclusions can be made out after an hour of search in the whole preparation.
As described by Lindner we came across two types of inclusion bodies, (1) initial bodies and (2) elementary bodies.
The various forms of initial bodies seen during this study were
- Small deep blue granules, scattered in the cytoplasm mostly away from the nucleus [Figure - 5]a.
- Large, deeper blue granules, more in number, still discrete but nearer the nucleus [Figure - 5]b.
- Large deep blue granules, some discrete, some coalesced, away from the nucleus or surrounding the nucleus usually at one pole but sometimes on all sides [Figure - 5]c.
- A little intermingling of tiny red granules with blue granules paler than the granules seen in 1, 2, 3 above. Rarely blue granules are surrounded by a clear area separating them from the cytoplasm.
The cytoplasm usually shows no change. In heavy infestations the nucleus shows vacuolation of varying degrees.
We came across two types of elementary bodies which are described below:--
1. Some were clear, distinct and demarcated from the nucleus over which they form a cape at one pole. Usually they were light pink in colour and paler than the nucleus but with no blue granules in them [Figure - 6]A. The capes are large and out of all proportion in size to the blue granules of which they are supposed to be derivatives. They are present in a fairly large percentage of cases. Sometimes the blue granules are present in the same cell [Figure - 6]B although their presence in the same slide in other cells is usually demonstrable. With the usual magnification sometimes the capes look amorphous and at other times they appear to be made up of tiny granules of light violet tinge.
2. As opposed to the capes described above, which are separate from the nucleus, quite often one finds these capes to be continuous with the nucleus which is vacuolated and appears to extrude the cape from its interior [Figure - 6]Cb. This so-called cape then has the same colour as the nucleus with sometimes a tell-tale appearance of vacuoles in its structure. This raises two questions in our minds. Are these so-called capes a part of the nuclear substance thrown out as a result of degeneration of the nucleus with its invasion by the trachoma virus or are they art effects produced by some pressure in the preparation of slides ?
Biopsy was taken both from the upper and lower fornices and sections were stained by Haematoxylin-Eosin technique and Thionine stain. In our experience Thionine staining had no advantage over the Haematoxylin-Eosin method. It is almost impossible to demonstrate the inclusions in the sections although Dr. Mitsui showed us two slides wherein he demonstrated inclusion bodies.
- There is an early change in the nature of epithelial cells. They become not only flat and squamous but also many-layered. The usual conjunctival epithelium becomes columnar superficially and cuboidal at the base, 2 to 3 layers thick in the lower fornix and 4 to 5 in the upper.
- Vascularization becomes more marked with lymphocytic infiltration of the subepithelial layers. [Figure - 7].
- Goblet cells are a prominent feature in early cases [Figure - 8]. They are not only present in the superficial epithelial layers but also in the basal layers. This shows that they may arise from any epithelial cell. However, their size is largest in the basal layer and smaller in the superficial layers.
- Epithelial changes remain the same but sometimes pigment granules are found deposited in the basal layers of the epithelium.
- Papillary formations grow outwards towards the surface [Figure - 7],[Figure - 10] or inwards towards the adenoid tissue layer [Figure - 8],[Figure - 9]. They are processes of circumscribed hyperplasia of epithelial cells. Clinically they give a velvety appearance or stand out as granules if projecting outwards, but produce a thickening of the conjunctiva if growing inwards.
- Follicles consist usually of well defined collections of lymphocytes and other cells [Figure - 10] but more frequently in this country one finds diffuse lymphocytic infiltration in the sub-epithelial tissue [Figure - 7],[Figure - 8]. Later on follicles become vascularised, larger, indistinct and coalescent.
- Sections of fornix show scarring. Early scarring is very delicate, indistinct and irregular. The infiltration goes on getting less and less as the scarring progresses.
- It will be clear from the above that the histopathological changes are neither early nor pathognomonic of trachoma. When trachoma is diagnosed clinically, the follicles, discrete as well as coalescent, and papilla with changes in the character of epithelium may be of supporting evidence.
| Comments and Discussion|| |
Trachoma is a progressive disease but its progress can be arrested at any stage. Comparing the stages of trachoma and its fearful sequelx in the different types of patients one finds that trachoma in its fourth stage with the sequelx is confined mostly to people belonging to the lower strata of social life, e.g. the sweepers and the farm labourers. So severe are the sequelx that they are to be seen at a very young age and entropion may be present at the age of 2 to 4 years. Even in stage II one finds both lids heavy and thick with marked infiltration, both diffuse and local, (folliculosis and follicle formation) making eversion of the lid difficult.
In the Punjab where trachoma has an incidence of over 80% it is not confined only to the poor and the unhygienic only, for it is to be found in the richer and cleaner class of people as well, but the trachoma of the rich and of the poor present two widely different pictures. In the former it exists in a very mild form without the patient's knowledge, chronic in nature and gets easily arrested at any stage. In them the scarring may be so thin and delicate that the whole of the conjunctiva looks atrophic but there is no accompanying sequela. Even here inclusion bodies are demonstrable bilaterally in 60% of the cases in stage II and 56.2% of cases in stage III. This suggests that the virus does not disappear even though the trachomatous lesion may heal. It is the superseding secondary infection which is responsible for the more marked clinical signs, the complications and sequelae.
The value of hygienic environment is evident from a separate survey of a village with a population of about 1500. In those who took care of personal cleanliness and lived in cleaner surroundings trachoma though present was found in a very mild form. The worst cases were encountered in the poorer class of people, living huddled together with poor ventilation and dirty environment.
The diagnosis of trachoma sometimes presents some difficulty, for the clinical picture and the presence of inclusion and elementary bodies are to be found in other clinical conditions and at the same time the inclusion bodies can be so evasive under the microscope. In the established stages the clinical diagnosis presents little difficulty. The diagnosis is difficult and more important in the early stages when fortunately inclusion and elementary bodies can be detected more easily in the conjunctival smears. The clinical picture of an early stage together with detection of the inclusion bodies therefore should be considered confirmatory evidence.
The importance of examination of the lower fornix cannot be over-emphasized, as the percentage of detection of inclusion bodies from the scrapings of upper and lower fornices is just the same. The changes can be seen earlier and more easily in the lower fornix as its exposure is so simple, the conjunctiva is comparatively thinner, adenoid tissue is less well developed and the continuation of the lower fornix on to the delicate bulbar conjunctiva is clearly visible. This has led us to put up a new classification of trachoma which does not supplant the universally accepted classification of McCallan. This classification will, however, stimulate a closer study of the manifestations of trachoma in the lower fornix.
From the description of the advancing subepithelial infiltration beginning from the fornix and reaching the limbus, pannus may be considered as a result of continuity of the infiltration. If it is solely a process of continuity then pannus should appear first in the lower lid since the distance to be covered to the limbus is longer in the upper bulbar conjunctiva than the lower. As pannus is usually evident earlier in the upper limbus than in the lower it cannot be solely a process of continuity. There must be an additional process of contiguity. The horizontal finish of the advancing edge of the pannus corresponding with the shape of the upper lid margin favours a process of contiguity. The accepted method of spread of trachoma is by direct transplantation. In pannus, as the upper 1 /6th of the cornea is rubbed against by the infected upper tarsal conjunctiva, the infection is transplanted on the epithelium of that part of the cornea. In the lower limbus, absence of this factor explains the late appearance of pannus, which results from the slower spread by continuity.
Pannus cannot be due to mere mechanical rubbing of the roughened conjunctiva, because in spring cattarh, where the follicles are larger and harder pannus does not form.
What is the nature of the trachoma virus ?
The latest conception about the causative organism of trachoma is that it belongs to the group of large viruses such as psittacosis, lymphogranuloma inguinale and inclusion conjunctivitis. Bland (1945) calls them basophilic viruses as the initial bodies of trachoma alone, even in this group, stain blue with Giemsa. The points of resemblance of trachoma bodies with Rickettsia and large viruses are summed up by him as follows : -
- They are minute in size.
- Show pleomorphism.
- Gram negative.
- Do not stain easily with aniline dyes.
- Stain easily with Giemsa; take various tints from red to blue.
- They stain easily with Castaneda's stain.
- Filtration is almost like Rickettsia, a little more easily.
- Non-cultivable apart from living cells.
Points against being Rickettsia are:
- No arthropod host.
- Do not show any bacillary or thread forms.
- Form inclusions with matrix therefore stand in intermediate position between virus and Rickettsia.
Points against being large viruses are:
- They possess initial bodies which stain blue with Giemsa stain.
- Show greater pleomorphism.
- Form inclusions with basophill matrix.
- Stain with Castaneda's stain.
Although this study has not been undertaken to determine the nature of the causative virus, the description of the stained specimens generally agree with Bland's description of the staining properties of the large virus group described above.
Those forms of elementary bodies where cape-like bodies appear to be continuous with the nucleus which appears vacuolated [Figure - 6]Cb do they represent a part of the nucleus which is extruded as a result of degeneration of the nucleus by its invasion by the trachoma virus or are they art effects produced in the preparation of the slides. The latter seems unlikely for particular care was taken in the preparation of the slides not to apply any pressure.
With finfie technique, it is nowadays possible to do microdissections and isolate blue granules, capes, so-called capes and vacuolated nuclear substance. Biochemical analysis will help a great deal to identify the various forms or the electron microscope may disclose a very fine line of separation between the nucleus and the so-called capes, not discernible under the unusual magnification.
The prevalent view about trachoma virus is that the virus disappears from the epithelial cells usually after the stage I. Our observations, however, reveal that inclusions are demonstratable in fairly large percentage even in stage II and stage III, 60% in the former 56.2% in the latter, though they are present in much fewer numbers and need greater patience and time for their demonstration.
| Summary|| |
- A study of 500 patients of trachoma covering a wide range of age groups, social status and occupations in the city of Amritsar is presented. This is supplemented by a survey of one village of about 1,500 people living in hygienic and unhygienic surroundings.
- A new classification supplementing Mac Callan's classification of trachoma, based on clinical and laboratory examination of the lower fornix is given. The importance of examination of the lower fornix in the early diagnosis of trachoma is stressed.
- A difference between the clinical severities of trachoma in the rich and poor is realised and the influence of hygienic surroundings on the course and sequelae of trachoma demonstrated.
- The importance of smear examinations for inclusion bodies in the early as well as later stages of trachoma is mentioned.
- The technique of staining of inclusion bodies with Giemsa is described and the probable nature of the infecting virus is discussed.
- Histopathological examination of fornical conjunctiva in early diagnosis of trachoma did not prove to be of practical value.
We are thankful to Chas. Pfizer & Co., U.S.A. for the grant given by them to start this work.
| References|| |
Bland, J. O. W. ( 1945) The Etiology of Trachoma. A critical review of present knowledge. Fourteenth Report of the Memorial Ophthalmic Laboratory, Giza, Schindler's Press, Cairo.
Duke Elder, W. S. ( 1938) `Text Book of Ophthalmology', Vol. 2. 6. 1609, C. V. Mosby Company, St. Louis.
Lindner, K. ( 1948) in van Rooyen, C. E. and Rhodes. A. J. "Virus Diseases of Man", p. 701, Thomas Nelson and Sons, New York.
MacCallan, A. F. ( 1936) "Trachoma", p. 135, Butterworth & Co., Ltd., London.
(1936 ) ibid p. 10.
Mitsui, Y. ( 1949) Am. J. of Ophth. 32, 1189-96.
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9], [Figure - 10]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]